fixing unit test

* Moving lock to directory/

* added fs2

* doc

* Using fs2 for locking

* Added unit test

* Fixed error message related unit test

* Fixing location of import

CHANGELOG.md

@@ -1,5 +1,28 @@
+Tantivy 0.9.0
+=====================
+- Removed most unsafe (@fulmicoton)
+- Indexer memory footprint improved. (VInt comp, inlining the first block. (@fulmicoton)
+- Stemming in other language possible (@pentlander)
+- Segments with no docs are deleted earlier (@barrotsteindev)
+
+Tantivy 0.8.1
+=====================
+Hotfix of #476.
+
+Merge was reflecting deletes before commit was passed. 
+Thanks @barrotsteindev  for reporting the bug.
+
+
+Tantivy 0.8.0
+=====================
+*No change in the index format*
+- API Breaking change in the collector API. (@jwolfe, @fulmicoton)
+- Multithreaded search (@jwolfe, @fulmicoton) 
+
+
 Tantivy 0.7.1
 =====================
+*No change in the index format*
 - Bugfix: NGramTokenizer panics on non ascii chars
 - Added a space usage API
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tantivy"
-version = "0.7.1"
+version = "0.9.0-dev"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 license = "MIT"
 categories = ["database-implementations", "data-structures"]
@@ -29,32 +29,34 @@ serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
 num_cpus = "1.2"
-itertools = "0.7"
+fs2={version="0.4", optional=true}
+itertools = "0.8"
 levenshtein_automata = {version="0.1", features=["fst_automaton"]}
 bit-set = "0.5"
 uuid = { version = "0.7", features = ["v4", "serde"] }
-crossbeam = "0.4"
-crossbeam-channel = "0.2"
+crossbeam = "0.5"
 futures = "0.1"
 futures-cpupool = "0.1"
 owning_ref = "0.4"
 stable_deref_trait = "1.0.0"
 rust-stemmers = "1"
-downcast = { version="0.9" }
+downcast-rs = { version="1.0" }
 matches = "0.1"
 bitpacking = "0.5"
-census = "0.1"
+census = "0.2"
 fnv = "1.0.6"
 owned-read = "0.4"
 failure = "0.1"
 htmlescape = "0.3.1"
 fail = "0.2"
+scoped-pool = "1.0"
+murmurhash32 = "0.2"
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.2"
 
 [dev-dependencies]
-rand = "0.5"
+rand = "0.6"
 maplit = "1"
 
 [profile.release]
@@ -69,7 +71,7 @@ overflow-checks = true
 [features]
 # by default no-fail is disabled. We manually enable it when running test.
 default = ["mmap", "no_fail"]
-mmap = ["fst/mmap", "atomicwrites"]
+mmap = ["fst/mmap", "atomicwrites", "fs2"]
 lz4-compression = ["lz4"]
 no_fail = ["fail/no_fail"]
 unstable = [] # useful for benches.

README.md

@@ -21,7 +21,7 @@
 
 **Tantivy** is a **full text search engine library** written in rust.
 
-It is closer to [Apache Lucene](https://lucene.apache.org/) than to [Elastic Search](https://www.elastic.co/products/elasticsearch) and [Apache Solr](https://lucene.apache.org/solr/) in the sense it is not
+It is closer to [Apache Lucene](https://lucene.apache.org/) than to [Elasticsearch](https://www.elastic.co/products/elasticsearch) and [Apache Solr](https://lucene.apache.org/solr/) in the sense it is not
 an off-the-shelf search engine server, but rather a crate that can be used
 to build such a search engine.
 
@@ -76,7 +76,7 @@ It will walk you through getting a wikipedia search engine up and running in a f
 Tantivy compiles on stable rust but requires `Rust >= 1.27`.
 To check out and run tests, you can simply run :
 
-    git clone git@github.com:tantivy-search/tantivy.git
+    git clone https://github.com/tantivy-search/tantivy.git
     cd tantivy
     cargo build
 

doc/src/SUMMARY.md

@@ -4,9 +4,8 @@
 
 [Avant Propos](./avant-propos.md)
 
-- [Schema](./schema.md)
-- [Indexing](./indexing.md)
 - [Segments](./basis.md)
+- [Defining your schema](./schema.md)
 - [Facetting](./facetting.md)
 - [Innerworkings](./innerworkings.md)
   - [Inverted index](./inverted_index.md)

doc/src/avant-propos.md

@@ -31,3 +31,4 @@ relevancy, collapsing, highlighting, spatial search.
   index from a different format.
 
   Tantivy exposes a lot of low level API to do all of these things.
+  

doc/src/schema.md

@@ -1,50 +1 @@
-# Schema
-
-When starting a new project using tantivy, your first step will be to your schema. Be aware that changing it will probably require you to reindex all of your data.
-It is strongly recommended you keep the means to iterate through your original data when this happens.
-
-If not specified otherwise, tantivy does not keep a raw version of your data,
-so the good practise is to rely on a distinct storage to store your
-raw documents.
-
-The schema defines both the type of the fields you are indexing, but also the type of indexing you want to apply to them. The set of search operations that you will be able to perform depends on the way you set up your schema.
-
-Here is what defining your schema could look like.
-
-```Rust
-use tantivy::schema::{Schema, TEXT, STORED, INT_INDEXED};
-
-let mut schema_builder = SchemaBuilder::default();
-let text_field = schema_builder.add_text_field("name", TEXT | STORED);
-let tag_field = schema_builder.add_facet_field("tags");
-let timestamp_field = schema_buider.add_u64_field("timestamp", INT_INDEXED)
-let schema = schema_builder.build();
-```
-
-Notice how adding a new field to your schema builder
-follows the following pattern :
-
-```verbatim
-  schema_builder.add_<fieldtype>_field("<fieldname>", <field_configuration>);
-```
-
-This method returns a `Field` handle that will be used for all kind of 
-
-# Field types
-
-Tantivy currently supports only 4 types.
-
-- `text` (understand `&str`)
-- `u64` and `i64`
-- `HierarchicalFacet`
-
-Let's go into their specificities.
-
-# Text
-
-Full-text search is the bread and butter of search engine.
-The key idea is fairly simple. Your text is broken apart into tokens (that's
-what we call tokenization). Tantivy then keeps track of the list of the documents containing each token.
-
-In order to increase recall you might want to normalize tokens. For instance,
-you most likely want to lowercase your tokens so that documents match the query `cat` regardless of whether your they contain the token `cat` or `Cat`.
+# Defining your schema

examples/basic_search.rs

@@ -16,10 +16,11 @@ extern crate tempdir;
 // Importing tantivy...
 #[macro_use]
 extern crate tantivy;
-use tantivy::collector::TopCollector;
+use tantivy::collector::TopDocs;
 use tantivy::query::QueryParser;
 use tantivy::schema::*;
 use tantivy::Index;
+use tempdir::TempDir;
 
 fn main() -> tantivy::Result<()> {
     // Let's create a temporary directory for the
@@ -34,7 +35,7 @@ fn main() -> tantivy::Result<()> {
     // be indexed".
 
     // first we need to define a schema ...
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     // Our first field is title.
     // We want full-text search for it, and we also want
@@ -105,37 +106,37 @@ fn main() -> tantivy::Result<()> {
     // For convenience, tantivy also comes with a macro to
     // reduce the boilerplate above.
     index_writer.add_document(doc!(
-        title => "Of Mice and Men",
-        body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
-                bank and runs deep and green. The water is warm too, for it has slipped twinkling \
-                over the yellow sands in the sunlight before reaching the narrow pool. On one \
-                side of the river the golden foothill slopes curve up to the strong and rocky \
-                Gabilan Mountains, but on the valley side the water is lined with trees—willows \
-                fresh and green with every spring, carrying in their lower leaf junctures the \
-                debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
-                limbs and branches that arch over the pool"
+    title => "Of Mice and Men",
+    body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
+            bank and runs deep and green. The water is warm too, for it has slipped twinkling \
+            over the yellow sands in the sunlight before reaching the narrow pool. On one \
+            side of the river the golden foothill slopes curve up to the strong and rocky \
+            Gabilan Mountains, but on the valley side the water is lined with trees—willows \
+            fresh and green with every spring, carrying in their lower leaf junctures the \
+            debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
+            limbs and branches that arch over the pool"
     ));
 
     index_writer.add_document(doc!(
-        title => "Of Mice and Men",
-        body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
-                bank and runs deep and green. The water is warm too, for it has slipped twinkling \
-                over the yellow sands in the sunlight before reaching the narrow pool. On one \
-                side of the river the golden foothill slopes curve up to the strong and rocky \
-                Gabilan Mountains, but on the valley side the water is lined with trees—willows \
-                fresh and green with every spring, carrying in their lower leaf junctures the \
-                debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
-                limbs and branches that arch over the pool"
+    title => "Of Mice and Men",
+    body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
+            bank and runs deep and green. The water is warm too, for it has slipped twinkling \
+            over the yellow sands in the sunlight before reaching the narrow pool. On one \
+            side of the river the golden foothill slopes curve up to the strong and rocky \
+            Gabilan Mountains, but on the valley side the water is lined with trees—willows \
+            fresh and green with every spring, carrying in their lower leaf junctures the \
+            debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
+            limbs and branches that arch over the pool"
     ));
 
     // Multivalued field just need to be repeated.
     index_writer.add_document(doc!(
-       title => "Frankenstein",
-       title => "The Modern Prometheus",
-       body => "You will rejoice to hear that no disaster has accompanied the commencement of an \
-                enterprise which you have regarded with such evil forebodings.  I arrived here \
-                yesterday, and my first task is to assure my dear sister of my welfare and \
-                increasing confidence in the success of my undertaking."
+    title => "Frankenstein",
+    title => "The Modern Prometheus",
+    body => "You will rejoice to hear that no disaster has accompanied the commencement of an \
+             enterprise which you have regarded with such evil forebodings.  I arrived here \
+             yesterday, and my first task is to assure my dear sister of my welfare and \
+             increasing confidence in the success of my undertaking."
     ));
 
     // This is an example, so we will only index 3 documents
@@ -212,15 +213,10 @@ fn main() -> tantivy::Result<()> {
     //
     // We are not interested in all of the documents but
     // only in the top 10. Keeping track of our top 10 best documents
-    // is the role of the TopCollector.
-    let mut top_collector = TopCollector::with_limit(10);
+    // is the role of the TopDocs.
 
     // We can now perform our query.
-    searcher.search(&*query, &mut top_collector)?;
-
-    // Our top collector now contains the 10
-    // most relevant doc ids...
-    let doc_addresses = top_collector.docs();
+    let top_docs = searcher.search(&query, &TopDocs::with_limit(10))?;
 
     // The actual documents still need to be
     // retrieved from Tantivy's store.
@@ -229,12 +225,10 @@ fn main() -> tantivy::Result<()> {
     // the document returned will only contain
     // a title.
 
-    for doc_address in doc_addresses {
+    for (_score, doc_address) in top_docs {
         let retrieved_doc = searcher.doc(doc_address)?;
         println!("{}", schema.to_json(&retrieved_doc));
     }
 
     Ok(())
 }
-
-use tempdir::TempDir;

examples/custom_collector.rs

@@ -0,0 +1,187 @@
+// # Custom collector example
+//
+// This example shows how you can implement your own
+// collector. As an example, we will compute a collector
+// that computes the standard deviation of a given fast field.
+//
+// Of course, you can have a look at the tantivy's built-in collectors
+// such as the `CountCollector` for more examples.
+
+extern crate tempdir;
+
+// ---
+// Importing tantivy...
+#[macro_use]
+extern crate tantivy;
+use tantivy::collector::{Collector, SegmentCollector};
+use tantivy::fastfield::FastFieldReader;
+use tantivy::query::QueryParser;
+use tantivy::schema::Field;
+use tantivy::schema::{Schema, FAST, INT_INDEXED, TEXT};
+use tantivy::Index;
+use tantivy::SegmentReader;
+
+#[derive(Default)]
+struct Stats {
+    count: usize,
+    sum: f64,
+    squared_sum: f64,
+}
+
+impl Stats {
+    pub fn count(&self) -> usize {
+        self.count
+    }
+
+    pub fn mean(&self) -> f64 {
+        self.sum / (self.count as f64)
+    }
+
+    fn square_mean(&self) -> f64 {
+        self.squared_sum / (self.count as f64)
+    }
+
+    pub fn standard_deviation(&self) -> f64 {
+        let mean = self.mean();
+        (self.square_mean() - mean * mean).sqrt()
+    }
+
+    fn non_zero_count(self) -> Option<Stats> {
+        if self.count == 0 {
+            None
+        } else {
+            Some(self)
+        }
+    }
+}
+
+struct StatsCollector {
+    field: Field,
+}
+
+impl StatsCollector {
+    fn with_field(field: Field) -> StatsCollector {
+        StatsCollector { field }
+    }
+}
+
+impl Collector for StatsCollector {
+    // That's the type of our result.
+    // Our standard deviation will be a float.
+    type Fruit = Option<Stats>;
+
+    type Child = StatsSegmentCollector;
+
+    fn for_segment(
+        &self,
+        _segment_local_id: u32,
+        segment: &SegmentReader,
+    ) -> tantivy::Result<StatsSegmentCollector> {
+        let fast_field_reader = segment.fast_field_reader(self.field)?;
+        Ok(StatsSegmentCollector {
+            fast_field_reader,
+            stats: Stats::default(),
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        // this collector does not care about score.
+        false
+    }
+
+    fn merge_fruits(&self, segment_stats: Vec<Option<Stats>>) -> tantivy::Result<Option<Stats>> {
+        let mut stats = Stats::default();
+        for segment_stats_opt in segment_stats {
+            if let Some(segment_stats) = segment_stats_opt {
+                stats.count += segment_stats.count;
+                stats.sum += segment_stats.sum;
+                stats.squared_sum += segment_stats.squared_sum;
+            }
+        }
+        Ok(stats.non_zero_count())
+    }
+}
+
+struct StatsSegmentCollector {
+    fast_field_reader: FastFieldReader<u64>,
+    stats: Stats,
+}
+
+impl SegmentCollector for StatsSegmentCollector {
+    type Fruit = Option<Stats>;
+
+    fn collect(&mut self, doc: u32, _score: f32) {
+        let value = self.fast_field_reader.get(doc) as f64;
+        self.stats.count += 1;
+        self.stats.sum += value;
+        self.stats.squared_sum += value * value;
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        self.stats.non_zero_count()
+    }
+}
+
+fn main() -> tantivy::Result<()> {
+    // # Defining the schema
+    //
+    // The Tantivy index requires a very strict schema.
+    // The schema declares which fields are in the index,
+    // and for each field, its type and "the way it should
+    // be indexed".
+
+    // first we need to define a schema ...
+    let mut schema_builder = Schema::builder();
+
+    // We'll assume a fictional index containing
+    // products, and with a name, a description, and a price.
+    let product_name = schema_builder.add_text_field("name", TEXT);
+    let product_description = schema_builder.add_text_field("description", TEXT);
+    let price = schema_builder.add_u64_field("price", INT_INDEXED | FAST);
+    let schema = schema_builder.build();
+
+    // # Indexing documents
+    //
+    // Lets index a bunch of fake documents for the sake of
+    // this example.
+    let index = Index::create_in_ram(schema.clone());
+
+    let mut index_writer = index.writer(50_000_000)?;
+    index_writer.add_document(doc!(
+        product_name => "Super Broom 2000",
+        product_description => "While it is ok for short distance travel, this broom \
+        was designed quiditch. It will up your game.",
+        price => 30_200u64
+    ));
+    index_writer.add_document(doc!(
+        product_name => "Turbulobroom",
+        product_description => "You might have heard of this broom before : it is the sponsor of the Wales team.\
+            You'll enjoy its sharp turns, and rapid acceleration",
+        price => 29_240u64
+    ));
+    index_writer.add_document(doc!(
+        product_name => "Broomio",
+        product_description => "Great value for the price. This broom is a market favorite",
+        price => 21_240u64
+    ));
+    index_writer.add_document(doc!(
+        product_name => "Whack a Mole",
+        product_description => "Prime quality bat.",
+        price => 5_200u64
+    ));
+    index_writer.commit()?;
+    index.load_searchers()?;
+
+    let searcher = index.searcher();
+    let query_parser = QueryParser::for_index(&index, vec![product_name, product_description]);
+
+    // here we want to get a hit on the 'ken' in Frankenstein
+    let query = query_parser.parse_query("broom")?;
+    if let Some(stats) = searcher.search(&query, &StatsCollector::with_field(price))? {
+        println!("count: {}", stats.count());
+        println!("mean: {}", stats.mean());
+        println!("standard deviation: {}", stats.standard_deviation());
+    }
+
+    Ok(())
+}

examples/custom_tokenizer.rs

@@ -5,7 +5,7 @@
 
 #[macro_use]
 extern crate tantivy;
-use tantivy::collector::TopCollector;
+use tantivy::collector::TopDocs;
 use tantivy::query::QueryParser;
 use tantivy::schema::*;
 use tantivy::tokenizer::NgramTokenizer;
@@ -20,7 +20,7 @@ fn main() -> tantivy::Result<()> {
     // be indexed".
 
     // first we need to define a schema ...
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     // Our first field is title.
     // In this example we want to use NGram searching
@@ -68,12 +68,12 @@ fn main() -> tantivy::Result<()> {
     // heap for the indexer can increase its throughput.
     let mut index_writer = index.writer(50_000_000)?;
     index_writer.add_document(doc!(
-        title => "The Old Man and the Sea",
-        body => "He was an old man who fished alone in a skiff in the Gulf Stream and \
-         he had gone eighty-four days now without taking a fish."
+    title => "The Old Man and the Sea",
+    body => "He was an old man who fished alone in a skiff in the Gulf Stream and \
+     he had gone eighty-four days now without taking a fish."
     ));
     index_writer.add_document(doc!(
-       title => "Of Mice and Men",
+    title => "Of Mice and Men",
        body => r#"A few miles south of Soledad, the Salinas River drops in close to the hillside
                 bank and runs deep and green. The water is warm too, for it has slipped twinkling
                 over the yellow sands in the sunlight before reaching the narrow pool. On one
@@ -84,7 +84,7 @@ fn main() -> tantivy::Result<()> {
                 limbs and branches that arch over the pool"#
     ));
     index_writer.add_document(doc!(
-        title => "Frankenstein",
+    title => "Frankenstein",
         body => r#"You will rejoice to hear that no disaster has accompanied the commencement of an
                 enterprise which you have regarded with such evil forebodings.  I arrived here
                 yesterday, and my first task is to assure my dear sister of my welfare and
@@ -104,11 +104,9 @@ fn main() -> tantivy::Result<()> {
     // here we want to get a hit on the 'ken' in Frankenstein
     let query = query_parser.parse_query("ken")?;
 
-    let mut top_collector = TopCollector::with_limit(10);
-    searcher.search(&*query, &mut top_collector)?;
+    let top_docs = searcher.search(&query, &TopDocs::with_limit(10))?;
 
-    let doc_addresses = top_collector.docs();
-    for doc_address in doc_addresses {
+    for (_, doc_address) in top_docs {
         let retrieved_doc = searcher.doc(doc_address)?;
         println!("{}", schema.to_json(&retrieved_doc));
     }

examples/deleting_updating_documents.rs

@@ -10,7 +10,7 @@
 // Importing tantivy...
 #[macro_use]
 extern crate tantivy;
-use tantivy::collector::TopCollector;
+use tantivy::collector::TopDocs;
 use tantivy::query::TermQuery;
 use tantivy::schema::*;
 use tantivy::Index;
@@ -27,10 +27,9 @@ fn extract_doc_given_isbn(index: &Index, isbn_term: &Term) -> tantivy::Result<Op
     // The second argument is here to tell we don't care about decoding positions,
     // or term frequencies.
     let term_query = TermQuery::new(isbn_term.clone(), IndexRecordOption::Basic);
-    let mut top_collector = TopCollector::with_limit(1);
-    searcher.search(&term_query, &mut top_collector)?;
+    let top_docs = searcher.search(&term_query, &TopDocs::with_limit(1))?;
 
-    if let Some(doc_address) = top_collector.docs().first() {
+    if let Some((_score, doc_address)) = top_docs.first() {
         let doc = searcher.doc(*doc_address)?;
         Ok(Some(doc))
     } else {
@@ -44,7 +43,7 @@ fn main() -> tantivy::Result<()> {
     //
     // Check out the *basic_search* example if this makes
     // small sense to you.
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     // Tantivy does not really have a notion of primary id.
     // This may change in the future.

examples/faceted_search.rs

@@ -25,7 +25,7 @@ fn main() -> tantivy::Result<()> {
     // Let's create a temporary directory for the
     // sake of this example
     let index_path = TempDir::new("tantivy_facet_example_dir")?;
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     schema_builder.add_text_field("name", TEXT | STORED);
 
@@ -62,11 +62,10 @@ fn main() -> tantivy::Result<()> {
     let mut facet_collector = FacetCollector::for_field(tags);
     facet_collector.add_facet("/pools");
 
-    searcher.search(&AllQuery, &mut facet_collector).unwrap();
+    let facet_counts = searcher.search(&AllQuery, &facet_collector).unwrap();
 
-    let counts = facet_collector.harvest();
     // This lists all of the facet counts
-    let facets: Vec<(&Facet, u64)> = counts.get("/pools").collect();
+    let facets: Vec<(&Facet, u64)> = facet_counts.get("/pools").collect();
     assert_eq!(
         facets,
         vec![

examples/iterating_docs_and_positions.rs

@@ -18,7 +18,7 @@ use tantivy::{DocId, DocSet, Postings};
 fn main() -> tantivy::Result<()> {
     // We first create a schema for the sake of the
     // example. Check the `basic_search` example for more information.
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     // For this example, we need to make sure to index positions for our title
     // field. `TEXT` precisely does this.

examples/snippet.rs

@@ -10,11 +10,11 @@ extern crate tempdir;
 // Importing tantivy...
 #[macro_use]
 extern crate tantivy;
-use tantivy::collector::TopCollector;
+use tantivy::collector::TopDocs;
 use tantivy::query::QueryParser;
 use tantivy::schema::*;
 use tantivy::Index;
-use tantivy::SnippetGenerator;
+use tantivy::{Snippet, SnippetGenerator};
 use tempdir::TempDir;
 
 fn main() -> tantivy::Result<()> {
@@ -23,7 +23,7 @@ fn main() -> tantivy::Result<()> {
     let index_path = TempDir::new("tantivy_example_dir")?;
 
     // # Defining the schema
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
     let title = schema_builder.add_text_field("title", TEXT | STORED);
     let body = schema_builder.add_text_field("body", TEXT | STORED);
     let schema = schema_builder.build();
@@ -35,15 +35,15 @@ fn main() -> tantivy::Result<()> {
 
     // we'll only need one doc for this example.
     index_writer.add_document(doc!(
-        title => "Of Mice and Men",
-        body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
-                bank and runs deep and green. The water is warm too, for it has slipped twinkling \
-                over the yellow sands in the sunlight before reaching the narrow pool. On one \
-                side of the river the golden foothill slopes curve up to the strong and rocky \
-                Gabilan Mountains, but on the valley side the water is lined with trees—willows \
-                fresh and green with every spring, carrying in their lower leaf junctures the \
-                debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
-                limbs and branches that arch over the pool"
+    title => "Of Mice and Men",
+    body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
+            bank and runs deep and green. The water is warm too, for it has slipped twinkling \
+            over the yellow sands in the sunlight before reaching the narrow pool. On one \
+            side of the river the golden foothill slopes curve up to the strong and rocky \
+            Gabilan Mountains, but on the valley side the water is lined with trees—willows \
+            fresh and green with every spring, carrying in their lower leaf junctures the \
+            debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
+            limbs and branches that arch over the pool"
     ));
     // ...
     index_writer.commit()?;
@@ -54,18 +54,34 @@ fn main() -> tantivy::Result<()> {
     let query_parser = QueryParser::for_index(&index, vec![title, body]);
     let query = query_parser.parse_query("sycamore spring")?;
 
-    let mut top_collector = TopCollector::with_limit(10);
-    searcher.search(&*query, &mut top_collector)?;
+    let top_docs = searcher.search(&query, &TopDocs::with_limit(10))?;
 
-    let snippet_generator = SnippetGenerator::new(&searcher, &*query, body)?;
+    let snippet_generator = SnippetGenerator::create(&searcher, &*query, body)?;
 
-    let doc_addresses = top_collector.docs();
-    for doc_address in doc_addresses {
+    for (score, doc_address) in top_docs {
         let doc = searcher.doc(doc_address)?;
         let snippet = snippet_generator.snippet_from_doc(&doc);
+        println!("Document score {}:", score);
         println!("title: {}", doc.get_first(title).unwrap().text().unwrap());
         println!("snippet: {}", snippet.to_html());
+        println!("custom highlighting: {}", highlight(snippet));
     }
 
     Ok(())
 }
+
+fn highlight(snippet: Snippet) -> String {
+    let mut result = String::new();
+    let mut start_from = 0;
+
+    for (start, end) in snippet.highlighted().iter().map(|h| h.bounds()) {
+        result.push_str(&snippet.fragments()[start_from..start]);
+        result.push_str(" --> ");
+        result.push_str(&snippet.fragments()[start..end]);
+        result.push_str(" <-- ");
+        start_from = end;
+    }
+
+    result.push_str(&snippet.fragments()[start_from..]);
+    result
+}

examples/stop_words.rs

@@ -15,7 +15,7 @@ extern crate tempdir;
 // Importing tantivy...
 #[macro_use]
 extern crate tantivy;
-use tantivy::collector::TopCollector;
+use tantivy::collector::TopDocs;
 use tantivy::query::QueryParser;
 use tantivy::schema::*;
 use tantivy::tokenizer::*;
@@ -23,7 +23,7 @@ use tantivy::Index;
 
 fn main() -> tantivy::Result<()> {
     // this example assumes you understand the content in `basic_search`
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     // This configures your custom options for how tantivy will
     // store and process your content in the index; The key
@@ -72,26 +72,26 @@ fn main() -> tantivy::Result<()> {
     title => "The Old Man and the Sea",
     body => "He was an old man who fished alone in a skiff in the Gulf Stream and \
      he had gone eighty-four days now without taking a fish."
-  ));
+    ));
 
     index_writer.add_document(doc!(
-      title => "Of Mice and Men",
-      body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
-              bank and runs deep and green. The water is warm too, for it has slipped twinkling \
-              over the yellow sands in the sunlight before reaching the narrow pool. On one \
-              side of the river the golden foothill slopes curve up to the strong and rocky \
-              Gabilan Mountains, but on the valley side the water is lined with trees—willows \
-              fresh and green with every spring, carrying in their lower leaf junctures the \
-              debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
-              limbs and branches that arch over the pool"
-  ));
+    title => "Of Mice and Men",
+    body => "A few miles south of Soledad, the Salinas River drops in close to the hillside \
+            bank and runs deep and green. The water is warm too, for it has slipped twinkling \
+            over the yellow sands in the sunlight before reaching the narrow pool. On one \
+            side of the river the golden foothill slopes curve up to the strong and rocky \
+            Gabilan Mountains, but on the valley side the water is lined with trees—willows \
+            fresh and green with every spring, carrying in their lower leaf junctures the \
+            debris of the winter’s flooding; and sycamores with mottled, white, recumbent \
+            limbs and branches that arch over the pool"
+    ));
 
     index_writer.add_document(doc!(
-       title => "Frankenstein",
-       body => "You will rejoice to hear that no disaster has accompanied the commencement of an \
-                enterprise which you have regarded with such evil forebodings.  I arrived here \
-                yesterday, and my first task is to assure my dear sister of my welfare and \
-                increasing confidence in the success of my undertaking."
+    title => "Frankenstein",
+    body => "You will rejoice to hear that no disaster has accompanied the commencement of an \
+             enterprise which you have regarded with such evil forebodings.  I arrived here \
+             yesterday, and my first task is to assure my dear sister of my welfare and \
+             increasing confidence in the success of my undertaking."
     ));
 
     index_writer.commit()?;
@@ -105,15 +105,11 @@ fn main() -> tantivy::Result<()> {
     // stop words are applied on the query as well.
     // The following will be equivalent to `title:frankenstein`
     let query = query_parser.parse_query("title:\"the Frankenstein\"")?;
+    let top_docs = searcher.search(&query, &TopDocs::with_limit(10))?;
 
-    let mut top_collector = TopCollector::with_limit(10);
-
-    searcher.search(&*query, &mut top_collector)?;
-
-    let doc_addresses = top_collector.docs();
-
-    for doc_address in doc_addresses {
+    for (score, doc_address) in top_docs {
         let retrieved_doc = searcher.doc(doc_address)?;
+        println!("\n==\nDocument score {}:", score);
         println!("{}", schema.to_json(&retrieved_doc));
     }
 

examples/working_with_json.rs

@@ -9,7 +9,7 @@ fn main() -> tantivy::Result<()> {
     // Check out the basic example if this is confusing to you.
     //
     // first we need to define a schema ...
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
     schema_builder.add_text_field("title", TEXT | STORED);
     schema_builder.add_text_field("body", TEXT);
     schema_builder.add_u64_field("year", INT_INDEXED);

src/collector/chained_collector.rs

@@ -1,142 +0,0 @@
-use collector::Collector;
-use DocId;
-use Result;
-use Score;
-use SegmentLocalId;
-use SegmentReader;
-
-/// Collector that does nothing.
-/// This is used in the chain Collector and will hopefully
-/// be optimized away by the compiler.
-pub struct DoNothingCollector;
-impl Collector for DoNothingCollector {
-    #[inline]
-    fn set_segment(&mut self, _: SegmentLocalId, _: &SegmentReader) -> Result<()> {
-        Ok(())
-    }
-    #[inline]
-    fn collect(&mut self, _doc: DocId, _score: Score) {}
-    #[inline]
-    fn requires_scoring(&self) -> bool {
-        false
-    }
-}
-
-/// Zero-cost abstraction used to collect on multiple collectors.
-/// This contraption is only usable if the type of your collectors
-/// are known at compile time.
-///
-/// ```rust
-/// #[macro_use]
-/// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
-/// use tantivy::{Index, Result};
-/// use tantivy::collector::{CountCollector, TopCollector, chain};
-/// use tantivy::query::QueryParser;
-///
-/// # fn main() { example().unwrap(); }
-/// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
-///     let title = schema_builder.add_text_field("title", TEXT);
-///     let schema = schema_builder.build();
-///     let index = Index::create_in_ram(schema);
-///     {
-///         let mut index_writer = index.writer(3_000_000)?;
-///         index_writer.add_document(doc!(
-///             title => "The Name of the Wind",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of Muadib",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "A Dairy Cow",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of a Young Girl",
-///         ));
-///         index_writer.commit().unwrap();
-///     }
-///
-///     index.load_searchers()?;
-///     let searcher = index.searcher();
-///
-///     {
-///         let mut top_collector = TopCollector::with_limit(2);
-///         let mut count_collector = CountCollector::default();
-///         {
-///             let mut collectors = chain().push(&mut top_collector).push(&mut count_collector);
-///             let query_parser = QueryParser::for_index(&index, vec![title]);
-///             let query = query_parser.parse_query("diary")?;
-///             searcher.search(&*query, &mut collectors).unwrap();
-///         }
-///         assert_eq!(count_collector.count(), 2);
-///         assert!(top_collector.at_capacity());
-///     }
-///
-///     Ok(())
-/// }
-/// ```
-pub struct ChainedCollector<Left: Collector, Right: Collector> {
-    left: Left,
-    right: Right,
-}
-
-impl<Left: Collector, Right: Collector> ChainedCollector<Left, Right> {
-    /// Adds a collector
-    pub fn push<C: Collector>(self, new_collector: &mut C) -> ChainedCollector<Self, &mut C> {
-        ChainedCollector {
-            left: self,
-            right: new_collector,
-        }
-    }
-}
-
-impl<Left: Collector, Right: Collector> Collector for ChainedCollector<Left, Right> {
-    fn set_segment(
-        &mut self,
-        segment_local_id: SegmentLocalId,
-        segment: &SegmentReader,
-    ) -> Result<()> {
-        self.left.set_segment(segment_local_id, segment)?;
-        self.right.set_segment(segment_local_id, segment)?;
-        Ok(())
-    }
-
-    fn collect(&mut self, doc: DocId, score: Score) {
-        self.left.collect(doc, score);
-        self.right.collect(doc, score);
-    }
-
-    fn requires_scoring(&self) -> bool {
-        self.left.requires_scoring() || self.right.requires_scoring()
-    }
-}
-
-/// Creates a `ChainedCollector`
-pub fn chain() -> ChainedCollector<DoNothingCollector, DoNothingCollector> {
-    ChainedCollector {
-        left: DoNothingCollector,
-        right: DoNothingCollector,
-    }
-}
-
-#[cfg(test)]
-mod tests {
-
-    use super::*;
-    use collector::{Collector, CountCollector, TopCollector};
-
-    #[test]
-    fn test_chained_collector() {
-        let mut top_collector = TopCollector::with_limit(2);
-        let mut count_collector = CountCollector::default();
-        {
-            let mut collectors = chain().push(&mut top_collector).push(&mut count_collector);
-            collectors.collect(1, 0.2);
-            collectors.collect(2, 0.1);
-            collectors.collect(3, 0.5);
-        }
-        assert_eq!(count_collector.count(), 3);
-        assert!(top_collector.at_capacity());
-    }
-}

src/collector/count_collector.rs

@@ -1,4 +1,5 @@
 use super::Collector;
+use collector::SegmentCollector;
 use DocId;
 use Result;
 use Score;
@@ -11,14 +12,14 @@ use SegmentReader;
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
+/// use tantivy::schema::{Schema, TEXT};
 /// use tantivy::{Index, Result};
-/// use tantivy::collector::CountCollector;
+/// use tantivy::collector::Count;
 /// use tantivy::query::QueryParser;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -43,59 +44,86 @@ use SegmentReader;
 ///     let searcher = index.searcher();
 ///
 ///     {
-///	        let mut count_collector = CountCollector::default();
 ///         let query_parser = QueryParser::for_index(&index, vec![title]);
 ///         let query = query_parser.parse_query("diary")?;
-///         searcher.search(&*query, &mut count_collector).unwrap();
+///         let count = searcher.search(&query, &Count).unwrap();
 ///
-///         assert_eq!(count_collector.count(), 2);
+///         assert_eq!(count, 2);
 ///     }
 ///
 ///     Ok(())
 /// }
 /// ```
-#[derive(Default)]
-pub struct CountCollector {
-    count: usize,
-}
+pub struct Count;
 
-impl CountCollector {
-    /// Returns the count of documents that were
-    /// collected.
-    pub fn count(&self) -> usize {
-        self.count
-    }
-}
+impl Collector for Count {
+    type Fruit = usize;
 
-impl Collector for CountCollector {
-    fn set_segment(&mut self, _: SegmentLocalId, _: &SegmentReader) -> Result<()> {
-        Ok(())
-    }
+    type Child = SegmentCountCollector;
 
-    fn collect(&mut self, _: DocId, _: Score) {
-        self.count += 1;
+    fn for_segment(&self, _: SegmentLocalId, _: &SegmentReader) -> Result<SegmentCountCollector> {
+        Ok(SegmentCountCollector::default())
     }
 
     fn requires_scoring(&self) -> bool {
         false
     }
+
+    fn merge_fruits(&self, segment_counts: Vec<usize>) -> Result<usize> {
+        Ok(segment_counts.into_iter().sum())
+    }
+}
+
+#[derive(Default)]
+pub struct SegmentCountCollector {
+    count: usize,
+}
+
+impl SegmentCollector for SegmentCountCollector {
+    type Fruit = usize;
+
+    fn collect(&mut self, _: DocId, _: Score) {
+        self.count += 1;
+    }
+
+    fn harvest(self) -> usize {
+        self.count
+    }
 }
 
 #[cfg(test)]
 mod tests {
-
-    use collector::{Collector, CountCollector};
+    use super::{Count, SegmentCountCollector};
+    use collector::Collector;
+    use collector::SegmentCollector;
 
     #[test]
-    fn test_count_collector() {
-        let mut count_collector = CountCollector::default();
-        assert_eq!(count_collector.count(), 0);
-        count_collector.collect(0u32, 1f32);
-        assert_eq!(count_collector.count(), 1);
-        assert_eq!(count_collector.count(), 1);
-        count_collector.collect(1u32, 1f32);
-        assert_eq!(count_collector.count(), 2);
-        assert!(!count_collector.requires_scoring());
+    fn test_count_collect_does_not_requires_scoring() {
+        assert!(!Count.requires_scoring());
+    }
+
+    #[test]
+    fn test_segment_count_collector() {
+        {
+            let count_collector = SegmentCountCollector::default();
+            assert_eq!(count_collector.harvest(), 0);
+        }
+        {
+            let mut count_collector = SegmentCountCollector::default();
+            count_collector.collect(0u32, 1f32);
+            assert_eq!(count_collector.harvest(), 1);
+        }
+        {
+            let mut count_collector = SegmentCountCollector::default();
+            count_collector.collect(0u32, 1f32);
+            assert_eq!(count_collector.harvest(), 1);
+        }
+        {
+            let mut count_collector = SegmentCountCollector::default();
+            count_collector.collect(0u32, 1f32);
+            count_collector.collect(1u32, 1f32);
+            assert_eq!(count_collector.harvest(), 2);
+        }
     }
 
 }

src/collector/facet_collector.rs

@@ -1,20 +1,17 @@
 use collector::Collector;
+use collector::SegmentCollector;
 use docset::SkipResult;
 use fastfield::FacetReader;
 use schema::Facet;
 use schema::Field;
-use std::cell::UnsafeCell;
+use std::cmp::Ordering;
 use std::collections::btree_map;
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
 use std::collections::BinaryHeap;
 use std::collections::Bound;
 use std::iter::Peekable;
-use std::mem;
 use std::{u64, usize};
-use termdict::TermMerger;
-
-use std::cmp::Ordering;
 use DocId;
 use Result;
 use Score;
@@ -46,12 +43,6 @@ impl<'a> Ord for Hit<'a> {
     }
 }
 
-struct SegmentFacetCounter {
-    pub facet_reader: FacetReader,
-    pub facet_ords: Vec<u64>,
-    pub facet_counts: Vec<u64>,
-}
-
 fn facet_depth(facet_bytes: &[u8]) -> usize {
     if facet_bytes.is_empty() {
         0
@@ -91,14 +82,14 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{Facet, SchemaBuilder, TEXT};
+/// use tantivy::schema::{Facet, Schema, TEXT};
 /// use tantivy::{Index, Result};
 /// use tantivy::collector::FacetCollector;
 /// use tantivy::query::AllQuery;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///
 ///     // Facet have their own specific type.
 ///     // It is not a bad practise to put all of your
@@ -141,13 +132,10 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 ///			let mut facet_collector = FacetCollector::for_field(facet);
 ///         facet_collector.add_facet("/lang");
 ///         facet_collector.add_facet("/category");
-///         searcher.search(&AllQuery, &mut facet_collector).unwrap();
-///
-///         // this object contains count aggregate for all of the facets.
-///         let counts = facet_collector.harvest();
+///         let facet_counts = searcher.search(&AllQuery, &facet_collector).unwrap();
 ///
 ///         // This lists all of the facet counts
-///         let facets: Vec<(&Facet, u64)> = counts
+///         let facets: Vec<(&Facet, u64)> = facet_counts
 ///             .get("/category")
 ///             .collect();
 ///         assert_eq!(facets, vec![
@@ -159,13 +147,10 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 ///     {
 ///			let mut facet_collector = FacetCollector::for_field(facet);
 ///         facet_collector.add_facet("/category/fiction");
-///         searcher.search(&AllQuery, &mut facet_collector).unwrap();
-///
-///         // this object contains count aggregate for all of the facets.
-///         let counts = facet_collector.harvest();
+///         let facet_counts = searcher.search(&AllQuery, &facet_collector).unwrap();
 ///
 ///         // This lists all of the facet counts
-///         let facets: Vec<(&Facet, u64)> = counts
+///         let facets: Vec<(&Facet, u64)> = facet_counts
 ///             .get("/category/fiction")
 ///             .collect();
 ///         assert_eq!(facets, vec![
@@ -178,13 +163,10 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 ///    {
 ///			let mut facet_collector = FacetCollector::for_field(facet);
 ///         facet_collector.add_facet("/category/fiction");
-///         searcher.search(&AllQuery, &mut facet_collector).unwrap();
-///
-///         // this object contains count aggregate for all of the facets.
-///         let counts = facet_collector.harvest();
+///         let facet_counts = searcher.search(&AllQuery, &facet_collector).unwrap();
 ///
 ///         // This lists all of the facet counts
-///         let facets: Vec<(&Facet, u64)> = counts.top_k("/category/fiction", 1);
+///         let facets: Vec<(&Facet, u64)> = facet_counts.top_k("/category/fiction", 1);
 ///         assert_eq!(facets, vec![
 ///             (&Facet::from("/category/fiction/fantasy"), 2)
 ///         ]);
@@ -194,28 +176,28 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 /// }
 /// ```
 pub struct FacetCollector {
-    facet_ords: Vec<u64>,
     field: Field,
-    ff_reader: Option<UnsafeCell<FacetReader>>,
-    segment_counters: Vec<SegmentFacetCounter>,
-
-    // facet_ord -> collapse facet_id
-    current_segment_collapse_mapping: Vec<usize>,
-    // collapse facet_id -> count
-    current_segment_counts: Vec<u64>,
-    // collapse facet_id -> facet_ord
-    current_collapse_facet_ords: Vec<u64>,
-
     facets: BTreeSet<Facet>,
 }
 
+pub struct FacetSegmentCollector {
+    reader: FacetReader,
+    facet_ords_buf: Vec<u64>,
+    // facet_ord -> collapse facet_id
+    collapse_mapping: Vec<usize>,
+    // collapse facet_id -> count
+    counts: Vec<u64>,
+    // collapse facet_id -> facet_ord
+    collapse_facet_ords: Vec<u64>,
+}
+
 fn skip<'a, I: Iterator<Item = &'a Facet>>(
     target: &[u8],
     collapse_it: &mut Peekable<I>,
 ) -> SkipResult {
     loop {
         match collapse_it.peek() {
-            Some(facet_bytes) => match facet_bytes.encoded_bytes().cmp(target) {
+            Some(facet_bytes) => match facet_bytes.encoded_str().as_bytes().cmp(target) {
                 Ordering::Less => {}
                 Ordering::Greater => {
                     return SkipResult::OverStep;
@@ -240,15 +222,8 @@ impl FacetCollector {
     /// is of the proper type.
     pub fn for_field(field: Field) -> FacetCollector {
         FacetCollector {
-            facet_ords: Vec::with_capacity(255),
-            segment_counters: Vec::new(),
             field,
-            ff_reader: None,
-            facets: BTreeSet::new(),
-
-            current_segment_collapse_mapping: Vec::new(),
-            current_collapse_facet_ords: Vec::new(),
-            current_segment_counts: Vec::new(),
+            facets: BTreeSet::default(),
         }
     }
 
@@ -278,143 +253,100 @@ impl FacetCollector {
         }
         self.facets.insert(facet);
     }
-
-    fn set_collapse_mapping(&mut self, facet_reader: &FacetReader) {
-        self.current_segment_collapse_mapping.clear();
-        self.current_collapse_facet_ords.clear();
-        self.current_segment_counts.clear();
-        let mut collapse_facet_it = self.facets.iter().peekable();
-        self.current_collapse_facet_ords.push(0);
-        let mut facet_streamer = facet_reader.facet_dict().range().into_stream();
-        if !facet_streamer.advance() {
-            return;
-        }
-        'outer: loop {
-            // at the begining of this loop, facet_streamer
-            // is positionned on a term that has not been processed yet.
-            let skip_result = skip(facet_streamer.key(), &mut collapse_facet_it);
-            match skip_result {
-                SkipResult::Reached => {
-                    // we reach a facet we decided to collapse.
-                    let collapse_depth = facet_depth(facet_streamer.key());
-                    let mut collapsed_id = 0;
-                    self.current_segment_collapse_mapping.push(0);
-                    while facet_streamer.advance() {
-                        let depth = facet_depth(facet_streamer.key());
-                        if depth <= collapse_depth {
-                            continue 'outer;
-                        }
-                        if depth == collapse_depth + 1 {
-                            collapsed_id = self.current_collapse_facet_ords.len();
-                            self.current_collapse_facet_ords
-                                .push(facet_streamer.term_ord());
-                            self.current_segment_collapse_mapping.push(collapsed_id);
-                        } else {
-                            self.current_segment_collapse_mapping.push(collapsed_id);
-                        }
-                    }
-                    break;
-                }
-                SkipResult::End | SkipResult::OverStep => {
-                    self.current_segment_collapse_mapping.push(0);
-                    if !facet_streamer.advance() {
-                        break;
-                    }
-                }
-            }
-        }
-    }
-
-    fn finalize_segment(&mut self) {
-        if self.ff_reader.is_some() {
-            self.segment_counters.push(SegmentFacetCounter {
-                facet_reader: self.ff_reader.take().unwrap().into_inner(),
-                facet_ords: mem::replace(&mut self.current_collapse_facet_ords, Vec::new()),
-                facet_counts: mem::replace(&mut self.current_segment_counts, Vec::new()),
-            });
-        }
-    }
-
-    /// Returns the results of the collection.
-    ///
-    /// This method does not just return the counters,
-    /// it also translates the facet ordinals of the last segment.
-    pub fn harvest(mut self) -> FacetCounts {
-        self.finalize_segment();
-
-        let collapsed_facet_ords: Vec<&[u64]> = self
-            .segment_counters
-            .iter()
-            .map(|segment_counter| &segment_counter.facet_ords[..])
-            .collect();
-        let collapsed_facet_counts: Vec<&[u64]> = self
-            .segment_counters
-            .iter()
-            .map(|segment_counter| &segment_counter.facet_counts[..])
-            .collect();
-
-        let facet_streams = self
-            .segment_counters
-            .iter()
-            .map(|seg_counts| seg_counts.facet_reader.facet_dict().range().into_stream())
-            .collect::<Vec<_>>();
-
-        let mut facet_merger = TermMerger::new(facet_streams);
-        let mut facet_counts = BTreeMap::new();
-
-        while facet_merger.advance() {
-            let count = facet_merger
-                .current_kvs()
-                .iter()
-                .map(|it| {
-                    let seg_ord = it.segment_ord;
-                    let term_ord = it.streamer.term_ord();
-                    collapsed_facet_ords[seg_ord]
-                        .binary_search(&term_ord)
-                        .map(|collapsed_term_id| {
-                            if collapsed_term_id == 0 {
-                                0
-                            } else {
-                                collapsed_facet_counts[seg_ord][collapsed_term_id]
-                            }
-                        }).unwrap_or(0)
-                }).sum();
-            if count > 0u64 {
-                let bytes: Vec<u8> = facet_merger.key().to_owned();
-                // may create an corrupted facet if the term dicitonary is corrupted
-                let facet = unsafe { Facet::from_encoded(bytes) };
-                facet_counts.insert(facet, count);
-            }
-        }
-        FacetCounts { facet_counts }
-    }
 }
 
 impl Collector for FacetCollector {
-    fn set_segment(&mut self, _: SegmentLocalId, reader: &SegmentReader) -> Result<()> {
-        self.finalize_segment();
+    type Fruit = FacetCounts;
+
+    type Child = FacetSegmentCollector;
+
+    fn for_segment(
+        &self,
+        _: SegmentLocalId,
+        reader: &SegmentReader,
+    ) -> Result<FacetSegmentCollector> {
         let facet_reader = reader.facet_reader(self.field)?;
-        self.set_collapse_mapping(&facet_reader);
-        self.current_segment_counts
-            .resize(self.current_collapse_facet_ords.len(), 0);
-        self.ff_reader = Some(UnsafeCell::new(facet_reader));
-        Ok(())
+
+        let mut collapse_mapping = Vec::new();
+        let mut counts = Vec::new();
+        let mut collapse_facet_ords = Vec::new();
+
+        let mut collapse_facet_it = self.facets.iter().peekable();
+        collapse_facet_ords.push(0);
+        {
+            let mut facet_streamer = facet_reader.facet_dict().range().into_stream();
+            if facet_streamer.advance() {
+                'outer: loop {
+                    // at the begining of this loop, facet_streamer
+                    // is positionned on a term that has not been processed yet.
+                    let skip_result = skip(facet_streamer.key(), &mut collapse_facet_it);
+                    match skip_result {
+                        SkipResult::Reached => {
+                            // we reach a facet we decided to collapse.
+                            let collapse_depth = facet_depth(facet_streamer.key());
+                            let mut collapsed_id = 0;
+                            collapse_mapping.push(0);
+                            while facet_streamer.advance() {
+                                let depth = facet_depth(facet_streamer.key());
+                                if depth <= collapse_depth {
+                                    continue 'outer;
+                                }
+                                if depth == collapse_depth + 1 {
+                                    collapsed_id = collapse_facet_ords.len();
+                                    collapse_facet_ords.push(facet_streamer.term_ord());
+                                    collapse_mapping.push(collapsed_id);
+                                } else {
+                                    collapse_mapping.push(collapsed_id);
+                                }
+                            }
+                            break;
+                        }
+                        SkipResult::End | SkipResult::OverStep => {
+                            collapse_mapping.push(0);
+                            if !facet_streamer.advance() {
+                                break;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        counts.resize(collapse_facet_ords.len(), 0);
+
+        Ok(FacetSegmentCollector {
+            reader: facet_reader,
+            facet_ords_buf: Vec::with_capacity(255),
+            collapse_mapping,
+            counts,
+            collapse_facet_ords,
+        })
     }
 
