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 */
017package org.apache.activemq.util;
018
019import java.util.List;
020import java.util.concurrent.CopyOnWriteArrayList;
021import java.util.concurrent.atomic.AtomicBoolean;
022
023import org.apache.activemq.Service;
024import org.slf4j.Logger;
025import 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 */
033public 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}