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                doStart();
055                success = true;
056            } finally {
057                started.set(success);
058            }
059            for(ServiceListener l:this.serviceListeners) {
060                l.started(this);
061            }
062        }
063    }
064
065    public void stop() throws Exception {
066        if (stopped.compareAndSet(false, true)) {
067            stopping.set(true);
068            ServiceStopper stopper = new ServiceStopper();
069            try {
070                doStop(stopper);
071            } catch (Exception e) {
072                stopper.onException(this, e);
073            }
074            stopped.set(true);
075            started.set(false);
076            stopping.set(false);
077            for(ServiceListener l:this.serviceListeners) {
078                l.stopped(this);
079            }
080            stopper.throwFirstException();
081        }
082    }
083
084    /**
085     * @return true if this service has been started
086     */
087    public boolean isStarted() {
088        return started.get();
089    }
090
091    /**
092     * @return true if this service is in the process of closing
093     */
094    public boolean isStopping() {
095        return stopping.get();
096    }
097
098    /**
099     * @return true if this service is closed
100     */
101    public boolean isStopped() {
102        return stopped.get();
103    }
104    
105    public void addServiceListener(ServiceListener l) {
106        this.serviceListeners.add(l);
107    }
108    
109    public void removeServiceListener(ServiceListener l) {
110        this.serviceListeners.remove(l);
111    }
112
113    protected abstract void doStop(ServiceStopper stopper) throws Exception;
114
115    protected abstract void doStart() throws Exception;
116}