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(&self, segments_facet_counts: Vec<FacetCounts>) -> Result<FacetCounts> {
+        let mut facet_counts: BTreeMap<Facet, u64> = BTreeMap::new();
+        for segment_facet_counts in segments_facet_counts {
+            for (facet, count) in segment_facet_counts.facet_counts {
+                *(facet_counts.entry(facet).or_insert(0)) += count;
+            }
+        }
+        Ok(FacetCounts { facet_counts })
+    }
+}
+
+impl SegmentCollector for FacetSegmentCollector {
+    type Fruit = FacetCounts;
+
     fn collect(&mut self, doc: DocId, _: Score) {
-        let facet_reader: &mut FacetReader = unsafe {
-            &mut *self
-                .ff_reader
-                .as_ref()
-                .expect("collect() was called before set_segment. This should never happen.")
-                .get()
-        };
-        facet_reader.facet_ords(doc, &mut self.facet_ords);
+        self.reader.facet_ords(doc, &mut self.facet_ords_buf);
         let mut previous_collapsed_ord: usize = usize::MAX;
-        for &facet_ord in &self.facet_ords {
-            let collapsed_ord = self.current_segment_collapse_mapping[facet_ord as usize];
-            self.current_segment_counts[collapsed_ord] += if collapsed_ord == previous_collapsed_ord
-            {
+        for &facet_ord in &self.facet_ords_buf {
+            let collapsed_ord = self.collapse_mapping[facet_ord as usize];
+            self.counts[collapsed_ord] += if collapsed_ord == previous_collapsed_ord {
                 0
             } else {
                 1
@@ -423,8 +355,24 @@ impl Collector for FacetCollector {
         }
     }
 
-    fn requires_scoring(&self) -> bool {
-        false
+    /// Returns the results of the collection.
+    ///
+    /// This method does not just return the counters,
+    /// it also translates the facet ordinals of the last segment.
+    fn harvest(self) -> FacetCounts {
+        let mut facet_counts = BTreeMap::new();
+        let facet_dict = self.reader.facet_dict();
+        for (collapsed_facet_ord, count) in self.counts.iter().cloned().enumerate() {
+            if count == 0 {
+                continue;
+            }
+            let mut facet = vec![];
+            let facet_ord = self.collapse_facet_ords[collapsed_facet_ord];
+            facet_dict.ord_to_term(facet_ord as u64, &mut facet);
+            // TODO
+            facet_counts.insert(Facet::from_encoded(facet).unwrap(), count);
+        }
+        FacetCounts { facet_counts }
     }
 }
 
@@ -456,9 +404,9 @@ impl FacetCounts {
         let right_bound = if facet.is_root() {
             Bound::Unbounded
         } else {
-            let mut facet_after_bytes: Vec<u8> = facet.encoded_bytes().to_owned();
-            facet_after_bytes.push(1u8);
-            let facet_after = unsafe { Facet::from_encoded(facet_after_bytes) }; // ok logic
+            let mut facet_after_bytes: String = facet.encoded_str().to_owned();
+            facet_after_bytes.push('\u{1}');
+            let facet_after = Facet::from_encoded_string(facet_after_bytes);
             Bound::Excluded(facet_after)
         };
         let underlying: btree_map::Range<_, _> = self.facet_counts.range((left_bound, right_bound));
@@ -505,14 +453,14 @@ mod tests {
     use core::Index;
     use query::AllQuery;
     use rand::distributions::Uniform;
+    use rand::prelude::SliceRandom;
     use rand::{thread_rng, Rng};
-    use schema::Field;
-    use schema::{Document, Facet, SchemaBuilder};
+    use schema::{Document, Facet, Field, Schema};
     use std::iter;
 
     #[test]
     fn test_facet_collector_drilldown() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facet");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -527,7 +475,8 @@ mod tests {
                 n /= 4;
                 let leaf = n % 5;
                 Facet::from(&format!("/top{}/mid{}/leaf{}", top, mid, leaf))
-            }).collect();
+            })
+            .collect();
         for i in 0..num_facets * 10 {
             let mut doc = Document::new();
             doc.add_facet(facet_field, facets[i % num_facets].clone());
@@ -536,12 +485,10 @@ mod tests {
         index_writer.commit().unwrap();
         index.load_searchers().unwrap();
         let searcher = index.searcher();
-
         let mut facet_collector = FacetCollector::for_field(facet_field);
         facet_collector.add_facet(Facet::from("/top1"));
-        searcher.search(&AllQuery, &mut facet_collector).unwrap();
+        let counts = searcher.search(&AllQuery, &facet_collector).unwrap();
 
-        let counts: FacetCounts = facet_collector.harvest();
         {
             let facets: Vec<(String, u64)> = counts
                 .get("/top1")
@@ -555,18 +502,16 @@ mod tests {
                     ("/top1/mid2", 50),
                     ("/top1/mid3", 50),
                 ]
-                    .iter()
-                    .map(|&(facet_str, count)| (String::from(facet_str), count))
-                    .collect::<Vec<_>>()
+                .iter()
+                .map(|&(facet_str, count)| (String::from(facet_str), count))
+                .collect::<Vec<_>>()
             );
         }
     }
 
     #[test]
-    #[should_panic(
-        expected = "Tried to add a facet which is a descendant of \
-                    an already added facet."
-    )]
+    #[should_panic(expected = "Tried to add a facet which is a descendant of \
+                               an already added facet.")]
     fn test_misused_facet_collector() {
         let mut facet_collector = FacetCollector::for_field(Field(0));
         facet_collector.add_facet(Facet::from("/country"));
@@ -575,7 +520,7 @@ mod tests {
 
     #[test]
     fn test_doc_unsorted_multifacet() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facets");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -592,8 +537,7 @@ mod tests {
         assert_eq!(searcher.num_docs(), 1);
         let mut facet_collector = FacetCollector::for_field(facet_field);
         facet_collector.add_facet("/subjects");
-        searcher.search(&AllQuery, &mut facet_collector).unwrap();
-        let counts = facet_collector.harvest();
+        let counts = searcher.search(&AllQuery, &facet_collector).unwrap();
         let facets: Vec<(&Facet, u64)> = counts.get("/subjects").collect();
         assert_eq!(facets[0].1, 1);
     }
@@ -607,7 +551,7 @@ mod tests {
 
     #[test]
     fn test_facet_collector_topk() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facet");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -619,14 +563,16 @@ mod tests {
                 let facet = Facet::from(&format!("/facet/{}", c));
                 let doc = doc!(facet_field => facet);
                 iter::repeat(doc).take(count)
-            }).map(|mut doc| {
+            })
+            .map(|mut doc| {
                 doc.add_facet(
                     facet_field,
                     &format!("/facet/{}", thread_rng().sample(&uniform)),
                 );
                 doc
-            }).collect();
-        thread_rng().shuffle(&mut docs[..]);
+            })
+            .collect();
+        docs[..].shuffle(&mut thread_rng());
 
         let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         for doc in docs {
@@ -639,9 +585,8 @@ mod tests {
 
         let mut facet_collector = FacetCollector::for_field(facet_field);
         facet_collector.add_facet("/facet");
-        searcher.search(&AllQuery, &mut facet_collector).unwrap();
+        let counts: FacetCounts = searcher.search(&AllQuery, &facet_collector).unwrap();
 
-        let counts: FacetCounts = facet_collector.harvest();
         {
             let facets: Vec<(&Facet, u64)> = counts.top_k("/facet", 3);
             assert_eq!(
@@ -664,13 +609,13 @@ mod bench {
     use query::AllQuery;
     use rand::{thread_rng, Rng};
     use schema::Facet;
-    use schema::SchemaBuilder;
+    use schema::Schema;
     use test::Bencher;
     use Index;
 
     #[bench]
     fn bench_facet_collector(b: &mut Bencher) {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facet");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -694,8 +639,8 @@ mod bench {
 
         b.iter(|| {
             let searcher = index.searcher();
-            let mut facet_collector = FacetCollector::for_field(facet_field);
-            searcher.search(&AllQuery, &mut facet_collector).unwrap();
+            let facet_collector = FacetCollector::for_field(facet_field);
+            searcher.search(&AllQuery, &facet_collector).unwrap();
         });
     }
 }

src/collector/int_facet_collector.rs

@@ -79,7 +79,7 @@ mod tests {
     // make sure we have facet counters correctly filled
     fn test_facet_collector_results() {
 
-        let mut schema_builder = schema::SchemaBuilder::new();
+        let mut schema_builder = schema::Schema::builder();
         let num_field_i64 = schema_builder.add_i64_field("num_i64", FAST);
         let num_field_u64 = schema_builder.add_u64_field("num_u64", FAST);
         let text_field = schema_builder.add_text_field("text", STRING);
@@ -88,7 +88,7 @@ mod tests {
         let index = Index::create_in_ram(schema.clone());
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 for i in 0u64..10u64 {
                     index_writer.add_document(doc!(

src/collector/mod.rs

@@ -1,7 +1,91 @@
 /*!
-Defines how the documents matching a search query should be processed.
+
+# Collectors
+
+Collectors define the information you want to extract from the documents matching the queries.
+In tantivy jargon, we call this information your search "fruit".
+
+Your fruit could for instance be :
+- [the count of matching documents](./struct.Count.html)
+- [the top 10 documents, by relevancy or by a fast field](./struct.TopDocs.html)
+- [facet counts](./struct.FacetCollector.html)
+
+At one point in your code, you will trigger the actual search operation by calling
+[the `search(...)` method of your `Searcher` object](../struct.Searcher.html#method.search).
+This call will look like this.
+
+```verbatim
+let fruit = searcher.search(&query, &collector)?;
+```
+
+Here the type of fruit is actually determined as an associated type of the collector (`Collector::Fruit`).
+
+
+# Combining several collectors
+
+A rich search experience often requires to run several collectors on your search query.
+For instance,
+- selecting the top-K products matching your query
+- counting the matching documents
+- computing several facets
+- computing statistics about the matching product prices
+
+A simple and efficient way to do that is to pass your collectors as one tuple.
+The resulting `Fruit` will then be a typed tuple with each collector's original fruits
+in their respective position.
+
+```rust
+# extern crate tantivy;
+# use tantivy::schema::*;
+# use tantivy::*;
+# use tantivy::query::*;
+use tantivy::collector::{Count, TopDocs};
+#
+# fn main() -> tantivy::Result<()> {
+# let mut schema_builder = Schema::builder();
+#     let title = schema_builder.add_text_field("title", TEXT);
+#     let schema = schema_builder.build();
+#     let index = Index::create_in_ram(schema);
+#     let mut index_writer = index.writer(3_000_000)?;
+#       index_writer.add_document(doc!(
+#       title => "The Name of the Wind",
+#      ));
+#     index_writer.add_document(doc!(
+#        title => "The Diary of Muadib",
+#     ));
+#     index_writer.commit().unwrap();
+#     index.load_searchers()?;
+#     let searcher = index.searcher();
+#     let query_parser = QueryParser::for_index(&index, vec![title]);
+#     let query = query_parser.parse_query("diary")?;
+let (doc_count, top_docs): (usize, Vec<(Score, DocAddress)>) =
+    searcher.search(&query, &(Count, TopDocs::with_limit(2)))?;
+#     Ok(())
+# }
+```
+
+The `Collector` trait is implemented for up to 4 collectors.
+If you have more than 4 collectors, you can either group them into
+tuples of tuples `(a,(b,(c,d)))`, or rely on `MultiCollector`'s.
+
+# Combining several collectors dynamically
+
+Combining collectors into a tuple is a zero-cost abstraction: everything
+happens as if you had manually implemented a single collector
+combining all of our features.
+
+Unfortunately it requires you to know at compile time your collector types.
+If on the other hand, the collectors depend on some query parameter,
+you can rely on `MultiCollector`'s.
+
+
+# Implementing your own collectors.
+
+See the `custom_collector` example.
+
 */
 
+use downcast_rs;
 use DocId;
 use Result;
 use Score;
@@ -9,7 +93,7 @@ use SegmentLocalId;
 use SegmentReader;
 
 mod count_collector;
-pub use self::count_collector::CountCollector;
+pub use self::count_collector::Count;
 
 mod multi_collector;
 pub use self::multi_collector::MultiCollector;
@@ -17,237 +101,264 @@ pub use self::multi_collector::MultiCollector;
 mod top_collector;
 
 mod top_score_collector;
-pub use self::top_score_collector::TopScoreCollector;
-#[deprecated]
-pub use self::top_score_collector::TopScoreCollector as TopCollector;
+pub use self::top_score_collector::TopDocs;
 
 mod top_field_collector;
-pub use self::top_field_collector::TopFieldCollector;
+pub use self::top_field_collector::TopDocsByField;
 
 mod facet_collector;
 pub use self::facet_collector::FacetCollector;
 
-mod chained_collector;
-pub use self::chained_collector::{chain, ChainedCollector};
+/// `Fruit` is the type for the result of our collection.
+/// e.g. `usize` for the `Count` collector.
+pub trait Fruit: Send + downcast_rs::Downcast {}
+
+impl<T> Fruit for T where T: Send + downcast_rs::Downcast {}
 
 /// Collectors are in charge of collecting and retaining relevant
 /// information from the document found and scored by the query.
 ///
-///
 /// For instance,
 ///
 /// - keeping track of the top 10 best documents
 /// - computing a breakdown over a fast field
 /// - computing the number of documents matching the query
 ///
-/// Queries are in charge of pushing the `DocSet` to the collector.
+/// Our search index is in fact a collection of segments, so
+/// a `Collector` trait is actually more of a factory to instance
+/// `SegmentCollector`s for each segments.
 ///
-/// As they work on multiple segments, they first inform
-/// the collector of a change in a segment and then
-/// call the `collect` method to push the document to the collector.
-///
-/// Temporally, our collector will receive calls
-/// - `.set_segment(0, segment_reader_0)`
-/// - `.collect(doc0_of_segment_0)`
-/// - `.collect(...)`
-/// - `.collect(last_doc_of_segment_0)`
-/// - `.set_segment(1, segment_reader_1)`
-/// - `.collect(doc0_of_segment_1)`
-/// - `.collect(...)`
-/// - `.collect(last_doc_of_segment_1)`
-/// - `...`
-/// - `.collect(last_doc_of_last_segment)`
+/// The collection logic itself is in the `SegmentCollector`.
 ///
 /// Segments are not guaranteed to be visited in any specific order.
-pub trait Collector {
+pub trait Collector: Sync {
+    /// `Fruit` is the type for the result of our collection.
+    /// e.g. `usize` for the `Count` collector.
+    type Fruit: Fruit;
+
+    /// Type of the `SegmentCollector` associated to this collector.
+    type Child: SegmentCollector<Fruit = Self::Fruit>;
+
     /// `set_segment` is called before beginning to enumerate
     /// on this segment.
-    fn set_segment(
-        &mut self,
+    fn for_segment(
+        &self,
         segment_local_id: SegmentLocalId,
         segment: &SegmentReader,
-    ) -> Result<()>;
-    /// The query pushes the scored document to the collector via this method.
-    fn collect(&mut self, doc: DocId, score: Score);
+    ) -> Result<Self::Child>;
 
     /// Returns true iff the collector requires to compute scores for documents.
     fn requires_scoring(&self) -> bool;
+
+    /// Combines the fruit associated to the collection of each segments
+    /// into one fruit.
+    fn merge_fruits(&self, segment_fruits: Vec<Self::Fruit>) -> Result<Self::Fruit>;
 }
 
-impl<'a, C: Collector> Collector for &'a mut C {
-    fn set_segment(
-        &mut self,
-        segment_local_id: SegmentLocalId,
-        segment: &SegmentReader,
-    ) -> Result<()> {
-        (*self).set_segment(segment_local_id, segment)
-    }
+/// The `SegmentCollector` is the trait in charge of defining the
+/// collect operation at the scale of the segment.
+///
+/// `.collect(doc, score)` will be called for every documents
+/// matching the query.
+pub trait SegmentCollector: 'static {
+    /// `Fruit` is the type for the result of our collection.
+    /// e.g. `usize` for the `Count` collector.
+    type Fruit: Fruit;
+
     /// The query pushes the scored document to the collector via this method.
-    fn collect(&mut self, doc: DocId, score: Score) {
-        C::collect(self, doc, score)
+    fn collect(&mut self, doc: DocId, score: Score);
+
+    /// Extract the fruit of the collection from the `SegmentCollector`.
+    fn harvest(self) -> Self::Fruit;
+}
+
+// -----------------------------------------------
+// Tuple implementations.
+
+impl<Left, Right> Collector for (Left, Right)
+where
+    Left: Collector,
+    Right: Collector,
+{
+    type Fruit = (Left::Fruit, Right::Fruit);
+    type Child = (Left::Child, Right::Child);
+
+    fn for_segment(&self, segment_local_id: u32, segment: &SegmentReader) -> Result<Self::Child> {
+        let left = self.0.for_segment(segment_local_id, segment)?;
+        let right = self.1.for_segment(segment_local_id, segment)?;
+        Ok((left, right))
     }
 
     fn requires_scoring(&self) -> bool {
-        C::requires_scoring(self)
+        self.0.requires_scoring() || self.1.requires_scoring()
+    }
+
+    fn merge_fruits(
+        &self,
+        children: Vec<(Left::Fruit, Right::Fruit)>,
+    ) -> Result<(Left::Fruit, Right::Fruit)> {
+        let mut left_fruits = vec![];
+        let mut right_fruits = vec![];
+        for (left_fruit, right_fruit) in children {
+            left_fruits.push(left_fruit);
+            right_fruits.push(right_fruit);
+        }
+        Ok((
+            self.0.merge_fruits(left_fruits)?,
+            self.1.merge_fruits(right_fruits)?,
+        ))
     }
 }
 
+impl<Left, Right> SegmentCollector for (Left, Right)
+where
+    Left: SegmentCollector,
+    Right: SegmentCollector,
+{
+    type Fruit = (Left::Fruit, Right::Fruit);
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        self.0.collect(doc, score);
+        self.1.collect(doc, score);
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        (self.0.harvest(), self.1.harvest())
+    }
+}
+
+// 3-Tuple
+
+impl<One, Two, Three> Collector for (One, Two, Three)
+where
+    One: Collector,
+    Two: Collector,
+    Three: Collector,
+{
+    type Fruit = (One::Fruit, Two::Fruit, Three::Fruit);
+    type Child = (One::Child, Two::Child, Three::Child);
+
+    fn for_segment(&self, segment_local_id: u32, segment: &SegmentReader) -> Result<Self::Child> {
+        let one = self.0.for_segment(segment_local_id, segment)?;
+        let two = self.1.for_segment(segment_local_id, segment)?;
+        let three = self.2.for_segment(segment_local_id, segment)?;
+        Ok((one, two, three))
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.0.requires_scoring() || self.1.requires_scoring() || self.2.requires_scoring()
+    }
+
+    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> Result<Self::Fruit> {
+        let mut one_fruits = vec![];
+        let mut two_fruits = vec![];
+        let mut three_fruits = vec![];
+        for (one_fruit, two_fruit, three_fruit) in children {
+            one_fruits.push(one_fruit);
+            two_fruits.push(two_fruit);
+            three_fruits.push(three_fruit);
+        }
+        Ok((
+            self.0.merge_fruits(one_fruits)?,
+            self.1.merge_fruits(two_fruits)?,
+            self.2.merge_fruits(three_fruits)?,
+        ))
+    }
+}
+
+impl<One, Two, Three> SegmentCollector for (One, Two, Three)
+where
+    One: SegmentCollector,
+    Two: SegmentCollector,
+    Three: SegmentCollector,
+{
+    type Fruit = (One::Fruit, Two::Fruit, Three::Fruit);
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        self.0.collect(doc, score);
+        self.1.collect(doc, score);
+        self.2.collect(doc, score);
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        (self.0.harvest(), self.1.harvest(), self.2.harvest())
+    }
+}
+
+// 4-Tuple
+
+impl<One, Two, Three, Four> Collector for (One, Two, Three, Four)
+where
+    One: Collector,
+    Two: Collector,
+    Three: Collector,
+    Four: Collector,
+{
+    type Fruit = (One::Fruit, Two::Fruit, Three::Fruit, Four::Fruit);
+    type Child = (One::Child, Two::Child, Three::Child, Four::Child);
+
+    fn for_segment(&self, segment_local_id: u32, segment: &SegmentReader) -> Result<Self::Child> {
+        let one = self.0.for_segment(segment_local_id, segment)?;
+        let two = self.1.for_segment(segment_local_id, segment)?;
+        let three = self.2.for_segment(segment_local_id, segment)?;
+        let four = self.3.for_segment(segment_local_id, segment)?;
+        Ok((one, two, three, four))
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.0.requires_scoring()
+            || self.1.requires_scoring()
+            || self.2.requires_scoring()
+            || self.3.requires_scoring()
+    }
+
+    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> Result<Self::Fruit> {
+        let mut one_fruits = vec![];
+        let mut two_fruits = vec![];
+        let mut three_fruits = vec![];
+        let mut four_fruits = vec![];
+        for (one_fruit, two_fruit, three_fruit, four_fruit) in children {
+            one_fruits.push(one_fruit);
+            two_fruits.push(two_fruit);
+            three_fruits.push(three_fruit);
+            four_fruits.push(four_fruit);
+        }
+        Ok((
+            self.0.merge_fruits(one_fruits)?,
+            self.1.merge_fruits(two_fruits)?,
+            self.2.merge_fruits(three_fruits)?,
+            self.3.merge_fruits(four_fruits)?,
+        ))
+    }
+}
+
+impl<One, Two, Three, Four> SegmentCollector for (One, Two, Three, Four)
+where
+    One: SegmentCollector,
+    Two: SegmentCollector,
+    Three: SegmentCollector,
+    Four: SegmentCollector,
+{
+    type Fruit = (One::Fruit, Two::Fruit, Three::Fruit, Four::Fruit);
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        self.0.collect(doc, score);
+        self.1.collect(doc, score);
+        self.2.collect(doc, score);
+        self.3.collect(doc, score);
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        (
+            self.0.harvest(),
+            self.1.harvest(),
+            self.2.harvest(),
+            self.3.harvest(),
+        )
+    }
+}
+
+impl_downcast!(Fruit);
+
 #[cfg(test)]
-pub mod tests {
-
-    use super::*;
-    use core::SegmentReader;
-    use fastfield::BytesFastFieldReader;
-    use fastfield::FastFieldReader;
-    use schema::Field;
-    use DocId;
-    use Score;
-    use SegmentLocalId;
-
-    /// Stores all of the doc ids.
-    /// This collector is only used for tests.
-    /// It is unusable in practise, as it does not store
-    /// the segment ordinals
-    pub struct TestCollector {
-        offset: DocId,
-        segment_max_doc: DocId,
-        docs: Vec<DocId>,
-        scores: Vec<Score>,
-    }
-
-    impl TestCollector {
-        /// Return the exhalist of documents.
-        pub fn docs(self) -> Vec<DocId> {
-            self.docs
-        }
-
-        pub fn scores(self) -> Vec<Score> {
-            self.scores
-        }
-    }
-
-    impl Default for TestCollector {
-        fn default() -> TestCollector {
-            TestCollector {
-                offset: 0,
-                segment_max_doc: 0,
-                docs: Vec::new(),
-                scores: Vec::new(),
-            }
-        }
-    }
-
-    impl Collector for TestCollector {
-        fn set_segment(&mut self, _: SegmentLocalId, reader: &SegmentReader) -> Result<()> {
-            self.offset += self.segment_max_doc;
-            self.segment_max_doc = reader.max_doc();
-            Ok(())
-        }
-
-        fn collect(&mut self, doc: DocId, score: Score) {
-            self.docs.push(doc + self.offset);
-            self.scores.push(score);
-        }
-
-        fn requires_scoring(&self) -> bool {
-            true
-        }
-    }
-
-    /// Collects in order all of the fast fields for all of the
-    /// doc in the `DocSet`
-    ///
-    /// This collector is mainly useful for tests.
-    pub struct FastFieldTestCollector {
-        vals: Vec<u64>,
-        field: Field,
-        ff_reader: Option<FastFieldReader<u64>>,
-    }
-
-    impl FastFieldTestCollector {
-        pub fn for_field(field: Field) -> FastFieldTestCollector {
-            FastFieldTestCollector {
-                vals: Vec::new(),
-                field,
-                ff_reader: None,
-            }
-        }
-
-        pub fn vals(self) -> Vec<u64> {
-            self.vals
-        }
-    }
-
-    impl Collector for FastFieldTestCollector {
-        fn set_segment(&mut self, _: SegmentLocalId, reader: &SegmentReader) -> Result<()> {
-            self.ff_reader = Some(reader.fast_field_reader(self.field)?);
-            Ok(())
-        }
-
-        fn collect(&mut self, doc: DocId, _score: Score) {
-            let val = self.ff_reader.as_ref().unwrap().get(doc);
-            self.vals.push(val);
-        }
-        fn requires_scoring(&self) -> bool {
-            false
-        }
-    }
-
-    /// Collects in order all of the fast field bytes for all of the
-    /// docs in the `DocSet`
-    ///
-    /// This collector is mainly useful for tests.
-    pub struct BytesFastFieldTestCollector {
-        vals: Vec<u8>,
-        field: Field,
-        ff_reader: Option<BytesFastFieldReader>,
-    }
-
-    impl BytesFastFieldTestCollector {
-        pub fn for_field(field: Field) -> BytesFastFieldTestCollector {
-            BytesFastFieldTestCollector {
-                vals: Vec::new(),
-                field,
-                ff_reader: None,
-            }
-        }
-
-        pub fn vals(self) -> Vec<u8> {
-            self.vals
-        }
-    }
-
-    impl Collector for BytesFastFieldTestCollector {
-        fn set_segment(&mut self, _segment_local_id: u32, segment: &SegmentReader) -> Result<()> {
-            self.ff_reader = Some(segment.bytes_fast_field_reader(self.field)?);
-            Ok(())
-        }
-
-        fn collect(&mut self, doc: u32, _score: f32) {
-            let val = self.ff_reader.as_ref().unwrap().get_val(doc);
-            self.vals.extend(val);
-        }
-
-        fn requires_scoring(&self) -> bool {
-            false
-        }
-    }
-}
-
-#[cfg(all(test, feature = "unstable"))]
-mod bench {
-    use collector::{Collector, CountCollector};
-    use test::Bencher;
-
-    #[bench]
-    fn build_collector(b: &mut Bencher) {
-        b.iter(|| {
-            let mut count_collector = CountCollector::default();
-            let docs: Vec<u32> = (0..1_000_000).collect();
-            for doc in docs {
-                count_collector.collect(doc, 1f32);
-            }
-            count_collector.count()
-        });
-    }
-}
+pub mod tests;

src/collector/multi_collector.rs

@@ -1,26 +1,115 @@
 use super::Collector;
+use super::SegmentCollector;
+use collector::Fruit;
+use std::marker::PhantomData;
 use DocId;
 use Result;
 use Score;
 use SegmentLocalId;
 use SegmentReader;
+use TantivyError;
+
+pub struct MultiFruit {
+    sub_fruits: Vec<Option<Box<Fruit>>>,
+}
+
+pub struct CollectorWrapper<TCollector: Collector>(TCollector);
+
+impl<TCollector: Collector> Collector for CollectorWrapper<TCollector> {
+    type Fruit = Box<Fruit>;
+    type Child = Box<BoxableSegmentCollector>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: u32,
+        reader: &SegmentReader,
+    ) -> Result<Box<BoxableSegmentCollector>> {
+        let child = self.0.for_segment(segment_local_id, reader)?;
+        Ok(Box::new(SegmentCollectorWrapper(child)))
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.0.requires_scoring()
+    }
+
+    fn merge_fruits(&self, children: Vec<<Self as Collector>::Fruit>) -> Result<Box<Fruit>> {
+        let typed_fruit: Vec<TCollector::Fruit> = children
+            .into_iter()
+            .map(|untyped_fruit| {
+                untyped_fruit.downcast::<TCollector::Fruit>()
+                    .map(|boxed_but_typed| *boxed_but_typed)
+                    .map_err(|_| {
+                        TantivyError::InvalidArgument("Failed to cast child fruit.".to_string())
+                    })
+            })
+            .collect::<Result<_>>()?;
+        let merged_fruit = self.0.merge_fruits(typed_fruit)?;
+        Ok(Box::new(merged_fruit))
+    }
+}
+
+impl SegmentCollector for Box<BoxableSegmentCollector> {
+    type Fruit = Box<Fruit>;
+
+    fn collect(&mut self, doc: u32, score: f32) {
+        self.as_mut().collect(doc, score);
+    }
+
+    fn harvest(self) -> Box<Fruit> {
+        BoxableSegmentCollector::harvest_from_box(self)
+    }
+}
+
+pub trait BoxableSegmentCollector {
+    fn collect(&mut self, doc: u32, score: f32);
+    fn harvest_from_box(self: Box<Self>) -> Box<Fruit>;
+}
+
+pub struct SegmentCollectorWrapper<TSegmentCollector: SegmentCollector>(TSegmentCollector);
+
+impl<TSegmentCollector: SegmentCollector> BoxableSegmentCollector
+    for SegmentCollectorWrapper<TSegmentCollector>
+{
+    fn collect(&mut self, doc: u32, score: f32) {
+        self.0.collect(doc, score);
+    }
+
+    fn harvest_from_box(self: Box<Self>) -> Box<Fruit> {
+        Box::new(self.0.harvest())
+    }
+}
+
+pub struct FruitHandle<TFruit: Fruit> {
+    pos: usize,
+    _phantom: PhantomData<TFruit>,
+}
+
+impl<TFruit: Fruit> FruitHandle<TFruit> {
+    pub fn extract(self, fruits: &mut MultiFruit) -> TFruit {
+        let boxed_fruit = fruits.sub_fruits[self.pos].take().expect("");
+        *boxed_fruit.downcast::<TFruit>().map_err(|_| ()).expect("Failed to downcast collector fruit.")
+    }
+}
 
 /// Multicollector makes it possible to collect on more than one collector.
 /// It should only be used for use cases where the Collector types is unknown
 /// at compile time.
-/// If the type of the collectors is known, you should prefer to use `ChainedCollector`.
+///
+/// If the type of the collectors is known, you can just group yours collectors
+/// in a tuple. See the
+/// [Combining several collectors section of the collector documentation](./index.html#combining-several-collectors).
 ///
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
+/// use tantivy::schema::{Schema, TEXT};
 /// use tantivy::{Index, Result};
-/// use tantivy::collector::{CountCollector, TopCollector, MultiCollector};
+/// use tantivy::collector::{Count, TopDocs, MultiCollector};
 /// use tantivy::query::QueryParser;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -44,55 +133,115 @@ use SegmentReader;
 ///     index.load_searchers()?;
 ///     let searcher = index.searcher();
 ///
-///     {
-///         let mut top_collector = TopCollector::with_limit(2);
-///         let mut count_collector = CountCollector::default();
-///         {
-///             let mut collectors =
-///                 MultiCollector::from(vec![&mut top_collector, &mut count_collector]);
-///             let query_parser = QueryParser::for_index(&index, vec![title]);
-///             let query = query_parser.parse_query("diary")?;
-///             searcher.search(&*query, &mut collectors).unwrap();
-///         }
-///         assert_eq!(count_collector.count(), 2);
-///         assert!(top_collector.at_capacity());
-///     }
+///     let mut collectors = MultiCollector::new();
+///     let top_docs_handle = collectors.add_collector(TopDocs::with_limit(2));
+///     let count_handle = collectors.add_collector(Count);
+///     let query_parser = QueryParser::for_index(&index, vec![title]);
+///     let query = query_parser.parse_query("diary")?;
+///     let mut multi_fruit = searcher.search(&query, &collectors)?;
+///
+///     let count = count_handle.extract(&mut multi_fruit);
+///     let top_docs = top_docs_handle.extract(&mut multi_fruit);
+///
+///     # assert_eq!(count, 2);
+///     # assert_eq!(top_docs.len(), 2);
 ///
 ///     Ok(())
 /// }
 /// ```
+#[allow(clippy::type_complexity)]
+#[derive(Default)]
 pub struct MultiCollector<'a> {
-    collectors: Vec<&'a mut Collector>,
+    collector_wrappers:
+        Vec<Box<Collector<Child = Box<BoxableSegmentCollector>, Fruit = Box<Fruit>> + 'a>>,
 }
 
 impl<'a> MultiCollector<'a> {
-    /// Constructor
-    pub fn from(collectors: Vec<&'a mut Collector>) -> MultiCollector {
-        MultiCollector { collectors }
+    /// Create a new `MultiCollector`
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// Add a new collector to our `MultiCollector`.
+    pub fn add_collector<'b: 'a, TCollector: Collector + 'b>(
+        &mut self,
+        collector: TCollector,
+    ) -> FruitHandle<TCollector::Fruit> {
+        let pos = self.collector_wrappers.len();
+        self.collector_wrappers
+            .push(Box::new(CollectorWrapper(collector)));
+        FruitHandle {
+            pos,
+            _phantom: PhantomData,
+        }
     }
 }
 
 impl<'a> Collector for MultiCollector<'a> {
-    fn set_segment(
-        &mut self,
+    type Fruit = MultiFruit;
+    type Child = MultiCollectorChild;
+
+    fn for_segment(
+        &self,
         segment_local_id: SegmentLocalId,
         segment: &SegmentReader,
-    ) -> Result<()> {
-        for collector in &mut self.collectors {
-            collector.set_segment(segment_local_id, segment)?;
-        }
-        Ok(())
+    ) -> Result<MultiCollectorChild> {
+        let children = self
+            .collector_wrappers
+            .iter()
+            .map(|collector_wrapper| collector_wrapper.for_segment(segment_local_id, segment))
+            .collect::<Result<Vec<_>>>()?;
+        Ok(MultiCollectorChild { children })
     }
 
+    fn requires_scoring(&self) -> bool {
+        self.collector_wrappers.iter().any(|c| c.requires_scoring())
+    }
+
+    fn merge_fruits(&self, segments_multifruits: Vec<MultiFruit>) -> Result<MultiFruit> {
+        let mut segment_fruits_list: Vec<Vec<Box<Fruit>>> = (0..self.collector_wrappers.len())
+            .map(|_| Vec::with_capacity(segments_multifruits.len()))
+            .collect::<Vec<_>>();
+        for segment_multifruit in segments_multifruits {
+            for (idx, segment_fruit_opt) in segment_multifruit.sub_fruits.into_iter().enumerate() {
+                if let Some(segment_fruit) = segment_fruit_opt {
+                    segment_fruits_list[idx].push(segment_fruit);
+                }
+            }
+        }
+        let sub_fruits = self
+            .collector_wrappers
+            .iter()
+            .zip(segment_fruits_list)
+            .map(|(child_collector, segment_fruits)| {
+                Ok(Some(child_collector.merge_fruits(segment_fruits)?))
+            })
+            .collect::<Result<_>>()?;
+        Ok(MultiFruit { sub_fruits })
+    }
+}
+
+pub struct MultiCollectorChild {
+    children: Vec<Box<BoxableSegmentCollector>>,
+}
+
+impl SegmentCollector for MultiCollectorChild {
+    type Fruit = MultiFruit;
+
     fn collect(&mut self, doc: DocId, score: Score) {
-        for collector in &mut self.collectors {
-            collector.collect(doc, score);
+        for child in &mut self.children {
+            child.collect(doc, score);
         }
     }
-    fn requires_scoring(&self) -> bool {
-        self.collectors
-            .iter()
-            .any(|collector| collector.requires_scoring())
+
+    fn harvest(self) -> MultiFruit {
+        MultiFruit {
+            sub_fruits: self
+                .children
+                .into_iter()
+                .map(|child| Some(child.harvest()))
+                .collect(),
+        }
     }
 }
 
@@ -100,20 +249,42 @@ impl<'a> Collector for MultiCollector<'a> {
 mod tests {
 
     use super::*;
-    use collector::{Collector, CountCollector, TopScoreCollector};
+    use collector::{Count, TopDocs};
+    use query::TermQuery;
+    use schema::IndexRecordOption;
+    use schema::{Schema, TEXT};
+    use Index;
+    use Term;
 
     #[test]
     fn test_multi_collector() {
-        let mut top_collector = TopScoreCollector::with_limit(2);
-        let mut count_collector = CountCollector::default();
+        let mut schema_builder = Schema::builder();
+        let text = schema_builder.add_text_field("text", TEXT);
+        let schema = schema_builder.build();
+
+        let index = Index::create_in_ram(schema);
         {
-            let mut collectors =
-                MultiCollector::from(vec![&mut top_collector, &mut count_collector]);
-            collectors.collect(1, 0.2);
-            collectors.collect(2, 0.1);
-            collectors.collect(3, 0.5);
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            index_writer.add_document(doc!(text=>"abc"));
+            index_writer.add_document(doc!(text=>"abc abc abc"));
+            index_writer.add_document(doc!(text=>"abc abc"));
+            index_writer.commit().unwrap();
+            index_writer.add_document(doc!(text=>""));
+            index_writer.add_document(doc!(text=>"abc abc abc abc"));
+            index_writer.add_document(doc!(text=>"abc"));
+            index_writer.commit().unwrap();
         }
-        assert_eq!(count_collector.count(), 3);
-        assert!(top_collector.at_capacity());
+        index.load_searchers().unwrap();
+        let searcher = index.searcher();
+        let term = Term::from_field_text(text, "abc");
+        let query = TermQuery::new(term, IndexRecordOption::Basic);
+
+        let mut collectors = MultiCollector::new();
+        let topdocs_handler = collectors.add_collector(TopDocs::with_limit(2));
+        let count_handler = collectors.add_collector(Count);
+        let mut multifruits = searcher.search(&query, &mut collectors).unwrap();
+
+        assert_eq!(count_handler.extract(&mut multifruits), 5);
+        assert_eq!(topdocs_handler.extract(&mut multifruits).len(), 2);
     }
 }

src/collector/tests.rs

@@ -0,0 +1,201 @@
+use super::*;
+use core::SegmentReader;
+use fastfield::BytesFastFieldReader;
+use fastfield::FastFieldReader;
+use schema::Field;
+use DocAddress;
+use DocId;
+use Score;
+use SegmentLocalId;
+
+/// Stores all of the doc ids.
+/// This collector is only used for tests.
+/// It is unusable in pr
+///
+/// actise, as it does not store
+/// the segment ordinals
+pub struct TestCollector;
+
+pub struct TestSegmentCollector {
+    segment_id: SegmentLocalId,
+    fruit: TestFruit,
+}
+
+#[derive(Default)]
+pub struct TestFruit {
+    docs: Vec<DocAddress>,
+    scores: Vec<Score>,
+}
+
+impl TestFruit {
+    /// Return the list of matching documents exhaustively.
+    pub fn docs(&self) -> &[DocAddress] {
+        &self.docs[..]
+    }
+
+    pub fn scores(&self) -> &[Score] {
+        &self.scores[..]
+    }
+}
+
+impl Collector for TestCollector {
+    type Fruit = TestFruit;
+    type Child = TestSegmentCollector;
+
+    fn for_segment(
+        &self,
+        segment_id: SegmentLocalId,
+        _reader: &SegmentReader,
+    ) -> Result<TestSegmentCollector> {
+        Ok(TestSegmentCollector {
+            segment_id,
+            fruit: TestFruit::default(),
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        true
+    }
+
+    fn merge_fruits(&self, mut children: Vec<TestFruit>) -> Result<TestFruit> {
+        children.sort_by_key(|fruit| {
+            if fruit.docs().is_empty() {
+                0
+            } else {
+                fruit.docs()[0].segment_ord()
+            }
+        });
+        let mut docs = vec![];
+        let mut scores = vec![];
+        for child in children {
+            docs.extend(child.docs());
+            scores.extend(child.scores);
+        }
+        Ok(TestFruit { docs, scores })
+    }
+}
+
+impl SegmentCollector for TestSegmentCollector {
+    type Fruit = TestFruit;
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        self.fruit.docs.push(DocAddress(self.segment_id, doc));
+        self.fruit.scores.push(score);
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        self.fruit
+    }
+}
+
+/// Collects in order all of the fast fields for all of the
+/// doc in the `DocSet`
+///
+/// This collector is mainly useful for tests.
+pub struct FastFieldTestCollector {
+    field: Field,
+}
+
+pub struct FastFieldSegmentCollector {
+    vals: Vec<u64>,
+    reader: FastFieldReader<u64>,
+}
+
+impl FastFieldTestCollector {
+    pub fn for_field(field: Field) -> FastFieldTestCollector {
+        FastFieldTestCollector { field }
+    }
+}
+
+impl Collector for FastFieldTestCollector {
+    type Fruit = Vec<u64>;
+    type Child = FastFieldSegmentCollector;
+
+    fn for_segment(
+        &self,
+        _: SegmentLocalId,
+        reader: &SegmentReader,
+    ) -> Result<FastFieldSegmentCollector> {
+        Ok(FastFieldSegmentCollector {
+            vals: Vec::new(),
+            reader: reader.fast_field_reader(self.field)?,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(&self, children: Vec<Vec<u64>>) -> Result<Vec<u64>> {
+        Ok(children.into_iter().flat_map(|v| v.into_iter()).collect())
+    }
+}
+
+impl SegmentCollector for FastFieldSegmentCollector {
+    type Fruit = Vec<u64>;
+
+    fn collect(&mut self, doc: DocId, _score: Score) {
+        let val = self.reader.get(doc);
+        self.vals.push(val);
+    }
+
+    fn harvest(self) -> Vec<u64> {
+        self.vals
+    }
+}
+
+/// Collects in order all of the fast field bytes for all of the
+/// docs in the `DocSet`
+///
+/// This collector is mainly useful for tests.
+pub struct BytesFastFieldTestCollector {
+    field: Field,
+}
+
+pub struct BytesFastFieldSegmentCollector {
+    vals: Vec<u8>,
+    reader: BytesFastFieldReader,
+}
+
+impl BytesFastFieldTestCollector {
+    pub fn for_field(field: Field) -> BytesFastFieldTestCollector {
+        BytesFastFieldTestCollector { field }
+    }
+}
+
+impl Collector for BytesFastFieldTestCollector {
+    type Fruit = Vec<u8>;
+    type Child = BytesFastFieldSegmentCollector;
+
+    fn for_segment(
+        &self,
+        _segment_local_id: u32,
+        segment: &SegmentReader,
+    ) -> Result<BytesFastFieldSegmentCollector> {
+        Ok(BytesFastFieldSegmentCollector {
+            vals: Vec::new(),
+            reader: segment.bytes_fast_field_reader(self.field)?,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(&self, children: Vec<Vec<u8>>) -> Result<Vec<u8>> {
+        Ok(children.into_iter().flat_map(|c| c.into_iter()).collect())
+    }
+}
+
+impl SegmentCollector for BytesFastFieldSegmentCollector {
+    type Fruit = Vec<u8>;
+
+    fn collect(&mut self, doc: u32, _score: f32) {
+        let data = self.reader.get_val(doc);
+        self.vals.extend(data);
+    }
+
+    fn harvest(self) -> <Self as SegmentCollector>::Fruit {
+        self.vals
+    }
+}

src/collector/top_collector.rs

@@ -1,56 +1,59 @@
+use serde::export::PhantomData;
 use std::cmp::Ordering;
 use std::collections::BinaryHeap;
 use DocAddress;
 use DocId;
+use Result;
 use SegmentLocalId;
+use SegmentReader;
 
 /// Contains a feature (field, score, etc.) of a document along with the document address.
 ///
 /// It has a custom implementation of `PartialOrd` that reverses the order. This is because the
 /// default Rust heap is a max heap, whereas a min heap is needed.
-#[derive(Clone, Copy)]
-pub struct ComparableDoc<T> {
+///
+/// WARNING: equality is not what you would expect here.
+/// Two elements are equal if their feature is equal, and regardless of whether `doc`
+/// is equal. This should be perfectly fine for this usage, but let's make sure this
+/// struct is never public.
+struct ComparableDoc<T, D> {
     feature: T,
-    doc_address: DocAddress,
+    doc: D,
 }
 
-impl<T: PartialOrd> PartialOrd for ComparableDoc<T> {
+impl<T: PartialOrd, D> PartialOrd for ComparableDoc<T, D> {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))
     }
 }
 
-impl<T: PartialOrd> Ord for ComparableDoc<T> {
+impl<T: PartialOrd, D> Ord for ComparableDoc<T, D> {
     #[inline]
     fn cmp(&self, other: &Self) -> Ordering {
         other
             .feature
             .partial_cmp(&self.feature)
-            .unwrap_or_else(|| other.doc_address.cmp(&self.doc_address))
+            .unwrap_or_else(|| Ordering::Equal)
     }
 }
 
-impl<T: PartialOrd> PartialEq for ComparableDoc<T> {
+impl<T: PartialOrd, D> PartialEq for ComparableDoc<T, D> {
     fn eq(&self, other: &Self) -> bool {
         self.cmp(other) == Ordering::Equal
     }
 }
 
-impl<T: PartialOrd> Eq for ComparableDoc<T> {}
+impl<T: PartialOrd, D> Eq for ComparableDoc<T, D> {}
 
-/// The Top Collector keeps track of the K documents
-/// sorted by type `T`.
-///
-/// The implementation is based on a `BinaryHeap`.
-/// The theorical complexity for collecting the top `K` out of `n` documents
-/// is `O(n log K)`.
-pub struct TopCollector<T> {
+pub(crate) struct TopCollector<T> {
     limit: usize,
-    heap: BinaryHeap<ComparableDoc<T>>,
-    segment_id: u32,
+    _marker: PhantomData<T>,
 }
 
-impl<T: PartialOrd + Clone> TopCollector<T> {
+impl<T> TopCollector<T>
+where
+    T: PartialOrd + Clone,
+{
     /// Creates a top collector, with a number of documents equal to "limit".
     ///
     /// # Panics
@@ -61,127 +64,156 @@ impl<T: PartialOrd + Clone> TopCollector<T> {
         }
         TopCollector {
             limit,
-            heap: BinaryHeap::with_capacity(limit),
-            segment_id: 0,
+            _marker: PhantomData,
         }
     }
 
-    /// Returns K best documents sorted in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn docs(&self) -> Vec<DocAddress> {
-        self.top_docs()
-            .into_iter()
-            .map(|(_feature, doc)| doc)
-            .collect()
+    pub fn limit(&self) -> usize {
+        self.limit
     }
 
-    /// Returns K best FeatureDocuments sorted in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn top_docs(&self) -> Vec<(T, DocAddress)> {
-        let mut feature_docs: Vec<ComparableDoc<T>> = self.heap.iter().cloned().collect();
-        feature_docs.sort();
-        feature_docs
+    pub fn merge_fruits(
+        &self,
+        children: Vec<Vec<(T, DocAddress)>>,
+    ) -> Result<Vec<(T, DocAddress)>> {
+        if self.limit == 0 {
+            return Ok(Vec::new());
+        }
+        let mut top_collector = BinaryHeap::new();
+        for child_fruit in children {
+            for (feature, doc) in child_fruit {
+                if top_collector.len() < self.limit {
+                    top_collector.push(ComparableDoc { feature, doc });
+                } else if let Some(mut head) = top_collector.peek_mut() {
+                    if head.feature < feature {
+                        *head = ComparableDoc { feature, doc };
+                    }
+                }
+            }
+        }
+        Ok(top_collector
+            .into_sorted_vec()
             .into_iter()
-            .map(
-                |ComparableDoc {
-                     feature,
-                     doc_address,
-                 }| (feature, doc_address),
-            ).collect()
+            .map(|cdoc| (cdoc.feature, cdoc.doc))
+            .collect())
+    }
+
+    pub(crate) fn for_segment(
+        &self,
+        segment_id: SegmentLocalId,
+        _: &SegmentReader,
+    ) -> Result<TopSegmentCollector<T>> {
+        Ok(TopSegmentCollector::new(segment_id, self.limit))
+    }
+}
+
+/// The Top Collector keeps track of the K documents
+/// sorted by type `T`.
+///
+/// The implementation is based on a `BinaryHeap`.
+/// The theorical complexity for collecting the top `K` out of `n` documents
+/// is `O(n log K)`.
+pub(crate) struct TopSegmentCollector<T> {
+    limit: usize,
+    heap: BinaryHeap<ComparableDoc<T, DocId>>,
+    segment_id: u32,
+}
+
+impl<T: PartialOrd> TopSegmentCollector<T> {
+    fn new(segment_id: SegmentLocalId, limit: usize) -> TopSegmentCollector<T> {
+        TopSegmentCollector {
+            limit,
+            heap: BinaryHeap::with_capacity(limit),
+            segment_id,
+        }
+    }
+}
+
+impl<T: PartialOrd + Clone> TopSegmentCollector<T> {
+    pub fn harvest(self) -> Vec<(T, DocAddress)> {
+        let segment_id = self.segment_id;
+        self.heap
+            .into_sorted_vec()
+            .into_iter()
+            .map(|comparable_doc| {
+                (
+                    comparable_doc.feature,
+                    DocAddress(segment_id, comparable_doc.doc),
+                )
+            })
+            .collect()
     }
 
     /// Return true iff at least K documents have gone through
     /// the collector.
-    #[inline]
-    pub fn at_capacity(&self) -> bool {
+    #[inline(always)]
+    pub(crate) fn at_capacity(&self) -> bool {
         self.heap.len() >= self.limit
     }
 
-    /// Sets the segment local ID for the collector
-    pub fn set_segment_id(&mut self, segment_id: SegmentLocalId) {
-        self.segment_id = segment_id;
-    }
-
     /// Collects a document scored by the given feature
     ///
     /// It collects documents until it has reached the max capacity. Once it reaches capacity, it
     /// will compare the lowest scoring item with the given one and keep whichever is greater.
+    #[inline(always)]
     pub fn collect(&mut self, doc: DocId, feature: T) {
         if self.at_capacity() {
             // It's ok to unwrap as long as a limit of 0 is forbidden.
-            let limit_doc: ComparableDoc<T> = self
-                .heap
-                .peek()
-                .expect("Top collector with size 0 is forbidden")
-                .clone();
-            if limit_doc.feature < feature {
-                let mut mut_head = self
-                    .heap
-                    .peek_mut()
-                    .expect("Top collector with size 0 is forbidden");
-                mut_head.feature = feature;
-                mut_head.doc_address = DocAddress(self.segment_id, doc);
+            if let Some(limit_feature) = self.heap.peek().map(|head| head.feature.clone()) {
+                if limit_feature < feature {
+                    if let Some(mut head) = self.heap.peek_mut() {
+                        head.feature = feature;
+                        head.doc = doc;
+                    }
+                }
             }
         } else {
-            let wrapped_doc = ComparableDoc {
-                feature,
-                doc_address: DocAddress(self.segment_id, doc),
-            };
-            self.heap.push(wrapped_doc);
+            // we have not reached capacity yet, so we can just push the
+            // element.
+            self.heap.push(ComparableDoc { feature, doc });
         }
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
-    use DocId;
+    use super::{TopCollector, TopSegmentCollector};
+    use DocAddress;
     use Score;
 
