Ant example source code file (Watchdog.java)

This example Ant source code file (Watchdog.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Ant tags/keywords

enumeration, error_invalid_timeout, illegalargumentexception, interruptedexception, interruptedexception, runnable, string, thread, thread, timeoutobserver, util, vector, vector, watchdog, watchdog

The Watchdog.java source code

/*
 *  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.tools.ant.util;

import java.util.Enumeration;
import java.util.Vector;

/**
 * Generalization of <code>ExecuteWatchdog
 *
 * @since Ant 1.5
 *
 * @see org.apache.tools.ant.taskdefs.ExecuteWatchdog
 *
 */
public class Watchdog implements Runnable {

    private Vector observers = new Vector(1);
    private long timeout = -1;
    /**
     * marked as volatile to stop the compiler caching values or (in java1.5+,
     * reordering access)
     */
    private volatile boolean stopped = false;
    /**
     * Error string.
     * {@value}
     */
    public static final String ERROR_INVALID_TIMEOUT = "timeout less than 1.";

    /**
     * Constructor for Watchdog.
     * @param timeout the timeout to use in milliseconds (must be >= 1).
     */
    public Watchdog(long timeout) {
        if (timeout < 1) {
            throw new IllegalArgumentException(ERROR_INVALID_TIMEOUT);
        }
        this.timeout = timeout;
    }

    /**
     * Add a timeout observer.
     * @param to the timeout observer to add.
     */
    public void addTimeoutObserver(TimeoutObserver to) {
        //no need to synchronize, as Vector is always synchronized
        observers.addElement(to);
    }

    /**
     * Remove a timeout observer.
     * @param to the timeout observer to remove.
     */
    public void removeTimeoutObserver(TimeoutObserver to) {
        //no need to synchronize, as Vector is always synchronized
        observers.removeElement(to);
    }

    /**
     * Inform the observers that a timeout has occurred.
     * This happens in the watchdog thread.
     */
    protected final void fireTimeoutOccured() {
        Enumeration e = observers.elements();
        while (e.hasMoreElements()) {
            ((TimeoutObserver) e.nextElement()).timeoutOccured(this);
        }
    }

    /**
     * Start the watch dog.
     */
    public synchronized void start() {
        stopped = false;
        Thread t = new Thread(this, "WATCHDOG");
        t.setDaemon(true);
        t.start();
    }

    /**
     * Stop the watch dog.
     */
    public synchronized void stop() {
        stopped = true;
        notifyAll();
    }

    /**
     * The run method of the watch dog thread.
     * This simply does a wait for the timeout time, and
     * if the stop flag has not been set when the wait has returned or
     * has been interrupted, the watch dog listeners are informed.
     */
    public synchronized void run() {
        final long until = System.currentTimeMillis() + timeout;
        long now;
        while (!stopped && until > (now = System.currentTimeMillis())) {
            try {
                wait(until - now);
            } catch (InterruptedException e) {
                // Ignore exception
            }
        }
        if (!stopped) {
            fireTimeoutOccured();
        }
    }

}