| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.hadoop.service.launcher; |
| |
| import java.lang.ref.WeakReference; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.service.Service; |
| import org.apache.hadoop.util.ShutdownHookManager; |
| |
| /** |
| * JVM Shutdown hook for Service which will stop the |
| * Service gracefully in case of JVM shutdown. |
| * This hook uses a weak reference to the service, |
| * and when shut down, calls {@link Service#stop()} if the reference is valid. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| public class ServiceShutdownHook implements Runnable { |
| private static final Logger LOG = LoggerFactory.getLogger( |
| ServiceShutdownHook.class); |
| |
| /** |
| * A weak reference to the service. |
| */ |
| private final WeakReference<Service> serviceRef; |
| |
| /** |
| * Create an instance. |
| * @param service the service |
| */ |
| public ServiceShutdownHook(Service service) { |
| serviceRef = new WeakReference<>(service); |
| } |
| |
| /** |
| * Register the service for shutdown with Hadoop's |
| * {@link ShutdownHookManager}. |
| * @param priority shutdown hook priority |
| */ |
| public synchronized void register(int priority) { |
| unregister(); |
| ShutdownHookManager.get().addShutdownHook(this, priority); |
| } |
| |
| /** |
| * Unregister the hook. |
| */ |
| public synchronized void unregister() { |
| try { |
| ShutdownHookManager.get().removeShutdownHook(this); |
| } catch (IllegalStateException e) { |
| LOG.info("Failed to unregister shutdown hook: {}", e, e); |
| } |
| } |
| |
| /** |
| * Shutdown handler. |
| * Query the service hook reference -if it is still valid the |
| * {@link Service#stop()} operation is invoked. |
| */ |
| @Override |
| public void run() { |
| shutdown(); |
| } |
| |
| /** |
| * Shutdown operation. |
| * <p> |
| * Subclasses may extend it, but it is primarily |
| * made available for testing. |
| * @return true if the service was stopped and no exception was raised. |
| */ |
| protected boolean shutdown() { |
| Service service; |
| boolean result = false; |
| synchronized (this) { |
| service = serviceRef.get(); |
| serviceRef.clear(); |
| } |
| if (service != null) { |
| try { |
| // Stop the Service |
| service.stop(); |
| result = true; |
| } catch (Throwable t) { |
| LOG.info("Error stopping {}", service.getName(), t); |
| } |
| } |
| return result; |
| } |
| } |