     #[test]
     fn test_top_collector_not_at_capacity() {
-        let mut top_collector = TopCollector::with_limit(4);
+        let mut top_collector = TopSegmentCollector::new(0, 4);
         top_collector.collect(1, 0.8);
         top_collector.collect(3, 0.2);
         top_collector.collect(5, 0.3);
-        assert!(!top_collector.at_capacity());
-        let score_docs: Vec<(Score, DocId)> = top_collector
-            .top_docs()
-            .into_iter()
-            .map(|(score, doc_address)| (score, doc_address.doc()))
-            .collect();
-        assert_eq!(score_docs, vec![(0.8, 1), (0.3, 5), (0.2, 3)]);
+        assert_eq!(
+            top_collector.harvest(),
+            vec![
+                (0.8, DocAddress(0, 1)),
+                (0.3, DocAddress(0, 5)),
+                (0.2, DocAddress(0, 3))
+            ]
+        );
     }
 
     #[test]
     fn test_top_collector_at_capacity() {
-        let mut top_collector = TopCollector::with_limit(4);
+        let mut top_collector = TopSegmentCollector::new(0, 4);
         top_collector.collect(1, 0.8);
         top_collector.collect(3, 0.2);
         top_collector.collect(5, 0.3);
         top_collector.collect(7, 0.9);
         top_collector.collect(9, -0.2);
-        assert!(top_collector.at_capacity());
-        {
-            let score_docs: Vec<(Score, DocId)> = top_collector
-                .top_docs()
-                .into_iter()
-                .map(|(score, doc_address)| (score, doc_address.doc()))
-                .collect();
-            assert_eq!(score_docs, vec![(0.9, 7), (0.8, 1), (0.3, 5), (0.2, 3)]);
-        }
-        {
-            let docs: Vec<DocId> = top_collector
-                .docs()
-                .into_iter()
-                .map(|doc_address| doc_address.doc())
-                .collect();
-            assert_eq!(docs, vec![7, 1, 5, 3]);
-        }
+        assert_eq!(
+            top_collector.harvest(),
+            vec![
+                (0.9, DocAddress(0, 7)),
+                (0.8, DocAddress(0, 1)),
+                (0.3, DocAddress(0, 5)),
+                (0.2, DocAddress(0, 3))
+            ]
+        );
     }
 
     #[test]
@@ -189,5 +221,4 @@ mod tests {
     fn test_top_0() {
         let _collector: TopCollector<Score> = TopCollector::with_limit(0);
     }
-
 }

src/collector/top_field_collector.rs

@@ -1,12 +1,13 @@
 use super::Collector;
 use collector::top_collector::TopCollector;
+use collector::top_collector::TopSegmentCollector;
+use collector::SegmentCollector;
 use fastfield::FastFieldReader;
 use fastfield::FastValue;
 use schema::Field;
 use DocAddress;
-use DocId;
 use Result;
-use Score;
+use SegmentLocalId;
 use SegmentReader;
 
 /// The Top Field Collector keeps track of the K documents
@@ -19,67 +20,57 @@ use SegmentReader;
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT, FAST};
-/// use tantivy::{Index, Result, DocId};
-/// use tantivy::collector::TopFieldCollector;
-/// use tantivy::query::QueryParser;
+/// # use tantivy::schema::{Schema, Field, FAST, TEXT};
+/// # use tantivy::{Index, Result, DocAddress};
+/// # use tantivy::query::{Query, QueryParser};
+/// use tantivy::collector::TopDocs;
 ///
-/// # fn main() { example().unwrap(); }
-/// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
-///     let title = schema_builder.add_text_field("title", TEXT);
-///     let rating = schema_builder.add_u64_field("rating", FAST);
-///     let schema = schema_builder.build();
-///     let index = Index::create_in_ram(schema);
-///     {
-///         let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
-///         index_writer.add_document(doc!(
-///             title => "The Name of the Wind",
-///             rating => 92u64,
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of Muadib",
-///             rating => 97u64,
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "A Dairy Cow",
-///             rating => 63u64,
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of a Young Girl",
-///             rating => 80u64,
-///         ));
-///         index_writer.commit().unwrap();
-///     }
+/// # fn main() {
+/// #   let mut schema_builder = Schema::builder();
+/// #   let title = schema_builder.add_text_field("title", TEXT);
+/// #   let rating = schema_builder.add_u64_field("rating", FAST);
+/// #   let schema = schema_builder.build();
+/// #   let index = Index::create_in_ram(schema);
+/// #   let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+/// #   index_writer.add_document(doc!(
+/// #       title => "The Name of the Wind",
+/// #       rating => 92u64,
+/// #   ));
+/// #   index_writer.add_document(doc!(title => "The Diary of Muadib", rating => 97u64));
+/// #   index_writer.add_document(doc!(title => "A Dairy Cow", rating => 63u64));
+/// #   index_writer.add_document(doc!(title => "The Diary of a Young Girl", rating => 80u64));
+/// #   index_writer.commit().unwrap();
+/// #   index.load_searchers().unwrap();
+///	#   let query = QueryParser::for_index(&index, vec![title]).parse_query("diary").unwrap();
+/// #   let top_docs = docs_sorted_by_rating(&index, &query, rating).unwrap();
+/// #   assert_eq!(top_docs,
+/// #            vec![(97u64, DocAddress(0u32, 1)),
+/// #                 (80u64, DocAddress(0u32, 3))]);
+/// # }
+/// #
+/// /// Searches the document matching the given query, and
+/// /// collects the top 10 documents, order by the `field`
+/// /// given in argument.
+/// ///
+/// /// `field` is required to be a FAST field.
+/// fn docs_sorted_by_rating(index: &Index, query: &Query, sort_by_field: Field)
+///     -> Result<Vec<(u64, DocAddress)>> {
 ///
-///     index.load_searchers()?;
-///     let searcher = index.searcher();
+///     // This is where we build our collector!
+///     let top_docs_by_rating = TopDocs::with_limit(2).order_by_field(sort_by_field);
 ///
-///     {
-///	        let mut top_collector = TopFieldCollector::with_limit(rating, 2);
-///         let query_parser = QueryParser::for_index(&index, vec![title]);
-///         let query = query_parser.parse_query("diary")?;
-///         searcher.search(&*query, &mut top_collector).unwrap();
-///
-///         let score_docs: Vec<(u64, DocId)> = top_collector
-///           .top_docs()
-///           .into_iter()
-///           .map(|(field, doc_address)| (field, doc_address.doc()))
-///           .collect();
-///
-///         assert_eq!(score_docs, vec![(97u64, 1), (80, 3)]);
-///     }
-///
-///     Ok(())
+///     // ... and here is our documents. Not this is a simple vec.
+///     // The `u64` in the pair is the value of our fast field for each documents.
+///     index.searcher()
+///          .search(query, &top_docs_by_rating)
 /// }
 /// ```
-pub struct TopFieldCollector<T: FastValue> {
-    field: Field,
+pub struct TopDocsByField<T> {
     collector: TopCollector<T>,
-    fast_field: Option<FastFieldReader<T>>,
+    field: Field,
 }
 
-impl<T: FastValue + PartialOrd + Clone> TopFieldCollector<T> {
+impl<T: FastValue + PartialOrd + Clone> TopDocsByField<T> {
     /// Creates a top field collector, with a number of documents equal to "limit".
     ///
     /// The given field name must be a fast field, otherwise the collector have an error while
@@ -87,68 +78,72 @@ impl<T: FastValue + PartialOrd + Clone> TopFieldCollector<T> {
     ///
     /// # Panics
     /// The method panics if limit is 0
-    pub fn with_limit(field: Field, limit: usize) -> Self {
-        TopFieldCollector {
-            field,
+    pub(crate) fn new(field: Field, limit: usize) -> TopDocsByField<T> {
+        TopDocsByField {
             collector: TopCollector::with_limit(limit),
-            fast_field: None,
+            field,
         }
     }
-
-    /// Returns K best documents sorted the given field name in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn docs(&self) -> Vec<DocAddress> {
-        self.collector.docs()
-    }
-
-    /// Returns K best FieldDocuments sorted in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn top_docs(&self) -> Vec<(T, DocAddress)> {
-        self.collector.top_docs()
-    }
-
-    /// Return true iff at least K documents have gone through
-    /// the collector.
-    #[inline]
-    pub fn at_capacity(&self) -> bool {
-        self.collector.at_capacity()
-    }
 }
 
-impl<T: FastValue + PartialOrd + Clone> Collector for TopFieldCollector<T> {
-    fn set_segment(&mut self, segment_id: u32, segment: &SegmentReader) -> Result<()> {
-        self.collector.set_segment_id(segment_id);
-        self.fast_field = Some(segment.fast_field_reader(self.field)?);
-        Ok(())
-    }
+impl<T: FastValue + PartialOrd + Send + Sync + 'static> Collector for TopDocsByField<T> {
+    type Fruit = Vec<(T, DocAddress)>;
 
-    fn collect(&mut self, doc: DocId, _score: Score) {
-        let field_value = self
-            .fast_field
-            .as_ref()
-            .expect("collect() was called before set_segment. This should never happen.")
-            .get(doc);
-        self.collector.collect(doc, field_value);
+    type Child = TopFieldSegmentCollector<T>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: SegmentLocalId,
+        reader: &SegmentReader,
+    ) -> Result<TopFieldSegmentCollector<T>> {
+        let collector = self.collector.for_segment(segment_local_id, reader)?;
+        let reader = reader.fast_field_reader(self.field)?;
+        Ok(TopFieldSegmentCollector { collector, reader })
     }
 
     fn requires_scoring(&self) -> bool {
         false
     }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<Vec<(T, DocAddress)>>,
+    ) -> Result<Vec<(T, DocAddress)>> {
+        self.collector.merge_fruits(segment_fruits)
+    }
+}
+
+pub struct TopFieldSegmentCollector<T: FastValue + PartialOrd> {
+    collector: TopSegmentCollector<T>,
+    reader: FastFieldReader<T>,
+}
+
+impl<T: FastValue + PartialOrd + Send + Sync + 'static> SegmentCollector
+    for TopFieldSegmentCollector<T>
+{
+    type Fruit = Vec<(T, DocAddress)>;
+
+    fn collect(&mut self, doc: u32, _score: f32) {
+        let field_value = self.reader.get(doc);
+        self.collector.collect(doc, field_value);
+    }
+
+    fn harvest(self) -> Vec<(T, DocAddress)> {
+        self.collector.harvest()
+    }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use super::TopDocsByField;
+    use collector::Collector;
+    use collector::TopDocs;
     use query::Query;
     use query::QueryParser;
     use schema::Field;
     use schema::IntOptions;
-    use schema::Schema;
-    use schema::{SchemaBuilder, FAST, TEXT};
+    use schema::{Schema, FAST, TEXT};
+    use DocAddress;
     use Index;
     use IndexWriter;
     use TantivyError;
@@ -158,7 +153,7 @@ mod tests {
 
     #[test]
     fn test_top_collector_not_at_capacity() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field(TITLE, TEXT);
         let size = schema_builder.add_u64_field(SIZE, FAST);
         let schema = schema_builder.build();
@@ -178,22 +173,22 @@ mod tests {
         });
         let searcher = index.searcher();
 
-        let mut top_collector = TopFieldCollector::with_limit(size, 4);
-        searcher.search(&*query, &mut top_collector).unwrap();
-        assert!(!top_collector.at_capacity());
-
-        let score_docs: Vec<(u64, DocId)> = top_collector
-            .top_docs()
-            .into_iter()
-            .map(|(field, doc_address)| (field, doc_address.doc()))
-            .collect();
-        assert_eq!(score_docs, vec![(64, 1), (16, 2), (12, 0)]);
+        let top_collector = TopDocs::with_limit(4).order_by_field(size);
+        let top_docs: Vec<(u64, DocAddress)> = searcher.search(&query, &top_collector).unwrap();
+        assert_eq!(
+            top_docs,
+            vec![
+                (64, DocAddress(0, 1)),
+                (16, DocAddress(0, 2)),
+                (12, DocAddress(0, 0))
+            ]
+        );
     }
 
     #[test]
     #[should_panic]
     fn test_field_does_not_exist() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field(TITLE, TEXT);
         let size = schema_builder.add_u64_field(SIZE, FAST);
         let schema = schema_builder.build();
@@ -204,14 +199,16 @@ mod tests {
             ));
         });
         let searcher = index.searcher();
-        let segment = searcher.segment_reader(0);
-        let mut top_collector: TopFieldCollector<u64> = TopFieldCollector::with_limit(Field(2), 4);
-        let _ = top_collector.set_segment(0, segment);
+        let top_collector: TopDocsByField<u64> = TopDocs::with_limit(4).order_by_field(Field(2));
+        let segment_reader = searcher.segment_reader(0u32);
+        top_collector
+            .for_segment(0, segment_reader)
+            .expect("should panic");
     }
 
     #[test]
     fn test_field_not_fast_field() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field(TITLE, TEXT);
         let size = schema_builder.add_u64_field(SIZE, IntOptions::default());
         let schema = schema_builder.build();
@@ -223,26 +220,16 @@ mod tests {
         });
         let searcher = index.searcher();
         let segment = searcher.segment_reader(0);
-        let mut top_collector: TopFieldCollector<u64> = TopFieldCollector::with_limit(size, 4);
+        let top_collector: TopDocsByField<u64> = TopDocs::with_limit(4).order_by_field(size);
         assert_matches!(
-            top_collector.set_segment(0, segment),
-            Err(TantivyError::FastFieldError(_))
+            top_collector
+                .for_segment(0, segment)
+                .map(|_| ())
+                .unwrap_err(),
+            TantivyError::FastFieldError(_)
         );
     }
 
-    #[test]
-    #[should_panic]
-    fn test_collect_before_set_segment() {
-        let mut top_collector: TopFieldCollector<u64> = TopFieldCollector::with_limit(Field(0), 4);
-        top_collector.collect(0, 0f32);
-    }
-
-    #[test]
-    #[should_panic]
-    fn test_top_0() {
-        let _: TopFieldCollector<u64> = TopFieldCollector::with_limit(Field(0), 0);
-    }
-
     fn index(
         query: &str,
         query_field: Field,

src/collector/top_score_collector.rs

@@ -1,5 +1,10 @@
 use super::Collector;
 use collector::top_collector::TopCollector;
+use collector::top_collector::TopSegmentCollector;
+use collector::SegmentCollector;
+use collector::TopDocsByField;
+use fastfield::FastValue;
+use schema::Field;
 use DocAddress;
 use DocId;
 use Result;
@@ -17,14 +22,15 @@ use SegmentReader;
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
-/// use tantivy::{Index, Result, DocId, Score};
-/// use tantivy::collector::TopScoreCollector;
+/// use tantivy::DocAddress;
+/// use tantivy::schema::{Schema, TEXT};
+/// use tantivy::{Index, Result};
+/// use tantivy::collector::TopDocs;
 /// use tantivy::query::QueryParser;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -48,140 +54,147 @@ use SegmentReader;
 ///     index.load_searchers()?;
 ///     let searcher = index.searcher();
 ///
-///     {
-///	        let mut top_collector = TopScoreCollector::with_limit(2);
-///         let query_parser = QueryParser::for_index(&index, vec![title]);
-///         let query = query_parser.parse_query("diary")?;
-///         searcher.search(&*query, &mut top_collector).unwrap();
+///     let query_parser = QueryParser::for_index(&index, vec![title]);
+///     let query = query_parser.parse_query("diary")?;
+///     let top_docs = searcher.search(&query, &TopDocs::with_limit(2))?;
 ///
-///         let score_docs: Vec<(Score, DocId)> = top_collector
-///           .top_docs()
-///           .into_iter()
-///           .map(|(score, doc_address)| (score, doc_address.doc()))
-///           .collect();
-///
-///         assert_eq!(score_docs, vec![(0.7261542, 1), (0.6099695, 3)]);
-///     }
+///     assert_eq!(&top_docs[0], &(0.7261542, DocAddress(0, 1)));
+///     assert_eq!(&top_docs[1], &(0.6099695, DocAddress(0, 3)));
 ///
 ///     Ok(())
 /// }
 /// ```
-pub struct TopScoreCollector {
-    collector: TopCollector<Score>,
-}
+pub struct TopDocs(TopCollector<Score>);
 
-impl TopScoreCollector {
+impl TopDocs {
     /// Creates a top score collector, with a number of documents equal to "limit".
     ///
     /// # Panics
     /// The method panics if limit is 0
-    pub fn with_limit(limit: usize) -> TopScoreCollector {
-        TopScoreCollector {
-            collector: TopCollector::with_limit(limit),
-        }
+    pub fn with_limit(limit: usize) -> TopDocs {
+        TopDocs(TopCollector::with_limit(limit))
     }
 
-    /// Returns K best scored documents sorted in decreasing order.
+    /// Set top-K to rank documents by a given fast field.
     ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn docs(&self) -> Vec<DocAddress> {
-        self.collector.docs()
-    }
-
-    /// Returns K best ScoredDocuments sorted in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    pub fn top_docs(&self) -> Vec<(Score, DocAddress)> {
-        self.collector.top_docs()
-    }
-
-    /// Returns K best ScoredDocuments sorted in decreasing order.
-    ///
-    /// Calling this method triggers the sort.
-    /// The result of the sort is not cached.
-    #[deprecated]
-    pub fn score_docs(&self) -> Vec<(Score, DocAddress)> {
-        self.collector.top_docs()
-    }
-
-    /// Return true iff at least K documents have gone through
-    /// the collector.
-    #[inline]
-    pub fn at_capacity(&self) -> bool {
-        self.collector.at_capacity()
+    /// (By default, `TopDocs` collects the top-K documents sorted by
+    /// the similarity score.)
+    pub fn order_by_field<T: PartialOrd + FastValue + Clone>(
+        self,
+        field: Field,
+    ) -> TopDocsByField<T> {
+        TopDocsByField::new(field, self.0.limit())
     }
 }
 
-impl Collector for TopScoreCollector {
-    fn set_segment(&mut self, segment_id: SegmentLocalId, _: &SegmentReader) -> Result<()> {
-        self.collector.set_segment_id(segment_id);
-        Ok(())
-    }
+impl Collector for TopDocs {
+    type Fruit = Vec<(Score, DocAddress)>;
 
-    fn collect(&mut self, doc: DocId, score: Score) {
-        self.collector.collect(doc, score);
+    type Child = TopScoreSegmentCollector;
+
+    fn for_segment(
+        &self,
+        segment_local_id: SegmentLocalId,
+        reader: &SegmentReader,
+    ) -> Result<Self::Child> {
+        let collector = self.0.for_segment(segment_local_id, reader)?;
+        Ok(TopScoreSegmentCollector(collector))
     }
 
     fn requires_scoring(&self) -> bool {
         true
     }
+
+    fn merge_fruits(&self, child_fruits: Vec<Vec<(Score, DocAddress)>>) -> Result<Self::Fruit> {
+        self.0.merge_fruits(child_fruits)
+    }
+}
+
+/// Segment Collector associated to `TopDocs`.
+pub struct TopScoreSegmentCollector(TopSegmentCollector<Score>);
+
+impl SegmentCollector for TopScoreSegmentCollector {
+    type Fruit = Vec<(Score, DocAddress)>;
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        self.0.collect(doc, score)
+    }
+
+    fn harvest(self) -> Vec<(Score, DocAddress)> {
+        self.0.harvest()
+    }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
-    use collector::Collector;
-    use DocId;
+    use super::TopDocs;
+    use query::QueryParser;
+    use schema::Schema;
+    use schema::TEXT;
+    use DocAddress;
+    use Index;
     use Score;
 
+    fn make_index() -> Index {
+        let mut schema_builder = Schema::builder();
+        let text_field = schema_builder.add_text_field("text", TEXT);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        {
+            // writing the segment
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            index_writer.add_document(doc!(text_field=>"Hello happy tax payer."));
+            index_writer.add_document(doc!(text_field=>"Droopy says hello happy tax payer"));
+            index_writer.add_document(doc!(text_field=>"I like Droopy"));
+            assert!(index_writer.commit().is_ok());
+        }
+        index.load_searchers().unwrap();
+        index
+    }
+
     #[test]
     fn test_top_collector_not_at_capacity() {
-        let mut top_collector = TopScoreCollector::with_limit(4);
-        top_collector.collect(1, 0.8);
-        top_collector.collect(3, 0.2);
-        top_collector.collect(5, 0.3);
-        assert!(!top_collector.at_capacity());
-        let score_docs: Vec<(Score, DocId)> = top_collector
-            .top_docs()
-            .into_iter()
-            .map(|(score, doc_address)| (score, doc_address.doc()))
-            .collect();
-        assert_eq!(score_docs, vec![(0.8, 1), (0.3, 5), (0.2, 3)]);
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let score_docs: Vec<(Score, DocAddress)> = index
+            .searcher()
+            .search(&text_query, &TopDocs::with_limit(4))
+            .unwrap();
+        assert_eq!(
+            score_docs,
+            vec![
+                (0.81221175, DocAddress(0u32, 1)),
+                (0.5376842, DocAddress(0u32, 2)),
+                (0.48527452, DocAddress(0, 0))
+            ]
+        );
     }
 
     #[test]
     fn test_top_collector_at_capacity() {
-        let mut top_collector = TopScoreCollector::with_limit(4);
-        top_collector.collect(1, 0.8);
-        top_collector.collect(3, 0.2);
-        top_collector.collect(5, 0.3);
-        top_collector.collect(7, 0.9);
-        top_collector.collect(9, -0.2);
-        assert!(top_collector.at_capacity());
-        {
-            let score_docs: Vec<(Score, DocId)> = top_collector
-                .top_docs()
-                .into_iter()
-                .map(|(score, doc_address)| (score, doc_address.doc()))
-                .collect();
-            assert_eq!(score_docs, vec![(0.9, 7), (0.8, 1), (0.3, 5), (0.2, 3)]);
-        }
-        {
-            let docs: Vec<DocId> = top_collector
-                .docs()
-                .into_iter()
-                .map(|doc_address| doc_address.doc())
-                .collect();
-            assert_eq!(docs, vec![7, 1, 5, 3]);
-        }
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let score_docs: Vec<(Score, DocAddress)> = index
+            .searcher()
+            .search(&text_query, &TopDocs::with_limit(2))
+            .unwrap();
+        assert_eq!(
+            score_docs,
+            vec![
+                (0.81221175, DocAddress(0u32, 1)),
+                (0.5376842, DocAddress(0u32, 2)),
+            ]
+        );
     }
 
     #[test]
     #[should_panic]
     fn test_top_0() {
-        TopScoreCollector::with_limit(0);
+        TopDocs::with_limit(0);
     }
 
 }

src/common/bitpacker.rs

@@ -1,9 +1,6 @@
-use common::serialize::BinarySerializable;
+use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use std::io;
-use std::io::Write;
-use std::mem;
 use std::ops::Deref;
-use std::ptr;
 
 pub(crate) struct BitPacker {
     mini_buffer: u64,
@@ -18,7 +15,7 @@ impl BitPacker {
         }
     }
 
-    pub fn write<TWrite: Write>(
+    pub fn write<TWrite: io::Write>(
         &mut self,
         val: u64,
         num_bits: u8,
@@ -28,14 +25,14 @@ impl BitPacker {
         let num_bits = num_bits as usize;
         if self.mini_buffer_written + num_bits > 64 {
             self.mini_buffer |= val_u64.wrapping_shl(self.mini_buffer_written as u32);
-            self.mini_buffer.serialize(output)?;
+            output.write_u64::<LittleEndian>(self.mini_buffer)?;
             self.mini_buffer = val_u64.wrapping_shr((64 - self.mini_buffer_written) as u32);
             self.mini_buffer_written = self.mini_buffer_written + num_bits - 64;
         } else {
             self.mini_buffer |= val_u64 << self.mini_buffer_written;
             self.mini_buffer_written += num_bits;
             if self.mini_buffer_written == 64 {
-                self.mini_buffer.serialize(output)?;
+                output.write_u64::<LittleEndian>(self.mini_buffer)?;
                 self.mini_buffer_written = 0;
                 self.mini_buffer = 0u64;
             }
@@ -43,17 +40,18 @@ impl BitPacker {
         Ok(())
     }
 
-    pub fn flush<TWrite: Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
+    pub fn flush<TWrite: io::Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
         if self.mini_buffer_written > 0 {
             let num_bytes = (self.mini_buffer_written + 7) / 8;
-            let arr: [u8; 8] = unsafe { mem::transmute::<u64, [u8; 8]>(self.mini_buffer.to_le()) };
+            let mut arr: [u8; 8] = [0u8; 8];
+            LittleEndian::write_u64(&mut arr, self.mini_buffer);
             output.write_all(&arr[..num_bytes])?;
             self.mini_buffer_written = 0;
         }
         Ok(())
     }
 
-    pub fn close<TWrite: Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
+    pub fn close<TWrite: io::Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
         self.flush(output)?;
         // Padding the write file to simplify reads.
         output.write_all(&[0u8; 7])?;
@@ -102,39 +100,10 @@ where
             addr + 8 <= data.len(),
             "The fast field field should have been padded with 7 bytes."
         );
-        #[cfg_attr(feature = "cargo-clippy", allow(clippy::cast_ptr_alignment))]
-        let val_unshifted_unmasked: u64 =
-            u64::from_le(unsafe { ptr::read_unaligned(data[addr..].as_ptr() as *const u64) });
+        let val_unshifted_unmasked: u64 = LittleEndian::read_u64(&data[addr..]);
         let val_shifted = (val_unshifted_unmasked >> bit_shift) as u64;
         val_shifted & mask
     }
-
-    /// Reads a range of values from the fast field.
-    ///
-    /// The range of values read is from
-    /// `[start..start + output.len()[`
-    pub fn get_range(&self, start: u32, output: &mut [u64]) {
-        if self.num_bits == 0 {
-            for val in output.iter_mut() {
-                *val = 0u64;
-            }
-        } else {
-            let data: &[u8] = &*self.data;
-            let num_bits = self.num_bits;
-            let mask = self.mask;
-            let mut addr_in_bits = (start as usize) * num_bits;
-            for output_val in output.iter_mut() {
-                let addr = addr_in_bits >> 3;
-                let bit_shift = addr_in_bits & 7;
-                #[cfg_attr(feature = "cargo-clippy", allow(clippy::cast_ptr_alignment))]
-                let val_unshifted_unmasked: u64 =
-                    unsafe { ptr::read_unaligned(data[addr..].as_ptr() as *const u64) };
-                let val_shifted = (val_unshifted_unmasked >> bit_shift) as u64;
-                *output_val = val_shifted & mask;
-                addr_in_bits += num_bits;
-            }
-        }
-    }
 }
 
 #[cfg(test)]
@@ -172,17 +141,4 @@ mod test {
         test_bitpacker_util(6, 14);
         test_bitpacker_util(1000, 14);
     }
-
-    #[test]
-    fn test_bitpacker_range() {
-        let (bitunpacker, vals) = create_fastfield_bitpacker(100_000, 12);
-        let buffer_len = 100;
-        let mut buffer = vec![0u64; buffer_len];
-        for start in vec![0, 10, 20, 100, 1_000] {
-            bitunpacker.get_range(start as u32, &mut buffer[..]);
-            for i in 0..buffer_len {
-                assert_eq!(buffer[i], vals[start + i]);
-            }
-        }
-    }
 }

src/common/composite_file.rs

@@ -4,8 +4,8 @@ use common::VInt;
 use directory::ReadOnlySource;
 use directory::WritePtr;
 use schema::Field;
-use space_usage::PerFieldSpaceUsage;
 use space_usage::FieldUsage;
+use space_usage::PerFieldSpaceUsage;
 use std::collections::HashMap;
 use std::io::Write;
 use std::io::{self, Read};
@@ -172,7 +172,8 @@ impl CompositeFile {
     pub fn space_usage(&self) -> PerFieldSpaceUsage {
         let mut fields = HashMap::new();
         for (&field_addr, &(start, end)) in self.offsets_index.iter() {
-            fields.entry(field_addr.field)
+            fields
+                .entry(field_addr.field)
                 .or_insert_with(|| FieldUsage::empty(field_addr.field))
                 .add_field_idx(field_addr.idx, end - start);
         }

src/common/mod.rs

@@ -10,7 +10,7 @@ pub(crate) use self::bitset::TinySet;
 pub(crate) use self::composite_file::{CompositeFile, CompositeWrite};
 pub use self::counting_writer::CountingWriter;
 pub use self::serialize::{BinarySerializable, FixedSize};
-pub use self::vint::VInt;
+pub use self::vint::{read_u32_vint, serialize_vint_u32, write_u32_vint, VInt};
 pub use byteorder::LittleEndian as Endianness;
 
 use std::io;

src/common/vint.rs

@@ -1,4 +1,5 @@
 use super::BinarySerializable;
+use byteorder::{ByteOrder, LittleEndian};
 use std::io;
 use std::io::Read;
 use std::io::Write;
@@ -9,6 +10,100 @@ pub struct VInt(pub u64);
 
 const STOP_BIT: u8 = 128;
 
+pub fn serialize_vint_u32(val: u32) -> (u64, usize) {
+    const START_2: u64 = 1 << 7;
+    const START_3: u64 = 1 << 14;
+    const START_4: u64 = 1 << 21;
+    const START_5: u64 = 1 << 28;
+
+    const STOP_1: u64 = START_2 - 1;
+    const STOP_2: u64 = START_3 - 1;
+    const STOP_3: u64 = START_4 - 1;
+    const STOP_4: u64 = START_5 - 1;
+
+    const MASK_1: u64 = 127;
+    const MASK_2: u64 = MASK_1 << 7;
+    const MASK_3: u64 = MASK_2 << 7;
+    const MASK_4: u64 = MASK_3 << 7;
+    const MASK_5: u64 = MASK_4 << 7;
+
+    let val = u64::from(val);
+    const STOP_BIT: u64 = 128u64;
+    match val {
+        0...STOP_1 => (val | STOP_BIT, 1),
+        START_2...STOP_2 => (
+            (val & MASK_1) | ((val & MASK_2) << 1) | (STOP_BIT << (8)),
+            2,
+        ),
+        START_3...STOP_3 => (
+            (val & MASK_1) | ((val & MASK_2) << 1) | ((val & MASK_3) << 2) | (STOP_BIT << (8 * 2)),
+            3,
+        ),
+        START_4...STOP_4 => (
+            (val & MASK_1)
+                | ((val & MASK_2) << 1)
+                | ((val & MASK_3) << 2)
+                | ((val & MASK_4) << 3)
+                | (STOP_BIT << (8 * 3)),
+            4,
+        ),
+        _ => (
+            (val & MASK_1)
+                | ((val & MASK_2) << 1)
+                | ((val & MASK_3) << 2)
+                | ((val & MASK_4) << 3)
+                | ((val & MASK_5) << 4)
+                | (STOP_BIT << (8 * 4)),
+            5,
+        ),
+    }
+}
+
+/// Returns the number of bytes covered by a
+/// serialized vint `u32`.
+///
+/// Expects a buffer data that starts
+/// by the serialized `vint`, scans at most 5 bytes ahead until
+/// it finds the vint final byte.
+///
+/// # May Panic
+/// If the payload does not start by a valid `vint`
+fn vint_len(data: &[u8]) -> usize {
+    for (i, &val) in data.iter().enumerate().take(5) {
+        if val >= STOP_BIT {
+            return i + 1;
+        }
+    }
+    panic!("Corrupted data. Invalid VInt 32");
+}
+
+/// Reads a vint `u32` from a buffer, and
+/// consumes its payload data.
+///
+/// # Panics
+///
+/// If the buffer does not start by a valid
+/// vint payload
+pub fn read_u32_vint(data: &mut &[u8]) -> u32 {
+    let vlen = vint_len(*data);
+    let mut result = 0u32;
+    let mut shift = 0u64;
+    for &b in &data[..vlen] {
+        result |= u32::from(b & 127u8) << shift;
+        shift += 7;
+    }
+    *data = &data[vlen..];
+    result
+}
+
+/// Write a `u32` as a vint payload.
+pub fn write_u32_vint<W: io::Write>(val: u32, writer: &mut W) -> io::Result<()> {
+    let (val, num_bytes) = serialize_vint_u32(val);
+    let mut buffer = [0u8; 8];
+    LittleEndian::write_u64(&mut buffer, val);
+    writer.write_all(&buffer[..num_bytes])
+}
+
 impl VInt {
     pub fn val(&self) -> u64 {
         self.0
@@ -24,7 +119,7 @@ impl VInt {
         output.extend(&buffer[0..num_bytes]);
     }
 
-    fn serialize_into(&self, buffer: &mut [u8; 10]) -> usize {
+    pub fn serialize_into(&self, buffer: &mut [u8; 10]) -> usize {
         let mut remaining = self.0;
         for (i, b) in buffer.iter_mut().enumerate() {
             let next_byte: u8 = (remaining % 128u64) as u8;
@@ -64,7 +159,7 @@ impl BinarySerializable for VInt {
                     return Err(io::Error::new(
                         io::ErrorKind::InvalidData,
                         "Reach end of buffer while reading VInt",
-                    ))
+                    ));
                 }
             }
         }
@@ -74,7 +169,9 @@ impl BinarySerializable for VInt {
 #[cfg(test)]
 mod tests {
 
+    use super::serialize_vint_u32;
     use super::VInt;
+    use byteorder::{ByteOrder, LittleEndian};
     use common::BinarySerializable;
 
     fn aux_test_vint(val: u64) {
@@ -108,4 +205,28 @@ mod tests {
         }
         aux_test_vint(10);
     }
+
+    fn aux_test_serialize_vint_u32(val: u32) {
+        let mut buffer = [0u8; 10];
+        let mut buffer2 = [0u8; 10];
+        let len_vint = VInt(val as u64).serialize_into(&mut buffer);
+        let (vint, len) = serialize_vint_u32(val);
+        assert_eq!(len, len_vint, "len wrong for val {}", val);
+        LittleEndian::write_u64(&mut buffer2, vint);
+        assert_eq!(&buffer[..len], &buffer2[..len], "array wrong for {}", val);
+    }
+
+    #[test]
+    fn test_vint_u32() {
+        aux_test_serialize_vint_u32(0);
+        aux_test_serialize_vint_u32(1);
+        aux_test_serialize_vint_u32(5);
+        for i in 1..3 {
+            let power_of_128 = 1u32 << (7 * i);
+            aux_test_serialize_vint_u32(power_of_128 - 1u32);
+            aux_test_serialize_vint_u32(power_of_128);
+            aux_test_serialize_vint_u32(power_of_128 + 1u32);
+        }
+        aux_test_serialize_vint_u32(u32::max_value());
+    }
 }

src/core/executor.rs

@@ -0,0 +1,137 @@
+use crossbeam::channel;
+use scoped_pool::{Pool, ThreadConfig};
+use Result;
+
+/// Search executor whether search request are single thread or multithread.
+///
+/// We don't expose Rayon thread pool directly here for several reasons.
+///
+/// First dependency hell. It is not a good idea to expose the
+/// API of a dependency, knowing it might conflict with a different version
+/// used by the client. Second, we may stop using rayon in the future.
+pub enum Executor {
+    SingleThread,
+    ThreadPool(Pool),
+}
+
+impl Executor {
+    /// Creates an Executor that performs all task in the caller thread.
+    pub fn single_thread() -> Executor {
+        Executor::SingleThread
+    }
+
+    // Creates an Executor that dispatches the tasks in a thread pool.
+    pub fn multi_thread(num_threads: usize, prefix: &'static str) -> Executor {
+        let thread_config = ThreadConfig::new().prefix(prefix);
+        let pool = Pool::with_thread_config(num_threads, thread_config);
+        Executor::ThreadPool(pool)
+    }
+
+    // Perform a map in the thread pool.
+    //
+    // Regardless of the executor (`SingleThread` or `ThreadPool`), panics in the task
+    // will propagate to the caller.
+    pub fn map<
+        A: Send,
+        R: Send,
+        AIterator: Iterator<Item = A>,
+        F: Sized + Sync + Fn(A) -> Result<R>,
+    >(
+        &self,
+        f: F,
+        args: AIterator,
+    ) -> Result<Vec<R>> {
+        match self {
+            Executor::SingleThread => args.map(f).collect::<Result<_>>(),
+            Executor::ThreadPool(pool) => {
+                let args_with_indices: Vec<(usize, A)> = args.enumerate().collect();
+                let num_fruits = args_with_indices.len();
+                let fruit_receiver = {
+                    let (fruit_sender, fruit_receiver) = channel::unbounded();
+                    pool.scoped(|scope| {
+                        for arg_with_idx in args_with_indices {
+                            scope.execute(|| {
+                                let (idx, arg) = arg_with_idx;
+                                let fruit = f(arg);
+                                if let Err(err) = fruit_sender.send((idx, fruit)) {
+                                    error!("Failed to send search task. It probably means all search threads have panicked. {:?}", err);
+                                }
+                            });
+                        }
+                    });
+                    fruit_receiver
+                    // This ends the scope of fruit_sender.
+                    // This is important as it makes it possible for the fruit_receiver iteration to
+                    // terminate.
+                };
+                // This is lame, but safe.
+                let mut results_with_position = Vec::with_capacity(num_fruits);
+                for (pos, fruit_res) in fruit_receiver {
+                    let fruit = fruit_res?;
+                    results_with_position.push((pos, fruit));
+                }
+                results_with_position.sort_by_key(|(pos, _)| *pos);
+                assert_eq!(results_with_position.len(), num_fruits);
+                Ok(results_with_position
+                    .into_iter()
+                    .map(|(_, fruit)| fruit)
+                    .collect::<Vec<_>>())
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::Executor;
+
+    #[test]
+    #[should_panic(expected = "panic should propagate")]
+    fn test_panic_propagates_single_thread() {
+        let _result: Vec<usize> = Executor::single_thread()
+            .map(
+                |_| {
+                    panic!("panic should propagate");
+                },
+                vec![0].into_iter(),
+            )
+            .unwrap();
+    }
+
+    #[test]
+    #[should_panic] //< unfortunately the panic message is not propagated
+    fn test_panic_propagates_multi_thread() {
+        let _result: Vec<usize> = Executor::multi_thread(1, "search-test")
+            .map(
+                |_| {
+                    panic!("panic should propagate");
+                },
+                vec![0].into_iter(),
+            )
+            .unwrap();
+    }
+
+    #[test]
+    fn test_map_singlethread() {
+        let result: Vec<usize> = Executor::single_thread()
+            .map(|i| Ok(i * 2), 0..1_000)
+            .unwrap();
+        assert_eq!(result.len(), 1_000);
+        for i in 0..1_000 {
+            assert_eq!(result[i], i * 2);
+        }
+    }
+
+}
+
+#[test]
+fn test_map_multithread() {
+    let result: Vec<usize> = Executor::multi_thread(3, "search-test")
+        .map(|i| Ok(i * 2), 0..10)
+        .unwrap();
+    assert_eq!(result.len(), 10);
+    for i in 0..10 {
+        assert_eq!(result[i], i * 2);
+    }
+}

src/core/index.rs

@@ -3,6 +3,7 @@ use super::pool::Pool;
 use super::segment::create_segment;
 use super::segment::Segment;
 use core::searcher::Searcher;
+use core::Executor;
 use core::IndexMeta;
 use core::SegmentId;
 use core::SegmentMeta;
@@ -11,12 +12,14 @@ use core::META_FILEPATH;
 use directory::ManagedDirectory;
 #[cfg(feature = "mmap")]
 use directory::MmapDirectory;
+use directory::INDEX_WRITER_LOCK;
+use directory::META_LOCK;
 use directory::{Directory, RAMDirectory};
+use error::DataCorruption;
 use error::TantivyError;
 use indexer::index_writer::open_index_writer;
 use indexer::index_writer::HEAP_SIZE_MIN;
 use indexer::segment_updater::save_new_metas;
-use indexer::LockType;
 use num_cpus;
 use schema::Field;
 use schema::FieldType;
@@ -36,7 +39,13 @@ fn load_metas(directory: &Directory) -> Result<IndexMeta> {
     let meta_data = directory.atomic_read(&META_FILEPATH)?;
     let meta_string = String::from_utf8_lossy(&meta_data);
     serde_json::from_str(&meta_string)
-        .map_err(|_| TantivyError::CorruptedFile(META_FILEPATH.clone()))
+        .map_err(|e| {
+            DataCorruption::new(
+                META_FILEPATH.clone(),
+                format!("Meta file cannot be deserialized. {:?}.", e),
+            )
+        })
+        .map_err(From::from)
 }
 
 /// Search Index
@@ -45,6 +54,7 @@ pub struct Index {
     schema: Schema,
     num_searchers: Arc<AtomicUsize>,
     searcher_pool: Arc<Pool<Searcher>>,
+    executor: Arc<Executor>,
     tokenizers: TokenizerManager,
 }
 
@@ -54,6 +64,29 @@ impl Index {
         dir.exists(&META_FILEPATH)
     }
 
+    /// Accessor to the search executor.
+    ///
+    /// This pool is used by default when calling `searcher.search(...)`
+    /// to perform search on the individual segments.
+    ///
+    /// By default the executor is single thread, and simply runs in the calling thread.
+    pub fn search_executor(&self) -> &Executor {
+        self.executor.as_ref()
+    }
+
+    /// Replace the default single thread search executor pool
+    /// by a thread pool with a given number of threads.
+    pub fn set_multithread_executor(&mut self, num_threads: usize) {
+        self.executor = Arc::new(Executor::multi_thread(num_threads, "thrd-tantivy-search-"));
+    }
+
+    /// Replace the default single thread search executor pool
+    /// by a thread pool with a given number of threads.
+    pub fn set_default_multithread_executor(&mut self) {
+        let default_num_threads = num_cpus::get();
+        self.set_multithread_executor(default_num_threads);
+    }
+
     /// Creates a new index using the `RAMDirectory`.
     ///
     /// The index will be allocated in anonymous memory.
@@ -85,7 +118,9 @@ impl Index {
             if index.schema() == schema {
                 Ok(index)
             } else {
-                Err(TantivyError::SchemaError("An index exists but the schema does not match.".to_string()))
+                Err(TantivyError::SchemaError(
+                    "An index exists but the schema does not match.".to_string(),
+                ))
             }
         } else {
             Index::create(dir, schema)
@@ -108,7 +143,7 @@ impl Index {
 
     /// Creates a new index given an implementation of the trait `Directory`
     pub fn create<Dir: Directory>(dir: Dir, schema: Schema) -> Result<Index> {
-        let directory = ManagedDirectory::new(dir)?;
+        let directory = ManagedDirectory::wrap(dir)?;
         Index::from_directory(directory, schema)
     }
 
@@ -116,7 +151,7 @@ impl Index {
     ///
     /// This will overwrite existing meta.json
     fn from_directory(mut directory: ManagedDirectory, schema: Schema) -> Result<Index> {
-        save_new_metas(schema.clone(), 0, directory.borrow_mut())?;
+        save_new_metas(schema.clone(), directory.borrow_mut())?;
         let metas = IndexMeta::with_schema(schema);
         Index::create_from_metas(directory, &metas)
     }
@@ -131,6 +166,7 @@ impl Index {
             num_searchers: Arc::new(AtomicUsize::new(n_cpus)),
             searcher_pool: Arc::new(Pool::new()),
             tokenizers: TokenizerManager::default(),
+            executor: Arc::new(Executor::single_thread()),
         };
         index.load_searchers()?;
         Ok(index)
@@ -171,7 +207,7 @@ impl Index {
 
     /// Open the index using the provided directory
     pub fn open<D: Directory>(directory: D) -> Result<Index> {
-        let directory = ManagedDirectory::new(directory)?;
+        let directory = ManagedDirectory::wrap(directory)?;
         let metas = load_metas(&directory)?;
         Index::create_from_metas(directory, &metas)
     }
@@ -197,7 +233,8 @@ impl Index {
     /// Each thread will receive a budget of  `overall_heap_size_in_bytes / num_threads`.
     ///
     /// # Errors
-    /// If the lockfile already exists, returns `Error::FileAlreadyExists`.
+    /// If the lockfile already exists, returns `Error::DirectoryLockBusy` or an `Error::IOError`.
+    ///
     /// # Panics
     /// If the heap size per thread is too small, panics.
     pub fn writer_with_num_threads(
@@ -205,7 +242,21 @@ impl Index {
         num_threads: usize,
         overall_heap_size_in_bytes: usize,
     ) -> Result<IndexWriter> {
-        let directory_lock = LockType::IndexWriterLock.acquire_lock(&self.directory)?;
+        let directory_lock = self
+            .directory
+            .acquire_lock(&INDEX_WRITER_LOCK)
+            .map_err(|err| {
+                TantivyError::LockFailure(
+                    err,
+                    Some(
+                        "Failed to acquire index lock. If you are using\
+                         a regular directory, this means there is already an \
+                         `IndexWriter` working on this `Directory`, in this process \
+                         or in a different process."
+                            .to_string(),
+                    ),
+                )
+            })?;
         let heap_size_in_bytes_per_thread = overall_heap_size_in_bytes / num_threads;
         open_index_writer(
             self,
@@ -304,7 +355,7 @@ impl Index {
     /// get the freshest `index` at all time, is to watch `meta.json` and
     /// call `load_searchers` whenever a changes happen.
     pub fn load_searchers(&self) -> Result<()> {
-        let _meta_lock = LockType::MetaLock.acquire_lock(self.directory())?;
+        let _meta_lock = self.directory().acquire_lock(&META_LOCK)?;
         let searchable_segments = self.searchable_segments()?;
         let segment_readers: Vec<SegmentReader> = searchable_segments
             .iter()
@@ -348,19 +399,20 @@ impl Clone for Index {
             num_searchers: Arc::clone(&self.num_searchers),
             searcher_pool: Arc::clone(&self.searcher_pool),
             tokenizers: self.tokenizers.clone(),
+            executor: self.executor.clone(),
         }
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use schema::{Schema, SchemaBuilder, INT_INDEXED, TEXT};
-    use Index;
     use directory::RAMDirectory;
+    use schema::{Schema, INT_INDEXED, TEXT};
+    use Index;
 
     #[test]
     fn test_indexer_for_field() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let num_likes_field = schema_builder.add_u64_field("num_likes", INT_INDEXED);
         let body_field = schema_builder.add_text_field("body", TEXT);
         let schema = schema_builder.build();
@@ -388,7 +440,6 @@ mod tests {
         assert!(Index::exists(&directory));
     }
 
-
     #[test]
     fn open_or_create_should_open() {
         let directory = RAMDirectory::create();
@@ -402,7 +453,7 @@ mod tests {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
         assert!(Index::exists(&directory));
-        assert!(Index::create(directory.clone(), SchemaBuilder::default().build()).is_ok());
+        assert!(Index::create(directory.clone(), Schema::builder().build()).is_ok());
     }
 
     #[test]
@@ -411,12 +462,15 @@ mod tests {
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
         assert!(Index::exists(&directory));
         assert!(Index::open_or_create(directory.clone(), throw_away_schema()).is_ok());
-        let err = Index::open_or_create(directory, SchemaBuilder::default().build());
-        assert_eq!(format!("{:?}", err.unwrap_err()), "SchemaError(\"An index exists but the schema does not match.\")");
+        let err = Index::open_or_create(directory, Schema::builder().build());
+        assert_eq!(
+            format!("{:?}", err.unwrap_err()),
+            "SchemaError(\"An index exists but the schema does not match.\")"
+        );
     }
 
     fn throw_away_schema() -> Schema {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let _ = schema_builder.add_u64_field("num_likes", INT_INDEXED);
         schema_builder.build()
     }

src/core/index_meta.rs

@@ -46,13 +46,13 @@ impl fmt::Debug for IndexMeta {
 mod tests {
 
     use super::IndexMeta;
-    use schema::{SchemaBuilder, TEXT};
+    use schema::{Schema, TEXT};
     use serde_json;
 
     #[test]
     fn test_serialize_metas() {
         let schema = {
-            let mut schema_builder = SchemaBuilder::new();
+            let mut schema_builder = Schema::builder();
             schema_builder.add_text_field("text", TEXT);
             schema_builder.build()
         };

src/core/inverted_index_reader.rs

@@ -32,10 +32,7 @@ pub struct InvertedIndexReader {
 }
 
 impl InvertedIndexReader {
-    #[cfg_attr(
-        feature = "cargo-clippy",
-        allow(clippy::needless_pass_by_value)
-    )] // for symetry
+    #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_pass_by_value))] // for symetry
     pub(crate) fn new(
         termdict: TermDictionary,
         postings_source: ReadOnlySource,

src/core/mod.rs

@@ -1,3 +1,4 @@
+mod executor;
 pub mod index;
 mod index_meta;
 mod inverted_index_reader;
@@ -9,6 +10,7 @@ mod segment_id;
 mod segment_meta;
 mod segment_reader;
 
+pub use self::executor::Executor;
 pub use self::index::Index;
 pub use self::index_meta::IndexMeta;
 pub use self::inverted_index_reader::InvertedIndexReader;

src/core/searcher.rs

@@ -1,18 +1,43 @@
 use collector::Collector;
+use collector::SegmentCollector;
+use core::Executor;
 use core::InvertedIndexReader;
 use core::SegmentReader;
 use query::Query;
+use query::Scorer;
+use query::Weight;
 use schema::Document;
 use schema::Schema;
 use schema::{Field, Term};
 use space_usage::SearcherSpaceUsage;
 use std::fmt;
 use std::sync::Arc;
+use store::StoreReader;
 use termdict::TermMerger;
 use DocAddress;
 use Index;
 use Result;
 
