Java tutorial
/* * 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. * */ import java.util.Enumeration; import java.util.Vector; /** * Generalization of <code>ExecuteWatchdog</code> * * @see org.apache.commons.exec.ExecuteWatchdog */ public class Watchdog implements Runnable { private Vector observers = new Vector(1); private final long timeout; private boolean stopped = false; public Watchdog(final long timeout) { if (timeout < 1) { throw new IllegalArgumentException("timeout must not be less than 1."); } this.timeout = timeout; } public void addTimeoutObserver(final TimeoutObserver to) { observers.addElement(to); } public void removeTimeoutObserver(final TimeoutObserver to) { observers.removeElement(to); } protected final void fireTimeoutOccured() { Enumeration e = observers.elements(); while (e.hasMoreElements()) { ((TimeoutObserver) e.nextElement()).timeoutOccured(this); } } public synchronized void start() { stopped = false; Thread t = new Thread(this, "WATCHDOG"); t.setDaemon(true); t.start(); } public synchronized void stop() { stopped = true; notifyAll(); } 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) { } } if (!stopped) { fireTimeoutOccured(); } } } /** * Interface for classes that want to be notified by Watchdog. * * @see org.apache.commons.exec.Watchdog */ interface TimeoutObserver { /** * Called when the watchdow times out. * * @param w * the watchdog that timed out. */ void timeoutOccured(Watchdog w); }