Allow to listen to garbage collector events

A new event type is introduced that allows to listen to garbage
collector events. This enables to trigger actions that depend on
changes in the file size footprint of a project such as quota
enforcement or usage data monitoring.

Change-Id: I1eb913a618df5fe972f3f516af504c13871e5fa5

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

@@ -27,6 +27,7 @@ import com.google.gerrit.extensions.events.HeadUpdatedListener;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.extensions.events.NewProjectCreatedListener;
 import com.google.gerrit.extensions.events.ProjectDeletedListener;
+import com.google.gerrit.extensions.events.GarbageCollectorListener;
 import com.google.gerrit.extensions.events.UsageDataPublishedListener;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.extensions.registration.DynamicMap;
@@ -253,6 +254,7 @@ public class GerritGlobalModule extends FactoryModule {
     DynamicSet.setOf(binder(), PreUploadHook.class);
     DynamicSet.setOf(binder(), NewProjectCreatedListener.class);
     DynamicSet.setOf(binder(), ProjectDeletedListener.class);
+    DynamicSet.setOf(binder(), GarbageCollectorListener.class);
     DynamicSet.setOf(binder(), HeadUpdatedListener.class);
     DynamicSet.setOf(binder(), UsageDataPublishedListener.class);
     DynamicSet.bind(binder(), GitReferenceUpdatedListener.class).to(ReindexAfterUpdate.class);

gerrit-server/src/main/java/com/google/gerrit/server/git/GarbageCollection.java

@@ -16,6 +16,9 @@ package com.google.gerrit.server.git;
 
 import com.google.common.collect.Sets;
 import com.google.gerrit.common.data.GarbageCollectionResult;
+import com.google.gerrit.extensions.events.GarbageCollectorListener;
+import com.google.gerrit.extensions.events.GarbageCollectorListener.Event;
+import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.config.GcConfig;
 import com.google.inject.Inject;
@@ -48,6 +51,7 @@ public class GarbageCollection {
   private final GitRepositoryManager repoManager;
   private final GarbageCollectionQueue gcQueue;
   private final GcConfig gcConfig;
+  private final DynamicSet<GarbageCollectorListener> listeners;
 
   public interface Factory {
     GarbageCollection create();
@@ -55,10 +59,12 @@ public class GarbageCollection {
 
   @Inject
   GarbageCollection(GitRepositoryManager repoManager,
-      GarbageCollectionQueue gcQueue, GcConfig config) {
+      GarbageCollectionQueue gcQueue, GcConfig config,
+      DynamicSet<GarbageCollectorListener> listeners) {
     this.repoManager = repoManager;
     this.gcQueue = gcQueue;
     this.gcConfig = config;
+    this.listeners = listeners;
   }
 
   public GarbageCollectionResult run(List<Project.NameKey> projectNames) {
@@ -93,6 +99,7 @@ public class GarbageCollection {
         Properties statistics = gc.call();
         logGcInfo(p, "after: ", statistics);
         print(writer, "done.\n\n");
+        fire(p, statistics);
       } catch (RepositoryNotFoundException e) {
         logGcError(writer, p, e);
         result.addError(new GarbageCollectionResult.Error(
@@ -112,6 +119,27 @@ public class GarbageCollection {
     return result;
   }
 
+  private void fire(final Project.NameKey p, final Properties statistics) {
+    Event event = new GarbageCollectorListener.Event() {
+      @Override
+      public String getProjectName() {
+        return p.get();
+      }
+
+      @Override
+      public Properties getStatistics() {
+        return statistics;
+      }
+    };
+    for (GarbageCollectorListener l : listeners) {
+      try {
+        l.onGarbageCollected(event);
+      } catch (RuntimeException e) {
+        log.warn("Failure in GarbageCollectorListener", e);
+      }
+    }
+  }
+
   private static void logGcInfo(Project.NameKey projectName, String msg) {
     logGcInfo(projectName, msg, null);
   }