+fn collect_segment<C: Collector>(
+    collector: &C,
+    weight: &Weight,
+    segment_ord: u32,
+    segment_reader: &SegmentReader,
+) -> Result<C::Fruit> {
+    let mut scorer = weight.scorer(segment_reader)?;
+    let mut segment_collector = collector.for_segment(segment_ord as u32, segment_reader)?;
+    if let Some(delete_bitset) = segment_reader.delete_bitset() {
+        scorer.for_each(&mut |doc, score| {
+            if !delete_bitset.is_deleted(doc) {
+                segment_collector.collect(doc, score);
+            }
+        });
+    } else {
+        scorer.for_each(&mut |doc, score| segment_collector.collect(doc, score));
+    }
+    Ok(segment_collector.harvest())
+}
+
 /// Holds a list of `SegmentReader`s ready for search.
 ///
 /// It guarantees that the `Segment` will not be removed before
@@ -22,6 +47,7 @@ pub struct Searcher {
     schema: Schema,
     index: Index,
     segment_readers: Vec<SegmentReader>,
+    store_readers: Vec<StoreReader>,
 }
 
 impl Searcher {
@@ -31,10 +57,15 @@ impl Searcher {
         index: Index,
         segment_readers: Vec<SegmentReader>,
     ) -> Searcher {
+        let store_readers = segment_readers
+            .iter()
+            .map(|segment_reader| segment_reader.get_store_reader())
+            .collect();
         Searcher {
             schema,
             index,
             segment_readers,
+            store_readers,
         }
     }
 
@@ -49,8 +80,8 @@ impl Searcher {
     /// the request to the right `Segment`.
     pub fn doc(&self, doc_address: DocAddress) -> Result<Document> {
         let DocAddress(segment_local_id, doc_id) = doc_address;
-        let segment_reader = &self.segment_readers[segment_local_id as usize];
-        segment_reader.doc(doc_id)
+        let store_reader = &self.store_readers[segment_local_id as usize];
+        store_reader.get(doc_id)
     }
 
     /// Access the schema associated to the index of this searcher.
@@ -73,7 +104,8 @@ impl Searcher {
             .iter()
             .map(|segment_reader| {
                 u64::from(segment_reader.inverted_index(term.field()).doc_freq(term))
-            }).sum::<u64>()
+            })
+            .sum::<u64>()
     }
 
     /// Return the list of segment readers
@@ -86,9 +118,58 @@ impl Searcher {
         &self.segment_readers[segment_ord as usize]
     }
 
-    /// Runs a query on the segment readers wrapped by the searcher
-    pub fn search<C: Collector>(&self, query: &Query, collector: &mut C) -> Result<()> {
-        query.search(self, collector)
+    /// Runs a query on the segment readers wrapped by the searcher.
+    ///
+    /// Search works as follows :
+    ///
+    ///  First the weight object associated to the query is created.
+    ///
+    ///  Then, the query loops over the segments and for each segment :
+    ///  - setup the collector and informs it that the segment being processed has changed.
+    ///  - creates a SegmentCollector for collecting documents associated to the segment
+    ///  - creates a `Scorer` object associated for this segment
+    ///  - iterate through the matched documents and push them to the segment collector.
+    ///
+    ///  Finally, the Collector merges each of the child collectors into itself for result usability
+    ///  by the caller.
+    pub fn search<C: Collector>(&self, query: &Query, collector: &C) -> Result<C::Fruit> {
+        let executor = self.index.search_executor();
+        self.search_with_executor(query, collector, executor)
+    }
+
+    /// Same as [`search(...)`](#method.search) but multithreaded.
+    ///
+    /// The current implementation is rather naive :
+    /// multithreading is by splitting search into as many task
+    /// as there are segments.
+    ///
+    /// It is powerless at making search faster if your index consists in
+    /// one large segment.
+    ///
+    /// Also, keep in my multithreading a single query on several
+    /// threads will not improve your throughput. It can actually
+    /// hurt it. It will however, decrease the average response time.
+    pub fn search_with_executor<C: Collector>(
+        &self,
+        query: &Query,
+        collector: &C,
+        executor: &Executor,
+    ) -> Result<C::Fruit> {
+        let scoring_enabled = collector.requires_scoring();
+        let weight = query.weight(self, scoring_enabled)?;
+        let segment_readers = self.segment_readers();
+        let fruits = executor.map(
+            |(segment_ord, segment_reader)| {
+                collect_segment(
+                    collector,
+                    weight.as_ref(),
+                    segment_ord as u32,
+                    segment_reader,
+                )
+            },
+            segment_readers.iter().enumerate(),
+        )?;
+        collector.merge_fruits(fruits)
     }
 
     /// Return the field searcher associated to a `Field`.

src/core/segment_component.rs

@@ -41,6 +41,6 @@ impl SegmentComponent {
             SegmentComponent::STORE,
             SegmentComponent::DELETE,
         ];
-        SEGMENT_COMPONENTS.into_iter()
+        SEGMENT_COMPONENTS.iter()
     }
 }

src/core/segment_reader.rs

@@ -4,6 +4,7 @@ use core::InvertedIndexReader;
 use core::Segment;
 use core::SegmentComponent;
 use core::SegmentId;
+use directory::ReadOnlySource;
 use error::TantivyError;
 use fastfield::DeleteBitSet;
 use fastfield::FacetReader;
@@ -12,7 +13,6 @@ use fastfield::{self, FastFieldNotAvailableError};
 use fastfield::{BytesFastFieldReader, FastValue, MultiValueIntFastFieldReader};
 use fieldnorm::FieldNormReader;
 use schema::Cardinality;
-use schema::Document;
 use schema::Field;
 use schema::FieldType;
 use schema::Schema;
@@ -54,7 +54,7 @@ pub struct SegmentReader {
     fast_fields_composite: CompositeFile,
     fieldnorms_composite: CompositeFile,
 
-    store_reader: StoreReader,
+    store_source: ReadOnlySource,
     delete_bitset_opt: Option<DeleteBitSet>,
     schema: Schema,
 }
@@ -197,8 +197,7 @@ impl SegmentReader {
     /// Accessor to the segment's `Field norms`'s reader.
     ///
     /// Field norms are the length (in tokens) of the fields.
-    /// It is used in the computation of the [TfIdf]
-    /// (https://fulmicoton.gitbooks.io/tantivy-doc/content/tfidf.html).
+    /// It is used in the computation of the [TfIdf](https://fulmicoton.gitbooks.io/tantivy-doc/content/tfidf.html).
     ///
     /// They are simply stored as a fast field, serialized in
     /// the `.fieldnorm` file of the segment.
@@ -216,8 +215,8 @@ impl SegmentReader {
     }
 
     /// Accessor to the segment's `StoreReader`.
-    pub fn get_store_reader(&self) -> &StoreReader {
-        &self.store_reader
+    pub fn get_store_reader(&self) -> StoreReader {
+        StoreReader::from_source(self.store_source.clone())
     }
 
     /// Open a new segment for reading.
@@ -226,7 +225,6 @@ impl SegmentReader {
         let termdict_composite = CompositeFile::open(&termdict_source)?;
 
         let store_source = segment.open_read(SegmentComponent::STORE)?;
-        let store_reader = StoreReader::from_source(store_source);
 
         fail_point!("SegmentReader::open#middle");
 
@@ -272,7 +270,7 @@ impl SegmentReader {
             fast_fields_composite,
             fieldnorms_composite,
             segment_id: segment.id(),
-            store_reader,
+            store_source,
             delete_bitset_opt,
             positions_composite,
             positions_idx_composite,
@@ -351,14 +349,6 @@ impl SegmentReader {
         inv_idx_reader
     }
 
-    /// Returns the document (or to be accurate, its stored field)
-    /// bearing the given doc id.
-    /// This method is slow and should seldom be called from
-    /// within a collector.
-    pub fn doc(&self, doc_id: DocId) -> Result<Document> {
-        self.store_reader.get(doc_id)
-    }
-
     /// Returns the segment id
     pub fn segment_id(&self) -> SegmentId {
         self.segment_id
@@ -393,8 +383,11 @@ impl SegmentReader {
             self.positions_idx_composite.space_usage(),
             self.fast_fields_composite.space_usage(),
             self.fieldnorms_composite.space_usage(),
-            self.store_reader.space_usage(),
-            self.delete_bitset_opt.as_ref().map(|x| x.space_usage()).unwrap_or(0),
+            self.get_store_reader().space_usage(),
+            self.delete_bitset_opt
+                .as_ref()
+                .map(|x| x.space_usage())
+                .unwrap_or(0),
         )
     }
 }
@@ -454,12 +447,12 @@ impl<'a> Iterator for SegmentReaderAliveDocsIterator<'a> {
 #[cfg(test)]
 mod test {
     use core::Index;
-    use schema::{SchemaBuilder, Term, STORED, TEXT};
+    use schema::{Schema, Term, STORED, TEXT};
     use DocId;
 
     #[test]
     fn test_alive_docs_iterator() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         schema_builder.add_text_field("name", TEXT | STORED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema.clone());

src/directory/directory.rs

@@ -1,11 +1,102 @@
+use directory::directory_lock::Lock;
+use directory::error::LockError;
 use directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use directory::{ReadOnlySource, WritePtr};
 use std::fmt;
 use std::io;
+use std::io::Write;
 use std::marker::Send;
 use std::marker::Sync;
 use std::path::Path;
+use std::path::PathBuf;
 use std::result;
+use std::thread;
+use std::time::Duration;
+
+/// Retry the logic of acquiring locks is pretty simple.
+/// We just retry `n` times after a given `duratio`, both
+/// depending on the type of lock.
+struct RetryPolicy {
+    num_retries: usize,
+    wait_in_ms: u64,
+}
+
+impl RetryPolicy {
+    fn no_retry() -> RetryPolicy {
+        RetryPolicy {
+            num_retries: 0,
+            wait_in_ms: 0,
+        }
+    }
+
+    fn wait_and_retry(&mut self) -> bool {
+        if self.num_retries == 0 {
+            false
+        } else {
+            self.num_retries -= 1;
+            let wait_duration = Duration::from_millis(self.wait_in_ms);
+            thread::sleep(wait_duration);
+            true
+        }
+    }
+}
+
+/// The `DirectoryLock` is an object that represents a file lock.
+/// See  [`LockType`](struct.LockType.html)
+///
+/// It is transparently associated to a lock file, that gets deleted
+/// on `Drop.` The lock is released automatically on `Drop`.
+pub struct DirectoryLock(Box<Drop + Send + 'static>);
+
+struct DirectoryLockGuard {
+    directory: Box<Directory>,
+    path: PathBuf,
+}
+
+impl<T: Drop + Send + 'static> From<Box<T>> for DirectoryLock {
+    fn from(underlying: Box<T>) -> Self {
+        DirectoryLock(underlying)
+    }
+}
+
+impl Drop for DirectoryLockGuard {
+    fn drop(&mut self) {
+        if let Err(e) = self.directory.delete(&*self.path) {
+            error!("Failed to remove the lock file. {:?}", e);
+        }
+    }
+}
+
+enum TryAcquireLockError {
+    FileExists,
+    IOError(io::Error),
+}
+
+fn try_acquire_lock(
+    filepath: &Path,
+    directory: &mut Directory,
+) -> Result<DirectoryLock, TryAcquireLockError> {
+    let mut write = directory.open_write(filepath).map_err(|e| match e {
+        OpenWriteError::FileAlreadyExists(_) => TryAcquireLockError::FileExists,
+        OpenWriteError::IOError(io_error) => TryAcquireLockError::IOError(io_error.into()),
+    })?;
+    write.flush().map_err(TryAcquireLockError::IOError)?;
+    Ok(DirectoryLock::from(Box::new(DirectoryLockGuard {
+        directory: directory.box_clone(),
+        path: filepath.to_owned(),
+    })))
+}
+
+fn retry_policy(is_blocking: bool) -> RetryPolicy {
+    if is_blocking {
+        RetryPolicy {
+            num_retries: 100,
+            wait_in_ms: 100,
+        }
+    } else {
+        RetryPolicy::no_retry()
+    }
+}
 
 /// Write-once read many (WORM) abstraction for where
 /// tantivy's data should be stored.
@@ -73,6 +164,29 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     ///
     /// The file may or may not previously exist.
     fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()>;
+
+    /// Acquire a lock in the given directory.
+    ///
+    /// The method is blocking or not depending on the `Lock` object.
+    fn acquire_lock(&self, lock: &Lock) -> Result<DirectoryLock, LockError> {
+        let mut box_directory = self.box_clone();
+        let mut retry_policy = retry_policy(lock.is_blocking);
+        loop {
+            match try_acquire_lock(&lock.filepath, &mut *box_directory) {
+                Ok(result) => {
+                    return Ok(result);
+                }
+                Err(TryAcquireLockError::FileExists) => {
+                    if !retry_policy.wait_and_retry() {
+                        return Err(LockError::LockBusy);
+                    }
+                }
+                Err(TryAcquireLockError::IOError(io_error)) => {
+                    return Err(LockError::IOError(io_error));
+                }
+            }
+        }
+    }
 }
 
 /// DirectoryClone

src/directory/directory_lock.rs

@@ -0,0 +1,56 @@
+use std::path::PathBuf;
+
+/// A directory lock.
+///
+/// A lock is associated to a specific path and some
+/// [`LockParams`](./enum.LockParams.html).
+/// Tantivy itself uses only two locks but client application
+/// can use the directory facility to define their own locks.
+/// - [INDEX_WRITER_LOCK](./struct.INDEX_WRITER_LOCK.html)
+/// - [META_LOCK](./struct.META_LOCK.html)
+///
+/// Check out these locks documentation for more information.
+///
+#[derive(Debug)]
+pub struct Lock {
+    /// The lock needs to be associated with its own file `path`.
+    /// Depending on the platform, the lock might rely on the creation
+    /// and deletion of this filepath.
+    pub filepath: PathBuf,
+    /// `lock_params` describes whether acquiring the lock is meant
+    /// to be a blocking operation or a non-blocking.
+    ///
+    /// Acquiring a blocking lock blocks until the lock is
+    /// available.
+    /// Acquiring a blocking lock returns rapidly, either successfully
+    /// or with an error signifying that someone is already holding
+    /// the lock.
+    pub is_blocking: bool,
+}
+
+lazy_static! {
+     /// Only one process should be able to write tantivy's index at a time.
+    /// This lock file, when present, is in charge of preventing other processes to open an IndexWriter.
+    ///
+    /// If the process is killed and this file remains, it is safe to remove it manually.
+    ///
+    /// Failing to acquire this lock usually means a misuse of tantivy's API,
+    /// (creating more than one instance of the `IndexWriter`), are a spurious
+    /// lock file remaining after a crash. In the latter case, removing the file after
+    /// checking no process running tantivy is running is safe.
+    pub static ref INDEX_WRITER_LOCK: Lock = Lock {
+        filepath: PathBuf::from(".tantivy-writer.lock"),
+        is_blocking: false
+    };
+    /// The meta lock file is here to protect the segment files being opened by
+    /// `.load_searchers()` from being garbage collected.
+    /// It makes it possible for another process to safely consume
+    /// our index in-writing. Ideally, we may have prefered `RWLock` semantics
+    /// here, but it is difficult to achieve on Windows.
+    ///
+    /// Opening segment readers is a very fast process.
+    pub static ref META_LOCK: Lock = Lock {
+        filepath: PathBuf::from(".tantivy-meta.lock"),
+        is_blocking: true
+    };
+}

src/directory/error.rs

@@ -3,6 +3,22 @@ use std::fmt;
 use std::io;
 use std::path::PathBuf;
 
+/// Error while trying to acquire a directory lock.
+#[derive(Debug, Fail)]
+pub enum LockError {
+    /// Failed to acquired a lock as it is already hold by another
+    /// client.
+    /// - In the context of a blocking lock, this means the lock was not released within some `timeout` period.
+    /// - In the context of a non-blocking lock, this means the lock was busy at the moment of the call.
+    #[fail(
+        display = "Could not acquire lock as it is already held, possibly by a different process."
+    )]
+    LockBusy,
+    /// Trying to acquire a lock failed with an `IOError`
+    #[fail(display = "Failed to acquire the lock due to an io:Error.")]
+    IOError(io::Error),
+}
+
 /// General IO error with an optional path to the offending file.
 #[derive(Debug)]
 pub struct IOError {
@@ -10,6 +26,12 @@ pub struct IOError {
     err: io::Error,
 }
 
+impl Into<io::Error> for IOError {
+    fn into(self) -> io::Error {
+        self.err
+    }
+}
+
 impl fmt::Display for IOError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.path {

src/directory/managed_directory.rs

@@ -1,8 +1,10 @@
 use core::MANAGED_FILEPATH;
-use directory::error::{DeleteError, IOError, OpenReadError, OpenWriteError};
+use directory::error::{DeleteError, IOError, LockError, OpenReadError, OpenWriteError};
+use directory::DirectoryLock;
+use directory::Lock;
+use directory::META_LOCK;
 use directory::{ReadOnlySource, WritePtr};
-use error::TantivyError;
-use indexer::LockType;
+use error::DataCorruption;
 use serde_json;
 use std::collections::HashSet;
 use std::io;
@@ -59,12 +61,17 @@ fn save_managed_paths(
 
 impl ManagedDirectory {
     /// Wraps a directory as managed directory.
-    pub fn new<Dir: Directory>(directory: Dir) -> Result<ManagedDirectory> {
+    pub fn wrap<Dir: Directory>(directory: Dir) -> Result<ManagedDirectory> {
         match directory.atomic_read(&MANAGED_FILEPATH) {
             Ok(data) => {
                 let managed_files_json = String::from_utf8_lossy(&data);
                 let managed_files: HashSet<PathBuf> = serde_json::from_str(&managed_files_json)
-                    .map_err(|_| TantivyError::CorruptedFile(MANAGED_FILEPATH.clone()))?;
+                    .map_err(|e| {
+                        DataCorruption::new(
+                            MANAGED_FILEPATH.clone(),
+                            format!("Managed file cannot be deserialized: {:?}. ", e),
+                        )
+                    })?;
                 Ok(ManagedDirectory {
                     directory: Box::new(directory),
                     meta_informations: Arc::new(RwLock::new(MetaInformation {
@@ -87,6 +94,9 @@ impl ManagedDirectory {
     ///
     /// * `living_files` - List of files that are still used by the index.
     ///
+    /// The use a callback ensures that the list of living_files is computed
+    /// while we hold the lock on meta.
+    ///
     /// This method does not panick nor returns errors.
     /// If a file cannot be deleted (for permission reasons for instance)
     /// an error is simply logged, and the file remains in the list of managed
@@ -117,7 +127,7 @@ impl ManagedDirectory {
             // 2) writer change meta.json (for instance after a merge or a commit)
             // 3) gc kicks in.
             // 4) gc removes a file that was useful for process B, before process B opened it.
-            if let Ok(_meta_lock) = LockType::MetaLock.acquire_lock(self) {
+            if let Ok(_meta_lock) = self.acquire_lock(&META_LOCK) {
                 let living_files = get_living_files();
                 for managed_path in &meta_informations_rlock.managed_paths {
                     if !living_files.contains(managed_path) {
@@ -227,6 +237,10 @@ impl Directory for ManagedDirectory {
     fn exists(&self, path: &Path) -> bool {
         self.directory.exists(path)
     }
+
+    fn acquire_lock(&self, lock: &Lock) -> result::Result<DirectoryLock, LockError> {
+        self.directory.acquire_lock(lock)
+    }
 }
 
 impl Clone for ManagedDirectory {
@@ -260,7 +274,7 @@ mod tests {
         let tempdir_path = PathBuf::from(tempdir.path());
         {
             let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
-            let mut managed_directory = ManagedDirectory::new(mmap_directory).unwrap();
+            let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
             {
                 let mut write_file = managed_directory.open_write(*TEST_PATH1).unwrap();
                 write_file.flush().unwrap();
@@ -286,7 +300,7 @@ mod tests {
         }
         {
             let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
-            let mut managed_directory = ManagedDirectory::new(mmap_directory).unwrap();
+            let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
             {
                 assert!(managed_directory.exists(*TEST_PATH1));
                 assert!(!managed_directory.exists(*TEST_PATH2));
@@ -310,7 +324,7 @@ mod tests {
         let living_files = HashSet::new();
 
         let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
-        let mut managed_directory = ManagedDirectory::new(mmap_directory).unwrap();
+        let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
         managed_directory
             .atomic_write(*TEST_PATH1, &vec![0u8, 1u8])
             .unwrap();

src/directory/mmap_directory.rs

@@ -1,8 +1,14 @@
+extern crate fs2;
+
+use self::fs2::FileExt;
 use atomicwrites;
 use common::make_io_err;
+use directory::error::LockError;
 use directory::error::{DeleteError, IOError, OpenDirectoryError, OpenReadError, OpenWriteError};
 use directory::shared_vec_slice::SharedVecSlice;
 use directory::Directory;
+use directory::DirectoryLock;
+use directory::Lock;
 use directory::ReadOnlySource;
 use directory::WritePtr;
 use fst::raw::MmapReadOnly;
@@ -115,6 +121,14 @@ impl MmapCache {
 ///
 /// The Mmap object are cached to limit the
 /// system calls.
+///
+/// In the `MmapDirectory`, locks are implemented using the `fs2` crate definition of locks.
+///
+/// On MacOS & linux, it relies on `flock` (aka `BSD Lock`). These locks solve most of the
+/// problems related to POSIX Locks, but may their contract may not be respected on `NFS`
+/// depending on the implementation.
+///
+/// On Windows the semantics are again different.
 #[derive(Clone)]
 pub struct MmapDirectory {
     root_path: PathBuf,
@@ -213,6 +227,21 @@ impl MmapDirectory {
     }
 }
 
+/// We rely on fs2 for file locking. On Windows & MacOS this
+/// uses BSD locks (`flock`). The lock is actually released when
+/// the `File` object is dropped and its associated file descriptor
+/// is closed.
+struct ReleaseLockFile {
+    _file: File,
+    path: PathBuf,
+}
+
+impl Drop for ReleaseLockFile {
+    fn drop(&mut self) {
+        debug!("Releasing lock {:?}", self.path);
+    }
+}
+
 /// This Write wraps a File, but has the specificity of
 /// call `sync_all` on flush.
 struct SafeFileWriter(File);
@@ -354,6 +383,26 @@ impl Directory for MmapDirectory {
         meta_file.write(|f| f.write_all(data))?;
         Ok(())
     }
+
+    fn acquire_lock(&self, lock: &Lock) -> Result<DirectoryLock, LockError> {
+        let full_path = self.resolve_path(&lock.filepath);
+        // We make sure that the file exists.
+        let file: File = OpenOptions::new()
+            .write(true)
+            .create(true) //< if the file does not exist yet, create it.
+            .open(&full_path)
+            .map_err(LockError::IOError)?;
+        if lock.is_blocking {
+            file.lock_exclusive().map_err(LockError::IOError)?;
+        } else {
+            file.try_lock_exclusive().map_err(|_| LockError::LockBusy)?
+        }
+        // dropping the file handle will release the lock.
+        Ok(DirectoryLock::from(Box::new(ReleaseLockFile {
+            path: lock.filepath.clone(),
+            _file: file,
+        })))
+    }
 }
 
 #[cfg(test)]

src/directory/mod.rs

@@ -8,6 +8,7 @@ WORM directory abstraction.
 mod mmap_directory;
 
 mod directory;
+mod directory_lock;
 mod managed_directory;
 mod ram_directory;
 mod read_only_source;
@@ -16,11 +17,12 @@ mod shared_vec_slice;
 /// Errors specific to the directory module.
 pub mod error;
 
-use std::io::{BufWriter, Seek, Write};
-
+pub use self::directory::DirectoryLock;
 pub use self::directory::{Directory, DirectoryClone};
+pub use self::directory_lock::{Lock, INDEX_WRITER_LOCK, META_LOCK};
 pub use self::ram_directory::RAMDirectory;
 pub use self::read_only_source::ReadOnlySource;
+use std::io::{BufWriter, Seek, Write};
 
 #[cfg(feature = "mmap")]
 pub use self::mmap_directory::MmapDirectory;
@@ -38,128 +40,4 @@ impl<T: Seek + Write> SeekableWrite for T {}
 pub type WritePtr = BufWriter<Box<SeekableWrite>>;
 
 #[cfg(test)]
-mod tests {
-
-    use super::*;
-    use std::io::{Seek, SeekFrom, Write};
-    use std::path::Path;
-
-    lazy_static! {
-        static ref TEST_PATH: &'static Path = Path::new("some_path_for_test");
-    }
-
-    #[test]
-    fn test_ram_directory() {
-        let mut ram_directory = RAMDirectory::create();
-        test_directory(&mut ram_directory);
-    }
-
-    #[test]
-    #[cfg(feature = "mmap")]
-    fn test_mmap_directory() {
-        let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
-        test_directory(&mut mmap_directory);
-    }
-
-    #[test]
-    #[should_panic]
-    fn ram_directory_panics_if_flush_forgotten() {
-        let mut ram_directory = RAMDirectory::create();
-        let mut write_file = ram_directory.open_write(*TEST_PATH).unwrap();
-        assert!(write_file.write_all(&[4]).is_ok());
-    }
-
-    fn test_simple(directory: &mut Directory) {
-        {
-            {
-                let mut write_file = directory.open_write(*TEST_PATH).unwrap();
-                assert!(directory.exists(*TEST_PATH));
-                write_file.write_all(&[4]).unwrap();
-                write_file.write_all(&[3]).unwrap();
-                write_file.write_all(&[7, 3, 5]).unwrap();
-                write_file.flush().unwrap();
-            }
-            let read_file = directory.open_read(*TEST_PATH).unwrap();
-            let data: &[u8] = &*read_file;
-            assert_eq!(data, &[4u8, 3u8, 7u8, 3u8, 5u8]);
-        }
-
-        assert!(directory.delete(*TEST_PATH).is_ok());
-        assert!(!directory.exists(*TEST_PATH));
-    }
-
-    fn test_seek(directory: &mut Directory) {
-        {
-            {
-                let mut write_file = directory.open_write(*TEST_PATH).unwrap();
-                write_file.write_all(&[4, 3, 7, 3, 5]).unwrap();
-                write_file.seek(SeekFrom::Start(0)).unwrap();
-                write_file.write_all(&[3, 1]).unwrap();
-                write_file.flush().unwrap();
-            }
-            let read_file = directory.open_read(*TEST_PATH).unwrap();
-            let data: &[u8] = &*read_file;
-            assert_eq!(data, &[3u8, 1u8, 7u8, 3u8, 5u8]);
-        }
-
-        assert!(directory.delete(*TEST_PATH).is_ok());
-    }
-
-    fn test_rewrite_forbidden(directory: &mut Directory) {
-        {
-            directory.open_write(*TEST_PATH).unwrap();
-            assert!(directory.exists(*TEST_PATH));
-        }
-        {
-            assert!(directory.open_write(*TEST_PATH).is_err());
-        }
-        assert!(directory.delete(*TEST_PATH).is_ok());
-    }
-
-    fn test_write_create_the_file(directory: &mut Directory) {
-        {
-            assert!(directory.open_read(*TEST_PATH).is_err());
-            let _w = directory.open_write(*TEST_PATH).unwrap();
-            assert!(directory.exists(*TEST_PATH));
-            assert!(directory.open_read(*TEST_PATH).is_ok());
-            assert!(directory.delete(*TEST_PATH).is_ok());
-        }
-    }
-
-    fn test_directory_delete(directory: &mut Directory) {
-        assert!(directory.open_read(*TEST_PATH).is_err());
-        let mut write_file = directory.open_write(*TEST_PATH).unwrap();
-        write_file.write_all(&[1, 2, 3, 4]).unwrap();
-        write_file.flush().unwrap();
-        {
-            let read_handle = directory.open_read(*TEST_PATH).unwrap();
-            {
-                assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
-
-                // Mapped files can't be deleted on Windows
-                if !cfg!(windows) {
-                    assert!(directory.delete(*TEST_PATH).is_ok());
-                    assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
-                }
-
-                assert!(directory.delete(Path::new("SomeOtherPath")).is_err());
-            }
-        }
-
-        if cfg!(windows) {
-            assert!(directory.delete(*TEST_PATH).is_ok());
-        }
-
-        assert!(directory.open_read(*TEST_PATH).is_err());
-        assert!(directory.delete(*TEST_PATH).is_err());
-    }
-
-    fn test_directory(directory: &mut Directory) {
-        test_simple(directory);
-        test_seek(directory);
-        test_rewrite_forbidden(directory);
-        test_write_create_the_file(directory);
-        test_directory_delete(directory);
-    }
-
-}
+mod tests;

src/directory/ram_directory.rs

@@ -100,7 +100,8 @@ impl InnerDirectory {
                 );
                 let io_err = make_io_err(msg);
                 OpenReadError::IOError(IOError::with_path(path.to_owned(), io_err))
-            }).and_then(|readable_map| {
+            })
+            .and_then(|readable_map| {
                 readable_map
                     .get(path)
                     .ok_or_else(|| OpenReadError::FileDoesNotExist(PathBuf::from(path)))
@@ -120,7 +121,8 @@ impl InnerDirectory {
                 );
                 let io_err = make_io_err(msg);
                 DeleteError::IOError(IOError::with_path(path.to_owned(), io_err))
-            }).and_then(|mut writable_map| match writable_map.remove(path) {
+            })
+            .and_then(|mut writable_map| match writable_map.remove(path) {
                 Some(_) => Ok(()),
                 None => Err(DeleteError::FileDoesNotExist(PathBuf::from(path))),
             })

src/directory/tests.rs

@@ -0,0 +1,182 @@
+use super::*;
+use std::io::{Seek, SeekFrom, Write};
+use std::path::{Path, PathBuf};
+use std::time;
+
+lazy_static! {
+    static ref TEST_PATH: &'static Path = Path::new("some_path_for_test");
+}
+
+#[test]
+fn test_ram_directory() {
+    let mut ram_directory = RAMDirectory::create();
+    test_directory(&mut ram_directory);
+}
+
+#[test]
+#[cfg(feature = "mmap")]
+fn test_mmap_directory() {
+    let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
+    test_directory(&mut mmap_directory);
+}
+
+#[test]
+#[should_panic]
+fn ram_directory_panics_if_flush_forgotten() {
+    let mut ram_directory = RAMDirectory::create();
+    let mut write_file = ram_directory.open_write(*TEST_PATH).unwrap();
+    assert!(write_file.write_all(&[4]).is_ok());
+}
+
+fn test_simple(directory: &mut Directory) {
+    {
+        {
+            let mut write_file = directory.open_write(*TEST_PATH).unwrap();
+            assert!(directory.exists(*TEST_PATH));
+            write_file.write_all(&[4]).unwrap();
+            write_file.write_all(&[3]).unwrap();
+            write_file.write_all(&[7, 3, 5]).unwrap();
+            write_file.flush().unwrap();
+        }
+        let read_file = directory.open_read(*TEST_PATH).unwrap();
+        let data: &[u8] = &*read_file;
+        assert_eq!(data, &[4u8, 3u8, 7u8, 3u8, 5u8]);
+    }
+
+    assert!(directory.delete(*TEST_PATH).is_ok());
+    assert!(!directory.exists(*TEST_PATH));
+}
+
+fn test_seek(directory: &mut Directory) {
+    {
+        {
+            let mut write_file = directory.open_write(*TEST_PATH).unwrap();
+            write_file.write_all(&[4, 3, 7, 3, 5]).unwrap();
+            write_file.seek(SeekFrom::Start(0)).unwrap();
+            write_file.write_all(&[3, 1]).unwrap();
+            write_file.flush().unwrap();
+        }
+        let read_file = directory.open_read(*TEST_PATH).unwrap();
+        let data: &[u8] = &*read_file;
+        assert_eq!(data, &[3u8, 1u8, 7u8, 3u8, 5u8]);
+    }
+
+    assert!(directory.delete(*TEST_PATH).is_ok());
+}
+
+fn test_rewrite_forbidden(directory: &mut Directory) {
+    {
+        directory.open_write(*TEST_PATH).unwrap();
+        assert!(directory.exists(*TEST_PATH));
+    }
+    {
+        assert!(directory.open_write(*TEST_PATH).is_err());
+    }
+    assert!(directory.delete(*TEST_PATH).is_ok());
+}
+
+fn test_write_create_the_file(directory: &mut Directory) {
+    {
+        assert!(directory.open_read(*TEST_PATH).is_err());
+        let _w = directory.open_write(*TEST_PATH).unwrap();
+        assert!(directory.exists(*TEST_PATH));
+        assert!(directory.open_read(*TEST_PATH).is_ok());
+        assert!(directory.delete(*TEST_PATH).is_ok());
+    }
+}
+
+fn test_directory_delete(directory: &mut Directory) {
+    assert!(directory.open_read(*TEST_PATH).is_err());
+    let mut write_file = directory.open_write(*TEST_PATH).unwrap();
+    write_file.write_all(&[1, 2, 3, 4]).unwrap();
+    write_file.flush().unwrap();
+    {
+        let read_handle = directory.open_read(*TEST_PATH).unwrap();
+        {
+            assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+
+            // Mapped files can't be deleted on Windows
+            if !cfg!(windows) {
+                assert!(directory.delete(*TEST_PATH).is_ok());
+                assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+            }
+
+            assert!(directory.delete(Path::new("SomeOtherPath")).is_err());
+        }
+    }
+
+    if cfg!(windows) {
+        assert!(directory.delete(*TEST_PATH).is_ok());
+    }
+
+    assert!(directory.open_read(*TEST_PATH).is_err());
+    assert!(directory.delete(*TEST_PATH).is_err());
+}
+
+fn test_directory(directory: &mut Directory) {
+    test_simple(directory);
+    test_seek(directory);
+    test_rewrite_forbidden(directory);
+    test_write_create_the_file(directory);
+    test_directory_delete(directory);
+    test_lock_non_blocking(directory);
+    test_lock_blocking(directory);
+}
+
+fn test_lock_non_blocking(directory: &mut Directory) {
+    {
+        let lock_a_res = directory.acquire_lock(&Lock {
+            filepath: PathBuf::from("a.lock"),
+            is_blocking: false,
+        });
+        assert!(lock_a_res.is_ok());
+        let lock_b_res = directory.acquire_lock(&Lock {
+            filepath: PathBuf::from("b.lock"),
+            is_blocking: false,
+        });
+        assert!(lock_b_res.is_ok());
+        let lock_a_res2 = directory.acquire_lock(&Lock {
+            filepath: PathBuf::from("a.lock"),
+            is_blocking: false,
+        });
+        assert!(lock_a_res2.is_err());
+    }
+    let lock_a_res = directory.acquire_lock(&Lock {
+        filepath: PathBuf::from("a.lock"),
+        is_blocking: false,
+    });
+    assert!(lock_a_res.is_ok());
+}
+
+fn test_lock_blocking(directory: &mut Directory) {
+    let lock_a_res = directory.acquire_lock(&Lock {
+        filepath: PathBuf::from("a.lock"),
+        is_blocking: true,
+    });
+    assert!(lock_a_res.is_ok());
+    std::thread::spawn(move || {
+        //< lock_a_res is sent to the thread.
+        std::thread::sleep(time::Duration::from_millis(10));
+        // explicitely droping lock_a_res. It would have been sufficient to just force it
+        // to be part of the move, but the intent seems clearer that way.
+        drop(lock_a_res);
+    });
+    {
+        // A non-blocking call should fail, as the thread is running and holding the lock.
+        let lock_a_res = directory.acquire_lock(&Lock {
+            filepath: PathBuf::from("a.lock"),
+            is_blocking: false,
+        });
+        assert!(lock_a_res.is_err());
+    }
+    {
+        // the blocking call should wait for at least 10ms.
+        let start = time::Instant::now();
+        let lock_a_res = directory.acquire_lock(&Lock {
+            filepath: PathBuf::from("a.lock"),
+            is_blocking: true,
+        });
+        assert!(lock_a_res.is_ok());
+        assert!(start.elapsed().subsec_millis() >= 10);
+    }
+}

src/error.rs

@@ -2,56 +2,93 @@
 
 use std::io;
 
+use directory::error::LockError;
 use directory::error::{IOError, OpenDirectoryError, OpenReadError, OpenWriteError};
 use fastfield::FastFieldNotAvailableError;
-use indexer::LockType;
 use query;
 use schema;
 use serde_json;
+use std::fmt;
 use std::path::PathBuf;
 use std::sync::PoisonError;
 
+pub struct DataCorruption {
+    filepath: Option<PathBuf>,
+    comment: String,
+}
+
+impl DataCorruption {
+    pub fn new(filepath: PathBuf, comment: String) -> DataCorruption {
+        DataCorruption {
+            filepath: Some(filepath),
+            comment,
+        }
+    }
+
+    pub fn comment_only(comment: String) -> DataCorruption {
+        DataCorruption {
+            filepath: None,
+            comment,
+        }
+    }
+}
+
+impl fmt::Debug for DataCorruption {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        write!(f, "Data corruption: ")?;
+        if let Some(ref filepath) = &self.filepath {
+            write!(f, "(in file `{:?}`)", filepath)?;
+        }
+        write!(f, ": {}.", self.comment)?;
+        Ok(())
+    }
+}
+
 /// The library's failure based error enum
 #[derive(Debug, Fail)]
 pub enum TantivyError {
     /// Path does not exist.
-    #[fail(display = "path does not exist: '{:?}'", _0)]
+    #[fail(display = "Path does not exist: '{:?}'", _0)]
     PathDoesNotExist(PathBuf),
     /// File already exists, this is a problem when we try to write into a new file.
-    #[fail(display = "file already exists: '{:?}'", _0)]
+    #[fail(display = "File already exists: '{:?}'", _0)]
     FileAlreadyExists(PathBuf),
     /// Index already exists in this directory
-    #[fail(display = "index already exists")]
+    #[fail(display = "Index already exists")]
     IndexAlreadyExists,
     /// Failed to acquire file lock
-    #[fail(
-        display = "Failed to acquire Lockfile: {:?}. Possible causes: another IndexWriter instance or panic during previous lock drop.",
-        _0
-    )]
-    LockFailure(LockType),
+    #[fail(display = "Failed to acquire Lockfile: {:?}. {:?}", _0, _1)]
+    LockFailure(LockError, Option<String>),
     /// IO Error.
-    #[fail(display = "an IO error occurred: '{}'", _0)]
+    #[fail(display = "An IO error occurred: '{}'", _0)]
     IOError(#[cause] IOError),
-    /// The data within is corrupted.
-    ///
-    /// For instance, it contains invalid JSON.
-    #[fail(display = "file contains corrupted data: '{:?}'", _0)]
-    CorruptedFile(PathBuf),
+    /// Data corruption.
+    #[fail(display = "{:?}", _0)]
+    DataCorruption(DataCorruption),
     /// A thread holding the locked panicked and poisoned the lock.
-    #[fail(display = "a thread holding the locked panicked and poisoned the lock")]
+    #[fail(display = "A thread holding the locked panicked and poisoned the lock")]
     Poisoned,
     /// Invalid argument was passed by the user.
-    #[fail(display = "an invalid argument was passed: '{}'", _0)]
+    #[fail(display = "An invalid argument was passed: '{}'", _0)]
     InvalidArgument(String),
     /// An Error happened in one of the thread.
-    #[fail(display = "an error occurred in a thread: '{}'", _0)]
+    #[fail(display = "An error occurred in a thread: '{}'", _0)]
     ErrorInThread(String),
     /// An Error appeared related to the schema.
     #[fail(display = "Schema error: '{}'", _0)]
     SchemaError(String),
     /// Tried to access a fastfield reader for a field not configured accordingly.
-    #[fail(display = "fast field not available: '{:?}'", _0)]
+    #[fail(display = "Fast field not available: '{:?}'", _0)]
     FastFieldError(#[cause] FastFieldNotAvailableError),
+    /// System error. (e.g.: We failed spawning a new thread)
+    #[fail(display = "System error.'{}'", _0)]
+    SystemError(String),
+}
+
+impl From<DataCorruption> for TantivyError {
+    fn from(data_corruption: DataCorruption) -> TantivyError {
+        TantivyError::DataCorruption(data_corruption)
+    }
 }
 
 impl From<FastFieldNotAvailableError> for TantivyError {
@@ -60,6 +97,12 @@ impl From<FastFieldNotAvailableError> for TantivyError {
     }
 }
 
+impl From<LockError> for TantivyError {
+    fn from(lock_error: LockError) -> TantivyError {
+        TantivyError::LockFailure(lock_error, None)
+    }
+}
+
 impl From<IOError> for TantivyError {
     fn from(io_error: IOError) -> TantivyError {
         TantivyError::IOError(io_error)

src/fastfield/bytes/mod.rs

@@ -6,12 +6,12 @@ pub use self::writer::BytesFastFieldWriter;
 
 #[cfg(test)]
 mod tests {
-    use schema::SchemaBuilder;
+    use schema::Schema;
     use Index;
 
     #[test]
     fn test_bytes() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_bytes_field("bytesfield");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);

src/fastfield/facet_reader.rs

@@ -1,5 +1,6 @@
 use super::MultiValueIntFastFieldReader;
 use schema::Facet;
+use std::str;
 use termdict::TermDictionary;
 use termdict::TermOrdinal;
 use DocId;
@@ -20,6 +21,7 @@ use DocId;
 pub struct FacetReader {
     term_ords: MultiValueIntFastFieldReader<u64>,
     term_dict: TermDictionary,
+    buffer: Vec<u8>,
 }
 
 impl FacetReader {
@@ -37,6 +39,7 @@ impl FacetReader {
         FacetReader {
             term_ords,
             term_dict,
+            buffer: vec![],
         }
     }
 
@@ -55,11 +58,18 @@ impl FacetReader {
     }
 
     /// Given a term ordinal returns the term associated to it.
-    pub fn facet_from_ord(&self, facet_ord: TermOrdinal, output: &mut Facet) {
+    pub fn facet_from_ord(
+        &mut self,
+        facet_ord: TermOrdinal,
+        output: &mut Facet,
+    ) -> Result<(), str::Utf8Error> {
         let found_term = self
             .term_dict
-            .ord_to_term(facet_ord as u64, output.inner_buffer_mut());
+            .ord_to_term(facet_ord as u64, &mut self.buffer);
         assert!(found_term, "Term ordinal {} no found.", facet_ord);
+        let facet_str = str::from_utf8(&self.buffer[..])?;
+        output.set_facet_str(facet_str);
+        Ok(())
     }
 
     /// Return the list of facet ordinals associated to a document.

src/fastfield/mod.rs

@@ -127,19 +127,19 @@ mod tests {
     use common::CompositeFile;
     use directory::{Directory, RAMDirectory, WritePtr};
     use fastfield::FastFieldReader;
-    use rand::Rng;
+    use rand::prelude::SliceRandom;
+    use rand::rngs::StdRng;
     use rand::SeedableRng;
-    use rand::XorShiftRng;
     use schema::Document;
     use schema::Field;
+    use schema::Schema;
     use schema::FAST;
-    use schema::{Schema, SchemaBuilder};
     use std::collections::HashMap;
     use std::path::Path;
 
     lazy_static! {
         pub static ref SCHEMA: Schema = {
-            let mut schema_builder = SchemaBuilder::default();
+            let mut schema_builder = Schema::builder();
             schema_builder.add_u64_field("field", FAST);
             schema_builder.build()
         };
@@ -298,7 +298,7 @@ mod tests {
     fn test_signed_intfastfield() {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
 
         let i64_field = schema_builder.add_i64_field("field", FAST);
         let schema = schema_builder.build();
@@ -342,7 +342,7 @@ mod tests {
     fn test_signed_intfastfield_default_val() {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let i64_field = schema_builder.add_i64_field("field", FAST);
         let schema = schema_builder.build();
 
@@ -367,11 +367,10 @@ mod tests {
         }
     }
 
+    // Warning: this generates the same permutation at each call
     pub fn generate_permutation() -> Vec<u64> {
-        let seed: [u8; 16] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
-        let mut rng = XorShiftRng::from_seed(seed);
         let mut permutation: Vec<u64> = (0u64..100_000u64).collect();
-        rng.shuffle(&mut permutation);
+        permutation.shuffle(&mut StdRng::from_seed([1u8; 32]));
         permutation
     }
 

src/fastfield/multivalued/mod.rs

@@ -9,12 +9,12 @@ mod tests {
 
     use schema::Cardinality;
     use schema::IntOptions;
-    use schema::SchemaBuilder;
+    use schema::Schema;
     use Index;
 
     #[test]
     fn test_multivalued_u64() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_u64_field(
             "multifield",
             IntOptions::default().set_fast(Cardinality::MultiValues),
@@ -49,7 +49,7 @@ mod tests {
 
     #[test]
     fn test_multivalued_i64() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_i64_field(
             "multifield",
             IntOptions::default().set_fast(Cardinality::MultiValues),

src/fastfield/multivalued/reader.rs

@@ -47,11 +47,11 @@ impl<Item: FastValue> MultiValueIntFastFieldReader<Item> {
 mod tests {
 
     use core::Index;
-    use schema::{Document, Facet, SchemaBuilder};
+    use schema::{Document, Facet, Schema};
 
     #[test]
     fn test_multifastfield_reader() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let facet_field = schema_builder.add_facet_field("facets");
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -82,20 +82,20 @@ mod tests {
 
         let mut facet = Facet::root();
         {
-            facet_reader.facet_from_ord(1, &mut facet);
+            facet_reader.facet_from_ord(1, &mut facet).unwrap();
             assert_eq!(facet, Facet::from("/category"));
         }
         {
-            facet_reader.facet_from_ord(2, &mut facet);
+            facet_reader.facet_from_ord(2, &mut facet).unwrap();
             assert_eq!(facet, Facet::from("/category/cat1"));
         }
         {
-            facet_reader.facet_from_ord(3, &mut facet);
+            facet_reader.facet_from_ord(3, &mut facet).unwrap();
             assert_eq!(format!("{}", facet), "/category/cat2");
             assert_eq!(facet, Facet::from("/category/cat2"));
         }
         {
-            facet_reader.facet_from_ord(4, &mut facet);
+            facet_reader.facet_from_ord(4, &mut facet).unwrap();
             assert_eq!(facet, Facet::from("/category/cat3"));
         }
 

src/fastfield/reader.rs

@@ -7,7 +7,7 @@ use directory::ReadOnlySource;
 use directory::{Directory, RAMDirectory, WritePtr};
 use fastfield::{FastFieldSerializer, FastFieldsWriter};
 use owning_ref::OwningRef;
-use schema::SchemaBuilder;
+use schema::Schema;
 use schema::FAST;
 use std::collections::HashMap;
 use std::marker::PhantomData;
@@ -79,11 +79,8 @@ impl<Item: FastValue> FastFieldReader<Item> {
     // TODO change start to `u64`.
     // For multifastfield, start is an index in a second fastfield, not a `DocId`
     pub fn get_range(&self, start: u32, output: &mut [Item]) {
-        // ok: Item is either `u64` or `i64`
-        let output_u64: &mut [u64] = unsafe { &mut *(output as *mut [Item] as *mut [u64]) };
-        self.bit_unpacker.get_range(start, output_u64);
-        for out in output_u64.iter_mut() {
-            *out = Item::from_u64(*out + self.min_value_u64).as_u64();
+        for (i, out) in output.iter_mut().enumerate() {
+            *out = self.get(start + i as u32);
         }
     }
 
@@ -108,7 +105,7 @@ impl<Item: FastValue> FastFieldReader<Item> {
 
 impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
     fn from(vals: Vec<Item>) -> FastFieldReader<Item> {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_u64_field("field", FAST);
         let schema = schema_builder.build();
         let path = Path::new("__dummy__");

src/fieldnorm/mod.rs

@@ -15,7 +15,7 @@
 //! precompute computationally expensive functions of the fieldnorm
 //! in a very short array.
 //!
-//! This trick is used by the [BM25 similarity]().
+//! This trick is used by the BM25 similarity.
 mod code;
 mod reader;
 mod serializer;

src/functional_test.rs

@@ -1,7 +1,6 @@
 use rand::thread_rng;
 use std::collections::HashSet;
 
-use rand::distributions::Range;
 use rand::Rng;
 use schema::*;
 use Index;
@@ -16,7 +15,7 @@ fn check_index_content(searcher: &Searcher, vals: &HashSet<u64>) {
 #[ignore]
 #[cfg(feature = "mmap")]
 fn test_indexing() {
-    let mut schema_builder = SchemaBuilder::default();
+    let mut schema_builder = Schema::builder();
 
     let id_field = schema_builder.add_u64_field("id", INT_INDEXED);
     let multiples_field = schema_builder.add_u64_field("multiples", INT_INDEXED);
@@ -24,7 +23,6 @@ fn test_indexing() {
 
     let index = Index::create_from_tempdir(schema).unwrap();
 
