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/*
* 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</code>
*
* @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() {
long now = System.currentTimeMillis();
final long until = now + timeout;
try {
while (!stopped && until > now) {
wait(until - now);
now = System.currentTimeMillis();
}
} catch (InterruptedException e) {
// Ignore exception
}
if (!stopped) {
fireTimeoutOccured();
}
}
}
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