issue/54 Clone segment reader rather than reload.

Closes #54.

src/core/index.rs

@@ -202,16 +202,13 @@ impl Index {
     /// published or after a merge.
     pub fn load_searchers(&self) -> Result<()> {
         let searchable_segments = self.searchable_segments()?;
-        let mut searchers = Vec::new();
-        for _ in 0..NUM_SEARCHERS {
-            let searchable_segments_clone = searchable_segments.clone();
-            let segment_readers: Vec<SegmentReader> = try!(searchable_segments_clone
+        let segment_readers: Vec<SegmentReader> = try!(searchable_segments
                 .into_iter()
                 .map(SegmentReader::open)
                 .collect());
-            let searcher = Searcher::from(segment_readers);
-            searchers.push(searcher);
-        }
+        let searchers = (0..NUM_SEARCHERS)
+            .map(|_| Searcher::from(segment_readers.clone()))
+            .collect();
         self.searcher_pool.publish_new_generation(searchers);
         Ok(())
     }

src/core/segment_reader.rs

@@ -12,6 +12,7 @@ use DocId;
 use std::str;
 use postings::TermInfo;
 use datastruct::FstMap;
+use std::sync::Arc;
 use std::fmt;
 use rustc_serialize::json;
 use core::SegmentInfo;
@@ -37,14 +38,15 @@ use error::Error;
 /// The segment reader has a very low memory footprint,
 /// as close to all of the memory data is mmapped.
 ///
+#[derive(Clone)]
 pub struct SegmentReader {
     segment_info: SegmentInfo,
     segment_id: SegmentId,
-    term_infos: FstMap<TermInfo>,
+    term_infos: Arc<FstMap<TermInfo>>,
     postings_data: ReadOnlySource,
     store_reader: StoreReader,
-    fast_fields_reader: U32FastFieldsReader,
-    fieldnorms_reader: U32FastFieldsReader,
+    fast_fields_reader: Arc<U32FastFieldsReader>,
+    fieldnorms_reader: Arc<U32FastFieldsReader>,
     delete_bitset: DeleteBitSet,
     positions_data: ReadOnlySource,
     schema: Schema,
@@ -171,11 +173,11 @@ impl SegmentReader {
         Ok(SegmentReader {
             segment_info: segment_info,
             postings_data: postings_shared_mmap,
-            term_infos: term_infos,
+            term_infos: Arc::new(term_infos),
             segment_id: segment.id(),
             store_reader: store_reader,
-            fast_fields_reader: fast_fields_reader,
-            fieldnorms_reader: fieldnorms_reader,
+            fast_fields_reader: Arc::new(fast_fields_reader),
+            fieldnorms_reader: Arc::new(fieldnorms_reader),
             delete_bitset: delete_bitset,
             positions_data: positions_data,
             schema: schema,

src/store/reader.rs

@@ -11,6 +11,7 @@ use std::io::{self, Read};
 use datastruct::SkipList;
 use lz4;
 
+#[derive(Clone)]
 pub struct StoreReader {
     pub data: ReadOnlySource,
     pub offset_index_source: ReadOnlySource,