Lucene: close sub-indexes in parallel

The open and closed sub-indexes may each take a while to close as they
flush and commit writes. They are completely independent, so close
them in parallel, reusing the existing indexing executor, which
shouldn't be doing much else during shutdown.

Change-Id: I3c56a972d19c793e2b8601727c03b6e7bf53e77d

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneChangeIndex.java

@@ -23,6 +23,8 @@ import static org.apache.lucene.search.BooleanClause.Occur.SHOULD;
 
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListeningScheduledExecutorService;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.server.config.SitePaths;
@@ -73,6 +75,8 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
 
 /**
  * Secondary index implementation using Apache Lucene.
@@ -104,14 +108,17 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
 
   private final RefreshThread refreshThread;
   private final FillArgs fillArgs;
+  private final ExecutorService executor;
   private final boolean readOnly;
   private final SubIndex openIndex;
   private final SubIndex closedIndex;
 
-  LuceneChangeIndex(Config cfg, SitePaths sitePaths, FillArgs fillArgs,
+  LuceneChangeIndex(Config cfg, SitePaths sitePaths,
+      ListeningScheduledExecutorService executor, FillArgs fillArgs,
       boolean readOnly) throws IOException {
     this.refreshThread = new RefreshThread();
     this.fillArgs = fillArgs;
+    this.executor = executor;
     this.readOnly = readOnly;
     openIndex = new SubIndex(new File(sitePaths.index_dir, CHANGES_OPEN),
         getIndexWriterConfig(cfg, "changes_open"));
@@ -127,8 +134,22 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
   @Override
   public void stop() {
     refreshThread.halt();
-    openIndex.close();
-    closedIndex.close();
+    List<Future<?>> closeFutures = Lists.newArrayListWithCapacity(2);
+    closeFutures.add(executor.submit(new Runnable() {
+      @Override
+      public void run() {
+        openIndex.close();
+      }
+    }));
+    closeFutures.add(executor.submit(new Runnable() {
+      @Override
+      public void run() {
+        closedIndex.close();
+      }
+    }));
+    for (Future<?> future : closeFutures) {
+      Futures.getUnchecked(future);
+    }
   }
 
   @Override

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneIndexModule.java

@@ -14,11 +14,13 @@
 
 package com.google.gerrit.lucene;
 
+import com.google.common.util.concurrent.ListeningScheduledExecutorService;
 import com.google.gerrit.lifecycle.LifecycleModule;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.ChangeIndex;
 import com.google.gerrit.server.index.FieldDef.FillArgs;
+import com.google.gerrit.server.index.IndexExecutor;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.inject.Provides;
 import com.google.inject.Singleton;
@@ -56,7 +58,9 @@ public class LuceneIndexModule extends LifecycleModule {
   @Provides
   @Singleton
   public LuceneChangeIndex getChangeIndex(@GerritServerConfig Config cfg,
-      SitePaths sitePaths, FillArgs fillArgs) throws IOException {
-    return new LuceneChangeIndex(cfg, sitePaths, fillArgs, readOnly);
+      SitePaths sitePaths,
+      @IndexExecutor ListeningScheduledExecutorService executor,
+      FillArgs fillArgs) throws IOException {
+    return new LuceneChangeIndex(cfg, sitePaths, executor, fillArgs, readOnly);
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/index/IndexExecutor.java

@@ -27,5 +27,5 @@ import java.lang.annotation.Retention;
  */
 @Retention(RUNTIME)
 @BindingAnnotation
-@interface IndexExecutor {
+public @interface IndexExecutor {
 }