-    let universe = Range::new(0u64, 20u64);
     let mut rng = thread_rng();
 
     let mut index_writer = index.writer_with_num_threads(3, 120_000_000).unwrap();
@@ -33,7 +31,7 @@ fn test_indexing() {
     let mut uncommitted_docs: HashSet<u64> = HashSet::new();
 
     for _ in 0..200 {
-        let random_val = rng.sample(&universe);
+        let random_val = rng.gen_range(0, 20);
         if random_val == 0 {
             index_writer.commit().expect("Commit failed");
             committed_docs.extend(&uncommitted_docs);

src/indexer/delete_queue.rs

@@ -191,10 +191,7 @@ impl DeleteCursor {
         }
     }
 
-    #[cfg_attr(
-        feature = "cargo-clippy",
-        allow(clippy::wrong_self_convention)
-    )]
+    #[cfg_attr(feature = "cargo-clippy", allow(clippy::wrong_self_convention))]
     fn is_behind_opstamp(&mut self, target_opstamp: u64) -> bool {
         self.get()
             .map(|operation| operation.opstamp < target_opstamp)

src/indexer/directory_lock.rs

@@ -1,131 +0,0 @@
-use directory::error::OpenWriteError;
-use std::io::Write;
-use std::path::{Path, PathBuf};
-use std::thread;
-use std::time::Duration;
-use Directory;
-use TantivyError;
-
-#[derive(Debug, Clone, Copy)]
-pub enum LockType {
-    /// Only one process should be able to write tantivy's index at a time.
-    /// This lock file, when present, is in charge of preventing other processes to open an IndexWriter.
-    ///
-    /// If the process is killed and this file remains, it is safe to remove it manually.
-    ///
-    /// Failing to acquire this lock usually means a misuse of tantivy's API,
-    /// (creating more than one instance of the `IndexWriter`), are a spurious
-    /// lock file remaining after a crash. In the latter case, removing the file after
-    /// checking no process running tantivy is running is safe.
-    IndexWriterLock,
-    /// The meta lock file is here to protect the segment files being opened by
-    /// `.load_searchers()` from being garbage collected.
-    /// It makes it possible for another process to safely consume
-    /// our index in-writing. Ideally, we may have prefered `RWLock` semantics
-    /// here, but it is difficult to achieve on Windows.
-    ///
-    /// Opening segment readers is a very fast process.
-    /// Right now if the lock cannot be acquire on the first attempt, the logic
-    /// is very simplistic. We retry after `100ms` until we effectively
-    /// acquire the lock.
-    /// This lock should not have much contention in normal usage.
-    MetaLock,
-}
-
-/// Retry the logic of acquiring locks is pretty simple.
-/// We just retry `n` times after a given `duratio`, both
-/// depending on the type of lock.
-struct RetryPolicy {
-    num_retries: usize,
-    wait_in_ms: u64,
-}
-
-impl RetryPolicy {
-    fn no_retry() -> RetryPolicy {
-        RetryPolicy {
-            num_retries: 0,
-            wait_in_ms: 0,
-        }
-    }
-
-    fn wait_and_retry(&mut self) -> bool {
-        if self.num_retries == 0 {
-            false
-        } else {
-            self.num_retries -= 1;
-            let wait_duration = Duration::from_millis(self.wait_in_ms);
-            thread::sleep(wait_duration);
-            true
-        }
-    }
-}
-
-impl LockType {
-    fn retry_policy(self) -> RetryPolicy {
-        match self {
-            LockType::IndexWriterLock => RetryPolicy::no_retry(),
-            LockType::MetaLock => RetryPolicy {
-                num_retries: 100,
-                wait_in_ms: 100,
-            },
-        }
-    }
-
-    fn try_acquire_lock(self, directory: &mut Directory) -> Result<DirectoryLock, TantivyError> {
-        let path = self.filename();
-        let mut write = directory.open_write(path).map_err(|e| match e {
-            OpenWriteError::FileAlreadyExists(_) => TantivyError::LockFailure(self),
-            OpenWriteError::IOError(io_error) => TantivyError::IOError(io_error),
-        })?;
-        write.flush()?;
-        Ok(DirectoryLock {
-            directory: directory.box_clone(),
-            path: path.to_owned(),
-        })
-    }
-
-    /// Acquire a lock in the given directory.
-    pub fn acquire_lock(self, directory: &Directory) -> Result<DirectoryLock, TantivyError> {
-        let mut box_directory = directory.box_clone();
-        let mut retry_policy = self.retry_policy();
-        loop {
-            let lock_result = self.try_acquire_lock(&mut *box_directory);
-            match lock_result {
-                Ok(result) => {
-                    return Ok(result);
-                }
-                Err(TantivyError::LockFailure(ref filepath)) => {
-                    if !retry_policy.wait_and_retry() {
-                        return Err(TantivyError::LockFailure(filepath.to_owned()));
-                    }
-                }
-                Err(_) => {}
-            }
-        }
-    }
-
-    fn filename(&self) -> &Path {
-        match *self {
-            LockType::MetaLock => Path::new(".tantivy-meta.lock"),
-            LockType::IndexWriterLock => Path::new(".tantivy-indexer.lock"),
-        }
-    }
-}
-
-/// The `DirectoryLock` is an object that represents a file lock.
-/// See  [`LockType`](struct.LockType.html)
-///
-/// It is transparently associated to a lock file, that gets deleted
-/// on `Drop.` The lock is release automatically on `Drop`.
-pub struct DirectoryLock {
-    directory: Box<Directory>,
-    path: PathBuf,
-}
-
-impl Drop for DirectoryLock {
-    fn drop(&mut self) {
-        if let Err(e) = self.directory.delete(&*self.path) {
-            error!("Failed to remove the lock file. {:?}", e);
-        }
-    }
-}

src/indexer/index_writer.rs

@@ -8,16 +8,16 @@ use core::SegmentComponent;
 use core::SegmentId;
 use core::SegmentMeta;
 use core::SegmentReader;
-use crossbeam_channel as channel;
+use crossbeam::channel;
+use directory::DirectoryLock;
 use docset::DocSet;
 use error::TantivyError;
 use fastfield::write_delete_bitset;
-use futures::sync::oneshot::Receiver;
+use futures::{Canceled, Future};
 use indexer::delete_queue::{DeleteCursor, DeleteQueue};
 use indexer::doc_opstamp_mapping::DocToOpstampMapping;
 use indexer::operation::DeleteOperation;
 use indexer::stamper::Stamper;
-use indexer::DirectoryLock;
 use indexer::MergePolicy;
 use indexer::SegmentEntry;
 use indexer::SegmentWriter;
@@ -26,7 +26,7 @@ use schema::Document;
 use schema::IndexRecordOption;
 use schema::Term;
 use std::mem;
-use std::mem::swap;
+use std::sync::Arc;
 use std::thread;
 use std::thread::JoinHandle;
 use Result;
@@ -52,16 +52,19 @@ type DocumentReceiver = channel::Receiver<AddOperation>;
 ///
 /// Returns (the heap size in bytes, the hash table size in number of bits)
 fn initial_table_size(per_thread_memory_budget: usize) -> usize {
+    assert!(per_thread_memory_budget > 1_000);
     let table_size_limit: usize = per_thread_memory_budget / 3;
-    (1..)
+    if let Some(limit) = (1..)
         .take_while(|num_bits: &usize| compute_table_size(*num_bits) < table_size_limit)
         .last()
-        .unwrap_or_else(|| {
-            panic!(
-                "Per thread memory is too small: {}",
-                per_thread_memory_budget
-            )
-        }).min(19) // we cap it at 512K
+    {
+        limit.min(19) // we cap it at 2^19 = 512K.
+    } else {
+        unreachable!(
+            "Per thread memory is too small: {}",
+            per_thread_memory_budget
+        );
+    }
 }
 
 /// `IndexWriter` is the user entry-point to add document to an index.
@@ -139,7 +142,7 @@ pub fn open_index_writer(
     let stamper = Stamper::new(current_opstamp);
 
     let segment_updater =
-        SegmentUpdater::new(index.clone(), stamper.clone(), &delete_queue.cursor())?;
+        SegmentUpdater::create(index.clone(), stamper.clone(), &delete_queue.cursor())?;
 
     let mut index_writer = IndexWriter {
         _directory_lock: Some(directory_lock),
@@ -301,7 +304,7 @@ fn index_documents(
 
     let last_docstamp: u64 = *(doc_opstamps.last().unwrap());
 
-    let segment_entry: SegmentEntry = if delete_cursor.get().is_some() {
+    let delete_bitset_opt = if delete_cursor.get().is_some() {
         let doc_to_opstamps = DocToOpstampMapping::from(doc_opstamps);
         let segment_reader = SegmentReader::open(segment)?;
         let mut deleted_bitset = BitSet::with_capacity(num_docs as usize);
@@ -312,18 +315,17 @@ fn index_documents(
             &doc_to_opstamps,
             last_docstamp,
         )?;
-        SegmentEntry::new(segment_meta, delete_cursor, {
-            if may_have_deletes {
-                Some(deleted_bitset)
-            } else {
-                None
-            }
-        })
+        if may_have_deletes {
+            Some(deleted_bitset)
+        } else {
+            None
+        }
     } else {
         // if there are no delete operation in the queue, no need
         // to even open the segment.
-        SegmentEntry::new(segment_meta, delete_cursor, None)
+        None
     };
+    let segment_entry = SegmentEntry::new(segment_meta, delete_cursor, delete_bitset_opt);
     Ok(segment_updater.add_segment(generation, segment_entry))
 }
 
@@ -365,13 +367,16 @@ impl IndexWriter {
             .add_segment(self.generation, segment_entry);
     }
 
-    /// *Experimental & Advanced API* Creates a new segment.
-    /// and marks it as currently in write.
+    /// Creates a new segment.
     ///
     /// This method is useful only for users trying to do complex
     /// operations, like converting an index format to another.
+    ///
+    /// It is safe to start writing file associated to the new `Segment`.
+    /// These will not be garbage collected as long as an instance object of
+    /// `SegmentMeta` object associated to the new `Segment` is "alive".
     pub fn new_segment(&self) -> Segment {
-        self.segment_updater.new_segment()
+        self.index.new_segment()
     }
 
     /// Spawns a new worker thread for indexing.
@@ -386,13 +391,16 @@ impl IndexWriter {
         let mut delete_cursor = self.delete_queue.cursor();
 
         let mem_budget = self.heap_size_in_bytes_per_thread;
+        let index = self.index.clone();
         let join_handle: JoinHandle<Result<()>> = thread::Builder::new()
             .name(format!(
-                "indexing thread {} for gen {}",
+                "thrd-tantivy-index{}-gen{}",
                 self.worker_id, generation
-            )).spawn(move || {
+            ))
+            .spawn(move || {
                 loop {
-                    let mut document_iterator = document_receiver_clone.clone().peekable();
+                    let mut document_iterator =
+                        document_receiver_clone.clone().into_iter().peekable();
 
                     // the peeking here is to avoid
                     // creating a new segment's files
@@ -409,7 +417,7 @@ impl IndexWriter {
                         // was dropped.
                         return Ok(());
                     }
-                    let segment = segment_updater.new_segment();
+                    let segment = index.new_segment();
                     index_documents(
                         mem_budget,
                         &segment,
@@ -426,7 +434,7 @@ impl IndexWriter {
     }
 
     /// Accessor to the merge policy.
-    pub fn get_merge_policy(&self) -> Box<MergePolicy> {
+    pub fn get_merge_policy(&self) -> Arc<Box<MergePolicy>> {
         self.segment_updater.get_merge_policy()
     }
 
@@ -451,7 +459,10 @@ impl IndexWriter {
     /// Merges a given list of segments
     ///
     /// `segment_ids` is required to be non-empty.
-    pub fn merge(&mut self, segment_ids: &[SegmentId]) -> Result<Receiver<SegmentMeta>> {
+    pub fn merge(
+        &mut self,
+        segment_ids: &[SegmentId],
+    ) -> Result<impl Future<Item = SegmentMeta, Error = Canceled>> {
         self.segment_updater.start_merge(segment_ids)
     }
 
@@ -464,13 +475,10 @@ impl IndexWriter {
     ///
     /// Returns the former segment_ready channel.
     fn recreate_document_channel(&mut self) -> DocumentReceiver {
-        let (mut document_sender, mut document_receiver): (
-            DocumentSender,
-            DocumentReceiver,
-        ) = channel::bounded(PIPELINE_MAX_SIZE_IN_DOCS);
-        swap(&mut self.document_sender, &mut document_sender);
-        swap(&mut self.document_receiver, &mut document_receiver);
-        document_receiver
+        let (document_sender, document_receiver): (DocumentSender, DocumentReceiver) =
+            channel::bounded(PIPELINE_MAX_SIZE_IN_DOCS);
+        mem::replace(&mut self.document_sender, document_sender);
+        mem::replace(&mut self.document_receiver, document_receiver)
     }
 
     /// Rollback to the last commit
@@ -557,17 +565,12 @@ impl IndexWriter {
         // and recreate a new one channels.
         self.recreate_document_channel();
 
-        let mut former_workers_join_handle = Vec::new();
-        swap(
-            &mut former_workers_join_handle,
-            &mut self.workers_join_handle,
-        );
+        let former_workers_join_handle = mem::replace(&mut self.workers_join_handle, Vec::new());
 
         for worker_handle in former_workers_join_handle {
             let indexing_worker_result = worker_handle
                 .join()
                 .map_err(|e| TantivyError::ErrorInThread(format!("{:?}", e)))?;
-
             indexing_worker_result?;
             // add a new worker for the next generation.
             self.add_indexing_worker()?;
@@ -640,7 +643,10 @@ impl IndexWriter {
     pub fn add_document(&mut self, document: Document) -> u64 {
         let opstamp = self.stamper.stamp();
         let add_operation = AddOperation { opstamp, document };
-        self.document_sender.send(add_operation);
+        let send_result = self.document_sender.send(add_operation);
+        if let Err(e) = send_result {
+            panic!("Failed to index document. Sending to indexing channel failed. This probably means all of the indexing threads have panicked. {:?}", e);
+        }
         opstamp
     }
 }
@@ -649,6 +655,7 @@ impl IndexWriter {
 mod tests {
 
     use super::initial_table_size;
+    use directory::error::LockError;
     use error::*;
     use indexer::NoMergePolicy;
     use schema::{self, Document};
@@ -657,25 +664,24 @@ mod tests {
 
     #[test]
     fn test_lockfile_stops_duplicates() {
-        let schema_builder = schema::SchemaBuilder::default();
+        let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
-        let _index_writer = index.writer(40_000_000).unwrap();
-        match index.writer(40_000_000) {
-            Err(TantivyError::LockFailure(_)) => {}
-            _ => panic!("Expected FileAlreadyExists error"),
+        let _index_writer = index.writer(3_000_000).unwrap();
+        match index.writer(3_000_000) {
+            Err(TantivyError::LockFailure(LockError::LockBusy, _)) => {}
+            _ => panic!("Expected a `LockFailure` error"),
         }
     }
 
     #[test]
     fn test_lockfile_already_exists_error_msg() {
-        let schema_builder = schema::SchemaBuilder::default();
+        let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
         let _index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         match index.writer_with_num_threads(1, 3_000_000) {
             Err(err) => {
                 let err_msg = err.to_string();
-                assert!(err_msg.contains("Lockfile"));
-                assert!(err_msg.contains("Possible causes:"))
+                assert!(err_msg.contains("already an `IndexWriter`"));
             }
             _ => panic!("Expected LockfileAlreadyExists error"),
         }
@@ -683,9 +689,9 @@ mod tests {
 
     #[test]
     fn test_set_merge_policy() {
-        let schema_builder = schema::SchemaBuilder::default();
+        let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
-        let index_writer = index.writer(40_000_000).unwrap();
+        let index_writer = index.writer(3_000_000).unwrap();
         assert_eq!(
             format!("{:?}", index_writer.get_merge_policy()),
             "LogMergePolicy { min_merge_size: 8, min_layer_size: 10000, \
@@ -701,19 +707,19 @@ mod tests {
 
     #[test]
     fn test_lockfile_released_on_drop() {
-        let schema_builder = schema::SchemaBuilder::default();
+        let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
         {
-            let _index_writer = index.writer(40_000_000).unwrap();
+            let _index_writer = index.writer(3_000_000).unwrap();
             // the lock should be released when the
             // index_writer leaves the scope.
         }
-        let _index_writer_two = index.writer(40_000_000).unwrap();
+        let _index_writer_two = index.writer(3_000_000).unwrap();
     }
 
     #[test]
     fn test_commit_and_rollback() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 
@@ -735,7 +741,7 @@ mod tests {
                 index_writer.add_document(doc!(text_field=>"b"));
                 index_writer.add_document(doc!(text_field=>"c"));
             }
-            assert_eq!(index_writer.commit().unwrap(), 2u64);
+            assert!(index_writer.commit().is_ok());
             index.load_searchers().unwrap();
             assert_eq!(num_docs_containing("a"), 0);
             assert_eq!(num_docs_containing("b"), 1);
@@ -747,7 +753,7 @@ mod tests {
 
     #[test]
     fn test_with_merges() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
         let num_docs_containing = |s: &str| {
@@ -784,7 +790,7 @@ mod tests {
 
     #[test]
     fn test_prepare_with_commit_message() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 
@@ -798,7 +804,6 @@ mod tests {
             {
                 let mut prepared_commit = index_writer.prepare_commit().expect("commit failed");
                 prepared_commit.set_payload("first commit");
-                assert_eq!(prepared_commit.opstamp(), 100);
                 prepared_commit.commit().expect("commit failed");
             }
             {
@@ -818,7 +823,7 @@ mod tests {
 
     #[test]
     fn test_prepare_but_rollback() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 
@@ -832,7 +837,6 @@ mod tests {
             {
                 let mut prepared_commit = index_writer.prepare_commit().expect("commit failed");
                 prepared_commit.set_payload("first commit");
-                assert_eq!(prepared_commit.opstamp(), 100);
                 prepared_commit.abort().expect("commit failed");
             }
             {
@@ -866,7 +870,7 @@ mod tests {
     #[test]
     fn test_write_commit_fails() {
         use fail;
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 

src/indexer/merge_operation.rs

@@ -0,0 +1,64 @@
+use census::{Inventory, TrackedObject};
+use std::collections::HashSet;
+use SegmentId;
+
+#[derive(Default)]
+pub struct MergeOperationInventory(Inventory<InnerMergeOperation>);
+
+impl MergeOperationInventory {
+    pub fn segment_in_merge(&self) -> HashSet<SegmentId> {
+        let mut segment_in_merge = HashSet::default();
+        for merge_op in self.0.list() {
+            for &segment_id in &merge_op.segment_ids {
+                segment_in_merge.insert(segment_id);
+            }
+        }
+        segment_in_merge
+    }
+}
+
+/// A `MergeOperation` has two role.
+/// It carries all of the information required to describe a merge :
+/// - `target_opstamp` is the opstamp up to which we want to consume the
+/// delete queue and reflect their deletes.
+/// - `segment_ids` is the list of segment to be merged.
+///
+/// The second role is to ensure keep track of the fact that these
+/// segments are in merge and avoid starting a merge operation that
+/// may conflict with this one.
+///
+/// This works by tracking merge operations. When considering computing
+/// merge candidates, we simply list tracked merge operations and remove
+/// their segments from possible merge candidates.
+pub struct MergeOperation {
+    inner: TrackedObject<InnerMergeOperation>,
+}
+
+struct InnerMergeOperation {
+    target_opstamp: u64,
+    segment_ids: Vec<SegmentId>,
+}
+
+impl MergeOperation {
+    pub fn new(
+        inventory: &MergeOperationInventory,
+        target_opstamp: u64,
+        segment_ids: Vec<SegmentId>,
+    ) -> MergeOperation {
+        let inner_merge_operation = InnerMergeOperation {
+            target_opstamp,
+            segment_ids,
+        };
+        MergeOperation {
+            inner: inventory.0.track(inner_merge_operation),
+        }
+    }
+
+    pub fn target_opstamp(&self) -> u64 {
+        self.inner.target_opstamp
+    }
+
+    pub fn segment_ids(&self) -> &[SegmentId] {
+        &self.inner.segment_ids[..]
+    }
+}

src/indexer/merge_policy.rs

@@ -11,7 +11,7 @@ pub struct MergeCandidate(pub Vec<SegmentId>);
 ///
 /// Every time a the list of segments changes, the segment updater
 /// asks the merge policy if some segments should be merged.
-pub trait MergePolicy: MergePolicyClone + marker::Send + marker::Sync + Debug {
+pub trait MergePolicy: marker::Send + marker::Sync + Debug {
     /// Given the list of segment metas, returns the list of merge candidates.
     ///
     /// This call happens on the segment updater thread, and will block
@@ -19,21 +19,6 @@ pub trait MergePolicy: MergePolicyClone + marker::Send + marker::Sync + Debug {
     fn compute_merge_candidates(&self, segments: &[SegmentMeta]) -> Vec<MergeCandidate>;
 }
 
-/// MergePolicyClone
-pub trait MergePolicyClone {
-    /// Returns a boxed clone of the MergePolicy.
-    fn box_clone(&self) -> Box<MergePolicy>;
-}
-
-impl<T> MergePolicyClone for T
-where
-    T: 'static + MergePolicy + Clone,
-{
-    fn box_clone(&self) -> Box<MergePolicy> {
-        Box::new(self.clone())
-    }
-}
-
 /// Never merge segments.
 #[derive(Debug, Clone)]
 pub struct NoMergePolicy;

src/indexer/merger.rs

@@ -40,13 +40,15 @@ fn compute_total_num_tokens(readers: &[SegmentReader], field: Field) -> u64 {
             total_tokens += reader.inverted_index(field).total_num_tokens();
         }
     }
-    total_tokens + count
-        .iter()
-        .cloned()
-        .enumerate()
-        .map(|(fieldnorm_ord, count)| {
-            count as u64 * u64::from(FieldNormReader::id_to_fieldnorm(fieldnorm_ord as u8))
-        }).sum::<u64>()
+    total_tokens
+        + count
+            .iter()
+            .cloned()
+            .enumerate()
+            .map(|(fieldnorm_ord, count)| {
+                count as u64 * u64::from(FieldNormReader::id_to_fieldnorm(fieldnorm_ord as u8))
+            })
+            .sum::<u64>()
 }
 
 pub struct IndexMerger {
@@ -523,7 +525,8 @@ impl IndexMerger {
                         }
                     }
                     None
-                }).collect();
+                })
+                .collect();
 
             // At this point, `segment_postings` contains the posting list
             // of all of the segments containing the given term.
@@ -614,7 +617,7 @@ impl IndexMerger {
                     store_writer.store(&doc)?;
                 }
             } else {
-                store_writer.stack(store_reader)?;
+                store_writer.stack(&store_reader)?;
             }
         }
         Ok(())
@@ -635,10 +638,9 @@ impl SerializableSegment for IndexMerger {
 #[cfg(test)]
 mod tests {
     use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
-    use collector::chain;
     use collector::tests::TestCollector;
     use collector::tests::{BytesFastFieldTestCollector, FastFieldTestCollector};
-    use collector::FacetCollector;
+    use collector::{Count, FacetCollector};
     use core::Index;
     use futures::Future;
     use query::AllQuery;
@@ -647,10 +649,12 @@ mod tests {
     use schema;
     use schema::Cardinality;
     use schema::Document;
+    use schema::Facet;
     use schema::IndexRecordOption;
     use schema::IntOptions;
     use schema::Term;
     use schema::TextFieldIndexing;
+    use schema::INT_INDEXED;
     use std::io::Cursor;
     use DocAddress;
     use IndexWriter;
@@ -658,13 +662,14 @@ mod tests {
 
     #[test]
     fn test_index_merger_no_deletes() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_fieldtype = schema::TextOptions::default()
             .set_indexing_options(
                 TextFieldIndexing::default()
                     .set_tokenizer("default")
                     .set_index_option(IndexRecordOption::WithFreqs),
-            ).set_stored();
+            )
+            .set_stored();
         let text_field = schema_builder.add_text_field("text", text_fieldtype);
         let score_fieldtype = schema::IntOptions::default().set_fast(Cardinality::SingleValue);
         let score_field = schema_builder.add_u64_field("score", score_fieldtype);
@@ -742,27 +747,32 @@ mod tests {
             index.load_searchers().unwrap();
             let searcher = index.searcher();
             let get_doc_ids = |terms: Vec<Term>| {
-                let mut collector = TestCollector::default();
                 let query = BooleanQuery::new_multiterms_query(terms);
-                assert!(searcher.search(&query, &mut collector).is_ok());
-                collector.docs()
+                let top_docs = searcher.search(&query, &TestCollector).unwrap();
+                top_docs.docs().to_vec()
             };
             {
                 assert_eq!(
                     get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
-                    vec![1, 2, 4]
+                    vec![DocAddress(0, 1), DocAddress(0, 2), DocAddress(0, 4)]
                 );
                 assert_eq!(
                     get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
-                    vec![0, 3]
+                    vec![DocAddress(0, 0), DocAddress(0, 3)]
                 );
                 assert_eq!(
                     get_doc_ids(vec![Term::from_field_text(text_field, "g")]),
-                    vec![4]
+                    vec![DocAddress(0, 4)]
                 );
                 assert_eq!(
                     get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
-                    vec![0, 1, 2, 3, 4]
+                    vec![
+                        DocAddress(0, 0),
+                        DocAddress(0, 1),
+                        DocAddress(0, 2),
+                        DocAddress(0, 3),
+                        DocAddress(0, 4)
+                    ]
                 );
             }
             {
@@ -788,17 +798,18 @@ mod tests {
             {
                 let get_fast_vals = |terms: Vec<Term>| {
                     let query = BooleanQuery::new_multiterms_query(terms);
-                    let mut collector = FastFieldTestCollector::for_field(score_field);
-                    assert!(searcher.search(&query, &mut collector).is_ok());
-                    collector.vals()
+                    searcher
+                        .search(&query, &FastFieldTestCollector::for_field(score_field))
+                        .unwrap()
                 };
                 let get_fast_vals_bytes = |terms: Vec<Term>| {
                     let query = BooleanQuery::new_multiterms_query(terms);
-                    let mut collector = BytesFastFieldTestCollector::for_field(bytes_score_field);
                     searcher
-                        .search(&query, &mut collector)
-                        .expect("failed to search");
-                    collector.vals()
+                        .search(
+                            &query,
+                            &BytesFastFieldTestCollector::for_field(bytes_score_field),
+                        )
+                        .expect("failed to search")
                 };
                 assert_eq!(
                     get_fast_vals(vec![Term::from_field_text(text_field, "a")]),
@@ -814,34 +825,27 @@ mod tests {
 
     #[test]
     fn test_index_merger_with_deletes() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let text_fieldtype = schema::TextOptions::default()
             .set_indexing_options(
                 TextFieldIndexing::default().set_index_option(IndexRecordOption::WithFreqs),
-            ).set_stored();
+            )
+            .set_stored();
         let text_field = schema_builder.add_text_field("text", text_fieldtype);
         let score_fieldtype = schema::IntOptions::default().set_fast(Cardinality::SingleValue);
         let score_field = schema_builder.add_u64_field("score", score_fieldtype);
         let bytes_score_field = schema_builder.add_bytes_field("score_bytes");
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
 
         let search_term = |searcher: &Searcher, term: Term| {
-            let mut collector = FastFieldTestCollector::for_field(score_field);
-            let mut bytes_collector = BytesFastFieldTestCollector::for_field(bytes_score_field);
+            let collector = FastFieldTestCollector::for_field(score_field);
+            let bytes_collector = BytesFastFieldTestCollector::for_field(bytes_score_field);
             let term_query = TermQuery::new(term, IndexRecordOption::Basic);
-
-            {
-                let mut combined_collector =
-                    chain().push(&mut collector).push(&mut bytes_collector);
-                searcher
-                    .search(&term_query, &mut combined_collector)
-                    .unwrap();
-            }
-
-            let scores = collector.vals();
-
-            let mut score_bytes = Cursor::new(bytes_collector.vals());
+            let (scores, bytes) = searcher
+                .search(&term_query, &(collector, bytes_collector))
+                .unwrap();
+            let mut score_bytes = Cursor::new(bytes);
             for &score in &scores {
                 assert_eq!(score as u32, score_bytes.read_u32::<BigEndian>().unwrap());
             }
@@ -854,21 +858,21 @@ mod tests {
         {
             // a first commit
             index_writer.add_document(doc!(
-                    text_field => "a b d",
-                    score_field => 1u64,
-                    bytes_score_field => vec![0u8, 0, 0, 1],
-                ));
+                text_field => "a b d",
+                score_field => 1u64,
+                bytes_score_field => vec![0u8, 0, 0, 1],
+            ));
             index_writer.add_document(doc!(
-                    text_field => "b c",
-                    score_field => 2u64,
-                    bytes_score_field => vec![0u8, 0, 0, 2],
-                ));
+                text_field => "b c",
+                score_field => 2u64,
+                bytes_score_field => vec![0u8, 0, 0, 2],
+            ));
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
             index_writer.add_document(doc!(
-                    text_field => "c d",
-                    score_field => 3u64,
-                    bytes_score_field => vec![0u8, 0, 0, 3],
-                ));
+                text_field => "c d",
+                score_field => 3u64,
+                bytes_score_field => vec![0u8, 0, 0, 3],
+            ));
             index_writer.commit().expect("committed");
             index.load_searchers().unwrap();
             let ref searcher = *index.searcher();
@@ -895,37 +899,37 @@ mod tests {
         {
             // a second commit
             index_writer.add_document(doc!(
-                    text_field => "a d e",
-                    score_field => 4_000u64,
-                    bytes_score_field => vec![0u8, 0, 0, 4],
-                ));
+                text_field => "a d e",
+                score_field => 4_000u64,
+                bytes_score_field => vec![0u8, 0, 0, 4],
+            ));
             index_writer.add_document(doc!(
-                    text_field => "e f",
-                    score_field => 5_000u64,
-                    bytes_score_field => vec![0u8, 0, 0, 5],
-                ));
+                text_field => "e f",
+                score_field => 5_000u64,
+                bytes_score_field => vec![0u8, 0, 0, 5],
+            ));
             index_writer.delete_term(Term::from_field_text(text_field, "a"));
             index_writer.delete_term(Term::from_field_text(text_field, "f"));
             index_writer.add_document(doc!(
-                    text_field => "f g",
-                    score_field => 6_000u64,
-                    bytes_score_field => vec![0u8, 0, 23, 112],
-                ));
+                text_field => "f g",
+                score_field => 6_000u64,
+                bytes_score_field => vec![0u8, 0, 23, 112],
+            ));
             index_writer.add_document(doc!(
-                    text_field => "g h",
-                    score_field => 7_000u64,
-                    bytes_score_field => vec![0u8, 0, 27, 88],
-                ));
+                text_field => "g h",
+                score_field => 7_000u64,
+                bytes_score_field => vec![0u8, 0, 27, 88],
+            ));
             index_writer.commit().expect("committed");
             index.load_searchers().unwrap();
             let searcher = index.searcher();
 
             assert_eq!(searcher.segment_readers().len(), 2);
             assert_eq!(searcher.num_docs(), 3);
-            assert_eq!(searcher.segment_readers()[0].num_docs(), 1);
-            assert_eq!(searcher.segment_readers()[0].max_doc(), 3);
-            assert_eq!(searcher.segment_readers()[1].num_docs(), 2);
-            assert_eq!(searcher.segment_readers()[1].max_doc(), 4);
+            assert_eq!(searcher.segment_readers()[0].num_docs(), 2);
+            assert_eq!(searcher.segment_readers()[0].max_doc(), 4);
+            assert_eq!(searcher.segment_readers()[1].num_docs(), 1);
+            assert_eq!(searcher.segment_readers()[1].max_doc(), 3);
             assert_eq!(
                 search_term(&searcher, Term::from_field_text(text_field, "a")),
                 empty_vec
@@ -959,15 +963,15 @@ mod tests {
                 .segment_reader(0)
                 .fast_field_reader::<u64>(score_field)
                 .unwrap();
-            assert_eq!(score_field_reader.min_value(), 1);
-            assert_eq!(score_field_reader.max_value(), 3);
+            assert_eq!(score_field_reader.min_value(), 4000);
+            assert_eq!(score_field_reader.max_value(), 7000);
 
             let score_field_reader = searcher
                 .segment_reader(1)
                 .fast_field_reader::<u64>(score_field)
                 .unwrap();
-            assert_eq!(score_field_reader.min_value(), 4000);
-            assert_eq!(score_field_reader.max_value(), 7000);
+            assert_eq!(score_field_reader.min_value(), 1);
+            assert_eq!(score_field_reader.max_value(), 3);
         }
         {
             // merging the segments
@@ -980,7 +984,7 @@ mod tests {
                 .wait()
                 .expect("Merging failed");
             index.load_searchers().unwrap();
-            let ref searcher = *index.searcher();
+            let searcher = index.searcher();
             assert_eq!(searcher.segment_readers().len(), 1);
             assert_eq!(searcher.num_docs(), 3);
             assert_eq!(searcher.segment_readers()[0].num_docs(), 3);
@@ -1026,7 +1030,7 @@ mod tests {
             index_writer.commit().unwrap();
 
             index.load_searchers().unwrap();
-            let ref searcher = *index.searcher();
+            let searcher = index.searcher();
             assert_eq!(searcher.segment_readers().len(), 1);
             assert_eq!(searcher.num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].num_docs(), 2);
@@ -1122,30 +1126,26 @@ mod tests {
         {
             // Test removing all docs
             index_writer.delete_term(Term::from_field_text(text_field, "g"));
+            index_writer.commit().unwrap();
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            index_writer
-                .merge(&segment_ids)
-                .expect("Failed to initiate merge")
-                .wait()
-                .expect("Merging failed");
             index.load_searchers().unwrap();
 
             let ref searcher = *index.searcher();
-            assert_eq!(searcher.segment_readers().len(), 1);
+            assert!(segment_ids.is_empty());
+            assert!(searcher.segment_readers().is_empty());
             assert_eq!(searcher.num_docs(), 0);
         }
     }
 
     #[test]
     fn test_merge_facets() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let facet_field = schema_builder.add_facet_field("facet");
         let index = Index::create_in_ram(schema_builder.build());
-        use schema::Facet;
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             let index_doc = |index_writer: &mut IndexWriter, doc_facets: &[&str]| {
                 let mut doc = Document::default();
                 for facet in doc_facets {
@@ -1172,20 +1172,16 @@ mod tests {
             index_doc(&mut index_writer, &["/top/e", "/top/f"]);
             index_writer.commit().expect("committed");
         }
+
         index.load_searchers().unwrap();
         let test_searcher = |expected_num_docs: usize, expected: &[(&str, u64)]| {
             let searcher = index.searcher();
             let mut facet_collector = FacetCollector::for_field(facet_field);
             facet_collector.add_facet(Facet::from("/top"));
-            use collector::{CountCollector, MultiCollector};
-            let mut count_collector = CountCollector::default();
-            {
-                let mut multi_collectors =
-                    MultiCollector::from(vec![&mut count_collector, &mut facet_collector]);
-                searcher.search(&AllQuery, &mut multi_collectors).unwrap();
-            }
-            assert_eq!(count_collector.count(), expected_num_docs);
-            let facet_counts = facet_collector.harvest();
+            let (count, facet_counts) = searcher
+                .search(&AllQuery, &(Count, facet_collector))
+                .unwrap();
+            assert_eq!(count, expected_num_docs);
             let facets: Vec<(String, u64)> = facet_counts
                 .get("/top")
                 .map(|(facet, count)| (facet.to_string(), count))
@@ -1209,20 +1205,18 @@ mod tests {
                 ("/top/f", 1),
             ],
         );
-
         // Merging the segments
         {
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer
                 .merge(&segment_ids)
                 .expect("Failed to initiate merge")
                 .wait()
                 .expect("Merging failed");
             index_writer.wait_merging_threads().unwrap();
-
             index.load_searchers().unwrap();
             test_searcher(
                 11,
@@ -1239,7 +1233,7 @@ mod tests {
 
         // Deleting one term
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             let facet = Facet::from_path(vec!["top", "a", "firstdoc"]);
             let facet_term = Term::from_facet(facet_field, &facet);
             index_writer.delete_term(facet_term);
@@ -1259,9 +1253,37 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_bug_merge() {
+        let mut schema_builder = schema::Schema::builder();
+        let int_field = schema_builder.add_u64_field("intvals", INT_INDEXED);
+        let index = Index::create_in_ram(schema_builder.build());
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        index_writer.add_document(doc!(int_field => 1u64));
+        index_writer.commit().expect("commit failed");
+        index_writer.add_document(doc!(int_field => 1u64));
+        index_writer.commit().expect("commit failed");
+        index.load_searchers().unwrap();
+        let searcher = index.searcher();
+        assert_eq!(searcher.num_docs(), 2);
+        index_writer.delete_term(Term::from_field_u64(int_field, 1));
+        let segment_ids = index
+            .searchable_segment_ids()
+            .expect("Searchable segments failed.");
+        index_writer
+            .merge(&segment_ids)
+            .expect("Failed to initiate merge")
+            .wait()
+            .expect("Merging failed");
+        index.load_searchers().unwrap();
+        // commit has not been called yet. The document should still be
+        // there.
+        assert_eq!(index.searcher().num_docs(), 2);
+    }
+
     #[test]
     fn test_merge_multivalued_int_fields_all_deleted() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let int_options = IntOptions::default()
             .set_fast(Cardinality::MultiValues)
             .set_indexed();
@@ -1269,7 +1291,7 @@ mod tests {
         let index = Index::create_in_ram(schema_builder.build());
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             let mut doc = Document::default();
             doc.add_u64(int_field, 1);
             index_writer.add_document(doc.clone());
@@ -1277,24 +1299,26 @@ mod tests {
             index_writer.add_document(doc);
             index_writer.commit().expect("commit failed");
             index_writer.delete_term(Term::from_field_u64(int_field, 1));
-            index_writer.commit().expect("commit failed");
-        }
-        index.load_searchers().unwrap();
-        let searcher = index.searcher();
-        assert_eq!(searcher.num_docs(), 0);
-        // Merging the segments
-        {
+
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
             index_writer
                 .merge(&segment_ids)
                 .expect("Failed to initiate merge")
                 .wait()
                 .expect("Merging failed");
+
+            // assert delete has not been committed
+            index.load_searchers().unwrap();
+            let searcher = index.searcher();
+            assert_eq!(searcher.num_docs(), 2);
+
+            index_writer.commit().unwrap();
+
             index_writer.wait_merging_threads().unwrap();
         }
+
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         assert_eq!(searcher.num_docs(), 0);
@@ -1302,7 +1326,7 @@ mod tests {
 
     #[test]
     fn test_merge_multivalued_int_fields() {
-        let mut schema_builder = schema::SchemaBuilder::default();
+        let mut schema_builder = schema::Schema::builder();
         let int_options = IntOptions::default()
             .set_fast(Cardinality::MultiValues)
             .set_indexed();
@@ -1310,7 +1334,7 @@ mod tests {
         let index = Index::create_in_ram(schema_builder.build());
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             let index_doc = |index_writer: &mut IndexWriter, int_vals: &[u64]| {
                 let mut doc = Document::default();
                 for &val in int_vals {
@@ -1368,15 +1392,17 @@ mod tests {
             assert_eq!(&vals, &[17]);
         }
 
-        {
-            let segment = searcher.segment_reader(1u32);
-            let ff_reader = segment.multi_fast_field_reader(int_field).unwrap();
-            ff_reader.get_vals(0, &mut vals);
-            assert_eq!(&vals, &[20]);
-        }
+        println!(
+            "{:?}",
+            searcher
+                .segment_readers()
+                .iter()
+                .map(|reader| reader.max_doc())
+                .collect::<Vec<_>>()
+        );
 
         {
-            let segment = searcher.segment_reader(2u32);
+            let segment = searcher.segment_reader(1u32);
             let ff_reader = segment.multi_fast_field_reader(int_field).unwrap();
             ff_reader.get_vals(0, &mut vals);
             assert_eq!(&vals, &[28, 27]);
@@ -1385,12 +1411,19 @@ mod tests {
             assert_eq!(&vals, &[1_000]);
         }
 
+        {
+            let segment = searcher.segment_reader(2u32);
+            let ff_reader = segment.multi_fast_field_reader(int_field).unwrap();
+            ff_reader.get_vals(0, &mut vals);
+            assert_eq!(&vals, &[20]);
+        }
+
         // Merging the segments
         {
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer
                 .merge(&segment_ids)
                 .expect("Failed to initiate merge")
@@ -1403,6 +1436,14 @@ mod tests {
 
         {
             let searcher = index.searcher();
+            println!(
+                "{:?}",
+                searcher
+                    .segment_readers()
+                    .iter()
+                    .map(|reader| reader.max_doc())
+                    .collect::<Vec<_>>()
+            );
             let segment = searcher.segment_reader(0u32);
             let ff_reader = segment.multi_fast_field_reader(int_field).unwrap();
 
@@ -1428,13 +1469,13 @@ mod tests {
             assert_eq!(&vals, &[17]);
 
             ff_reader.get_vals(7, &mut vals);
-            assert_eq!(&vals, &[20]);
-
-            ff_reader.get_vals(8, &mut vals);
             assert_eq!(&vals, &[28, 27]);
 
-            ff_reader.get_vals(9, &mut vals);
+            ff_reader.get_vals(8, &mut vals);
             assert_eq!(&vals, &[1_000]);
+
+            ff_reader.get_vals(9, &mut vals);
+            assert_eq!(&vals, &[20]);
         }
     }
 }

src/indexer/mod.rs

@@ -1,8 +1,9 @@
 pub mod delete_queue;
-mod directory_lock;
+
 mod doc_opstamp_mapping;
 pub mod index_writer;
 mod log_merge_policy;
+mod merge_operation;
 pub mod merge_policy;
 pub mod merger;
 pub mod operation;
@@ -15,14 +16,12 @@ pub mod segment_updater;
 mod segment_writer;
 mod stamper;
 
-pub(crate) use self::directory_lock::DirectoryLock;
-pub use self::directory_lock::LockType;
-
 pub use self::index_writer::IndexWriter;
 pub use self::log_merge_policy::LogMergePolicy;
+pub use self::merge_operation::{MergeOperation, MergeOperationInventory};
 pub use self::merge_policy::{MergeCandidate, MergePolicy, NoMergePolicy};
 pub use self::prepared_commit::PreparedCommit;
-pub use self::segment_entry::{SegmentEntry, SegmentState};
+pub use self::segment_entry::SegmentEntry;
 pub use self::segment_manager::SegmentManager;
 pub use self::segment_serializer::SegmentSerializer;
 pub use self::segment_writer::SegmentWriter;

src/indexer/segment_entry.rs

@@ -4,21 +4,6 @@ use core::SegmentMeta;
 use indexer::delete_queue::DeleteCursor;
 use std::fmt;
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub enum SegmentState {
-    Ready,
-    InMerge,
-}
-
-impl SegmentState {
-    pub fn letter_code(self) -> char {
-        match self {
-            SegmentState::InMerge => 'M',
-            SegmentState::Ready => 'R',
-        }
-    }
-}
-
 /// A segment entry describes the state of
 /// a given segment, at a given instant.
 ///
@@ -35,7 +20,6 @@ impl SegmentState {
 #[derive(Clone)]
 pub struct SegmentEntry {
     meta: SegmentMeta,
-    state: SegmentState,
     delete_bitset: Option<BitSet>,
     delete_cursor: DeleteCursor,
 }
@@ -49,7 +33,6 @@ impl SegmentEntry {
     ) -> SegmentEntry {
         SegmentEntry {
             meta: segment_meta,
-            state: SegmentState::Ready,
             delete_bitset,
             delete_cursor,
         }
@@ -72,14 +55,6 @@ impl SegmentEntry {
         &mut self.delete_cursor
     }
 
-    /// Return the `SegmentEntry`.
-    ///
-    /// The state describes whether the segment is available for
-    /// a merge or not.
-    pub fn state(&self) -> SegmentState {
-        self.state
-    }
-
     /// Returns the segment id.
     pub fn segment_id(&self) -> SegmentId {
         self.meta.id()
@@ -89,33 +64,10 @@ impl SegmentEntry {
     pub fn meta(&self) -> &SegmentMeta {
         &self.meta
     }
-
-    /// Mark the `SegmentEntry` as in merge.
-    ///
-    /// Only segments that are not already
-    /// in a merge are elligible for future merge.
-    pub fn start_merge(&mut self) {
-        self.state = SegmentState::InMerge;
-    }
-
-    /// Cancel a merge
-    ///
-    /// If a merge fails, it is important to switch
-    /// the segment back to a idle state, so that it
-    /// may be elligible for future merges.
-    pub fn cancel_merge(&mut self) {
-        self.state = SegmentState::Ready;
-    }
-
-    /// Returns true iff a segment should
-    /// be considered for a merge.
-    pub fn is_ready(&self) -> bool {
-        self.state == SegmentState::Ready
-    }
 }
 
 impl fmt::Debug for SegmentEntry {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        write!(formatter, "SegmentEntry({:?}, {:?})", self.meta, self.state)
+        write!(formatter, "SegmentEntry({:?})", self.meta)
     }
 }

src/indexer/segment_manager.rs

@@ -16,7 +16,6 @@ use Result as TantivyResult;
 struct SegmentRegisters {
     uncommitted: SegmentRegister,
     committed: SegmentRegister,
-    writing: HashSet<SegmentId>,
 }
 
 /// The segment manager stores the list of segments
@@ -41,12 +40,17 @@ impl Debug for SegmentManager {
 }
 
 pub fn get_mergeable_segments(
+    in_merge_segment_ids: &HashSet<SegmentId>,
     segment_manager: &SegmentManager,
 ) -> (Vec<SegmentMeta>, Vec<SegmentMeta>) {
     let registers_lock = segment_manager.read();
     (
-        registers_lock.committed.get_mergeable_segments(),
-        registers_lock.uncommitted.get_mergeable_segments(),
+        registers_lock
+            .committed
+            .get_mergeable_segments(in_merge_segment_ids),
+        registers_lock
+            .uncommitted
+            .get_mergeable_segments(in_merge_segment_ids),
     )
 }
 
@@ -59,7 +63,6 @@ impl SegmentManager {
             registers: RwLock::new(SegmentRegisters {
                 uncommitted: SegmentRegister::default(),
                 committed: SegmentRegister::new(segment_metas, delete_cursor),
-                writing: HashSet::new(),
             }),
         }
     }
@@ -72,12 +75,6 @@ impl SegmentManager {
         segment_entries
     }
 
-    /// Returns the overall number of segments in the `SegmentManager`
-    pub fn num_segments(&self) -> usize {
-        let registers_lock = self.read();
-        registers_lock.committed.len() + registers_lock.uncommitted.len()
-    }
-
     /// List the files that are useful to the index.
     ///
     /// This does not include lock files, or files that are obsolete
@@ -106,6 +103,21 @@ impl SegmentManager {
             .expect("Failed to acquire write lock on SegmentManager.")
     }
 
+    /// Deletes all empty segments
+    fn remove_empty_segments(&self) {
+        let mut registers_lock = self.write();
+        registers_lock
+            .committed
+            .segment_entries()
+            .iter()
+            .filter(|segment| segment.meta().num_docs() == 0)
+            .for_each(|segment| {
+                registers_lock
+                    .committed
+                    .remove_segment(&segment.segment_id())
+            });
+    }
+
     pub fn commit(&self, segment_entries: Vec<SegmentEntry>) {
         let mut registers_lock = self.write();
         registers_lock.committed.clear();
@@ -121,25 +133,22 @@ impl SegmentManager {
     /// the `segment_ids` are not either all committed or all
     /// uncommitted.
     pub fn start_merge(&self, segment_ids: &[SegmentId]) -> TantivyResult<Vec<SegmentEntry>> {
-        let mut registers_lock = self.write();
+        let registers_lock = self.read();
         let mut segment_entries = vec![];
         if registers_lock.uncommitted.contains_all(segment_ids) {
             for segment_id in segment_ids {
                 let segment_entry = registers_lock.uncommitted
-                    .start_merge(segment_id)
+                    .get(segment_id)
                     .expect("Segment id not found {}. Should never happen because of the contains all if-block.");
                 segment_entries.push(segment_entry);
             }
         } else if registers_lock.committed.contains_all(segment_ids) {
             for segment_id in segment_ids {
                 let segment_entry = registers_lock.committed
-                    .start_merge(segment_id)
+                    .get(segment_id)
                     .expect("Segment id not found {}. Should never happen because of the contains all if-block.");
                 segment_entries.push(segment_entry);
             }
-            for segment_id in segment_ids {
-                registers_lock.committed.start_merge(segment_id);
-            }
         } else {
             let error_msg = "Merge operation sent for segments that are not \
                              all uncommited or commited."
@@ -149,50 +158,8 @@ impl SegmentManager {
         Ok(segment_entries)
     }
 
-    pub fn cancel_merge(
-        &self,
-        before_merge_segment_ids: &[SegmentId],
-        after_merge_segment_id: SegmentId,
-    ) {
-        let mut registers_lock = self.write();
-
-        // we mark all segments are ready for merge.
-        {
-            let target_segment_register: &mut SegmentRegister;
-            target_segment_register = {
-                if registers_lock
-                    .uncommitted
-                    .contains_all(before_merge_segment_ids)
-                {
-                    &mut registers_lock.uncommitted
-                } else if registers_lock
-                    .committed
-                    .contains_all(before_merge_segment_ids)
-                {
-                    &mut registers_lock.committed
-                } else {
-                    warn!("couldn't find segment in SegmentManager");
-                    return;
-                }
-            };
-            for segment_id in before_merge_segment_ids {
-                target_segment_register.cancel_merge(segment_id);
-            }
-        }
-
-        // ... and we make sure the target segment entry
-        // can be garbage collected.
-        registers_lock.writing.remove(&after_merge_segment_id);
-    }
-
-    pub fn write_segment(&self, segment_id: SegmentId) {
-        let mut registers_lock = self.write();
-        registers_lock.writing.insert(segment_id);
-    }
-
     pub fn add_segment(&self, segment_entry: SegmentEntry) {
         let mut registers_lock = self.write();
-        registers_lock.writing.remove(&segment_entry.segment_id());
         registers_lock.uncommitted.add_segment_entry(segment_entry);
     }
 
@@ -202,10 +169,6 @@ impl SegmentManager {
         after_merge_segment_entry: SegmentEntry,
     ) {
         let mut registers_lock = self.write();
-        registers_lock
-            .writing
-            .remove(&after_merge_segment_entry.segment_id());
-
         let target_register: &mut SegmentRegister = {
             if registers_lock
                 .uncommitted
@@ -229,6 +192,7 @@ impl SegmentManager {
     }
 
     pub fn committed_segment_metas(&self) -> Vec<SegmentMeta> {
+        self.remove_empty_segments();
         let registers_lock = self.read();
         registers_lock.committed.segment_metas()
     }

src/indexer/segment_register.rs

@@ -3,6 +3,7 @@ use core::SegmentMeta;
 use indexer::delete_queue::DeleteCursor;
 use indexer::segment_entry::SegmentEntry;
 use std::collections::HashMap;
+use std::collections::HashSet;
 use std::fmt::{self, Debug, Formatter};
 
