Create change-indexed extension point

Add a new extension point so that plugins can be notified when a change
has been indexed or removed from the secondary index.

This allows the new Sync-index plugin to keep the secondary index of two
Gerrit instances in sync. Listening to existing change/patch events
cause the plugin to miss other cases where index updating is done, e.g.,
deleted drafts or changes reindexed to update their mergeability status.

Change-Id: I87de17de26e907d77b2fb5175b5c90c5dd0381e9

Documentation/dev-plugins.txt

@@ -415,6 +415,10 @@ Publication of usage data
 +
 Garbage collection ran on a project
 
+* `com.google.gerrit.server.extensions.events.ChangeIndexedListener`:
++
+Update of the secondary index
+
 [[stream-events]]
 == Sending Events to the Events Stream
 

gerrit-server/src/main/java/com/google/gerrit/server/config/GerritGlobalModule.java

@@ -79,6 +79,7 @@ import com.google.gerrit.server.change.ChangeKindCacheImpl;
 import com.google.gerrit.server.change.MergeabilityCacheImpl;
 import com.google.gerrit.server.events.EventFactory;
 import com.google.gerrit.server.events.EventsMetrics;
+import com.google.gerrit.server.extensions.events.ChangeIndexedListener;
 import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
 import com.google.gerrit.server.git.BatchUpdate;
 import com.google.gerrit.server.git.EmailMerge;
@@ -272,6 +273,7 @@ public class GerritGlobalModule extends FactoryModule {
     DynamicSet.setOf(binder(), ReceivePackInitializer.class);
     DynamicSet.setOf(binder(), PostReceiveHook.class);
     DynamicSet.setOf(binder(), PreUploadHook.class);
+    DynamicSet.setOf(binder(), ChangeIndexedListener.class);
     DynamicSet.setOf(binder(), NewProjectCreatedListener.class);
     DynamicSet.setOf(binder(), ProjectDeletedListener.class);
     DynamicSet.setOf(binder(), GarbageCollectorListener.class);

gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/ChangeIndexedListener.java

@@ -0,0 +1,29 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.extensions.events;
+
+import com.google.gerrit.extensions.annotations.ExtensionPoint;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.server.query.change.ChangeData;
+
+/** Notified whenever a change is indexed or deleted from the index. */
+@ExtensionPoint
+public interface ChangeIndexedListener {
+  /** Invoked when a change is indexed. */
+  void onChangeIndexed(ChangeData change);
+
+  /** Invoked when a change is deleted from the index. */
+  void onChangeDeleted(Change.Id id);
+}

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

@@ -20,10 +20,12 @@ import com.google.common.util.concurrent.CheckedFuture;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.extensions.events.ChangeIndexedListener;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.util.RequestContext;
 import com.google.gerrit.server.util.ThreadLocalRequestContext;
@@ -94,11 +96,13 @@ public class ChangeIndexer {
   private final ChangeData.Factory changeDataFactory;
   private final ThreadLocalRequestContext context;
   private final ListeningExecutorService executor;
+  private final DynamicSet<ChangeIndexedListener> indexedListener;
 
   @AssistedInject
   ChangeIndexer(SchemaFactory<ReviewDb> schemaFactory,
       ChangeData.Factory changeDataFactory,
       ThreadLocalRequestContext context,
+      DynamicSet<ChangeIndexedListener> indexedListener,
       @Assisted ListeningExecutorService executor,
       @Assisted ChangeIndex index) {
     this.executor = executor;
@@ -107,12 +111,14 @@ public class ChangeIndexer {
     this.context = context;
     this.index = index;
     this.indexes = null;
+    this.indexedListener = indexedListener;
   }
 
   @AssistedInject
   ChangeIndexer(SchemaFactory<ReviewDb> schemaFactory,
       ChangeData.Factory changeDataFactory,
       ThreadLocalRequestContext context,
+      DynamicSet<ChangeIndexedListener> indexedListener,
       @Assisted ListeningExecutorService executor,
       @Assisted IndexCollection indexes) {
     this.executor = executor;
@@ -121,6 +127,7 @@ public class ChangeIndexer {
     this.context = context;
     this.index = null;
     this.indexes = indexes;
+    this.indexedListener = indexedListener;
   }
 
   /**
@@ -160,6 +167,19 @@ public class ChangeIndexer {
     for (ChangeIndex i : getWriteIndexes()) {
       i.replace(cd);
     }
+    fireChangeIndexedEvent(cd);
+  }
+
+  private void fireChangeIndexedEvent(ChangeData change) {
+    for (ChangeIndexedListener listener : indexedListener) {
+      listener.onChangeIndexed(change);
+    }
+  }
+
+  private void fireChangeDeletedFromIndexEvent(Change.Id id) {
+    for (ChangeIndexedListener listener : indexedListener) {
+      listener.onChangeDeleted(id);
+    }
   }
 
   /**
@@ -280,6 +300,7 @@ public class ChangeIndexer {
       for (ChangeIndex i : getWriteIndexes()) {
         i.delete(id);
       }
+      fireChangeDeletedFromIndexEvent(id);
       return null;
     }
   }