org.apache.hadoop.service.launcher.ServiceShutdownHook Maven / Gradle / Ivy
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* 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 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.
*
* 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;
}
}