Prepare commit is public again (#1202)

- Simplified some of the prepare commit & segment updater code using
async.
- Made PrepareCommit public again.

src/indexer/index_writer.rs

@@ -465,10 +465,8 @@ impl IndexWriter {
     }
 
     /// Detects and removes the files that are not used by the index anymore.
-    pub fn garbage_collect_files(
-        &self,
-    ) -> impl Future<Output = crate::Result<GarbageCollectionResult>> {
-        self.segment_updater.schedule_garbage_collect()
+    pub async fn garbage_collect_files(&self) -> crate::Result<GarbageCollectionResult> {
+        self.segment_updater.schedule_garbage_collect().await
     }
 
     /// Deletes all documents from the index
@@ -607,7 +605,7 @@ impl IndexWriter {
     /// It is also possible to add a payload to the `commit`
     /// using this API.
     /// See [`PreparedCommit::set_payload()`](PreparedCommit.html)
-    pub(crate) fn prepare_commit(&mut self) -> crate::Result<PreparedCommit> {
+    pub fn prepare_commit(&mut self) -> crate::Result<PreparedCommit> {
         // Here, because we join all of the worker threads,
         // all of the segment update for this commit have been
         // sent.

src/indexer/mod.rs

@@ -29,7 +29,7 @@ pub use self::index_writer::IndexWriter;
 pub use self::log_merge_policy::LogMergePolicy;
 pub use self::merge_operation::MergeOperation;
 pub use self::merge_policy::{MergeCandidate, MergePolicy, NoMergePolicy};
-pub(crate) use self::prepared_commit::PreparedCommit;
+pub use self::prepared_commit::PreparedCommit;
 pub use self::segment_entry::SegmentEntry;
 pub use self::segment_manager::SegmentManager;
 pub use self::segment_serializer::SegmentSerializer;

src/indexer/prepared_commit.rs

@@ -3,7 +3,7 @@ use crate::Opstamp;
 use futures::executor::block_on;
 
 /// A prepared commit
-pub(crate) struct PreparedCommit<'a> {
+pub struct PreparedCommit<'a> {
     index_writer: &'a mut IndexWriter,
     payload: Option<String>,
     opstamp: Opstamp,
@@ -18,25 +18,38 @@ impl<'a> PreparedCommit<'a> {
         }
     }
 
-    pub(crate) fn opstamp(&self) -> Opstamp {
+    /// Returns the opstamp associated to the prepared commit.
+    pub fn opstamp(&self) -> Opstamp {
         self.opstamp
     }
 
-    pub(crate) fn set_payload(&mut self, payload: &str) {
+    /// Adds an arbitrary payload to the commit.
+    pub fn set_payload(&mut self, payload: &str) {
         self.payload = Some(payload.to_string())
     }
 
-    pub(crate) fn abort(self) -> crate::Result<Opstamp> {
+    /// Rollbacks any change.
+    pub fn abort(self) -> crate::Result<Opstamp> {
         self.index_writer.rollback()
     }
 
-    pub(crate) fn commit(self) -> crate::Result<Opstamp> {
+    /// Proceeds to commit.
+    /// See `.commit_async()`.
+    pub fn commit(self) -> crate::Result<Opstamp> {
+        block_on(self.commit_async())
+    }
+
+    /// Proceeds to commit.
+    ///
+    /// Unfortunately, contrary to what `PrepareCommit` may suggests,
+    /// this operation is not at all really light.
+    /// At this point deletes have not been flushed yet.
+    pub async fn commit_async(self) -> crate::Result<Opstamp> {
         info!("committing {}", self.opstamp);
-        block_on(
-            self.index_writer
-                .segment_updater()
-                .schedule_commit(self.opstamp, self.payload),
-        )?;
+        self.index_writer
+            .segment_updater()
+            .schedule_commit(self.opstamp, self.payload)
+            .await?;
         Ok(self.opstamp)
     }
 }

src/indexer/segment_updater.rs

@@ -351,37 +351,39 @@ impl SegmentUpdater {
         *self.merge_policy.write().unwrap() = arc_merge_policy;
     }
 
