001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.activemq.util;
018
019 import java.util.List;
020 import java.util.concurrent.CopyOnWriteArrayList;
021 import java.util.concurrent.atomic.AtomicBoolean;
022
023 import org.apache.activemq.Service;
024 import org.slf4j.Logger;
025 import org.slf4j.LoggerFactory;
026
027 /**
028 * A helper class for working with services together with a useful base class
029 * for service implementations.
030 *
031 *
032 */
033 public abstract class ServiceSupport implements Service {
034 private static final Logger LOG = LoggerFactory.getLogger(ServiceSupport.class);
035
036 private AtomicBoolean started = new AtomicBoolean(false);
037 private AtomicBoolean stopping = new AtomicBoolean(false);
038 private AtomicBoolean stopped = new AtomicBoolean(false);
039 private List<ServiceListener>serviceListeners = new CopyOnWriteArrayList<ServiceListener>();
040
041 public static void dispose(Service service) {
042 try {
043 service.stop();
044 } catch (Exception e) {
045 LOG.debug("Could not stop service: " + service + ". Reason: " + e, e);
046 }
047 }
048
049 public void start() throws Exception {
050 if (started.compareAndSet(false, true)) {
051 boolean success = false;
052 stopped.set(false);
053 try {
054 preStart();
055 doStart();
056 success = true;
057 } finally {
058 started.set(success);
059 }
060 for(ServiceListener l:this.serviceListeners) {
061 l.started(this);
062 }
063 }
064 }
065
066 public void stop() throws Exception {
067 if (stopped.compareAndSet(false, true)) {
068 stopping.set(true);
069 ServiceStopper stopper = new ServiceStopper();
070 try {
071 doStop(stopper);
072 } catch (Exception e) {
073 stopper.onException(this, e);
074 } finally {
075 postStop(stopper);
076 }
077 stopped.set(true);
078 started.set(false);
079 stopping.set(false);
080 for(ServiceListener l:this.serviceListeners) {
081 l.stopped(this);
082 }
083 stopper.throwFirstException();
084 }
085 }
086
087 /**
088 * @return true if this service has been started
089 */
090 public boolean isStarted() {
091 return started.get();
092 }
093
094 /**
095 * @return true if this service is in the process of closing
096 */
097 public boolean isStopping() {
098 return stopping.get();
099 }
100
101 /**
102 * @return true if this service is closed
103 */
104 public boolean isStopped() {
105 return stopped.get();
106 }
107
108 public void addServiceListener(ServiceListener l) {
109 this.serviceListeners.add(l);
110 }
111
112 public void removeServiceListener(ServiceListener l) {
113 this.serviceListeners.remove(l);
114 }
115
116 /**
117 *
118 * handle for various operations after stopping the service (like locking)
119 *
120 * @throws Exception
121 */
122 protected void postStop(ServiceStopper stopper) throws Exception {}
123
124 protected abstract void doStop(ServiceStopper stopper) throws Exception;
125
126 /**
127 *
128 * handle for various operations before starting the service (like locking)
129 *
130 * @throws Exception
131 */
132 protected void preStart() throws Exception {}
133
134 protected abstract void doStart() throws Exception;
135 }