 /// The segment register keeps track
@@ -21,8 +22,8 @@ pub struct SegmentRegister {
 impl Debug for SegmentRegister {
     fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
         write!(f, "SegmentRegister(")?;
-        for (k, v) in &self.segment_states {
-            write!(f, "{}:{}, ", k.short_uuid_string(), v.state().letter_code())?;
+        for k in self.segment_states.keys() {
+            write!(f, "{}, ", k.short_uuid_string())?;
         }
         write!(f, ")")?;
         Ok(())
@@ -34,14 +35,13 @@ impl SegmentRegister {
         self.segment_states.clear();
     }
 
-    pub fn len(&self) -> usize {
-        self.segment_states.len()
-    }
-
-    pub fn get_mergeable_segments(&self) -> Vec<SegmentMeta> {
+    pub fn get_mergeable_segments(
+        &self,
+        in_merge_segment_ids: &HashSet<SegmentId>,
+    ) -> Vec<SegmentMeta> {
         self.segment_states
             .values()
-            .filter(|segment_entry| segment_entry.is_ready())
+            .filter(|segment_entry| !in_merge_segment_ids.contains(&segment_entry.segment_id()))
             .map(|segment_entry| segment_entry.meta().clone())
             .collect()
     }
@@ -60,7 +60,7 @@ impl SegmentRegister {
         segment_ids
     }
 
-    pub fn contains_all(&mut self, segment_ids: &[SegmentId]) -> bool {
+    pub fn contains_all(&self, segment_ids: &[SegmentId]) -> bool {
         segment_ids
             .iter()
             .all(|segment_id| self.segment_states.contains_key(segment_id))
@@ -75,20 +75,8 @@ impl SegmentRegister {
         self.segment_states.remove(segment_id);
     }
 
-    pub fn cancel_merge(&mut self, segment_id: &SegmentId) {
-        self.segment_states
-            .get_mut(segment_id)
-            .expect("Received a merge notification for a segment that is not registered")
-            .cancel_merge();
-    }
-
-    pub fn start_merge(&mut self, segment_id: &SegmentId) -> Option<SegmentEntry> {
-        if let Some(segment_entry) = self.segment_states.get_mut(segment_id) {
-            segment_entry.start_merge();
-            Some(segment_entry.clone())
-        } else {
-            None
-        }
+    pub fn get(&self, segment_id: &SegmentId) -> Option<SegmentEntry> {
+        self.segment_states.get(segment_id).cloned()
     }
 
     pub fn new(segment_metas: Vec<SegmentMeta>, delete_cursor: &DeleteCursor) -> SegmentRegister {
@@ -100,11 +88,6 @@ impl SegmentRegister {
         }
         SegmentRegister { segment_states }
     }
-
-    #[cfg(test)]
-    pub fn segment_entry(&self, segment_id: &SegmentId) -> Option<SegmentEntry> {
-        self.segment_states.get(segment_id).cloned()
-    }
 }
 
 #[cfg(test)]
@@ -113,7 +96,6 @@ mod tests {
     use core::SegmentId;
     use core::SegmentMeta;
     use indexer::delete_queue::*;
-    use indexer::SegmentState;
 
     fn segment_ids(segment_register: &SegmentRegister) -> Vec<SegmentId> {
         segment_register
@@ -137,42 +119,12 @@ mod tests {
             let segment_entry = SegmentEntry::new(segment_meta, delete_queue.cursor(), None);
             segment_register.add_segment_entry(segment_entry);
         }
-        assert_eq!(
-            segment_register
-                .segment_entry(&segment_id_a)
-                .unwrap()
-                .state(),
-            SegmentState::Ready
-        );
         assert_eq!(segment_ids(&segment_register), vec![segment_id_a]);
         {
             let segment_meta = SegmentMeta::new(segment_id_b, 0u32);
             let segment_entry = SegmentEntry::new(segment_meta, delete_queue.cursor(), None);
             segment_register.add_segment_entry(segment_entry);
         }
-        assert_eq!(
-            segment_register
-                .segment_entry(&segment_id_b)
-                .unwrap()
-                .state(),
-            SegmentState::Ready
-        );
-        segment_register.start_merge(&segment_id_a);
-        segment_register.start_merge(&segment_id_b);
-        assert_eq!(
-            segment_register
-                .segment_entry(&segment_id_a)
-                .unwrap()
-                .state(),
-            SegmentState::InMerge
-        );
-        assert_eq!(
-            segment_register
-                .segment_entry(&segment_id_b)
-                .unwrap()
-                .state(),
-            SegmentState::InMerge
-        );
         segment_register.remove_segment(&segment_id_a);
         segment_register.remove_segment(&segment_id_b);
         {

src/indexer/segment_updater.rs

@@ -16,9 +16,10 @@ use futures_cpupool::CpuFuture;
 use futures_cpupool::CpuPool;
 use indexer::delete_queue::DeleteCursor;
 use indexer::index_writer::advance_deletes;
+use indexer::merge_operation::MergeOperationInventory;
 use indexer::merger::IndexMerger;
 use indexer::stamper::Stamper;
-use indexer::MergeCandidate;
+use indexer::MergeOperation;
 use indexer::SegmentEntry;
 use indexer::SegmentSerializer;
 use indexer::{DefaultMergePolicy, MergePolicy};
@@ -26,6 +27,7 @@ use schema::Schema;
 use serde_json;
 use std::borrow::BorrowMut;
 use std::collections::HashMap;
+use std::collections::HashSet;
 use std::io::Write;
 use std::mem;
 use std::ops::DerefMut;
@@ -45,8 +47,16 @@ use Result;
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-pub fn save_new_metas(schema: Schema, opstamp: u64, directory: &mut Directory) -> Result<()> {
-    save_metas(vec![], schema, opstamp, None, directory)
+pub fn save_new_metas(schema: Schema, directory: &mut Directory) -> Result<()> {
+    save_metas(
+        &IndexMeta {
+            segments: Vec::new(),
+            schema,
+            opstamp: 0u64,
+            payload: None,
+        },
+        directory,
+    )
 }
 
 /// Save the index meta file.
@@ -58,20 +68,9 @@ pub fn save_new_metas(schema: Schema, opstamp: u64, directory: &mut Directory) -
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-pub fn save_metas(
-    segment_metas: Vec<SegmentMeta>,
-    schema: Schema,
-    opstamp: u64,
-    payload: Option<String>,
-    directory: &mut Directory,
-) -> Result<()> {
-    let metas = IndexMeta {
-        segments: segment_metas,
-        schema,
-        opstamp,
-        payload,
-    };
-    let mut buffer = serde_json::to_vec_pretty(&metas)?;
+fn save_metas(metas: &IndexMeta, directory: &mut Directory) -> Result<()> {
+    let mut buffer = serde_json::to_vec_pretty(metas)?;
+    // Just adding a new line at the end of the buffer.
     writeln!(&mut buffer)?;
     directory.atomic_write(&META_FILEPATH, &buffer[..])?;
     debug!("Saved metas {:?}", serde_json::to_string_pretty(&metas));
@@ -83,16 +82,21 @@ pub fn save_metas(
 //
 // All this processing happens on a single thread
 // consuming a common queue.
+//
+// We voluntarily pass a merge_operation ref to guarantee that
+// the merge_operation is alive during the process
 #[derive(Clone)]
 pub struct SegmentUpdater(Arc<InnerSegmentUpdater>);
 
 fn perform_merge(
+    merge_operation: &MergeOperation,
     index: &Index,
     mut segment_entries: Vec<SegmentEntry>,
-    mut merged_segment: Segment,
-    target_opstamp: u64,
 ) -> Result<SegmentEntry> {
+    let target_opstamp = merge_operation.target_opstamp();
+
     // first we need to apply deletes to our segment.
+    let mut merged_segment = index.new_segment();
 
     // TODO add logging
     let schema = index.schema();
@@ -126,19 +130,27 @@ fn perform_merge(
 }
 
 struct InnerSegmentUpdater {
+    // we keep a copy of the current active IndexMeta to
+    // avoid loading the file everytime we need it in the
+    // `SegmentUpdater`.
+    //
+    // This should be up to date as all update happen through
+    // the unique active `SegmentUpdater`.
+    active_metas: RwLock<Arc<IndexMeta>>,
     pool: CpuPool,
     index: Index,
     segment_manager: SegmentManager,
-    merge_policy: RwLock<Box<MergePolicy>>,
+    merge_policy: RwLock<Arc<Box<MergePolicy>>>,
     merging_thread_id: AtomicUsize,
     merging_threads: RwLock<HashMap<usize, JoinHandle<Result<()>>>>,
     generation: AtomicUsize,
     killed: AtomicBool,
     stamper: Stamper,
+    merge_operations: MergeOperationInventory,
 }
 
 impl SegmentUpdater {
-    pub fn new(
+    pub fn create(
         index: Index,
         stamper: Stamper,
         delete_cursor: &DeleteCursor,
@@ -149,32 +161,29 @@ impl SegmentUpdater {
             .name_prefix("segment_updater")
             .pool_size(1)
             .create();
+        let index_meta = index.load_metas()?;
         Ok(SegmentUpdater(Arc::new(InnerSegmentUpdater {
+            active_metas: RwLock::new(Arc::new(index_meta)),
             pool,
             index,
             segment_manager,
-            merge_policy: RwLock::new(Box::new(DefaultMergePolicy::default())),
+            merge_policy: RwLock::new(Arc::new(Box::new(DefaultMergePolicy::default()))),
             merging_thread_id: AtomicUsize::default(),
             merging_threads: RwLock::new(HashMap::new()),
             generation: AtomicUsize::default(),
             killed: AtomicBool::new(false),
             stamper,
+            merge_operations: Default::default(),
         })))
     }
 
-    pub fn new_segment(&self) -> Segment {
-        let new_segment = self.0.index.new_segment();
-        let segment_id = new_segment.id();
-        self.0.segment_manager.write_segment(segment_id);
-        new_segment
-    }
-
-    pub fn get_merge_policy(&self) -> Box<MergePolicy> {
-        self.0.merge_policy.read().unwrap().box_clone()
+    pub fn get_merge_policy(&self) -> Arc<Box<MergePolicy>> {
+        self.0.merge_policy.read().unwrap().clone()
     }
 
     pub fn set_merge_policy(&self, merge_policy: Box<MergePolicy>) {
-        *self.0.merge_policy.write().unwrap() = merge_policy;
+        let arc_merge_policy = Arc::new(merge_policy);
+        *self.0.merge_policy.write().unwrap() = arc_merge_policy;
     }
 
     fn get_merging_thread_id(&self) -> usize {
@@ -195,7 +204,8 @@ impl SegmentUpdater {
                 segment_updater.0.segment_manager.add_segment(segment_entry);
                 segment_updater.consider_merge_options();
                 true
-            }).forget();
+            })
+            .forget();
             true
         } else {
             false
@@ -227,20 +237,39 @@ impl SegmentUpdater {
         if self.is_alive() {
             let index = &self.0.index;
             let directory = index.directory();
-            save_metas(
-                self.0.segment_manager.committed_segment_metas(),
-                index.schema(),
+            let mut commited_segment_metas = self.0.segment_manager.committed_segment_metas();
+
+            // We sort segment_readers by number of documents.
+            // This is an heuristic to make multithreading more efficient.
+            //
+            // This is not done at the searcher level because I had a strange
+            // use case in which I was dealing with a large static index,
+            // dispatched over 5 SSD drives.
+            //
+            // A `UnionDirectory` makes it possible to read from these
+            // 5 different drives and creates a meta.json on the fly.
+            // In order to optimize the throughput, it creates a lasagna of segments
+            // from the different drives.
+            //
+            // Segment 1 from disk 1, Segment 1 from disk 2, etc.
+            commited_segment_metas.sort_by_key(|segment_meta| -(segment_meta.max_doc() as i32));
+            let index_meta = IndexMeta {
+                segments: commited_segment_metas,
+                schema: index.schema(),
                 opstamp,
-                commit_message,
-                directory.box_clone().borrow_mut(),
-            ).expect("Could not save metas.");
+                payload: commit_message,
+            };
+            save_metas(&index_meta, directory.box_clone().borrow_mut())
+                .expect("Could not save metas.");
+            self.store_meta(&index_meta);
         }
     }
 
     pub fn garbage_collect_files(&self) -> Result<()> {
         self.run_async(move |segment_updater| {
             segment_updater.garbage_collect_files_exec();
-        }).wait()
+        })
+        .wait()
     }
 
     fn garbage_collect_files_exec(&self) {
@@ -262,54 +291,67 @@ impl SegmentUpdater {
                 segment_updater.garbage_collect_files_exec();
                 segment_updater.consider_merge_options();
             }
-        }).wait()
+        })
+        .wait()
     }
 
     pub fn start_merge(&self, segment_ids: &[SegmentId]) -> Result<Receiver<SegmentMeta>> {
-        //let future_merged_segment = */
-        let segment_ids_vec = segment_ids.to_vec();
-        self.run_async(move |segment_updater| {
-            segment_updater.start_merge_impl(&segment_ids_vec[..])
-        }).wait()?
+        let commit_opstamp = self.load_metas().opstamp;
+        let merge_operation = MergeOperation::new(
+            &self.0.merge_operations,
+            commit_opstamp,
+            segment_ids.to_vec(),
+        );
+        self.run_async(move |segment_updater| segment_updater.start_merge_impl(merge_operation))
+            .wait()?
+    }
+
+    fn store_meta(&self, index_meta: &IndexMeta) {
+        *self.0.active_metas.write().unwrap() = Arc::new(index_meta.clone());
+    }
+    fn load_metas(&self) -> Arc<IndexMeta> {
+        self.0.active_metas.read().unwrap().clone()
     }
 
     // `segment_ids` is required to be non-empty.
-    fn start_merge_impl(&self, segment_ids: &[SegmentId]) -> Result<Receiver<SegmentMeta>> {
-        assert!(!segment_ids.is_empty(), "Segment_ids cannot be empty.");
+    fn start_merge_impl(&self, merge_operation: MergeOperation) -> Result<Receiver<SegmentMeta>> {
+        assert!(
+            !merge_operation.segment_ids().is_empty(),
+            "Segment_ids cannot be empty."
+        );
 
         let segment_updater_clone = self.clone();
-        let segment_entries: Vec<SegmentEntry> = self.0.segment_manager.start_merge(segment_ids)?;
+        let segment_entries: Vec<SegmentEntry> = self
+            .0
+            .segment_manager
+            .start_merge(merge_operation.segment_ids())?;
 
-        let segment_ids_vec = segment_ids.to_vec();
+        //        let segment_ids_vec = merge_operation.segment_ids.to_vec();
 
         let merging_thread_id = self.get_merging_thread_id();
         info!(
             "Starting merge thread #{} - {:?}",
-            merging_thread_id, segment_ids
+            merging_thread_id,
+            merge_operation.segment_ids()
         );
         let (merging_future_send, merging_future_recv) = oneshot();
 
-        let target_opstamp = self.0.stamper.stamp();
-
         // first we need to apply deletes to our segment.
         let merging_join_handle = thread::Builder::new()
             .name(format!("mergingthread-{}", merging_thread_id))
             .spawn(move || {
                 // first we need to apply deletes to our segment.
-                let merged_segment = segment_updater_clone.new_segment();
-                let merged_segment_id = merged_segment.id();
                 let merge_result = perform_merge(
+                    &merge_operation,
                     &segment_updater_clone.0.index,
                     segment_entries,
-                    merged_segment,
-                    target_opstamp,
                 );
 
                 match merge_result {
                     Ok(after_merge_segment_entry) => {
                         let merged_segment_meta = after_merge_segment_entry.meta().clone();
                         segment_updater_clone
-                            .end_merge(segment_ids_vec, after_merge_segment_entry)
+                            .end_merge(merge_operation, after_merge_segment_entry)
                             .expect("Segment updater thread is corrupted.");
 
                         // the future may fail if the listener of the oneshot future
@@ -320,13 +362,18 @@ impl SegmentUpdater {
                         let _merging_future_res = merging_future_send.send(merged_segment_meta);
                     }
                     Err(e) => {
-                        warn!("Merge of {:?} was cancelled: {:?}", segment_ids_vec, e);
+                        warn!(
+                            "Merge of {:?} was cancelled: {:?}",
+                            merge_operation.segment_ids(),
+                            e
+                        );
                         // ... cancel merge
                         if cfg!(test) {
                             panic!("Merge failed.");
                         }
-                        segment_updater_clone.cancel_merge(&segment_ids_vec, merged_segment_id);
-                        // merging_future_send will be dropped, sending an error to the future.
+                        // As `merge_operation` will be dropped, the segment in merge state will
+                        // be available for merge again.
+                        // `merging_future_send` will be dropped, sending an error to the future.
                     }
                 }
                 segment_updater_clone
@@ -336,7 +383,8 @@ impl SegmentUpdater {
                     .unwrap()
                     .remove(&merging_thread_id);
                 Ok(())
-            }).expect("Failed to spawn a thread.");
+            })
+            .expect("Failed to spawn a thread.");
         self.0
             .merging_threads
             .write()
@@ -346,16 +394,34 @@ impl SegmentUpdater {
     }
 
     fn consider_merge_options(&self) {
+        let merge_segment_ids: HashSet<SegmentId> = self.0.merge_operations.segment_in_merge();
         let (committed_segments, uncommitted_segments) =
-            get_mergeable_segments(&self.0.segment_manager);
+            get_mergeable_segments(&merge_segment_ids, &self.0.segment_manager);
+
         // Committed segments cannot be merged with uncommitted_segments.
         // We therefore consider merges using these two sets of segments independently.
         let merge_policy = self.get_merge_policy();
-        let mut merge_candidates = merge_policy.compute_merge_candidates(&uncommitted_segments);
-        let committed_merge_candidates = merge_policy.compute_merge_candidates(&committed_segments);
-        merge_candidates.extend_from_slice(&committed_merge_candidates[..]);
-        for MergeCandidate(segment_metas) in merge_candidates {
-            match self.start_merge_impl(&segment_metas) {
+
+        let current_opstamp = self.0.stamper.stamp();
+        let mut merge_candidates: Vec<MergeOperation> = merge_policy
+            .compute_merge_candidates(&uncommitted_segments)
+            .into_iter()
+            .map(|merge_candidate| {
+                MergeOperation::new(&self.0.merge_operations, current_opstamp, merge_candidate.0)
+            })
+            .collect();
+
+        let commit_opstamp = self.load_metas().opstamp;
+        let committed_merge_candidates = merge_policy
+            .compute_merge_candidates(&committed_segments)
+            .into_iter()
+            .map(|merge_candidate| {
+                MergeOperation::new(&self.0.merge_operations, commit_opstamp, merge_candidate.0)
+            })
+            .collect::<Vec<_>>();
+        merge_candidates.extend(committed_merge_candidates.into_iter());
+        for merge_operation in merge_candidates {
+            match self.start_merge_impl(merge_operation) {
                 Ok(merge_future) => {
                     if let Err(e) = merge_future.fuse().poll() {
                         error!("The merge task failed quickly after starting: {:?}", e);
@@ -371,31 +437,16 @@ impl SegmentUpdater {
         }
     }
 
-    fn cancel_merge(
-        &self,
-        before_merge_segment_ids: &[SegmentId],
-        after_merge_segment_entry: SegmentId,
-    ) {
-        self.0
-            .segment_manager
-            .cancel_merge(before_merge_segment_ids, after_merge_segment_entry);
-    }
-
     fn end_merge(
         &self,
-        before_merge_segment_ids: Vec<SegmentId>,
+        merge_operation: MergeOperation,
         mut after_merge_segment_entry: SegmentEntry,
     ) -> Result<()> {
         self.run_async(move |segment_updater| {
             info!("End merge {:?}", after_merge_segment_entry.meta());
             let mut delete_cursor = after_merge_segment_entry.delete_cursor().clone();
             if let Some(delete_operation) = delete_cursor.get() {
-                let committed_opstamp = segment_updater
-                    .0
-                    .index
-                    .load_metas()
-                    .expect("Failed to read opstamp")
-                    .opstamp;
+                let committed_opstamp = segment_updater.load_metas().opstamp;
                 if delete_operation.opstamp < committed_opstamp {
                     let index = &segment_updater.0.index;
                     let segment = index.segment(after_merge_segment_entry.meta().clone());
@@ -404,16 +455,15 @@ impl SegmentUpdater {
                     {
                         error!(
                             "Merge of {:?} was cancelled (advancing deletes failed): {:?}",
-                            before_merge_segment_ids, e
+                            merge_operation.segment_ids(),
+                            e
                         );
-                        // ... cancel merge
                         if cfg!(test) {
                             panic!("Merge failed.");
                         }
-                        segment_updater.cancel_merge(
-                            &before_merge_segment_ids,
-                            after_merge_segment_entry.segment_id(),
-                        );
+                        // ... cancel merge
+                        // `merge_operations` are tracked. As it is dropped, the
+                        // the segment_ids will be available again for merge.
                         return;
                     }
                 }
@@ -421,13 +471,14 @@ impl SegmentUpdater {
             segment_updater
                 .0
                 .segment_manager
-                .end_merge(&before_merge_segment_ids, after_merge_segment_entry);
+                .end_merge(merge_operation.segment_ids(), after_merge_segment_entry);
             segment_updater.consider_merge_options();
             info!("save metas");
-            let previous_metas = segment_updater.0.index.load_metas().unwrap();
-            segment_updater.save_metas(previous_metas.opstamp, previous_metas.payload);
+            let previous_metas = segment_updater.load_metas();
+            segment_updater.save_metas(previous_metas.opstamp, previous_metas.payload.clone());
             segment_updater.garbage_collect_files_exec();
-        }).wait()
+        })
+        .wait()
     }
 
     /// Wait for current merging threads.
@@ -446,32 +497,25 @@ impl SegmentUpdater {
     /// Obsolete files will eventually be cleaned up
     /// by the directory garbage collector.
     pub fn wait_merging_thread(&self) -> Result<()> {
-        let mut num_segments: usize;
         loop {
-            num_segments = self.0.segment_manager.num_segments();
-
-            let mut new_merging_threads = HashMap::new();
-            {
+            let merging_threads: HashMap<usize, JoinHandle<Result<()>>> = {
                 let mut merging_threads = self.0.merging_threads.write().unwrap();
-                mem::swap(&mut new_merging_threads, merging_threads.deref_mut());
+                mem::replace(merging_threads.deref_mut(), HashMap::new())
+            };
+            if merging_threads.is_empty() {
+                return Ok(());
             }
-            debug!("wait merging thread {}", new_merging_threads.len());
-            for (_, merging_thread_handle) in new_merging_threads {
+            debug!("wait merging thread {}", merging_threads.len());
+            for (_, merging_thread_handle) in merging_threads {
                 merging_thread_handle
                     .join()
                     .map(|_| ())
                     .map_err(|_| TantivyError::ErrorInThread("Merging thread failed.".into()))?;
             }
-            // Our merging thread may have queued their completed
+            // Our merging thread may have queued their completed merged segment.
+            // Let's wait for that too.
             self.run_async(move |_| {}).wait()?;
-
-            let new_num_segments = self.0.segment_manager.num_segments();
-
-            if new_num_segments >= num_segments {
-                break;
-            }
         }
-        Ok(())
     }
 }
 
@@ -484,14 +528,14 @@ mod tests {
 
     #[test]
     fn test_delete_during_merge() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         index_writer.set_merge_policy(Box::new(MergeWheneverPossible));
 
         {
@@ -535,4 +579,75 @@ mod tests {
         assert_eq!(index.searcher().segment_readers().len(), 1);
         assert_eq!(index.searcher().num_docs(), 302);
     }
+
+    #[test]
+    fn delete_all_docs() {
+        let mut schema_builder = Schema::builder();
+        let text_field = schema_builder.add_text_field("text", TEXT);
+        let schema = schema_builder.build();
+
+        let index = Index::create_in_ram(schema);
+
+        // writing the segment
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+
+        {
+            for _ in 0..100 {
+                index_writer.add_document(doc!(text_field=>"a"));
+                index_writer.add_document(doc!(text_field=>"b"));
+            }
+            assert!(index_writer.commit().is_ok());
+        }
+
+        {
+            for _ in 0..100 {
+                index_writer.add_document(doc!(text_field=>"c"));
+                index_writer.add_document(doc!(text_field=>"d"));
+            }
+            assert!(index_writer.commit().is_ok());
+        }
+
+        {
+            index_writer.add_document(doc!(text_field=>"e"));
+            index_writer.add_document(doc!(text_field=>"f"));
+            assert!(index_writer.commit().is_ok());
+        }
+
+        {
+            let seg_ids = index
+                .searchable_segment_ids()
+                .expect("Searchable segments failed.");
+            // docs exist, should have at least 1 segment
+            assert!(seg_ids.len() > 0);
+        }
+
+        {
+            let term_vals = vec!["a", "b", "c", "d", "e", "f"];
+            for term_val in term_vals {
+                let term = Term::from_field_text(text_field, term_val);
+                index_writer.delete_term(term);
+                assert!(index_writer.commit().is_ok());
+            }
+        }
+
+        {
+            index_writer
+                .wait_merging_threads()
+                .expect("waiting for merging threads");
+        }
+
+        index.load_searchers().unwrap();
+        assert_eq!(index.searcher().num_docs(), 0);
+
+        let seg_ids = index
+            .searchable_segment_ids()
+            .expect("Searchable segments failed.");
+        assert!(seg_ids.is_empty());
+
+        index.load_searchers().unwrap();
+        assert_eq!(index.searcher().num_docs(), 0);
+        // empty segments should be erased
+        assert!(index.searchable_segment_metas().unwrap().is_empty());
+        assert!(index.searcher().segment_readers().is_empty());
+    }
 }

src/indexer/segment_writer.rs

@@ -62,7 +62,8 @@ impl SegmentWriter {
                             segment.index().tokenizers().get(tokenizer_name)
                         }),
                     _ => None,
-                }).collect();
+                })
+                .collect();
         Ok(SegmentWriter {
             max_doc: 0,
             multifield_postings,
@@ -110,18 +111,18 @@ impl SegmentWriter {
             }
             match *field_options.field_type() {
                 FieldType::HierarchicalFacet => {
-                    let facets: Vec<&[u8]> = field_values
+                    let facets: Vec<&str> = field_values
                         .iter()
                         .flat_map(|field_value| match *field_value.value() {
-                            Value::Facet(ref facet) => Some(facet.encoded_bytes()),
+                            Value::Facet(ref facet) => Some(facet.encoded_str()),
                             _ => {
                                 panic!("Expected hierarchical facet");
                             }
-                        }).collect();
+                        })
+                        .collect();
                     let mut term = Term::for_field(field); // we set the Term
-                    for facet_bytes in facets {
+                    for fake_str in facets {
                         let mut unordered_term_id_opt = None;
-                        let fake_str = unsafe { str::from_utf8_unchecked(facet_bytes) };
                         FacetTokenizer.token_stream(fake_str).process(&mut |token| {
                             term.set_text(&token.text);
                             let unordered_term_id =
@@ -145,7 +146,8 @@ impl SegmentWriter {
                             .flat_map(|field_value| match *field_value.value() {
                                 Value::Str(ref text) => Some(text.as_str()),
                                 _ => None,
-                            }).collect();
+                            })
+                            .collect();
                         if texts.is_empty() {
                             0
                         } else {

src/indexer/stamper.rs

@@ -1,50 +1,66 @@
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
+
 // AtomicU64 have not landed in stable.
 // For the moment let's just use AtomicUsize on
 // x86/64 bit platform, and a mutex on other platform.
-
-#[cfg(target = "x86_64")]
+#[cfg(target_arch = "x86_64")]
 mod archicture_impl {
 
     use std::sync::atomic::{AtomicUsize, Ordering};
-    use std::sync::Arc;
 
-    #[derive(Clone, Default)]
-    pub struct Stamper(Arc<AtomicU64>);
+    #[derive(Default)]
+    pub struct AtomicU64Ersatz(AtomicUsize);
 
-    impl Stamper {
-        pub fn new(first_opstamp: u64) -> Stamper {
-            Stamper(Arc::new(AtomicU64::new(first_opstamp)))
+    impl AtomicU64Ersatz {
+        pub fn new(first_opstamp: u64) -> AtomicU64Ersatz {
+            AtomicU64Ersatz(AtomicUsize::new(first_opstamp as usize))
         }
 
-        pub fn stamp(&self) -> u64 {
-            self.0.fetch_add(1u64, Ordering::SeqCst) as u64
+        pub fn fetch_add(&self, val: u64, order: Ordering) -> u64 {
+            self.0.fetch_add(val as usize, order) as u64
         }
     }
 }
 
-#[cfg(not(target = "x86_64"))]
+#[cfg(not(target_arch = "x86_64"))]
 mod archicture_impl {
 
-    use std::sync::{Arc, Mutex};
+    use std::sync::atomic::Ordering;
+    /// Under other architecture, we rely on a mutex.
+    use std::sync::RwLock;
 
-    #[derive(Clone, Default)]
-    pub struct Stamper(Arc<Mutex<u64>>);
+    #[derive(Default)]
+    pub struct AtomicU64Ersatz(RwLock<u64>);
 
-    impl Stamper {
-        pub fn new(first_opstamp: u64) -> Stamper {
-            Stamper(Arc::new(Mutex::new(first_opstamp)))
+    impl AtomicU64Ersatz {
+        pub fn new(first_opstamp: u64) -> AtomicU64Ersatz {
+            AtomicU64Ersatz(RwLock::new(first_opstamp))
         }
 
-        pub fn stamp(&self) -> u64 {
-            let mut guard = self.0.lock().expect("Failed to lock the stamper");
-            let previous_val = *guard;
-            *guard = previous_val + 1;
+        pub fn fetch_add(&self, incr: u64, _order: Ordering) -> u64 {
+            let mut lock = self.0.write().unwrap();
+            let previous_val = *lock;
+            *lock = previous_val + incr;
             previous_val
         }
     }
 }
 
-pub use self::archicture_impl::Stamper;
+use self::archicture_impl::AtomicU64Ersatz;
+
+#[derive(Clone, Default)]
+pub struct Stamper(Arc<AtomicU64Ersatz>);
+
+impl Stamper {
+    pub fn new(first_opstamp: u64) -> Stamper {
+        Stamper(Arc::new(AtomicU64Ersatz::new(first_opstamp)))
+    }
+
+    pub fn stamp(&self) -> u64 {
+        self.0.fetch_add(1u64, Ordering::SeqCst) as u64
+    }
+}
 
 #[cfg(test)]
 mod test {

src/lib.rs

@@ -1,6 +1,5 @@
 #![doc(html_logo_url = "http://fulmicoton.com/tantivy-logo/tantivy-logo.png")]
 #![cfg_attr(all(feature = "unstable", test), feature(test))]
-#![cfg_attr(feature = "cargo-clippy", feature(tool_lints))]
 #![cfg_attr(feature = "cargo-clippy", allow(clippy::module_inception))]
 #![doc(test(attr(allow(unused_variables), deny(warnings))))]
 #![warn(missing_docs)]
@@ -24,7 +23,8 @@
 //! # use tempdir::TempDir;
 //! # use tantivy::Index;
 //! # use tantivy::schema::*;
-//! # use tantivy::collector::TopCollector;
+//! # use tantivy::{Score, DocAddress};
+//! # use tantivy::collector::TopDocs;
 //! # use tantivy::query::QueryParser;
 //! #
 //! # fn main() {
@@ -46,7 +46,7 @@
 //! // in a compressed, row-oriented key-value store.
 //! // This store is useful to reconstruct the
 //! // documents that were selected during the search phase.
-//! let mut schema_builder = SchemaBuilder::default();
+//! let mut schema_builder = Schema::builder();
 //! let title = schema_builder.add_text_field("title", TEXT | STORED);
 //! let body = schema_builder.add_text_field("body", TEXT);
 //! let schema = schema_builder.build();
@@ -86,13 +86,13 @@
 //! // A ticket has been opened regarding this problem.
 //! let query = query_parser.parse_query("sea whale")?;
 //!
-//! let mut top_collector = TopCollector::with_limit(10);
-//! searcher.search(&*query, &mut top_collector)?;
+//! // Perform search.
+//! // `topdocs` contains the 10 most relevant doc ids, sorted by decreasing scores...
+//! let top_docs: Vec<(Score, DocAddress)> =
+//!     searcher.search(&query, &TopDocs::with_limit(10))?;
 //!
-//! // Our top collector now contains the 10
-//! // most relevant doc ids...
-//! let doc_addresses = top_collector.docs();
-//! for doc_address in doc_addresses {
+//! for (_score, doc_address) in top_docs {
+//!     // Retrieve the actual content of documents given its `doc_address`.
 //!     let retrieved_doc = searcher.doc(doc_address)?;
 //!     println!("{}", schema.to_json(&retrieved_doc));
 //! }
@@ -129,11 +129,8 @@ extern crate base64;
 extern crate bit_set;
 extern crate bitpacking;
 extern crate byteorder;
-
 extern crate combine;
-
 extern crate crossbeam;
-extern crate crossbeam_channel;
 extern crate fnv;
 extern crate fst;
 extern crate fst_regex;
@@ -146,14 +143,13 @@ extern crate num_cpus;
 extern crate owning_ref;
 extern crate regex;
 extern crate rust_stemmers;
+extern crate scoped_pool;
 extern crate serde;
 extern crate stable_deref_trait;
 extern crate tempdir;
 extern crate tempfile;
 extern crate uuid;
 
-
-
 #[cfg(test)]
 #[macro_use]
 extern crate matches;
@@ -172,7 +168,7 @@ extern crate maplit;
 extern crate test;
 
 #[macro_use]
-extern crate downcast;
+extern crate downcast_rs;
 
 #[macro_use]
 extern crate fail;
@@ -185,10 +181,7 @@ mod macros;
 
 pub use error::TantivyError;
 
-#[deprecated(
-    since = "0.7.0",
-    note = "please use `tantivy::TantivyError` instead"
-)]
+#[deprecated(since = "0.7.0", note = "please use `tantivy::TantivyError` instead")]
 pub use error::TantivyError as Error;
 
 extern crate census;
@@ -218,7 +211,7 @@ pub mod store;
 pub mod termdict;
 
 mod snippet;
-pub use self::snippet::SnippetGenerator;
+pub use self::snippet::{Snippet, SnippetGenerator};
 
 mod docset;
 pub use self::docset::{DocSet, SkipResult};
@@ -236,11 +229,7 @@ pub use common::{i64_to_u64, u64_to_i64};
 /// Expose the current version of tantivy, as well
 /// whether it was compiled with the simd compression.
 pub fn version() -> &'static str {
-    if cfg!(feature = "simdcompression") {
-        concat!(env!("CARGO_PKG_VERSION"), "-simd")
-    } else {
-        concat!(env!("CARGO_PKG_VERSION"), "-nosimd")
-    }
+    env!("CARGO_PKG_VERSION")
 }
 
 /// Defines tantivy's merging strategy
@@ -301,9 +290,11 @@ mod tests {
     use docset::DocSet;
     use query::BooleanQuery;
     use rand::distributions::Bernoulli;
-    use rand::distributions::Range;
-    use rand::{Rng, SeedableRng, XorShiftRng};
+    use rand::distributions::Uniform;
+    use rand::rngs::StdRng;
+    use rand::{Rng, SeedableRng};
     use schema::*;
+    use DocAddress;
     use Index;
     use IndexWriter;
     use Postings;
@@ -322,16 +313,15 @@ mod tests {
     }
 
     pub fn generate_nonunique_unsorted(max_value: u32, n_elems: usize) -> Vec<u32> {
-        let seed: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
-        XorShiftRng::from_seed(seed)
-            .sample_iter(&Range::new(0u32, max_value))
+        let seed: [u8; 32] = [1; 32];
+        StdRng::from_seed(seed)
+            .sample_iter(&Uniform::new(0u32, max_value))
             .take(n_elems)
             .collect::<Vec<u32>>()
     }
 
     pub fn sample_with_seed(n: u32, ratio: f64, seed_val: u8) -> Vec<u32> {
-        let seed: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, seed_val];
-        XorShiftRng::from_seed(seed)
+        StdRng::from_seed([seed_val; 32])
             .sample_iter(&Bernoulli::new(ratio))
             .take(n as usize)
             .enumerate()
@@ -346,13 +336,13 @@ mod tests {
     #[test]
     #[cfg(feature = "mmap")]
     fn test_indexing() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_from_tempdir(schema).unwrap();
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field=>"af b");
                 index_writer.add_document(doc);
@@ -371,10 +361,10 @@ mod tests {
 
     #[test]
     fn test_docfreq1() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         {
             index_writer.add_document(doc!(text_field=>"a b c"));
             index_writer.commit().unwrap();
@@ -411,12 +401,12 @@ mod tests {
 
     #[test]
     fn test_fieldnorm_no_docs_with_field() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let title_field = schema_builder.add_text_field("title", TEXT);
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field=>"a b c");
                 index_writer.add_document(doc);
@@ -440,11 +430,11 @@ mod tests {
 
     #[test]
     fn test_fieldnorm() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field=>"a b c");
                 index_writer.add_document(doc);
@@ -481,7 +471,7 @@ mod tests {
 
     #[test]
     fn test_delete_postings1() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let term_abcd = Term::from_field_text(text_field, "abcd");
         let term_a = Term::from_field_text(text_field, "a");
@@ -491,43 +481,22 @@ mod tests {
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
-            {
-                // 0
-                let doc = doc!(text_field=>"a b");
-                index_writer.add_document(doc);
-            }
-            {
-                // 1
-                let doc = doc!(text_field=>" a c");
-                index_writer.add_document(doc);
-            }
-            {
-                // 2
-                let doc = doc!(text_field=>" b c");
-                index_writer.add_document(doc);
-            }
-            {
-                // 3
-                let doc = doc!(text_field=>" b d");
-                index_writer.add_document(doc);
-            }
-            {
-                index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            }
-            {
-                index_writer.delete_term(Term::from_field_text(text_field, "a"));
-            }
-            {
-                // 4
-                let doc = doc!(text_field=>" b c");
-                index_writer.add_document(doc);
-            }
-            {
-                // 5
-                let doc = doc!(text_field=>" a");
-                index_writer.add_document(doc);
-            }
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            // 0
+            index_writer.add_document(doc!(text_field=>"a b"));
+            // 1
+            index_writer.add_document(doc!(text_field=>" a c"));
+            // 2
+            index_writer.add_document(doc!(text_field=>" b c"));
+            // 3
+            index_writer.add_document(doc!(text_field=>" b d"));
+
+            index_writer.delete_term(Term::from_field_text(text_field, "c"));
+            index_writer.delete_term(Term::from_field_text(text_field, "a"));
+            // 4
+            index_writer.add_document(doc!(text_field=>" b c"));
+            // 5
+            index_writer.add_document(doc!(text_field=>" a"));
             index_writer.commit().unwrap();
         }
         {
@@ -535,11 +504,9 @@ mod tests {
             let searcher = index.searcher();
             let reader = searcher.segment_reader(0);
             let inverted_index = reader.inverted_index(text_field);
-            assert!(
-                inverted_index
-                    .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
-                    .is_none()
-            );
+            assert!(inverted_index
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .is_none());
             {
                 let mut postings = inverted_index
                     .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
@@ -561,16 +528,11 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
-            {
-                // 0
-                let doc = doc!(text_field=>"a b");
-                index_writer.add_document(doc);
-            }
-            {
-                // 1
-                index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            }
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            // 0
+            index_writer.add_document(doc!(text_field=>"a b"));
+            // 1
+            index_writer.delete_term(Term::from_field_text(text_field, "c"));
             index_writer.rollback().unwrap();
         }
         {
@@ -579,11 +541,9 @@ mod tests {
             let reader = searcher.segment_reader(0);
             let inverted_index = reader.inverted_index(term_abcd.field());
 
-            assert!(
-                inverted_index
-                    .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
-                    .is_none()
-            );
+            assert!(inverted_index
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .is_none());
             {
                 let mut postings = inverted_index
                     .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
@@ -605,14 +565,9 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
-            {
-                let doc = doc!(text_field=>"a b");
-                index_writer.add_document(doc);
-            }
-            {
-                index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            }
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            index_writer.add_document(doc!(text_field=>"a b"));
+            index_writer.delete_term(Term::from_field_text(text_field, "c"));
             index_writer.rollback().unwrap();
             index_writer.delete_term(Term::from_field_text(text_field, "a"));
             index_writer.commit().unwrap();
@@ -622,11 +577,9 @@ mod tests {
             let searcher = index.searcher();
             let reader = searcher.segment_reader(0);
             let inverted_index = reader.inverted_index(term_abcd.field());
-            assert!(
-                inverted_index
-                    .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
-                    .is_none()
-            );
+            assert!(inverted_index
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .is_none());
             {
                 let mut postings = inverted_index
                     .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
@@ -656,12 +609,12 @@ mod tests {
 
     #[test]
     fn test_indexed_u64() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_u64_field("value", INT_INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         index_writer.add_document(doc!(field=>1u64));
         index_writer.commit().unwrap();
         index.load_searchers().unwrap();
@@ -679,12 +632,12 @@ mod tests {
 
     #[test]
     fn test_indexed_i64() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let value_field = schema_builder.add_i64_field("value", INT_INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         let negative_val = -1i64;
         index_writer.add_document(doc!(value_field => negative_val));
         index_writer.commit().unwrap();
@@ -703,12 +656,12 @@ mod tests {
 
     #[test]
     fn test_indexedfield_not_in_documents() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let absent_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(2, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
         index_writer.add_document(doc!(text_field=>"a"));
         assert!(index_writer.commit().is_ok());
         assert!(index.load_searchers().is_ok());
@@ -719,13 +672,13 @@ mod tests {
 
     #[test]
     fn test_delete_postings2() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(2, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
 
         let add_document = |index_writer: &mut IndexWriter, val: &'static str| {
             let doc = doc!(text_field=>val);
@@ -755,13 +708,13 @@ mod tests {
 
     #[test]
     fn test_termfreq() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field=>"af af af bc bc");
                 index_writer.add_document(doc);
@@ -774,11 +727,9 @@ mod tests {
             let reader = searcher.segment_reader(0);
             let inverted_index = reader.inverted_index(text_field);
             let term_abcd = Term::from_field_text(text_field, "abcd");
-            assert!(
-                inverted_index
-                    .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
-                    .is_none()
-            );
+            assert!(inverted_index
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .is_none());
             let term_af = Term::from_field_text(text_field, "af");
             let mut postings = inverted_index
                 .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)
@@ -792,26 +743,17 @@ mod tests {
 
     #[test]
     fn test_searcher_1() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
-            {
-                let doc = doc!(text_field=>"af af af b");
-                index_writer.add_document(doc);
-            }
-            {
-                let doc = doc!(text_field=>"a b c");
-                index_writer.add_document(doc);
-            }
-            {
-                let doc = doc!(text_field=>"a b c d");
-                index_writer.add_document(doc);
-            }
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            index_writer.add_document(doc!(text_field=>"af af af b"));
+            index_writer.add_document(doc!(text_field=>"a b c"));
+            index_writer.add_document(doc!(text_field=>"a b c d"));
             index_writer.commit().unwrap();
         }
         {
@@ -819,62 +761,49 @@ mod tests {
             let searcher = index.searcher();
             let get_doc_ids = |terms: Vec<Term>| {
                 let query = BooleanQuery::new_multiterms_query(terms);
-                let mut collector = TestCollector::default();
-                assert!(searcher.search(&query, &mut collector).is_ok());
-                collector.docs()
+                let topdocs = searcher.search(&query, &TestCollector).unwrap();
+                topdocs.docs().to_vec()
             };
-            {
-                assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
-                    vec![1, 2]
-                );
-            }
-            {
-                assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
-                    vec![0]
-                );
-            }
-            {
-                assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
-                    vec![0, 1, 2]
-                );
-            }
-            {
-                assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "c")]),
-                    vec![1, 2]
-                );
-            }
-            {
-                assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "d")]),
-                    vec![2]
-                );
-            }
-            {
-                assert_eq!(
-                    get_doc_ids(vec![
-                        Term::from_field_text(text_field, "b"),
-                        Term::from_field_text(text_field, "a"),
-                    ]),
-                    vec![0, 1, 2]
-                );
-            }
+            assert_eq!(
+                get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
+                vec![DocAddress(0, 1), DocAddress(0, 2)]
+            );
+            assert_eq!(
+                get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
+                vec![DocAddress(0, 0)]
+            );
+            assert_eq!(
+                get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
+                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+            );
+            assert_eq!(
+                get_doc_ids(vec![Term::from_field_text(text_field, "c")]),
+                vec![DocAddress(0, 1), DocAddress(0, 2)]
+            );
+            assert_eq!(
+                get_doc_ids(vec![Term::from_field_text(text_field, "d")]),
+                vec![DocAddress(0, 2)]
+            );
+            assert_eq!(
+                get_doc_ids(vec![
+                    Term::from_field_text(text_field, "b"),
+                    Term::from_field_text(text_field, "a"),
+                ]),
+                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+            );
         }
     }
 
     #[test]
     fn test_searcher_2() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field=>"af b");
                 index_writer.add_document(doc);
@@ -894,7 +823,7 @@ mod tests {
 
     #[test]
     fn test_doc_macro() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let other_text_field = schema_builder.add_text_field("text2", TEXT);
         let document = doc!(text_field => "tantivy",
@@ -912,7 +841,7 @@ mod tests {
 
     #[test]
     fn test_wrong_fast_field_type() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let fast_field_unsigned = schema_builder.add_u64_field("unsigned", FAST);
         let fast_field_signed = schema_builder.add_i64_field("signed", FAST);
         let text_field = schema_builder.add_text_field("text", TEXT);

src/macros.rs

@@ -26,12 +26,12 @@
 /// #[macro_use]
 /// extern crate tantivy;
 ///
-/// use tantivy::schema::{SchemaBuilder, TEXT, FAST};
+/// use tantivy::schema::{Schema, TEXT, FAST};
 ///
 /// //...
 ///
 /// # fn main() {
-/// let mut schema_builder = SchemaBuilder::new();
+/// let mut schema_builder = Schema::builder();
 /// let title = schema_builder.add_text_field("title", TEXT);
 /// let author = schema_builder.add_text_field("text", TEXT);
 /// let likes = schema_builder.add_u64_field("num_u64", FAST);
@@ -67,33 +67,33 @@ macro_rules! doc(
 
 #[cfg(test)]
 mod test {
-    use schema::{SchemaBuilder, FAST, TEXT};
+    use schema::{Schema, FAST, TEXT};
 
     #[test]
     fn test_doc_basic() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field("title", TEXT);
         let author = schema_builder.add_text_field("text", TEXT);
         let likes = schema_builder.add_u64_field("num_u64", FAST);
         let _schema = schema_builder.build();
         let _doc = doc!(
-            title => "Life Aquatic",
-            author => "Wes Anderson",
-            likes => 4u64
-            );
+        title => "Life Aquatic",
+        author => "Wes Anderson",
+        likes => 4u64
+        );
     }
 
     #[test]
     fn test_doc_trailing_comma() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field("title", TEXT);
         let author = schema_builder.add_text_field("text", TEXT);
         let likes = schema_builder.add_u64_field("num_u64", FAST);
         let _schema = schema_builder.build();
         let _doc = doc!(
-            title => "Life Aquatic",
-            author => "Wes Anderson",
-            likes => 4u64,
-            );
+        title => "Life Aquatic",
+        author => "Wes Anderson",
+        likes => 4u64,
+        );
     }
 }

src/postings/compression/mod.rs

@@ -271,12 +271,9 @@ mod bench {
     use test::Bencher;
 
     fn generate_array_with_seed(n: usize, ratio: f64, seed_val: u8) -> Vec<u32> {
-        let seed: &[u8; 16] = &[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,seed_val];
+        let seed: &[u8; 16] = &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, seed_val];
         let mut rng: XorShiftRng = XorShiftRng::from_seed(*seed);
-        (0u32..)
-            .filter(|_| rng.gen_bool(ratio))
-            .take(n)
-            .collect()
+        (0u32..).filter(|_| rng.gen_bool(ratio)).take(n).collect()
     }
 
     pub fn generate_array(n: usize, ratio: f64) -> Vec<u32> {

src/postings/mod.rs

@@ -54,17 +54,18 @@ pub mod tests {
     use indexer::operation::AddOperation;
     use indexer::SegmentWriter;
     use query::Scorer;
-    use rand::{Rng, SeedableRng, XorShiftRng};
+    use rand::rngs::StdRng;
+    use rand::{Rng, SeedableRng};
     use schema::Field;
     use schema::IndexRecordOption;
-    use schema::{Document, SchemaBuilder, Term, INT_INDEXED, STRING, TEXT};
+    use schema::{Document, Schema, Term, INT_INDEXED, STRING, TEXT};
     use std::iter;
     use DocId;
     use Score;
 
     #[test]
     pub fn test_position_write() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -88,7 +89,7 @@ pub mod tests {
 
     #[test]
     pub fn test_skip_positions() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let title = schema_builder.add_text_field("title", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -163,7 +164,7 @@ pub mod tests {
     #[test]
     pub fn test_position_and_fieldnorm1() {
         let mut positions = Vec::new();
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema.clone());
@@ -220,12 +221,10 @@ pub mod tests {
             }
             {
                 let term_a = Term::from_field_text(text_field, "abcdef");
-                assert!(
-                    segment_reader
-                        .inverted_index(term_a.field())
-                        .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
-                        .is_none()
-                );
+                assert!(segment_reader
+                    .inverted_index(term_a.field())
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .is_none());
             }
             {
                 let term_a = Term::from_field_text(text_field, "a");
@@ -276,12 +275,12 @@ pub mod tests {
     #[test]
     pub fn test_position_and_fieldnorm2() {
         let mut positions: Vec<u32> = Vec::new();
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let mut doc = Document::default();
                 doc.add_text(text_field, "g b b d c g c");
@@ -317,13 +316,13 @@ pub mod tests {
         let num_docs = 300u32;
 
         let index = {
-            let mut schema_builder = SchemaBuilder::default();
+            let mut schema_builder = Schema::builder();
             let value_field = schema_builder.add_u64_field("value", INT_INDEXED);
             let schema = schema_builder.build();
 
             let index = Index::create_in_ram(schema);
             {
-                let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+                let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
                 for i in 0..num_docs {
                     let mut doc = Document::default();
                     doc.add_u64(value_field, 2);
@@ -400,7 +399,7 @@ pub mod tests {
 
