Add support for binding CacheRemovalListener

This can be used to dynamically bind removal listeners for use in
multi-master support.

Change-Id: I9c58740c54c89e5bd75accc64f03f1fdddc8d581

gerrit-server/src/main/java/com/google/gerrit/server/cache/CacheRemovalListener.java

@@ -0,0 +1,23 @@
+// Copyright (C) 2012 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.cache;
+
+import com.google.common.cache.RemovalNotification;
+
+public interface CacheRemovalListener<K,V> {
+  public void onRemoval(String pluginName,
+    String cacheName,
+    RemovalNotification<K, V> notification);
+}

gerrit-server/src/main/java/com/google/gerrit/server/cache/ForwardingRemovalListener.java

@@ -0,0 +1,60 @@
+// Copyright (C) 2012 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.cache;
+
+import com.google.common.base.Strings;
+import com.google.common.cache.RemovalListener;
+import com.google.common.cache.RemovalNotification;
+import com.google.gerrit.extensions.registration.DynamicSet;
+import com.google.inject.Inject;
+import com.google.inject.assistedinject.Assisted;
+
+/**
+ * This listener dispatches removal events to all other RemovalListeners
+ * attached via the DynamicSet API.
+ *
+ * @param <K>
+ * @param <V>
+ */
+@SuppressWarnings("rawtypes")
+public class ForwardingRemovalListener<K, V> implements RemovalListener<K, V> {
+  public interface Factory {
+    ForwardingRemovalListener create(String cacheName);
+  }
+
+  private final DynamicSet<CacheRemovalListener> listeners;
+  private final String cacheName;
+  private String pluginName = "gerrit";
+
+  @Inject
+  ForwardingRemovalListener(DynamicSet<CacheRemovalListener> listeners,
+      @Assisted String cacheName) {
+    this.listeners = listeners;
+    this.cacheName = cacheName;
+  }
+
+  @Inject(optional = true)
+  void setPluginName(String name) {
+    if (!Strings.isNullOrEmpty(name)) {
+      this.pluginName = name;
+    }
+  }
+
+  public void onRemoval(RemovalNotification<K, V> notification) {
+    for (CacheRemovalListener<K, V> l : listeners) {
+      l.onRemoval(pluginName, cacheName, notification);
+    }
+  }
+}