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.thread;
018    
019    import java.util.HashMap;
020    import java.util.Timer;
021    import java.util.TimerTask;
022    
023    /**
024     * Singelton, references maintained by users
025     * @version $Revision$
026     */
027    public final class Scheduler { 
028    
029            private final Timer CLOCK_DAEMON = new Timer("ActiveMQ Scheduler", true);
030        private final HashMap<Runnable, TimerTask> TIMER_TASKS = new HashMap<Runnable, TimerTask>();
031        private static Scheduler instance;
032        
033        static {
034            instance = new Scheduler();
035        }
036        
037        private Scheduler() {
038        }
039    
040        public static Scheduler getInstance() {
041            return instance;
042        }
043        
044        public synchronized void executePeriodically(final Runnable task, long period) {
045            TimerTask timerTask = new SchedulerTimerTask(task);
046            CLOCK_DAEMON.scheduleAtFixedRate(timerTask, period, period);
047            TIMER_TASKS.put(task, timerTask);
048        }
049    
050        /*
051         * execute on rough schedual based on termination of last execution. There is no
052         * compensation (two runs in quick succession) for delays
053         */
054        public synchronized void schedualPeriodically(final Runnable task, long period) {
055            TimerTask timerTask = new SchedulerTimerTask(task);
056            CLOCK_DAEMON.schedule(timerTask, period, period);
057            TIMER_TASKS.put(task, timerTask);
058        }
059        
060        public synchronized void cancel(Runnable task) {
061            TimerTask ticket = TIMER_TASKS.remove(task);
062            if (ticket != null) {
063                ticket.cancel();
064                CLOCK_DAEMON.purge();//remove cancelled TimerTasks
065            }
066        }
067    
068        public void executeAfterDelay(final Runnable task, long redeliveryDelay) {
069            TimerTask timerTask = new SchedulerTimerTask(task);
070            CLOCK_DAEMON.schedule(timerTask, redeliveryDelay);
071        }
072        
073        public void shutdown() {
074            CLOCK_DAEMON.cancel();
075        }
076    }