-    fn schedule_future<T: 'static + Send, F: Future<Output = crate::Result<T>> + 'static + Send>(
+    async fn schedule_task<
+        T: 'static + Send,
+        F: Future<Output = crate::Result<T>> + 'static + Send,
+    >(
         &self,
-        f: F,
-    ) -> impl Future<Output = crate::Result<T>> {
-        let (sender, receiver) = oneshot::channel();
-        if self.is_alive() {
-            self.pool.spawn_ok(async move {
-                let _ = sender.send(f.await);
-            });
-        } else {
-            let _ = sender.send(Err(crate::TantivyError::SystemError(
+        task: F,
+    ) -> crate::Result<T> {
+        if !self.is_alive() {
+            return Err(crate::TantivyError::SystemError(
                 "Segment updater killed".to_string(),
-            )));
+            ));
         }
-        receiver.unwrap_or_else(|_| {
+        let (sender, receiver) = oneshot::channel();
+        self.pool.spawn_ok(async move {
+            let task_result = task.await;
+            let _ = sender.send(task_result);
+        });
+        let task_result = receiver.await;
+        task_result.unwrap_or_else(|_| {
             let err_msg =
                 "A segment_updater future did not success. This should never happen.".to_string();
             Err(crate::TantivyError::SystemError(err_msg))
         })
     }
 
-    pub fn schedule_add_segment(
-        &self,
-        segment_entry: SegmentEntry,
-    ) -> impl Future<Output = crate::Result<()>> {
+    pub async fn schedule_add_segment(&self, segment_entry: SegmentEntry) -> crate::Result<()> {
         let segment_updater = self.clone();
-        self.schedule_future(async move {
+        self.schedule_task(async move {
             segment_updater.segment_manager.add_segment(segment_entry);
             segment_updater.consider_merge_options().await;
             Ok(())
         })
+        .await
     }
 
     /// Orders `SegmentManager` to remove all segments
@@ -448,11 +450,9 @@ impl SegmentUpdater {
         Ok(())
     }
 
-    pub fn schedule_garbage_collect(
-        &self,
-    ) -> impl Future<Output = crate::Result<GarbageCollectionResult>> {
+    pub async fn schedule_garbage_collect(&self) -> crate::Result<GarbageCollectionResult> {
         let garbage_collect_future = garbage_collect_files(self.clone());
-        self.schedule_future(garbage_collect_future)
+        self.schedule_task(garbage_collect_future).await
     }
 
     /// List the files that are useful to the index.
@@ -470,13 +470,13 @@ impl SegmentUpdater {
         files
     }
 
-    pub fn schedule_commit(
+    pub(crate) async fn schedule_commit(
         &self,
         opstamp: Opstamp,
         payload: Option<String>,
-    ) -> impl Future<Output = crate::Result<()>> {
+    ) -> crate::Result<()> {
         let segment_updater: SegmentUpdater = self.clone();
-        self.schedule_future(async move {
+        self.schedule_task(async move {
             let segment_entries = segment_updater.purge_deletes(opstamp)?;
             segment_updater.segment_manager.commit(segment_entries);
             segment_updater.save_metas(opstamp, payload)?;
@@ -484,6 +484,7 @@ impl SegmentUpdater {
             segment_updater.consider_merge_options().await;
             Ok(())
         })
+        .await
     }
 
     fn store_meta(&self, index_meta: &IndexMeta) {
@@ -611,14 +612,14 @@ impl SegmentUpdater {
         }
     }
 
-    fn end_merge(
+    async fn end_merge(
         &self,
         merge_operation: MergeOperation,
         mut after_merge_segment_entry: SegmentEntry,
-    ) -> impl Future<Output = crate::Result<SegmentMeta>> {
+    ) -> crate::Result<SegmentMeta> {
         let segment_updater = self.clone();
         let after_merge_segment_meta = after_merge_segment_entry.meta().clone();
-        let end_merge_future = self.schedule_future(async move {
+        self.schedule_task(async move {
             info!("End merge {:?}", after_merge_segment_entry.meta());
             {
                 let mut delete_cursor = after_merge_segment_entry.delete_cursor().clone();
@@ -661,8 +662,9 @@ impl SegmentUpdater {
 
             let _ = garbage_collect_files(segment_updater).await;
             Ok(())
-        });
-        end_merge_future.map_ok(|_| after_merge_segment_meta)
+        })
+        .await?;
+        Ok(after_merge_segment_meta)
     }
 
     /// Wait for current merging threads.

src/lib.rs

@@ -174,7 +174,7 @@ pub use crate::indexer::demuxer::*;
 pub use crate::indexer::merge_filtered_segments;
 pub use crate::indexer::merge_indices;
 pub use crate::indexer::operation::UserOperation;
-pub use crate::indexer::IndexWriter;
+pub use crate::indexer::{IndexWriter, PreparedCommit};
 pub use crate::postings::Postings;
 pub use crate::reader::LeasedItem;
 pub use crate::schema::{Document, Term};