         // delete some of the documents
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer.delete_term(term_0);
             assert!(index_writer.commit().is_ok());
         }
@@ -450,7 +449,7 @@ pub mod tests {
 
         // delete everything else
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer.delete_term(term_1);
 
             assert!(index_writer.commit().is_ok());
@@ -458,25 +457,14 @@ pub mod tests {
         index.load_searchers().unwrap();
 
         let searcher = index.searcher();
-        let segment_reader = searcher.segment_reader(0);
 
         // finally, check that it's empty
         {
-            let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
-                .unwrap();
-
-            assert_eq!(segment_postings.skip_next(0), SkipResult::Reached);
-            assert_eq!(segment_postings.doc(), 0);
-            assert!(segment_reader.is_deleted(0));
-
-            let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
-                .unwrap();
-
-            assert_eq!(segment_postings.skip_next(num_docs), SkipResult::End);
+            let searchable_segment_ids = index
+                .searchable_segment_ids()
+                .expect("could not get index segment ids");
+            assert!(searchable_segment_ids.is_empty());
+            assert_eq!(searcher.num_docs(), 0);
         }
     }
 
@@ -498,17 +486,16 @@ pub mod tests {
             Term::from_field_text(field, "d")
         };
         pub static ref INDEX: Index = {
-            let mut schema_builder = SchemaBuilder::default();
+            let mut schema_builder = Schema::builder();
             let text_field = schema_builder.add_text_field("text", STRING);
             let schema = schema_builder.build();
 
-            let seed: [u8; 16] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
-            let mut rng: XorShiftRng = XorShiftRng::from_seed(seed);
+            let mut rng: StdRng = StdRng::from_seed([1u8; 32]);
 
             let index = Index::create_in_ram(schema);
             let posting_list_size = 1_000_000;
             {
-                let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+                let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
                 for _ in 0..posting_list_size {
                     let mut doc = Document::default();
                     if rng.gen_bool(1f64 / 15f64) {

src/postings/postings_writer.rs

@@ -1,6 +1,8 @@
 use super::stacker::{Addr, MemoryArena, TermHashMap};
 
-use postings::recorder::{NothingRecorder, Recorder, TFAndPositionRecorder, TermFrequencyRecorder};
+use postings::recorder::{
+    BufferLender, NothingRecorder, Recorder, TFAndPositionRecorder, TermFrequencyRecorder,
+};
 use postings::UnorderedTermId;
 use postings::{FieldSerializer, InvertedIndexSerializer};
 use schema::IndexRecordOption;
@@ -29,7 +31,8 @@ fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<PostingsWriter> {
                 IndexRecordOption::WithFreqsAndPositions => {
                     SpecializedPostingsWriter::<TFAndPositionRecorder>::new_boxed()
                 }
-            }).unwrap_or_else(|| SpecializedPostingsWriter::<NothingRecorder>::new_boxed()),
+            })
+            .unwrap_or_else(|| SpecializedPostingsWriter::<NothingRecorder>::new_boxed()),
         FieldType::U64(_) | FieldType::I64(_) | FieldType::HierarchicalFacet => {
             SpecializedPostingsWriter::<NothingRecorder>::new_boxed()
         }
@@ -107,10 +110,8 @@ impl MultiFieldPostingsWriter {
             .map(|(key, _, _)| Term::wrap(key).field())
             .enumerate();
 
-        let mut unordered_term_mappings: HashMap<
-            Field,
-            HashMap<UnorderedTermId, TermOrdinal>,
-        > = HashMap::new();
+        let mut unordered_term_mappings: HashMap<Field, HashMap<UnorderedTermId, TermOrdinal>> =
+            HashMap::new();
 
         let mut prev_field = Field(u32::max_value());
         for (offset, field) in term_offsets_it {
@@ -138,7 +139,8 @@ impl MultiFieldPostingsWriter {
                         .enumerate()
                         .map(|(term_ord, unord_term_id)| {
                             (unord_term_id as UnorderedTermId, term_ord as TermOrdinal)
-                        }).collect();
+                        })
+                        .collect();
                     unordered_term_mappings.insert(field, mapping);
                 }
                 FieldType::U64(_) | FieldType::I64(_) => {}
@@ -213,7 +215,7 @@ pub trait PostingsWriter {
 
 /// The `SpecializedPostingsWriter` is just here to remove dynamic
 /// dispatch to the recorder information.
-pub struct SpecializedPostingsWriter<Rec: Recorder + 'static> {
+pub(crate) struct SpecializedPostingsWriter<Rec: Recorder + 'static> {
     total_num_tokens: u64,
     _recorder_type: PhantomData<Rec>,
 }
@@ -245,8 +247,7 @@ impl<Rec: Recorder + 'static> PostingsWriter for SpecializedPostingsWriter<Rec>
         debug_assert!(term.as_slice().len() >= 4);
         self.total_num_tokens += 1;
         term_index.mutate_or_create(term, |opt_recorder: Option<Rec>| {
-            if opt_recorder.is_some() {
-                let mut recorder = opt_recorder.unwrap();
+            if let Some(mut recorder) = opt_recorder {
                 let current_doc = recorder.current_doc();
                 if current_doc != doc {
                     recorder.close_doc(heap);
@@ -255,7 +256,7 @@ impl<Rec: Recorder + 'static> PostingsWriter for SpecializedPostingsWriter<Rec>
                 recorder.record_position(position, heap);
                 recorder
             } else {
-                let mut recorder = Rec::new(heap);
+                let mut recorder = Rec::new();
                 recorder.new_doc(doc, heap);
                 recorder.record_position(position, heap);
                 recorder
@@ -270,10 +271,11 @@ impl<Rec: Recorder + 'static> PostingsWriter for SpecializedPostingsWriter<Rec>
         termdict_heap: &MemoryArena,
         heap: &MemoryArena,
     ) -> io::Result<()> {
+        let mut buffer_lender = BufferLender::default();
         for &(term_bytes, addr, _) in term_addrs {
-            let recorder: Rec = unsafe { termdict_heap.read(addr) };
+            let recorder: Rec = termdict_heap.read(addr);
             serializer.new_term(&term_bytes[4..])?;
-            recorder.serialize(serializer, heap)?;
+            recorder.serialize(&mut buffer_lender, serializer, heap)?;
             serializer.close_term()?;
         }
         Ok(())

src/postings/recorder.rs

@@ -1,10 +1,51 @@
 use super::stacker::{ExpUnrolledLinkedList, MemoryArena};
+use common::{read_u32_vint, write_u32_vint};
 use postings::FieldSerializer;
-use std::{self, io};
+use std::io;
 use DocId;
 
 const EMPTY_ARRAY: [u32; 0] = [0u32; 0];
-const POSITION_END: u32 = std::u32::MAX;
+const POSITION_END: u32 = 0;
+
+#[derive(Default)]
+pub(crate) struct BufferLender {
+    buffer_u8: Vec<u8>,
+    buffer_u32: Vec<u32>,
+}
+
+impl BufferLender {
+    pub fn lend_u8(&mut self) -> &mut Vec<u8> {
+        self.buffer_u8.clear();
+        &mut self.buffer_u8
+    }
+    pub fn lend_all(&mut self) -> (&mut Vec<u8>, &mut Vec<u32>) {
+        self.buffer_u8.clear();
+        self.buffer_u32.clear();
+        (&mut self.buffer_u8, &mut self.buffer_u32)
+    }
+}
+
+pub struct VInt32Reader<'a> {
+    data: &'a [u8],
+}
+
+impl<'a> VInt32Reader<'a> {
+    fn new(data: &'a [u8]) -> VInt32Reader<'a> {
+        VInt32Reader { data }
+    }
+}
+
+impl<'a> Iterator for VInt32Reader<'a> {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<u32> {
+        if self.data.is_empty() {
+            None
+        } else {
+            Some(read_u32_vint(&mut self.data))
+        }
+    }
+}
 
 /// Recorder is in charge of recording relevant information about
 /// the presence of a term in a document.
@@ -15,9 +56,9 @@ const POSITION_END: u32 = std::u32::MAX;
 ///   * the document id
 ///   * the term frequency
 ///   * the term positions
-pub trait Recorder: Copy {
+pub(crate) trait Recorder: Copy + 'static {
     ///
-    fn new(heap: &mut MemoryArena) -> Self;
+    fn new() -> Self;
     /// Returns the current document
     fn current_doc(&self) -> u32;
     /// Starts recording information about a new document
@@ -29,7 +70,12 @@ pub trait Recorder: Copy {
     /// Close the document. It will help record the term frequency.
     fn close_doc(&mut self, heap: &mut MemoryArena);
     /// Pushes the postings information to the serializer.
-    fn serialize(&self, serializer: &mut FieldSerializer, heap: &MemoryArena) -> io::Result<()>;
+    fn serialize(
+        &self,
+        buffer_lender: &mut BufferLender,
+        serializer: &mut FieldSerializer,
+        heap: &MemoryArena,
+    ) -> io::Result<()>;
 }
 
 /// Only records the doc ids
@@ -40,9 +86,9 @@ pub struct NothingRecorder {
 }
 
 impl Recorder for NothingRecorder {
-    fn new(heap: &mut MemoryArena) -> Self {
+    fn new() -> Self {
         NothingRecorder {
-            stack: ExpUnrolledLinkedList::new(heap),
+            stack: ExpUnrolledLinkedList::new(),
             current_doc: u32::max_value(),
         }
     }
@@ -53,16 +99,23 @@ impl Recorder for NothingRecorder {
 
     fn new_doc(&mut self, doc: DocId, heap: &mut MemoryArena) {
         self.current_doc = doc;
-        self.stack.push(doc, heap);
+        let _ = write_u32_vint(doc, &mut self.stack.writer(heap));
     }
 
     fn record_position(&mut self, _position: u32, _heap: &mut MemoryArena) {}
 
     fn close_doc(&mut self, _heap: &mut MemoryArena) {}
 
-    fn serialize(&self, serializer: &mut FieldSerializer, heap: &MemoryArena) -> io::Result<()> {
-        for doc in self.stack.iter(heap) {
-            serializer.write_doc(doc, 0u32, &EMPTY_ARRAY)?;
+    fn serialize(
+        &self,
+        buffer_lender: &mut BufferLender,
+        serializer: &mut FieldSerializer,
+        heap: &MemoryArena,
+    ) -> io::Result<()> {
+        let buffer = buffer_lender.lend_u8();
+        self.stack.read_to_end(heap, buffer);
+        for doc in VInt32Reader::new(&buffer[..]) {
+            serializer.write_doc(doc as u32, 0u32, &EMPTY_ARRAY)?;
         }
         Ok(())
     }
@@ -77,9 +130,9 @@ pub struct TermFrequencyRecorder {
 }
 
 impl Recorder for TermFrequencyRecorder {
-    fn new(heap: &mut MemoryArena) -> Self {
+    fn new() -> Self {
         TermFrequencyRecorder {
-            stack: ExpUnrolledLinkedList::new(heap),
+            stack: ExpUnrolledLinkedList::new(),
             current_doc: u32::max_value(),
             current_tf: 0u32,
         }
@@ -91,7 +144,7 @@ impl Recorder for TermFrequencyRecorder {
 
     fn new_doc(&mut self, doc: DocId, heap: &mut MemoryArena) {
         self.current_doc = doc;
-        self.stack.push(doc, heap);
+        let _ = write_u32_vint(doc, &mut self.stack.writer(heap));
     }
 
     fn record_position(&mut self, _position: u32, _heap: &mut MemoryArena) {
@@ -100,24 +153,24 @@ impl Recorder for TermFrequencyRecorder {
 
     fn close_doc(&mut self, heap: &mut MemoryArena) {
         debug_assert!(self.current_tf > 0);
-        self.stack.push(self.current_tf, heap);
+        let _ = write_u32_vint(self.current_tf, &mut self.stack.writer(heap));
         self.current_tf = 0;
     }
 
-    fn serialize(&self, serializer: &mut FieldSerializer, heap: &MemoryArena) -> io::Result<()> {
-        // the last document has not been closed...
-        // its term freq is self.current_tf.
-        let mut doc_iter = self
-            .stack
-            .iter(heap)
-            .chain(Some(self.current_tf).into_iter());
-
-        while let Some(doc) = doc_iter.next() {
-            let term_freq = doc_iter
-                .next()
-                .expect("The IndexWriter recorded a doc without a term freq.");
-            serializer.write_doc(doc, term_freq, &EMPTY_ARRAY)?;
+    fn serialize(
+        &self,
+        buffer_lender: &mut BufferLender,
+        serializer: &mut FieldSerializer,
+        heap: &MemoryArena,
+    ) -> io::Result<()> {
+        let buffer = buffer_lender.lend_u8();
+        self.stack.read_to_end(heap, buffer);
+        let mut u32_it = VInt32Reader::new(&buffer[..]);
+        while let Some(doc) = u32_it.next() {
+            let term_freq = u32_it.next().unwrap_or(self.current_tf);
+            serializer.write_doc(doc as u32, term_freq, &EMPTY_ARRAY)?;
         }
+
         Ok(())
     }
 }
@@ -128,11 +181,10 @@ pub struct TFAndPositionRecorder {
     stack: ExpUnrolledLinkedList,
     current_doc: DocId,
 }
-
 impl Recorder for TFAndPositionRecorder {
-    fn new(heap: &mut MemoryArena) -> Self {
+    fn new() -> Self {
         TFAndPositionRecorder {
-            stack: ExpUnrolledLinkedList::new(heap),
+            stack: ExpUnrolledLinkedList::new(),
             current_doc: u32::max_value(),
         }
     }
@@ -143,33 +195,88 @@ impl Recorder for TFAndPositionRecorder {
 
     fn new_doc(&mut self, doc: DocId, heap: &mut MemoryArena) {
         self.current_doc = doc;
-        self.stack.push(doc, heap);
+        let _ = write_u32_vint(doc, &mut self.stack.writer(heap));
     }
 
     fn record_position(&mut self, position: u32, heap: &mut MemoryArena) {
-        self.stack.push(position, heap);
+        let _ = write_u32_vint(position + 1u32, &mut self.stack.writer(heap));
     }
 
     fn close_doc(&mut self, heap: &mut MemoryArena) {
-        self.stack.push(POSITION_END, heap);
+        let _ = write_u32_vint(POSITION_END, &mut self.stack.writer(heap));
     }
 
-    fn serialize(&self, serializer: &mut FieldSerializer, heap: &MemoryArena) -> io::Result<()> {
-        let mut doc_positions = Vec::with_capacity(100);
-        let mut positions_iter = self.stack.iter(heap);
-        while let Some(doc) = positions_iter.next() {
-            let mut prev_position = 0;
-            doc_positions.clear();
-            for position in &mut positions_iter {
-                if position == POSITION_END {
-                    break;
-                } else {
-                    doc_positions.push(position - prev_position);
-                    prev_position = position;
+    fn serialize(
+        &self,
+        buffer_lender: &mut BufferLender,
+        serializer: &mut FieldSerializer,
+        heap: &MemoryArena,
+    ) -> io::Result<()> {
+        let (buffer_u8, buffer_positions) = buffer_lender.lend_all();
+        self.stack.read_to_end(heap, buffer_u8);
+        let mut u32_it = VInt32Reader::new(&buffer_u8[..]);
+        while let Some(doc) = u32_it.next() {
+            let mut prev_position_plus_one = 1u32;
+            buffer_positions.clear();
+            loop {
+                match u32_it.next() {
+                    Some(POSITION_END) | None => {
+                        break;
+                    }
+                    Some(position_plus_one) => {
+                        let delta_position = position_plus_one - prev_position_plus_one;
+                        buffer_positions.push(delta_position);
+                        prev_position_plus_one = position_plus_one;
+                    }
                 }
             }
-            serializer.write_doc(doc, doc_positions.len() as u32, &doc_positions)?;
+            serializer.write_doc(doc, buffer_positions.len() as u32, &buffer_positions)?;
         }
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+
+    use super::write_u32_vint;
+    use super::BufferLender;
+    use super::VInt32Reader;
+
+    #[test]
+    fn test_buffer_lender() {
+        let mut buffer_lender = BufferLender::default();
+        {
+            let buf = buffer_lender.lend_u8();
+            assert!(buf.is_empty());
+            buf.push(1u8);
+        }
+        {
+            let buf = buffer_lender.lend_u8();
+            assert!(buf.is_empty());
+            buf.push(1u8);
+        }
+        {
+            let (_, buf) = buffer_lender.lend_all();
+            assert!(buf.is_empty());
+            buf.push(1u32);
+        }
+        {
+            let (_, buf) = buffer_lender.lend_all();
+            assert!(buf.is_empty());
+            buf.push(1u32);
+        }
+    }
+
+    #[test]
+    fn test_vint_u32() {
+        let mut buffer = vec![];
+        let vals = [0, 1, 324_234_234, u32::max_value()];
+        for &i in &vals {
+            assert!(write_u32_vint(i, &mut buffer).is_ok());
+        }
+        assert_eq!(buffer.len(), 1 + 1 + 5 + 5);
+        let res: Vec<u32> = VInt32Reader::new(&buffer[..]).collect();
+        assert_eq!(&res[..], &vals[..]);
+    }
+}

src/postings/segment_postings.rs

@@ -124,22 +124,17 @@ impl SegmentPostings {
 }
 
 fn exponential_search(target: u32, arr: &[u32]) -> (usize, usize) {
-    let mut start = 0;
     let end = arr.len();
-    debug_assert!(target >= arr[start]);
+    debug_assert!(arr.len() <= 128);
     debug_assert!(target <= arr[end - 1]);
-    let mut jump = 1;
-    loop {
-        let new = start + jump;
-        if new >= end {
-            return (start, end);
+    let mut begin = 0;
+    for &pivot in [1,3,7,15,31,63].iter().take_while(|&&el| el < end) {
+        if arr[pivot] > target {
+            return (begin, pivot);
         }
-        if arr[new] > target {
-            return (start, new);
-        }
-        start = new;
-        jump *= 2;
+        begin = pivot;
     }
+    (begin, end)
 }
 
 /// Search the first index containing an element greater or equal to the target.
@@ -216,11 +211,10 @@ impl DocSet for SegmentPostings {
 
         // we're in the right block now, start with an exponential search
         let block_docs = self.block_cursor.docs();
-
-        debug_assert!(target >= self.doc());
         let new_cur = self
             .cur
             .wrapping_add(search_within_block(&block_docs[self.cur..], target));
+
         if need_positions {
             sum_freqs_skipped += self.block_cursor.freqs()[self.cur..new_cur]
                 .iter()
@@ -533,7 +527,8 @@ impl BlockSegmentPostings {
                     } else {
                         BlockSegmentPostingsSkipResult::Terminated
                     }
-                }).unwrap_or(BlockSegmentPostingsSkipResult::Terminated);
+                })
+                .unwrap_or(BlockSegmentPostingsSkipResult::Terminated);
         }
         BlockSegmentPostingsSkipResult::Terminated
     }
@@ -621,6 +616,7 @@ impl<'b> Streamer<'b> for BlockSegmentPostings {
 #[cfg(test)]
 mod tests {
 
+    use super::exponential_search;
     use super::search_within_block;
     use super::BlockSegmentPostings;
     use super::BlockSegmentPostingsSkipResult;
@@ -630,10 +626,11 @@ mod tests {
     use docset::DocSet;
     use fst::Streamer;
     use schema::IndexRecordOption;
-    use schema::SchemaBuilder;
+    use schema::Schema;
     use schema::Term;
     use schema::INT_INDEXED;
     use DocId;
+    use SkipResult;
 
     #[test]
     fn test_empty_segment_postings() {
@@ -661,6 +658,16 @@ mod tests {
             .0
     }
 
+    #[test]
+    fn test_exponentiel_search() {
+        assert_eq!(exponential_search(0, &[1, 2]), (0, 1));
+        assert_eq!(exponential_search(1, &[1, 2]), (0, 1));
+        assert_eq!(
+            exponential_search(7, &[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]),
+            (3, 7)
+        );
+    }
+
     fn util_test_search_within_block(block: &[u32], target: u32) {
         assert_eq!(
             search_within_block(block, target),
@@ -692,7 +699,7 @@ mod tests {
 
     #[test]
     fn test_block_segment_postings() {
-        let mut block_segments = build_block_postings((0..100_000).collect::<Vec<u32>>());
+        let mut block_segments = build_block_postings(&(0..100_000).collect::<Vec<u32>>());
         let mut offset: u32 = 0u32;
         // checking that the block before calling advance is empty
         assert!(block_segments.docs().is_empty());
@@ -706,14 +713,44 @@ mod tests {
         }
     }
 
-    fn build_block_postings(docs: Vec<DocId>) -> BlockSegmentPostings {
-        let mut schema_builder = SchemaBuilder::default();
+    #[test]
+    fn test_skip_right_at_new_block() {
+        let mut doc_ids = (0..128).collect::<Vec<u32>>();
+        doc_ids.push(129);
+        doc_ids.push(130);
+        {
+            let block_segments = build_block_postings(&doc_ids);
+            let mut docset = SegmentPostings::from_block_postings(block_segments, None);
+            assert_eq!(docset.skip_next(128), SkipResult::OverStep);
+            assert_eq!(docset.doc(), 129);
+            assert!(docset.advance());
+            assert_eq!(docset.doc(), 130);
+            assert!(!docset.advance());
+        }
+        {
+            let block_segments = build_block_postings(&doc_ids);
+            let mut docset = SegmentPostings::from_block_postings(block_segments, None);
+            assert_eq!(docset.skip_next(129), SkipResult::Reached);
+            assert_eq!(docset.doc(), 129);
+            assert!(docset.advance());
+            assert_eq!(docset.doc(), 130);
+            assert!(!docset.advance());
+        }
+        {
+            let block_segments = build_block_postings(&doc_ids);
+            let mut docset = SegmentPostings::from_block_postings(block_segments, None);
+            assert_eq!(docset.skip_next(131), SkipResult::End);
+        }
+    }
+
+    fn build_block_postings(docs: &[DocId]) -> BlockSegmentPostings {
+        let mut schema_builder = Schema::builder();
         let int_field = schema_builder.add_u64_field("id", INT_INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         let mut last_doc = 0u32;
-        for doc in docs {
+        for &doc in docs {
             for _ in last_doc..doc {
                 index_writer.add_document(doc!(int_field=>1u64));
             }
@@ -733,7 +770,7 @@ mod tests {
     #[test]
     fn test_block_segment_postings_skip() {
         for i in 0..4 {
-            let mut block_postings = build_block_postings(vec![3]);
+            let mut block_postings = build_block_postings(&[3]);
             assert_eq!(
                 block_postings.skip_to(i),
                 BlockSegmentPostingsSkipResult::Success(0u32)
@@ -743,7 +780,7 @@ mod tests {
                 BlockSegmentPostingsSkipResult::Terminated
             );
         }
-        let mut block_postings = build_block_postings(vec![3]);
+        let mut block_postings = build_block_postings(&[3]);
         assert_eq!(
             block_postings.skip_to(4u32),
             BlockSegmentPostingsSkipResult::Terminated
@@ -756,7 +793,7 @@ mod tests {
         for i in 0..1300 {
             docs.push((i * i / 100) + i);
         }
-        let mut block_postings = build_block_postings(docs.clone());
+        let mut block_postings = build_block_postings(&docs[..]);
         for i in vec![0, 424, 10000] {
             assert_eq!(
                 block_postings.skip_to(i),
@@ -778,11 +815,11 @@ mod tests {
 
     #[test]
     fn test_reset_block_segment_postings() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let int_field = schema_builder.add_u64_field("id", INT_INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
         // create two postings list, one containg even number,
         // the other containing odd numbers.
         for i in 0..6 {

src/postings/serializer.rs

@@ -55,7 +55,7 @@ pub struct InvertedIndexSerializer {
 
 impl InvertedIndexSerializer {
     /// Open a new `PostingsSerializer` for the given segment
-    fn new(
+    fn create(
         terms_write: CompositeWrite<WritePtr>,
         postings_write: CompositeWrite<WritePtr>,
         positions_write: CompositeWrite<WritePtr>,
@@ -74,7 +74,7 @@ impl InvertedIndexSerializer {
     /// Open a new `PostingsSerializer` for the given segment
     pub fn open(segment: &mut Segment) -> Result<InvertedIndexSerializer> {
         use SegmentComponent::{POSITIONS, POSITIONSSKIP, POSTINGS, TERMS};
-        InvertedIndexSerializer::new(
+        InvertedIndexSerializer::create(
             CompositeWrite::wrap(segment.open_write(TERMS)?),
             CompositeWrite::wrap(segment.open_write(POSTINGS)?),
             CompositeWrite::wrap(segment.open_write(POSITIONS)?),
@@ -99,7 +99,7 @@ impl InvertedIndexSerializer {
         let positions_write = self.positions_write.for_field(field);
         let positionsidx_write = self.positionsidx_write.for_field(field);
         let field_type: FieldType = (*field_entry.field_type()).clone();
-        FieldSerializer::new(
+        FieldSerializer::create(
             &field_type,
             term_dictionary_write,
             postings_write,
@@ -130,7 +130,7 @@ pub struct FieldSerializer<'a> {
 }
 
 impl<'a> FieldSerializer<'a> {
-    fn new(
+    fn create(
         field_type: &FieldType,
         term_dictionary_write: &'a mut CountingWriter<WritePtr>,
         postings_write: &'a mut CountingWriter<WritePtr>,
@@ -152,7 +152,7 @@ impl<'a> FieldSerializer<'a> {
             _ => (false, false),
         };
         let term_dictionary_builder =
-            TermDictionaryBuilder::new(term_dictionary_write, &field_type)?;
+            TermDictionaryBuilder::create(term_dictionary_write, &field_type)?;
         let postings_serializer =
             PostingsSerializer::new(postings_write, term_freq_enabled, position_enabled);
         let positions_serializer_opt = if position_enabled {

src/postings/stacker/expull.rs

@@ -1,28 +1,37 @@
 use super::{Addr, MemoryArena};
 
-use common::is_power_of_2;
+use postings::stacker::memory_arena::load;
+use postings::stacker::memory_arena::store;
+use std::io;
 use std::mem;
 
 const MAX_BLOCK_LEN: u32 = 1u32 << 15;
+const FIRST_BLOCK: usize = 16;
+const INLINED_BLOCK_LEN: usize = FIRST_BLOCK + mem::size_of::<Addr>();
 
-const FIRST_BLOCK: u32 = 4u32;
+enum CapacityResult {
+    Available(u32),
+    NeedAlloc(u32),
+}
 
-#[inline]
-pub fn jump_needed(len: u32) -> Option<usize> {
+fn len_to_capacity(len: u32) -> CapacityResult {
     match len {
-        0...3 => None,
-        4...MAX_BLOCK_LEN => {
-            if is_power_of_2(len as usize) {
-                Some(len as usize)
+        0...15 => CapacityResult::Available(FIRST_BLOCK as u32 - len),
+        16...MAX_BLOCK_LEN => {
+            let cap = 1 << (32u32 - (len - 1u32).leading_zeros());
+            let available = cap - len;
+            if available == 0 {
+                CapacityResult::NeedAlloc(len)
             } else {
-                None
+                CapacityResult::Available(available)
             }
         }
         n => {
-            if n % MAX_BLOCK_LEN == 0 {
-                Some(MAX_BLOCK_LEN as usize)
+            let available = n % MAX_BLOCK_LEN;
+            if available == 0 {
+                CapacityResult::NeedAlloc(MAX_BLOCK_LEN)
             } else {
-                None
+                CapacityResult::Available(MAX_BLOCK_LEN - available)
             }
         }
     }
@@ -52,82 +61,119 @@ pub fn jump_needed(len: u32) -> Option<usize> {
 #[derive(Debug, Clone, Copy)]
 pub struct ExpUnrolledLinkedList {
     len: u32,
-    head: Addr,
     tail: Addr,
+    inlined_data: [u8; INLINED_BLOCK_LEN as usize],
+}
+
+pub struct ExpUnrolledLinkedListWriter<'a> {
+    eull: &'a mut ExpUnrolledLinkedList,
+    heap: &'a mut MemoryArena,
+}
+
+fn ensure_capacity<'a>(
+    eull: &'a mut ExpUnrolledLinkedList,
+    heap: &'a mut MemoryArena,
+) -> &'a mut [u8] {
+    if eull.len <= FIRST_BLOCK as u32 {
+        // We are still hitting the inline block.
+        if eull.len < FIRST_BLOCK as u32 {
+            return &mut eull.inlined_data[eull.len as usize..FIRST_BLOCK];
+        }
+        // We need to allocate a new block!
+        let new_block_addr: Addr = heap.allocate_space(FIRST_BLOCK + mem::size_of::<Addr>());
+        store(&mut eull.inlined_data[FIRST_BLOCK..], new_block_addr);
+        eull.tail = new_block_addr;
+        return heap.slice_mut(eull.tail, FIRST_BLOCK);
+    }
+    let len = match len_to_capacity(eull.len) {
+        CapacityResult::NeedAlloc(new_block_len) => {
+            let new_block_addr: Addr =
+                heap.allocate_space(new_block_len as usize + mem::size_of::<Addr>());
+            heap.write_at(eull.tail, new_block_addr);
+            eull.tail = new_block_addr;
+            new_block_len
+        }
+        CapacityResult::Available(available) => available,
+    };
+    heap.slice_mut(eull.tail, len as usize)
+}
+
+impl<'a> ExpUnrolledLinkedListWriter<'a> {
+    pub fn extend_from_slice(&mut self, mut buf: &[u8]) {
+        if buf.is_empty() {
+            // we need to cut early, because `ensure_capacity`
+            // allocates if there is no capacity at all right now.
+            return;
+        }
+        while !buf.is_empty() {
+            let add_len: usize;
+            {
+                let output_buf = ensure_capacity(self.eull, self.heap);
+                add_len = buf.len().min(output_buf.len());
+                output_buf[..add_len].copy_from_slice(&buf[..add_len]);
+            }
+            self.eull.len += add_len as u32;
+            self.eull.tail = self.eull.tail.offset(add_len as u32);
+            buf = &buf[add_len..];
+        }
+    }
+}
+
+impl<'a> io::Write for ExpUnrolledLinkedListWriter<'a> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        // There is no use case to only write the capacity.
+        // This is not IO after all, so we write the whole
+        // buffer even if the contract of `.write` is looser.
+        self.extend_from_slice(buf);
+        Ok(buf.len())
+    }
+
+    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
+        self.extend_from_slice(buf);
+        Ok(())
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
 }
 
 impl ExpUnrolledLinkedList {
-    pub fn new(heap: &mut MemoryArena) -> ExpUnrolledLinkedList {
-        let addr = heap.allocate_space((FIRST_BLOCK as usize) * mem::size_of::<u32>());
+    pub fn new() -> ExpUnrolledLinkedList {
         ExpUnrolledLinkedList {
             len: 0u32,
-            head: addr,
-            tail: addr,
+            tail: Addr::null_pointer(),
+            inlined_data: [0u8; INLINED_BLOCK_LEN as usize],
         }
     }
 
-    pub fn iter<'a>(&self, heap: &'a MemoryArena) -> ExpUnrolledLinkedListIterator<'a> {
-        ExpUnrolledLinkedListIterator {
-            heap,
-            addr: self.head,
-            len: self.len,
-            consumed: 0,
-        }
+    #[inline(always)]
+    pub fn writer<'a>(&'a mut self, heap: &'a mut MemoryArena) -> ExpUnrolledLinkedListWriter<'a> {
+        ExpUnrolledLinkedListWriter { eull: self, heap }
     }
 
-    /// Appends a new element to the current stack.
-    ///
-    /// If the current block end is reached, a new block is allocated.
-    pub fn push(&mut self, val: u32, heap: &mut MemoryArena) {
-        self.len += 1;
-        if let Some(new_block_len) = jump_needed(self.len) {
-            // We need to allocate another block.
-            // We also allocate an extra `u32` to store the pointer
-            // to the future next block.
-            let new_block_size: usize = (new_block_len + 1) * mem::size_of::<u32>();
-            let new_block_addr: Addr = heap.allocate_space(new_block_size);
-            unsafe {
-                // logic
-                heap.write(self.tail, new_block_addr)
-            };
-            self.tail = new_block_addr;
+    pub fn read_to_end(&self, heap: &MemoryArena, output: &mut Vec<u8>) {
+        let len = self.len as usize;
+        if len <= FIRST_BLOCK {
+            output.extend_from_slice(&self.inlined_data[..len]);
+            return;
         }
-        unsafe {
-            // logic
-            heap.write(self.tail, val);
-            self.tail = self.tail.offset(mem::size_of::<u32>() as u32);
-        }
-    }
-}
-
-pub struct ExpUnrolledLinkedListIterator<'a> {
-    heap: &'a MemoryArena,
-    addr: Addr,
-    len: u32,
-    consumed: u32,
-}
-
-impl<'a> Iterator for ExpUnrolledLinkedListIterator<'a> {
-    type Item = u32;
-
-    fn next(&mut self) -> Option<u32> {
-        if self.consumed == self.len {
-            None
-        } else {
-            self.consumed += 1;
-            let addr: Addr = if jump_needed(self.consumed).is_some() {
-                unsafe {
-                    // logic
-                    self.heap.read(self.addr)
-                }
-            } else {
-                self.addr
-            };
-            self.addr = addr.offset(mem::size_of::<u32>() as u32);
-            Some(unsafe {
-                // logic
-                self.heap.read(addr)
-            })
+        output.extend_from_slice(&self.inlined_data[..FIRST_BLOCK]);
+        let mut cur = FIRST_BLOCK;
+        let mut addr = load(&self.inlined_data[FIRST_BLOCK..]);
+        loop {
+            let cap = match len_to_capacity(cur as u32) {
+                CapacityResult::Available(capacity) => capacity,
+                CapacityResult::NeedAlloc(capacity) => capacity,
+            } as usize;
+            let data = heap.slice(addr, cap);
+            if cur + cap >= len {
+                output.extend_from_slice(&data[..(len - cur)]);
+                return;
+            }
+            output.extend_from_slice(data);
+            cur += cap;
+            addr = heap.read(addr.offset(cap as u32));
         }
     }
 }
@@ -136,46 +182,134 @@ impl<'a> Iterator for ExpUnrolledLinkedListIterator<'a> {
 mod tests {
 
     use super::super::MemoryArena;
-    use super::jump_needed;
+    use super::len_to_capacity;
     use super::*;
+    use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 
+    #[test]
     #[test]
     fn test_stack() {
         let mut heap = MemoryArena::new();
-        let mut stack = ExpUnrolledLinkedList::new(&mut heap);
-        stack.push(1u32, &mut heap);
-        stack.push(2u32, &mut heap);
-        stack.push(4u32, &mut heap);
-        stack.push(8u32, &mut heap);
+        let mut stack = ExpUnrolledLinkedList::new();
+        stack.writer(&mut heap).extend_from_slice(&[1u8]);
+        stack.writer(&mut heap).extend_from_slice(&[2u8]);
+        stack.writer(&mut heap).extend_from_slice(&[3u8, 4u8]);
+        stack.writer(&mut heap).extend_from_slice(&[5u8]);
         {
-            let mut it = stack.iter(&heap);
-            assert_eq!(it.next().unwrap(), 1u32);
-            assert_eq!(it.next().unwrap(), 2u32);
-            assert_eq!(it.next().unwrap(), 4u32);
-            assert_eq!(it.next().unwrap(), 8u32);
-            assert!(it.next().is_none());
+            let mut buffer = Vec::new();
+            stack.read_to_end(&heap, &mut buffer);
+            assert_eq!(&buffer[..], &[1u8, 2u8, 3u8, 4u8, 5u8]);
         }
     }
 
     #[test]
-    fn test_jump_if_needed() {
-        let mut block_len = 4u32;
-        let mut i = 0;
-        while i < 10_000_000 {
-            assert!(jump_needed(i + block_len - 1).is_none());
-            assert!(jump_needed(i + block_len + 1).is_none());
-            assert!(jump_needed(i + block_len).is_some());
-            let new_block_len = jump_needed(i + block_len).unwrap();
-            i += block_len;
-            block_len = new_block_len as u32;
+    fn test_stack_long() {
+        let mut heap = MemoryArena::new();
+        let mut stack = ExpUnrolledLinkedList::new();
+        let source: Vec<u32> = (0..100).collect();
+        for &el in &source {
+            assert!(stack
+                .writer(&mut heap)
+                .write_u32::<LittleEndian>(el)
+                .is_ok());
         }
+        let mut buffer = Vec::new();
+        stack.read_to_end(&heap, &mut buffer);
+        let mut result = vec![];
+        let mut remaining = &buffer[..];
+        while !remaining.is_empty() {
+            result.push(LittleEndian::read_u32(&remaining[..4]));
+            remaining = &remaining[4..];
+        }
+        assert_eq!(&result[..], &source[..]);
+    }
+
+    #[test]
+    fn test_stack_interlaced() {
+        let mut heap = MemoryArena::new();
+        let mut stack = ExpUnrolledLinkedList::new();
+        let mut stack2 = ExpUnrolledLinkedList::new();
+
+        let mut vec1: Vec<u8> = vec![];
+        let mut vec2: Vec<u8> = vec![];
+
+        for i in 0..9 {
+            assert!(stack.writer(&mut heap).write_u32::<LittleEndian>(i).is_ok());
+            assert!(vec1.write_u32::<LittleEndian>(i).is_ok());
+            if i % 2 == 0 {
+                assert!(stack2
+                    .writer(&mut heap)
+                    .write_u32::<LittleEndian>(i)
+                    .is_ok());
+                assert!(vec2.write_u32::<LittleEndian>(i).is_ok());
+            }
+        }
+        let mut res1 = vec![];
+        let mut res2 = vec![];
+        stack.read_to_end(&heap, &mut res1);
+        stack2.read_to_end(&heap, &mut res2);
+        assert_eq!(&vec1[..], &res1[..]);
+        assert_eq!(&vec2[..], &res2[..]);
+    }
+
+    #[test]
+    fn test_jump_if_needed() {
+        let mut available = 16u32;
+        for i in 0..10_000_000 {
+            match len_to_capacity(i) {
+                CapacityResult::NeedAlloc(cap) => {
+                    assert_eq!(available, 0, "Failed len={}: Expected 0 got {}", i, cap);
+                    available = cap;
+                }
+                CapacityResult::Available(cap) => {
+                    assert_eq!(
+                        available, cap,
+                        "Failed len={}: Expected {} Got {}",
+                        i, available, cap
+                    );
+                }
+            }
+            available -= 1;
+        }
+    }
+
+    #[test]
+    fn test_jump_if_needed_progression() {
+        let mut v = vec![];
+        for i in 0.. {
+            if v.len() >= 10 {
+                break;
+            }
+            match len_to_capacity(i) {
+                CapacityResult::NeedAlloc(cap) => {
+                    v.push((i, cap));
+                }
+                _ => {}
+            }
+        }
+        assert_eq!(
+            &v[..],
+            &[
+                (16, 16),
+                (32, 32),
+                (64, 64),
+                (128, 128),
+                (256, 256),
+                (512, 512),
+                (1024, 1024),
+                (2048, 2048),
+                (4096, 4096),
+                (8192, 8192)
+            ]
+        );
     }
 }
 
 #[cfg(all(test, feature = "unstable"))]
 mod bench {
-    use super::ExpUnrolledLinkedList;
     use super::super::MemoryArena;
+    use super::ExpUnrolledLinkedList;
+    use byteorder::{NativeEndian, WriteBytesExt};
     use test::Bencher;
 
     const NUM_STACK: usize = 10_000;
@@ -203,13 +337,13 @@ mod bench {
             let mut heap = MemoryArena::new();
             let mut stacks = Vec::with_capacity(100);
             for _ in 0..NUM_STACK {
-                let mut stack = ExpUnrolledLinkedList::new(&mut heap);
+                let mut stack = ExpUnrolledLinkedList::new();
                 stacks.push(stack);
             }
             for s in 0..NUM_STACK {
                 for i in 0u32..STACK_SIZE {
                     let t = s * 392017 % NUM_STACK;
-                    stacks[t].push(i, &mut heap);
+                    let _ = stacks[t].writer(&mut heap).write_u32::<NativeEndian>(i);
                 }
             }
         });

src/postings/stacker/memory_arena.rs

@@ -37,7 +37,7 @@ const PAGE_SIZE: usize = 1 << NUM_BITS_PAGE_ADDR; // pages are 1 MB large
 /// page of memory.
 ///
 /// The last 20 bits are an address within this page of memory.
-#[derive(Clone, Copy, Debug)]
+#[derive(Copy, Clone, Debug)]
 pub struct Addr(u32);
 
 impl Addr {
@@ -69,32 +69,16 @@ impl Addr {
     }
 }
 
-/// Trait required for an object to be `storable`.
-///
-/// # Warning
-///
-/// Most of the time you should not implement this trait,
-/// and only use the `MemoryArena` with object implementing `Copy`.
-///
-/// `ArenaStorable` is used in `tantivy` to force
-/// a `Copy` object and a `slice` of data to be stored contiguously.
-pub trait ArenaStorable {
-    fn num_bytes(&self) -> usize;
-    unsafe fn write_into(self, arena: &mut MemoryArena, addr: Addr);
+pub fn store<Item: Copy + 'static>(dest: &mut [u8], val: Item) {
+    assert_eq!(dest.len(), std::mem::size_of::<Item>());
+    unsafe {
+        ptr::write_unaligned(dest.as_mut_ptr() as *mut Item, val);
+    }
 }
 
-impl<V> ArenaStorable for V
-where
-    V: Copy,
-{
-    fn num_bytes(&self) -> usize {
-        mem::size_of::<V>()
-    }
-
-    unsafe fn write_into(self, arena: &mut MemoryArena, addr: Addr) {
-        let dst_ptr = arena.get_mut_ptr(addr) as *mut V;
-        ptr::write_unaligned(dst_ptr, self);
-    }
+pub fn load<Item: Copy + 'static>(data: &[u8]) -> Item {
+    assert_eq!(data.len(), std::mem::size_of::<Item>());
+    unsafe { ptr::read_unaligned(data.as_ptr() as *const Item) }
 }
 
 /// The `MemoryArena`
@@ -126,47 +110,9 @@ impl MemoryArena {
         self.pages.len() * PAGE_SIZE
     }
 
-    /// Writes a slice at the given address, assuming the
-    /// memory was allocated beforehands.
-    ///
-    ///  # Panics
-    ///
-    /// May panic or corrupt the heap if he space was not
-    /// properly allocated beforehands.
-    pub fn write_bytes<B: AsRef<[u8]>>(&mut self, addr: Addr, data: B) {
-        let bytes = data.as_ref();
-        self.pages[addr.page_id()]
-            .get_mut_slice(addr.page_local_addr(), bytes.len())
-            .copy_from_slice(bytes);
-    }
-
-    /// Returns the `len` bytes starting at `addr`
-    ///
-    /// # Panics
-    ///
-    /// Panics if the memory has not been allocated beforehands.
-    pub fn read_slice(&self, addr: Addr, len: usize) -> &[u8] {
-        self.pages[addr.page_id()].get_slice(addr.page_local_addr(), len)
-    }
-
-    unsafe fn get_mut_ptr(&mut self, addr: Addr) -> *mut u8 {
-        self.pages[addr.page_id()].get_mut_ptr(addr.page_local_addr())
-    }
-
-    /// Stores an item's data in the heap
-    ///
-    /// It allocates the `Item` beforehands.
-    pub fn store<Item: ArenaStorable>(&mut self, val: Item) -> Addr {
-        let num_bytes = val.num_bytes();
-        let addr = self.allocate_space(num_bytes);
-        unsafe {
-            self.write(addr, val);
-        };
-        addr
-    }
-
-    pub unsafe fn write<Item: ArenaStorable>(&mut self, addr: Addr, val: Item) {
-        val.write_into(self, addr)
+    pub fn write_at<Item: Copy + 'static>(&mut self, addr: Addr, val: Item) {
+        let dest = self.slice_mut(addr, std::mem::size_of::<Item>());
+        store(dest, val);
     }
 
     /// Read an item in the heap at the given `address`.
@@ -174,9 +120,21 @@ impl MemoryArena {
     /// # Panics
     ///
     /// If the address is erroneous
-    pub unsafe fn read<Item: Copy>(&self, addr: Addr) -> Item {
-        let ptr = self.pages[addr.page_id()].get_ptr(addr.page_local_addr());
-        ptr::read_unaligned(ptr as *const Item)
+    pub fn read<Item: Copy + 'static>(&self, addr: Addr) -> Item {
+        load(self.slice(addr, mem::size_of::<Item>()))
+    }
+
+    pub fn slice(&self, addr: Addr, len: usize) -> &[u8] {
+        self.pages[addr.page_id()].slice(addr.page_local_addr(), len)
+    }
+
+    pub fn slice_from(&self, addr: Addr) -> &[u8] {
+        self.pages[addr.page_id()].slice_from(addr.page_local_addr())
+    }
+
+    #[inline(always)]
+    pub fn slice_mut(&mut self, addr: Addr, len: usize) -> &mut [u8] {
+        self.pages[addr.page_id()].slice_mut(addr.page_local_addr(), len)
     }
 
     /// Allocates `len` bytes and returns the allocated address.
@@ -197,14 +155,10 @@ struct Page {
 
 impl Page {
     fn new(page_id: usize) -> Page {
-        let mut data: Vec<u8> = Vec::with_capacity(PAGE_SIZE);
-        unsafe {
-            data.set_len(PAGE_SIZE);
-        } // avoid initializing page
         Page {
             page_id,
             len: 0,
-            data: data.into_boxed_slice(),
+            data: vec![0u8; PAGE_SIZE].into_boxed_slice(),
         }
     }
 
@@ -213,12 +167,16 @@ impl Page {
         len + self.len <= PAGE_SIZE
     }
 
-    fn get_mut_slice(&mut self, local_addr: usize, len: usize) -> &mut [u8] {
-        &mut self.data[local_addr..][..len]
+    fn slice(&self, local_addr: usize, len: usize) -> &[u8] {
+        &self.slice_from(local_addr)[..len]
     }
 
-    fn get_slice(&self, local_addr: usize, len: usize) -> &[u8] {
-        &self.data[local_addr..][..len]
+    fn slice_from(&self, local_addr: usize) -> &[u8] {
+        &self.data[local_addr..]
+    }
+
+    fn slice_mut(&mut self, local_addr: usize, len: usize) -> &mut [u8] {
+        &mut self.data[local_addr..][..len]
     }
 
     fn allocate_space(&mut self, len: usize) -> Option<Addr> {
@@ -230,16 +188,6 @@ impl Page {
             None
         }
     }
-
-    #[inline(always)]
-    pub(crate) unsafe fn get_ptr(&self, addr: usize) -> *const u8 {
-        self.data.as_ptr().add(addr)
-    }
-
-    #[inline(always)]
-    pub(crate) unsafe fn get_mut_ptr(&mut self, addr: usize) -> *mut u8 {
-        self.data.as_mut_ptr().add(addr)
-    }
 }
 
 #[cfg(test)]
@@ -254,13 +202,13 @@ mod tests {
         let b = b"happy tax payer";
 
         let addr_a = arena.allocate_space(a.len());
-        arena.write_bytes(addr_a, a);
+        arena.slice_mut(addr_a, a.len()).copy_from_slice(a);
 
         let addr_b = arena.allocate_space(b.len());
-        arena.write_bytes(addr_b, b);
+        arena.slice_mut(addr_b, b.len()).copy_from_slice(b);
 
-        assert_eq!(arena.read_slice(addr_a, a.len()), a);
-        assert_eq!(arena.read_slice(addr_b, b.len()), b);
+        assert_eq!(arena.slice(addr_a, a.len()), a);
+        assert_eq!(arena.slice(addr_b, b.len()), b);
     }
 
     #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -283,9 +231,15 @@ mod tests {
             b: 221,
             c: 12,
         };
-        let addr_a = arena.store(a);
-        let addr_b = arena.store(b);
-        assert_eq!(unsafe { arena.read::<MyTest>(addr_a) }, a);
-        assert_eq!(unsafe { arena.read::<MyTest>(addr_b) }, b);
+
+        let num_bytes = std::mem::size_of::<MyTest>();
+        let addr_a = arena.allocate_space(num_bytes);
+        arena.write_at(addr_a, a);
+
+        let addr_b = arena.allocate_space(num_bytes);
+        arena.write_at(addr_b, b);
+
+        assert_eq!(arena.read::<MyTest>(addr_a), a);
+        assert_eq!(arena.read::<MyTest>(addr_b), b);
     }
 }

src/postings/stacker/mod.rs

@@ -1,9 +1,7 @@
 mod expull;
 mod memory_arena;
-mod murmurhash2;
 mod term_hashmap;
 
 pub use self::expull::ExpUnrolledLinkedList;
-pub use self::memory_arena::{Addr, ArenaStorable, MemoryArena};
-use self::murmurhash2::murmurhash2;
+pub use self::memory_arena::{Addr, MemoryArena};
 pub use self::term_hashmap::{compute_table_size, TermHashMap};

src/postings/stacker/murmurhash2.rs

@@ -1,87 +0,0 @@
-use std::ptr;
-const SEED: u32 = 3_242_157_231u32;
-const M: u32 = 0x5bd1_e995;
-
-#[inline(always)]
-pub fn murmurhash2(key: &[u8]) -> u32 {
-    #[cfg_attr(feature = "cargo-clippy", allow(clippy::cast_ptr_alignment))]
-    let mut key_ptr: *const u32 = key.as_ptr() as *const u32;
-    let len = key.len() as u32;
-    let mut h: u32 = SEED ^ len;
-
-    let num_blocks = len >> 2;
-    for _ in 0..num_blocks {
-        let mut k: u32 = unsafe { ptr::read_unaligned(key_ptr) }; // ok because of num_blocks definition
-        k = k.wrapping_mul(M);
-        k ^= k >> 24;
-        k = k.wrapping_mul(M);
-        h = h.wrapping_mul(M);
-        h ^= k;
-        key_ptr = key_ptr.wrapping_offset(1);
-    }
-
-    // Handle the last few bytes of the input array
-    let remaining: &[u8] = &key[key.len() & !3..];
-    match remaining.len() {
-        3 => {
-            h ^= u32::from(remaining[2]) << 16;
-            h ^= u32::from(remaining[1]) << 8;
-            h ^= u32::from(remaining[0]);
-            h = h.wrapping_mul(M);
-        }
-        2 => {
-            h ^= u32::from(remaining[1]) << 8;
-            h ^= u32::from(remaining[0]);
-            h = h.wrapping_mul(M);
-        }
-        1 => {
-            h ^= u32::from(remaining[0]);
-            h = h.wrapping_mul(M);
-        }
-        _ => {}
-    }
-    h ^= h >> 13;
-    h = h.wrapping_mul(M);
-    h ^ (h >> 15)
-}
-
-#[cfg(test)]
-mod test {
-
-    use super::murmurhash2;
-    use std::collections::HashSet;
-
-    #[test]
-    fn test_murmur() {
-        let s1 = "abcdef";
-        let s2 = "abcdeg";
-        for i in 0..5 {
-            assert_eq!(
-                murmurhash2(&s1[i..5].as_bytes()),
-                murmurhash2(&s2[i..5].as_bytes())
-            );
-        }
-    }
-
-    #[test]
-    fn test_murmur_against_reference_impl() {
-        assert_eq!(murmurhash2("".as_bytes()), 3632506080);
-        assert_eq!(murmurhash2("a".as_bytes()), 455683869);
-        assert_eq!(murmurhash2("ab".as_bytes()), 2448092234);
-        assert_eq!(murmurhash2("abc".as_bytes()), 2066295634);
-        assert_eq!(murmurhash2("abcd".as_bytes()), 2588571162);
-        assert_eq!(murmurhash2("abcde".as_bytes()), 2988696942);
-        assert_eq!(murmurhash2("abcdefghijklmnop".as_bytes()), 2350868870);
-    }
-
-    #[test]
-    fn test_murmur_collisions() {
-        let mut set: HashSet<u32> = HashSet::default();
-        for i in 0..10_000 {
-            let s = format!("hash{}", i);
-            let hash = murmurhash2(s.as_bytes());
-            set.insert(hash);
-        }
-        assert_eq!(set.len(), 10_000);
-    }
-}

src/postings/stacker/term_hashmap.rs

@@ -1,37 +1,16 @@
-use super::murmurhash2;
-use super::{Addr, ArenaStorable, MemoryArena};
+extern crate murmurhash32;
+
+use self::murmurhash32::murmurhash2;
+
+use super::{Addr, MemoryArena};
+use byteorder::{ByteOrder, NativeEndian};
+use postings::stacker::memory_arena::store;
 use std::iter;
 use std::mem;
 use std::slice;
 
 pub type BucketId = usize;
 
-struct KeyBytesValue<'a, V> {
-    key: &'a [u8],
-    value: V,
-}
-
-impl<'a, V> KeyBytesValue<'a, V> {
-    fn new(key: &'a [u8], value: V) -> KeyBytesValue<'a, V> {
-        KeyBytesValue { key, value }
-    }
-}
-
-impl<'a, V> ArenaStorable for KeyBytesValue<'a, V>
-where
-    V: ArenaStorable,
-{
-    fn num_bytes(&self) -> usize {
-        0u16.num_bytes() + self.key.len() + self.value.num_bytes()
-    }
-
-    unsafe fn write_into(self, arena: &mut MemoryArena, addr: Addr) {
-        arena.write(addr, self.key.len() as u16);
-        arena.write_bytes(addr.offset(2), self.key);
-        arena.write(addr.offset(2 + self.key.len() as u32), self.value);
-    }
-}
-
 /// Returns the actual memory size in bytes
 /// required to create a table of size $2^num_bits$.
 pub fn compute_table_size(num_bits: usize) -> usize {
@@ -111,8 +90,7 @@ impl<'a> Iterator for Iter<'a> {
     fn next(&mut self) -> Option<Self::Item> {
         self.inner.next().cloned().map(move |bucket: usize| {
             let kv = self.hashmap.table[bucket];
-            let (key, offset): (&'a [u8], Addr) =
-                unsafe { self.hashmap.get_key_value(kv.key_value_addr) };
+            let (key, offset): (&'a [u8], Addr) = self.hashmap.get_key_value(kv.key_value_addr);
             (key, offset, bucket as BucketId)
         })
     }
@@ -143,12 +121,22 @@ impl TermHashMap {
         self.table.len() < self.occupied.len() * 3
     }
 
-    unsafe fn get_key_value(&self, addr: Addr) -> (&[u8], Addr) {
-        let key_bytes_len = self.heap.read::<u16>(addr) as usize;
-        let key_addr = addr.offset(2u32);
-        let key_bytes: &[u8] = self.heap.read_slice(key_addr, key_bytes_len);
-        let val_addr: Addr = key_addr.offset(key_bytes.len() as u32);
-        (key_bytes, val_addr)
+    #[inline(always)]
+    fn get_key_value(&self, addr: Addr) -> (&[u8], Addr) {
+        let data = self.heap.slice_from(addr);
+        let key_bytes_len = NativeEndian::read_u16(data) as usize;
+        let key_bytes: &[u8] = &data[2..][..key_bytes_len];
+        (key_bytes, addr.offset(2u32 + key_bytes_len as u32))
+    }
+
+    #[inline(always)]
+    fn get_value_addr_if_key_match(&self, target_key: &[u8], addr: Addr) -> Option<Addr> {
+        let (stored_key, value_addr) = self.get_key_value(addr);
+        if stored_key == target_key {
+            Some(value_addr)
+        } else {
+            None
+        }
     }
 
     pub fn set_bucket(&mut self, hash: u32, key_value_addr: Addr, bucket: usize) {
@@ -199,36 +187,39 @@ impl TermHashMap {
     pub fn mutate_or_create<S, V, TMutator>(&mut self, key: S, mut updater: TMutator) -> BucketId
     where
         S: AsRef<[u8]>,
-        V: Copy,
+        V: Copy + 'static,
         TMutator: FnMut(Option<V>) -> V,
     {
         if self.is_saturated() {
             self.resize();
         }
         let key_bytes: &[u8] = key.as_ref();
-        let hash = murmurhash2::murmurhash2(key.as_ref());
+        let hash = murmurhash2(key.as_ref());
         let mut probe = self.probe(hash);
         loop {
             let bucket = probe.next_probe();
             let kv: KeyValue = self.table[bucket];
             if kv.is_empty() {
                 let val = updater(None);
-                let key_addr = self.heap.store(KeyBytesValue::new(key_bytes, val));
+                let num_bytes =
+                    std::mem::size_of::<u16>() + key_bytes.len() + std::mem::size_of::<V>();
+                let key_addr = self.heap.allocate_space(num_bytes);
+                {
+                    let data = self.heap.slice_mut(key_addr, num_bytes);
+                    NativeEndian::write_u16(data, key_bytes.len() as u16);
+                    let stop = 2 + key_bytes.len();
+                    data[2..stop].copy_from_slice(key_bytes);
+                    store(&mut data[stop..], val);
+                }
                 self.set_bucket(hash, key_addr, bucket);
                 return bucket as BucketId;
             } else if kv.hash == hash {
-                let (key_matches, val_addr) = {
-                    let (stored_key, val_addr): (&[u8], Addr) =
-                        unsafe { self.get_key_value(kv.key_value_addr) };
-                    (stored_key == key_bytes, val_addr)
-                };
-                if key_matches {
-                    unsafe {
-                        // logic
-                        let v = self.heap.read(val_addr);
-                        let new_v = updater(Some(v));
-                        self.heap.write(val_addr, new_v);
-                    };
+                if let Some(val_addr) =
+                    self.get_value_addr_if_key_match(key_bytes, kv.key_value_addr)
+                {
+                    let v = self.heap.read(val_addr);
+                    let new_v = updater(Some(v));
+                    self.heap.write_at(val_addr, new_v);
                     return bucket as BucketId;
                 }
             }
@@ -236,24 +227,6 @@ impl TermHashMap {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
-mod bench {
-    use super::murmurhash2::murmurhash2;
-    use test::Bencher;
-
-    #[bench]
-    fn bench_murmurhash2(b: &mut Bencher) {
-        let keys: [&'static str; 3] = ["wer qwe qwe qwe ", "werbq weqweqwe2 ", "weraq weqweqwe3 "];
-        b.iter(|| {
-            let mut s = 0;
-            for &key in &keys {
-                s ^= murmurhash2(key.as_bytes());
-            }
-            s
-        });
-    }
-}
-
 #[cfg(test)]
 mod tests {
 
@@ -285,10 +258,7 @@ mod tests {
         let mut vanilla_hash_map = HashMap::new();
         let mut iter_values = hash_map.iter();
         while let Some((key, addr, _)) = iter_values.next() {
-            let val: u32 = unsafe {
-                // test
-                hash_map.heap.read(addr)
-            };
+            let val: u32 = hash_map.heap.read(addr);
             vanilla_hash_map.insert(key.to_owned(), val);
         }
         assert_eq!(vanilla_hash_map.len(), 2);

src/query/all_query.rs

@@ -86,12 +86,12 @@ mod tests {
 
     use super::AllQuery;
     use query::Query;
-    use schema::{SchemaBuilder, TEXT};
+    use schema::{Schema, TEXT};
     use Index;
 
     #[test]
     fn test_all_query() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);

src/query/automaton_weight.rs

@@ -11,7 +11,7 @@ use Result;
 /// A weight struct for Fuzzy Term and Regex Queries
 pub struct AutomatonWeight<A>
 where
-    A: Automaton,
+    A: Automaton + Send + Sync + 'static,
 {
     field: Field,
     automaton: A,
@@ -19,7 +19,7 @@ where
 
 impl<A> AutomatonWeight<A>
 where
-    A: Automaton,
+    A: Automaton + Send + Sync + 'static,
 {
     /// Create a new AutomationWeight
     pub fn new(field: Field, automaton: A) -> AutomatonWeight<A> {
@@ -34,7 +34,7 @@ where
 
 impl<A> Weight for AutomatonWeight<A>
 where
-    A: Automaton,
+    A: Automaton + Send + Sync + 'static,
 {
     fn scorer(&self, reader: &SegmentReader) -> Result<Box<Scorer>> {
         let max_doc = reader.max_doc();

src/query/bm25.rs

@@ -63,7 +63,8 @@ impl BM25Weight {
             .map(|term| {
                 let term_doc_freq = searcher.doc_freq(term);
                 idf(term_doc_freq, total_num_docs)
-            }).sum::<f32>();
+            })
+            .sum::<f32>();
         BM25Weight::new(idf, average_fieldnorm)
     }
 

src/query/boolean_query/boolean_query.rs

@@ -47,7 +47,8 @@ impl Query for BooleanQuery {
             .iter()
             .map(|&(ref occur, ref subquery)| {
                 Ok((*occur, subquery.weight(searcher, scoring_enabled)?))
-            }).collect::<Result<_>>()?;
+            })
+            .collect::<Result<_>>()?;
         Ok(Box::new(BooleanWeight::new(sub_weights, scoring_enabled)))
     }
 
@@ -68,7 +69,8 @@ impl BooleanQuery {
                 let term_query: Box<Query> =
                     Box::new(TermQuery::new(term, IndexRecordOption::WithFreqs));
                 (Occur::Should, term_query)
-            }).collect();
+            })
+            .collect();
         BooleanQuery::from(occur_term_queries)
     }
 

src/query/boolean_query/boolean_weight.rs

@@ -1,5 +1,5 @@
 use core::SegmentReader;
-use downcast::Downcast;
+use downcast_rs::Downcast;
 use query::intersect_scorers;
 use query::score_combiner::{DoNothingCombiner, ScoreCombiner, SumWithCoordsCombiner};
 use query::term_query::TermScorer;
@@ -10,7 +10,6 @@ use query::RequiredOptionalScorer;
 use query::Scorer;
 use query::Union;
 use query::Weight;
-use std::borrow::Borrow;
 use std::collections::HashMap;
 use Result;
 
@@ -25,13 +24,12 @@ where
 
     {
         let is_all_term_queries = scorers.iter().all(|scorer| {
-            let scorer_ref: &Scorer = scorer.borrow();
-            Downcast::<TermScorer>::is_type(scorer_ref)
+            scorer.is::<TermScorer>()
         });
         if is_all_term_queries {
             let scorers: Vec<TermScorer> = scorers
                 .into_iter()
-                .map(|scorer| *Downcast::<TermScorer>::downcast(scorer).unwrap())
+                .map(|scorer| *(scorer.downcast::<TermScorer>().map_err(|_| ()).unwrap() ))
                 .collect();
             let scorer: Box<Scorer> = Box::new(Union::<TermScorer, TScoreCombiner>::from(scorers));
             return scorer;

src/query/boolean_query/mod.rs

@@ -8,7 +8,7 @@ mod tests {
 
     use super::*;
     use collector::tests::TestCollector;
-    use downcast::Downcast;
+    use downcast_rs::Downcast;
     use query::score_combiner::SumWithCoordsCombiner;
     use query::term_query::TermScorer;
     use query::Intersection;
@@ -19,16 +19,17 @@ mod tests {
     use query::Scorer;
     use query::TermQuery;
     use schema::*;
+    use DocId;
     use Index;
 
     fn aux_test_helper() -> (Index, Field) {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field => "a b c");
                 index_writer.add_document(doc);
@@ -71,7 +72,7 @@ mod tests {
         let searcher = index.searcher();
         let weight = query.weight(&searcher, true).unwrap();
         let scorer = weight.scorer(searcher.segment_reader(0u32)).unwrap();
-        assert!(Downcast::<TermScorer>::is_type(&*scorer));
+        assert!(scorer.is::<TermScorer>());
     }
 
     #[test]
@@ -83,13 +84,13 @@ mod tests {
             let query = query_parser.parse_query("+a +b +c").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
             let scorer = weight.scorer(searcher.segment_reader(0u32)).unwrap();
-            assert!(Downcast::<Intersection<TermScorer>>::is_type(&*scorer));
+            assert!(scorer.is::<Intersection<TermScorer>>());
         }
         {
             let query = query_parser.parse_query("+a +(b c)").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
             let scorer = weight.scorer(searcher.segment_reader(0u32)).unwrap();
-            assert!(Downcast::<Intersection<Box<Scorer>>>::is_type(&*scorer));
+            assert!(scorer.is::<Intersection<Box<Scorer>>>());
         }
     }
 
@@ -102,18 +103,16 @@ mod tests {
             let query = query_parser.parse_query("+a b").unwrap();
             let weight = query.weight(&searcher, true).unwrap();
             let scorer = weight.scorer(searcher.segment_reader(0u32)).unwrap();
-            assert!(Downcast::<
-                RequiredOptionalScorer<Box<Scorer>, Box<Scorer>, SumWithCoordsCombiner>,
-            >::is_type(&*scorer));
+            assert!(scorer.is::<RequiredOptionalScorer<Box<Scorer>, Box<Scorer>, SumWithCoordsCombiner>>());
         }
         {
             let query = query_parser.parse_query("+a b").unwrap();
             let weight = query.weight(&searcher, false).unwrap();
             let scorer = weight.scorer(searcher.segment_reader(0u32)).unwrap();
-            println!("{:?}", scorer.type_name());
-            assert!(Downcast::<TermScorer>::is_type(&*scorer));
+            assert!(scorer.is::<TermScorer>());
         }
-    }
+     }
+
 
     #[test]
     pub fn test_boolean_query() {
@@ -130,9 +129,13 @@ mod tests {
 
         let matching_docs = |boolean_query: &Query| {
             let searcher = index.searcher();
-            let mut test_collector = TestCollector::default();
-            searcher.search(boolean_query, &mut test_collector).unwrap();
-            test_collector.docs()
+            let test_docs = searcher.search(boolean_query, &TestCollector).unwrap();
+            test_docs
+                .docs()
+                .iter()
+                .cloned()
+                .map(|doc| doc.1)
+                .collect::<Vec<DocId>>()
         };
 
         {
@@ -186,9 +189,8 @@ mod tests {
 
         let score_docs = |boolean_query: &Query| {
             let searcher = index.searcher();
-            let mut test_collector = TestCollector::default();
-            searcher.search(boolean_query, &mut test_collector).unwrap();
-            test_collector.scores()
+            let fruit = searcher.search(boolean_query, &TestCollector).unwrap();
+            fruit.scores().to_vec()
         };
 
         {

src/query/fuzzy_query.rs

@@ -25,14 +25,14 @@ lazy_static! {
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
+/// use tantivy::schema::{Schema, TEXT};
 /// use tantivy::{Index, Result, Term};
-/// use tantivy::collector::{CountCollector, TopCollector, chain};
+/// use tantivy::collector::{Count, TopDocs};
 /// use tantivy::query::FuzzyTermQuery;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -57,16 +57,12 @@ lazy_static! {
 ///     let searcher = index.searcher();
 ///
 ///     {
-///         let mut top_collector = TopCollector::with_limit(2);
-///         let mut count_collector = CountCollector::default();
-///         {
-///             let mut collectors = chain().push(&mut top_collector).push(&mut count_collector);
-///             let term = Term::from_field_text(title, "Diary");
-///             let query = FuzzyTermQuery::new(term, 1, true);
-///             searcher.search(&query, &mut collectors).unwrap();
-///         }
-///         assert_eq!(count_collector.count(), 2);
-///         assert!(top_collector.at_capacity());
+///
+///         let term = Term::from_field_text(title, "Diary");
+///         let query = FuzzyTermQuery::new(term, 1, true);
+///         let (top_docs, count) = searcher.search(&query, &(TopDocs::with_limit(2), Count)).unwrap();
+///         assert_eq!(count, 2);
+///         assert_eq!(top_docs.len(), 2);
 ///     }
 ///
 ///     Ok(())
@@ -122,8 +118,8 @@ impl Query for FuzzyTermQuery {
 #[cfg(test)]
 mod test {
     use super::FuzzyTermQuery;
-    use collector::TopCollector;
-    use schema::SchemaBuilder;
+    use collector::TopDocs;
+    use schema::Schema;
     use schema::TEXT;
     use tests::assert_nearly_equals;
     use Index;
@@ -131,7 +127,7 @@ mod test {
 
     #[test]
     pub fn test_fuzzy_term() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let country_field = schema_builder.add_text_field("country", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -148,14 +144,14 @@ mod test {
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         {
-            let mut collector = TopCollector::with_limit(2);
             let term = Term::from_field_text(country_field, "japon");
 
             let fuzzy_query = FuzzyTermQuery::new(term, 1, true);
-            searcher.search(&fuzzy_query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
-            assert_eq!(scored_docs.len(), 1, "Expected only 1 document");
-            let (score, _) = scored_docs[0];
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 1, "Expected only 1 document");
+            let (score, _) = top_docs[0];
             assert_nearly_equals(1f32, score);
         }
     }

src/query/intersection.rs

@@ -1,11 +1,9 @@
 use docset::{DocSet, SkipResult};
-use downcast::Downcast;
-use query::term_query::TermScorer;
 use query::EmptyScorer;
 use query::Scorer;
-use std::borrow::Borrow;
 use DocId;
 use Score;
+use query::term_query::TermScorer;
 
 /// Returns the intersection scorer.
 ///
@@ -26,13 +24,12 @@ pub fn intersect_scorers(mut scorers: Vec<Box<Scorer>>) -> Box<Scorer> {
         (Some(single_docset), None) => single_docset,
         (Some(left), Some(right)) => {
             {
-                let all_term_scorers = [&left, &right].into_iter().all(|scorer| {
-                    let scorer_ref: &Scorer = (*scorer).borrow();
-                    Downcast::<TermScorer>::is_type(scorer_ref)
+                let all_term_scorers = [&left, &right].iter().all(|&scorer| {
+                    scorer.is::<TermScorer>()
                 });
                 if all_term_scorers {
-                    let left = *Downcast::<TermScorer>::downcast(left).unwrap();
-                    let right = *Downcast::<TermScorer>::downcast(right).unwrap();
+                    let left = *(left.downcast::<TermScorer>().map_err(|_| ()).unwrap());
+                    let right = *(right.downcast::<TermScorer>().map_err(|_| ()).unwrap());
                     return Box::new(Intersection {
                         left,
                         right,

src/query/mod.rs

@@ -56,15 +56,15 @@ pub use self::weight::Weight;
 
 #[cfg(test)]
 mod tests {
-    use Index;
-    use schema::{SchemaBuilder, TEXT};
     use query::QueryParser;
-    use Term;
+    use schema::{Schema, TEXT};
     use std::collections::BTreeSet;
+    use Index;
+    use Term;
 
     #[test]
     fn test_query_terms() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -73,33 +73,48 @@ mod tests {
         let term_b = Term::from_field_text(text_field, "b");
         {
             let mut terms_set: BTreeSet<Term> = BTreeSet::new();
-            query_parser.parse_query("a").unwrap().query_terms(&mut terms_set);
+            query_parser
+                .parse_query("a")
+                .unwrap()
+                .query_terms(&mut terms_set);
             let terms: Vec<&Term> = terms_set.iter().collect();
             assert_eq!(vec![&term_a], terms);
         }
         {
             let mut terms_set: BTreeSet<Term> = BTreeSet::new();
-            query_parser.parse_query("a b").unwrap().query_terms(&mut terms_set);
+            query_parser
+                .parse_query("a b")
+                .unwrap()
+                .query_terms(&mut terms_set);
             let terms: Vec<&Term> = terms_set.iter().collect();
             assert_eq!(vec![&term_a, &term_b], terms);
         }
         {
             let mut terms_set: BTreeSet<Term> = BTreeSet::new();
-            query_parser.parse_query("\"a b\"").unwrap().query_terms(&mut terms_set);
+            query_parser
+                .parse_query("\"a b\"")
+                .unwrap()
+                .query_terms(&mut terms_set);
             let terms: Vec<&Term> = terms_set.iter().collect();
             assert_eq!(vec![&term_a, &term_b], terms);
         }
         {
             let mut terms_set: BTreeSet<Term> = BTreeSet::new();
-            query_parser.parse_query("a a a a a").unwrap().query_terms(&mut terms_set);
+            query_parser
+                .parse_query("a a a a a")
+                .unwrap()
+                .query_terms(&mut terms_set);
             let terms: Vec<&Term> = terms_set.iter().collect();
             assert_eq!(vec![&term_a], terms);
         }
         {
             let mut terms_set: BTreeSet<Term> = BTreeSet::new();
-            query_parser.parse_query("a -b").unwrap().query_terms(&mut terms_set);
+            query_parser
+                .parse_query("a -b")
+                .unwrap()
+                .query_terms(&mut terms_set);
             let terms: Vec<&Term> = terms_set.iter().collect();
             assert_eq!(vec![&term_a, &term_b], terms);
         }
     }
-}
+}

src/query/phrase_query/mod.rs

@@ -13,16 +13,18 @@ mod tests {
     use collector::tests::TestCollector;
     use core::Index;
     use error::TantivyError;
-    use schema::{SchemaBuilder, Term, TEXT};
+    use schema::{Schema, Term, TEXT};
     use tests::assert_nearly_equals;
+    use DocAddress;
+    use DocId;
 
     fn create_index(texts: &[&'static str]) -> Index {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             for &text in texts {
                 let doc = doc!(text_field=>text);
                 index_writer.add_document(doc);
@@ -47,16 +49,19 @@ mod tests {
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         let test_query = |texts: Vec<&str>| {
-            let mut test_collector = TestCollector::default();
             let terms: Vec<Term> = texts
                 .iter()
                 .map(|text| Term::from_field_text(text_field, text))
                 .collect();
             let phrase_query = PhraseQuery::new(terms);
-            searcher
-                .search(&phrase_query, &mut test_collector)
+            let test_fruits = searcher
+                .search(&phrase_query, &TestCollector)
                 .expect("search should succeed");
-            test_collector.docs()
+            test_fruits
+                .docs()
+                .iter()
+                .map(|docaddr| docaddr.1)
+                .collect::<Vec<_>>()
         };
         assert_eq!(test_query(vec!["a", "b", "c"]), vec![2, 4]);
         assert_eq!(test_query(vec!["a", "b"]), vec![1, 2, 3, 4]);
@@ -67,7 +72,7 @@ mod tests {
 
     #[test]
     pub fn test_phrase_query_no_positions() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         use schema::IndexRecordOption;
         use schema::TextFieldIndexing;
         use schema::TextOptions;
@@ -81,7 +86,7 @@ mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer.add_document(doc!(text_field=>"a b c"));
             assert!(index_writer.commit().is_ok());
         }
@@ -91,9 +96,9 @@ mod tests {
             Term::from_field_text(text_field, "a"),
             Term::from_field_text(text_field, "b"),
         ]);
-        let mut test_collector = TestCollector::default();
         if let TantivyError::SchemaError(ref msg) = searcher
-            .search(&phrase_query, &mut test_collector)
+            .search(&phrase_query, &TestCollector)
+            .map(|_| ())
             .unwrap_err()
         {
             assert_eq!(
@@ -113,16 +118,16 @@ mod tests {
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         let test_query = |texts: Vec<&str>| {
-            let mut test_collector = TestCollector::default();
             let terms: Vec<Term> = texts
                 .iter()
                 .map(|text| Term::from_field_text(text_field, text))
                 .collect();
             let phrase_query = PhraseQuery::new(terms);
             searcher
-                .search(&phrase_query, &mut test_collector)
-                .expect("search should succeed");
-            test_collector.scores()
+                .search(&phrase_query, &TestCollector)
+                .expect("search should succeed")
+                .scores()
+                .to_vec()
         };
         let scores = test_query(vec!["a", "b"]);
         assert_nearly_equals(scores[0], 0.40618482);
@@ -131,72 +136,62 @@ mod tests {
 
     #[test] // motivated by #234
     pub fn test_phrase_query_docfreq_order() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
-            {
-                // 0
-                let doc = doc!(text_field=>"b");
-                index_writer.add_document(doc);
-            }
-            {
-                // 1
-                let doc = doc!(text_field=>"a b");
-                index_writer.add_document(doc);
-            }
-            {
-                // 2
-                let doc = doc!(text_field=>"b a");
-                index_writer.add_document(doc);
-            }
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            index_writer.add_document(doc!(text_field=>"b"));
+            index_writer.add_document(doc!(text_field=>"a b"));
+            index_writer.add_document(doc!(text_field=>"b a"));
             assert!(index_writer.commit().is_ok());
         }
 
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         let test_query = |texts: Vec<&str>| {
-            let mut test_collector = TestCollector::default();
             let terms: Vec<Term> = texts
                 .iter()
                 .map(|text| Term::from_field_text(text_field, text))
                 .collect();
             let phrase_query = PhraseQuery::new(terms);
             searcher
-                .search(&phrase_query, &mut test_collector)
-                .expect("search should succeed");
-            test_collector.docs()
+                .search(&phrase_query, &TestCollector)
+                .expect("search should succeed")
+                .docs()
+                .to_vec()
         };
-        assert_eq!(test_query(vec!["a", "b"]), vec![1]);
-        assert_eq!(test_query(vec!["b", "a"]), vec![2]);
+        assert_eq!(test_query(vec!["a", "b"]), vec![DocAddress(0, 1)]);
+        assert_eq!(test_query(vec!["b", "a"]), vec![DocAddress(0, 2)]);
     }
 
     #[test] // motivated by #234
     pub fn test_phrase_query_non_trivial_offsets() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             index_writer.add_document(doc!(text_field=>"a b c d e f g h"));
             assert!(index_writer.commit().is_ok());
         }
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         let test_query = |texts: Vec<(usize, &str)>| {
-            let mut test_collector = TestCollector::default();
             let terms: Vec<(usize, Term)> = texts
                 .iter()
                 .map(|(offset, text)| (*offset, Term::from_field_text(text_field, text)))
                 .collect();
             let phrase_query = PhraseQuery::new_with_offset(terms);
             searcher
-                .search(&phrase_query, &mut test_collector)
-                .expect("search should succeed");
-            test_collector.docs()
+                .search(&phrase_query, &TestCollector)
+                .expect("search should succeed")
+                .docs()
+                .iter()
+                .map(|doc_address| doc_address.1)
+                .collect::<Vec<DocId>>()
         };
         assert_eq!(test_query(vec![(0, "a"), (1, "b")]), vec![0]);
         assert_eq!(test_query(vec![(1, "b"), (0, "a")]), vec![0]);

src/query/phrase_query/phrase_scorer.rs

@@ -134,7 +134,8 @@ impl<TPostings: Postings> PhraseScorer<TPostings> {
             .into_iter()
             .map(|(offset, postings)| {
                 PostingsWithOffset::new(postings, (max_offset - offset) as u32)
-            }).collect::<Vec<_>>();
+            })
+            .collect::<Vec<_>>();
         PhraseScorer {
             intersection_docset: Intersection::new(postings_with_offsets),
             num_docsets,

src/query/query.rs

@@ -1,11 +1,9 @@
 use super::Weight;
-use collector::Collector;
 use core::searcher::Searcher;
-use downcast;
+use downcast_rs;
 use std::collections::BTreeSet;
 use std::fmt;
 use Result;
-use SegmentLocalId;
 use Term;
 
 /// The `Query` trait defines a set of documents and a scoring method
@@ -41,7 +39,7 @@ use Term;
 ///
 /// When implementing a new type of `Query`, it is normal to implement a
 /// dedicated `Query`, `Weight` and `Scorer`.
-pub trait Query: QueryClone + downcast::Any + fmt::Debug {
+pub trait Query: QueryClone + downcast_rs::Downcast + fmt::Debug {
     /// Create the weight associated to a query.
     ///
     /// If scoring is not required, setting `scoring_enabled` to `false`
@@ -63,26 +61,6 @@ pub trait Query: QueryClone + downcast::Any + fmt::Debug {
     /// Extract all of the terms associated to the query and insert them in the
     /// term set given in arguments.
     fn query_terms(&self, _term_set: &mut BTreeSet<Term>) {}
-
-    /// Search works as follows :
-    ///
-    /// First the weight object associated to the query is created.
-    ///
-    /// Then, the query loops over the segments and for each segment :
-    /// - setup the collector and informs it that the segment being processed has changed.
-    /// - creates a `Scorer` object associated for this segment
-    /// - iterate throw the matched documents and push them to the collector.
-    ///
-    fn search(&self, searcher: &Searcher, collector: &mut Collector) -> Result<()> {
-        let scoring_enabled = collector.requires_scoring();
-        let weight = self.weight(searcher, scoring_enabled)?;
-        for (segment_ord, segment_reader) in searcher.segment_readers().iter().enumerate() {
-            collector.set_segment(segment_ord as SegmentLocalId, segment_reader)?;
-            let mut scorer = weight.scorer(segment_reader)?;
-            scorer.collect(collector, segment_reader.delete_bitset());
-        }
-        Ok(())
-    }
 }
 
 pub trait QueryClone {
@@ -98,7 +76,24 @@ where
     }
 }
 
-#[allow(missing_docs)]
-mod downcast_impl {
-    downcast!(super::Query);
+impl Query for Box<Query> {
+    fn weight(&self, searcher: &Searcher, scoring_enabled: bool) -> Result<Box<Weight>> {
+        self.as_ref().weight(searcher, scoring_enabled)
+    }
+
+    fn count(&self, searcher: &Searcher) -> Result<usize> {
+        self.as_ref().count(searcher)
+    }
+
+    fn query_terms(&self, term_set: &mut BTreeSet<Term<Vec<u8>>>) {
+        self.as_ref().query_terms(term_set);
+    }
 }
+
+impl QueryClone for Box<Query> {
+    fn box_clone(&self) -> Box<Query> {
+        self.as_ref().box_clone()
+    }
+}
+
+impl_downcast!(Query);

src/query/query_parser/query_parser.rs

@@ -68,7 +68,8 @@ fn trim_ast(logical_ast: LogicalAST) -> Option<LogicalAST> {
                 .into_iter()
                 .flat_map(|(occur, child)| {
                     trim_ast(child).map(|trimmed_child| (occur, trimmed_child))
-                }).collect::<Vec<_>>();
+                })
+                .collect::<Vec<_>>();
             if trimmed_children.is_empty() {
                 None
             } else {
@@ -128,6 +129,7 @@ fn trim_ast(logical_ast: LogicalAST) -> Option<LogicalAST> {
 ///
 /// *  all docs query: A plain `*` will match all documents in the index.
 ///
+#[derive(Clone)]
 pub struct QueryParser {
     schema: Schema,
     default_fields: Vec<Field>,
@@ -421,7 +423,8 @@ impl QueryParser {
                             lower: self.resolve_bound(field, &lower)?,
                             upper: self.resolve_bound(field, &upper)?,
                         })))
-                    }).collect::<Result<Vec<_>, QueryParserError>>()?;
+                    })
+                    .collect::<Result<Vec<_>, QueryParserError>>()?;
                 let result_ast = if clauses.len() == 1 {
                     clauses.pop().unwrap()
                 } else {
@@ -484,12 +487,12 @@ mod test {
     use query::Query;
     use schema::Field;
     use schema::{IndexRecordOption, TextFieldIndexing, TextOptions};
-    use schema::{SchemaBuilder, Term, INT_INDEXED, STORED, STRING, TEXT};
+    use schema::{Schema, Term, INT_INDEXED, STORED, STRING, TEXT};
     use tokenizer::{LowerCaser, SimpleTokenizer, StopWordFilter, Tokenizer, TokenizerManager};
     use Index;
 
     fn make_query_parser() -> QueryParser {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field_indexing = TextFieldIndexing::default()
             .set_tokenizer("en_with_stop_words")
             .set_index_option(IndexRecordOption::WithFreqsAndPositions);
@@ -597,25 +600,19 @@ mod test {
         assert!(query_parser.parse_query("signed:2324").is_ok());
         assert!(query_parser.parse_query("signed:\"22\"").is_ok());
         assert!(query_parser.parse_query("signed:\"-2234\"").is_ok());
-        assert!(
-            query_parser
-                .parse_query("signed:\"-9999999999999\"")
-                .is_ok()
-        );
+        assert!(query_parser
+            .parse_query("signed:\"-9999999999999\"")
+            .is_ok());
         assert!(query_parser.parse_query("signed:\"a\"").is_err());
         assert!(query_parser.parse_query("signed:\"2a\"").is_err());
-        assert!(
-            query_parser
-                .parse_query("signed:\"18446744073709551615\"")
-                .is_err()
-        );
+        assert!(query_parser
+            .parse_query("signed:\"18446744073709551615\"")
+            .is_err());
         assert!(query_parser.parse_query("unsigned:\"2\"").is_ok());
         assert!(query_parser.parse_query("unsigned:\"-2\"").is_err());
-        assert!(
-            query_parser
-                .parse_query("unsigned:\"18446744073709551615\"")
-                .is_ok()
-        );
+        assert!(query_parser
+            .parse_query("unsigned:\"18446744073709551615\"")
+            .is_ok());
         test_parse_query_to_logical_ast_helper(
             "unsigned:2324",
             "Term([0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 9, 20])",
@@ -720,7 +717,7 @@ mod test {
 
     #[test]
     pub fn test_unknown_tokenizer() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field_indexing = TextFieldIndexing::default()
             .set_tokenizer("nonexistingtokenizer")
             .set_index_option(IndexRecordOption::Basic);
@@ -738,7 +735,7 @@ mod test {
 
     #[test]
     pub fn test_query_parser_no_positions() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field_indexing = TextFieldIndexing::default()
             .set_tokenizer("customtokenizer")
             .set_index_option(IndexRecordOption::Basic);

src/query/range_query.rs

@@ -40,14 +40,13 @@ fn map_bound<TFrom, TTo, Transform: Fn(&TFrom) -> TTo>(
 /// # #[macro_use]
 /// # extern crate tantivy;
 /// # use tantivy::Index;
-/// # use tantivy::schema::{SchemaBuilder, INT_INDEXED};
-/// # use tantivy::collector::CountCollector;
-/// # use tantivy::query::Query;
+/// # use tantivy::schema::{Schema, INT_INDEXED};
+/// # use tantivy::collector::Count;
 /// # use tantivy::Result;
 /// # use tantivy::query::RangeQuery;
 /// #
 /// # fn run() -> Result<()> {
-/// #     let mut schema_builder = SchemaBuilder::new();
+/// #     let mut schema_builder = Schema::builder();
 /// #     let year_field = schema_builder.add_u64_field("year", INT_INDEXED);
 /// #     let schema = schema_builder.build();
 /// #
@@ -67,10 +66,7 @@ fn map_bound<TFrom, TTo, Transform: Fn(&TFrom) -> TTo>(
 ///
 /// let docs_in_the_sixties = RangeQuery::new_u64(year_field, 1960..1970);
 ///
-/// let mut count_collector = CountCollector::default();
-/// docs_in_the_sixties.search(&searcher, &mut count_collector)?;
-///
-/// let num_60s_books = count_collector.count();
+/// let num_60s_books = searcher.search(&docs_in_the_sixties, &Count)?;
 ///
 /// #     assert_eq!(num_60s_books, 2285);
 /// #     Ok(())
@@ -296,9 +292,8 @@ impl Weight for RangeWeight {
 mod tests {
 
     use super::RangeQuery;
-    use collector::CountCollector;
-    use query::Query;
-    use schema::{Document, Field, SchemaBuilder, INT_INDEXED};
+    use collector::Count;
+    use schema::{Document, Field, Schema, INT_INDEXED};
     use std::collections::Bound;
     use Index;
     use Result;
@@ -306,7 +301,7 @@ mod tests {
     #[test]
     fn test_range_query_simple() {
         fn run() -> Result<()> {
-            let mut schema_builder = SchemaBuilder::new();
+            let mut schema_builder = Schema::builder();
             let year_field = schema_builder.add_u64_field("year", INT_INDEXED);
             let schema = schema_builder.build();
 
@@ -327,9 +322,8 @@ mod tests {
             let docs_in_the_sixties = RangeQuery::new_u64(year_field, 1960u64..1970u64);
 
             // ... or `1960..=1969` if inclusive range is enabled.
-            let mut count_collector = CountCollector::default();
-            docs_in_the_sixties.search(&searcher, &mut count_collector)?;
-            assert_eq!(count_collector.count(), 2285);
+            let count = searcher.search(&docs_in_the_sixties, &Count)?;
+            assert_eq!(count, 2285);
             Ok(())
         }
 
@@ -340,7 +334,7 @@ mod tests {
     fn test_range_query() {
         let int_field: Field;
         let schema = {
-            let mut schema_builder = SchemaBuilder::new();
+            let mut schema_builder = Schema::builder();
             int_field = schema_builder.add_i64_field("intfield", INT_INDEXED);
             schema_builder.build()
         };
@@ -363,11 +357,8 @@ mod tests {
         }
         index.load_searchers().unwrap();
         let searcher = index.searcher();
-        let count_multiples = |range_query: RangeQuery| {
-            let mut count_collector = CountCollector::default();
-            range_query.search(&searcher, &mut count_collector).unwrap();
-            count_collector.count()
-        };
+        let count_multiples =
+            |range_query: RangeQuery| searcher.search(&range_query, &Count).unwrap();
 
         assert_eq!(count_multiples(RangeQuery::new_i64(int_field, 10..11)), 9);
         assert_eq!(

src/query/regex_query.rs

@@ -16,14 +16,14 @@ use Searcher;
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT};
+/// use tantivy::schema::{Schema, TEXT};
 /// use tantivy::{Index, Result, Term};
-/// use tantivy::collector::{CountCollector, TopCollector, chain};
+/// use tantivy::collector::Count;
 /// use tantivy::query::RegexQuery;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -47,19 +47,10 @@ use Searcher;
 ///     index.load_searchers()?;
 ///     let searcher = index.searcher();
 ///
-///     {
-///         let mut top_collector = TopCollector::with_limit(2);
-///         let mut count_collector = CountCollector::default();
-///         {
-///             let mut collectors = chain().push(&mut top_collector).push(&mut count_collector);
-///             let term = Term::from_field_text(title, "Diary");
-///             let query = RegexQuery::new("d[ai]{2}ry".to_string(), title);
-///             searcher.search(&query, &mut collectors).unwrap();
-///         }
-///         assert_eq!(count_collector.count(), 3);
-///         assert!(top_collector.at_capacity());
-///     }
-///
+///     let term = Term::from_field_text(title, "Diary");
+///     let query = RegexQuery::new("d[ai]{2}ry".to_string(), title);
+///     let count = searcher.search(&query, &Count)?;
+///     assert_eq!(count, 3);
 ///     Ok(())
 /// }
 /// ```
@@ -95,15 +86,15 @@ impl Query for RegexQuery {
 #[cfg(test)]
 mod test {
     use super::RegexQuery;
-    use collector::TopCollector;
-    use schema::SchemaBuilder;
+    use collector::TopDocs;
+    use schema::Schema;
     use schema::TEXT;
     use tests::assert_nearly_equals;
     use Index;
 
     #[test]
     pub fn test_regex_query() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let country_field = schema_builder.add_text_field("country", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
@@ -120,20 +111,18 @@ mod test {
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         {
-            let mut collector = TopCollector::with_limit(2);
             let regex_query = RegexQuery::new("jap[ao]n".to_string(), country_field);
-            searcher.search(&regex_query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
+            let scored_docs = searcher
+                .search(&regex_query, &TopDocs::with_limit(2))
+                .unwrap();
             assert_eq!(scored_docs.len(), 1, "Expected only 1 document");
             let (score, _) = scored_docs[0];
             assert_nearly_equals(1f32, score);
         }
-        {
-            let mut collector = TopCollector::with_limit(2);
-            let regex_query = RegexQuery::new("jap[A-Z]n".to_string(), country_field);
-            searcher.search(&regex_query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
-            assert_eq!(scored_docs.len(), 0, "Expected ZERO document");
-        }
+        let regex_query = RegexQuery::new("jap[A-Z]n".to_string(), country_field);
+        let top_docs = searcher
+            .search(&regex_query, &TopDocs::with_limit(2))
+            .unwrap();
+        assert!(top_docs.is_empty(), "Expected ZERO document");
     }
 }

src/query/scorer.rs

@@ -1,8 +1,6 @@
-use collector::Collector;
 use common::BitSet;
 use docset::{DocSet, SkipResult};
-use downcast;
-use fastfield::DeleteBitSet;
+use downcast_rs;
 use std::ops::DerefMut;
 use DocId;
 use Score;
@@ -10,43 +8,32 @@ use Score;
 /// Scored set of documents matching a query within a specific segment.
 ///
 /// See [`Query`](./trait.Query.html).
-pub trait Scorer: downcast::Any + DocSet + 'static {
+pub trait Scorer: downcast_rs::Downcast + DocSet + 'static {
     /// Returns the score.
     ///
     /// This method will perform a bit of computation and is not cached.
     fn score(&mut self) -> Score;
 
-    /// Consumes the complete `DocSet` and
-    /// push the scored documents to the collector.
-    fn collect(&mut self, collector: &mut Collector, delete_bitset_opt: Option<&DeleteBitSet>) {
-        if let Some(delete_bitset) = delete_bitset_opt {
-            while self.advance() {
-                let doc = self.doc();
-                if !delete_bitset.is_deleted(doc) {
-                    collector.collect(doc, self.score());
-                }
-            }
-        } else {
-            while self.advance() {
-                collector.collect(self.doc(), self.score());
-            }
+    /// Iterates through all of the document matched by the DocSet
+    /// `DocSet` and push the scored documents to the collector.
+    fn for_each(&mut self, callback: &mut FnMut(DocId, Score)) {
+        while self.advance() {
+            callback(self.doc(), self.score());
         }
     }
 }
 
-#[allow(missing_docs)]
-mod downcast_impl {
-    downcast!(super::Scorer);
-}
+impl_downcast!(Scorer);
+
 
 impl Scorer for Box<Scorer> {
     fn score(&mut self) -> Score {
         self.deref_mut().score()
     }
 
-    fn collect(&mut self, collector: &mut Collector, delete_bitset: Option<&DeleteBitSet>) {
+    fn for_each(&mut self, callback: &mut FnMut(DocId, Score)) {
         let scorer = self.deref_mut();
-        scorer.collect(collector, delete_bitset);
+        scorer.for_each(callback);
     }
 }
 

src/query/term_query/mod.rs

@@ -9,23 +9,23 @@ pub use self::term_weight::TermWeight;
 #[cfg(test)]
 mod tests {
 
-    use collector::TopCollector;
+    use collector::TopDocs;
     use docset::DocSet;
     use query::{Query, QueryParser, Scorer, TermQuery};
-    use schema::{IndexRecordOption, SchemaBuilder, STRING, TEXT};
+    use schema::{IndexRecordOption, Schema, STRING, TEXT};
     use tests::assert_nearly_equals;
     use Index;
     use Term;
 
     #[test]
     pub fn test_term_query_no_freq() {
-        let mut schema_builder = SchemaBuilder::default();
+        let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", STRING);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
             {
                 let doc = doc!(text_field => "a");
                 index_writer.add_document(doc);
@@ -49,7 +49,7 @@ mod tests {
 
     #[test]
     pub fn test_term_weight() {
-        let mut schema_builder = SchemaBuilder::new();
+        let mut schema_builder = Schema::builder();
         let left_field = schema_builder.add_text_field("left", TEXT);
         let right_field = schema_builder.add_text_field("right", TEXT);
         let large_field = schema_builder.add_text_field("large", TEXT);
@@ -68,37 +68,35 @@ mod tests {
         index.load_searchers().unwrap();
         let searcher = index.searcher();
         {
-            let mut collector = TopCollector::with_limit(2);
             let term = Term::from_field_text(left_field, "left2");
             let term_query = TermQuery::new(term, IndexRecordOption::WithFreqs);
-            searcher.search(&term_query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
-            assert_eq!(scored_docs.len(), 1);
-            let (score, _) = scored_docs[0];
+            let topdocs = searcher
+                .search(&term_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(topdocs.len(), 1);
+            let (score, _) = topdocs[0];
             assert_nearly_equals(0.77802235, score);
         }
         {
-            let mut collector = TopCollector::with_limit(2);
             let term = Term::from_field_text(left_field, "left1");
             let term_query = TermQuery::new(term, IndexRecordOption::WithFreqs);
-            searcher.search(&term_query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
-            assert_eq!(scored_docs.len(), 2);
-            let (score1, _) = scored_docs[0];
+            let top_docs = searcher
+                .search(&term_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 2);
+            let (score1, _) = top_docs[0];
             assert_nearly_equals(0.27101856, score1);
-            let (score2, _) = scored_docs[1];
+            let (score2, _) = top_docs[1];
             assert_nearly_equals(0.13736556, score2);
         }
         {
             let query_parser = QueryParser::for_index(&index, vec![]);
             let query = query_parser.parse_query("left:left2 left:left1").unwrap();
-            let mut collector = TopCollector::with_limit(2);
-            searcher.search(&*query, &mut collector).unwrap();
-            let scored_docs = collector.top_docs();
-            assert_eq!(scored_docs.len(), 2);
-            let (score1, _) = scored_docs[0];
+            let top_docs = searcher.search(&query, &TopDocs::with_limit(2)).unwrap();
+            assert_eq!(top_docs.len(), 2);
+            let (score1, _) = top_docs[0];
             assert_nearly_equals(0.9153879, score1);
-            let (score2, _) = scored_docs[1];
+            let (score2, _) = top_docs[1];
             assert_nearly_equals(0.27101856, score2);
         }
     }

src/query/term_query/term_query.rs

@@ -21,14 +21,14 @@ use Term;
 /// ```rust
 /// #[macro_use]
 /// extern crate tantivy;
-/// use tantivy::schema::{SchemaBuilder, TEXT, IndexRecordOption};
+/// use tantivy::schema::{Schema, TEXT, IndexRecordOption};
 /// use tantivy::{Index, Result, Term};
-/// use tantivy::collector::{CountCollector, TopCollector, chain};
+/// use tantivy::collector::{Count, TopDocs};
 /// use tantivy::query::TermQuery;
 ///
 /// # fn main() { example().unwrap(); }
 /// fn example() -> Result<()> {
-///     let mut schema_builder = SchemaBuilder::new();
+///     let mut schema_builder = Schema::builder();
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -52,20 +52,12 @@ use Term;
 ///     index.load_searchers()?;
 ///     let searcher = index.searcher();
 ///
-///     {
-///         let mut top_collector = TopCollector::with_limit(2);
-///         let mut count_collector = CountCollector::default();
-///         {
-///             let mut collectors = chain().push(&mut top_collector).push(&mut count_collector);
-///             let query = TermQuery::new(
-///                 Term::from_field_text(title, "diary"),
-///                 IndexRecordOption::Basic,
-///             );
-///             searcher.search(&query, &mut collectors).unwrap();
-///         }
-///         assert_eq!(count_collector.count(), 2);
-///         assert!(top_collector.at_capacity());
-///     }
+///     let query = TermQuery::new(
+///         Term::from_field_text(title, "diary"),
+///         IndexRecordOption::Basic,
+///     );
+///     let (top_docs, count) = searcher.search(&query, &(TopDocs::with_limit(2), Count)).unwrap();
+///     assert_eq!(count, 2);
 ///
 ///     Ok(())
 /// }

src/query/union.rs

@@ -55,7 +55,8 @@ where
                         None
                     }
                 },
-            ).collect();
+            )
+            .collect();
         Union {
             docsets: non_empty_docsets,
             bitsets: Box::new([TinySet::empty(); HORIZON_NUM_TINYBITSETS]),
@@ -214,10 +215,7 @@ where
 
             // The target is outside of the buffered horizon.
             // advance all docsets to a doc >= to the target.
-            #[cfg_attr(
-                feature = "cargo-clippy",
-                allow(clippy::clippy::collapsible_if)
-            )]
+            #[cfg_attr(feature = "cargo-clippy", allow(clippy::clippy::collapsible_if))]
             unordered_drain_filter(&mut self.docsets, |docset| {
                 if docset.doc() < target {
                     if docset.skip_next(target) == SkipResult::End {