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 */
018
019package org.apache.commons.exec;
020
021import org.apache.commons.exec.util.DebugUtils;
022
023/**
024 * Destroys a process running for too long. For example:
025 *
026 * <pre>
027 * ExecuteWatchdog watchdog = new ExecuteWatchdog(30000);
028 * Executer exec = new Executer(myloghandler, watchdog);
029 * exec.setCommandLine(mycmdline);
030 * int exitvalue = exec.execute();
031 * if (Execute.isFailure(exitvalue) &amp;&amp; watchdog.killedProcess()) {
032 *     // it was killed on purpose by the watchdog
033 * }
034 * </pre>
035 *
036 * When starting an asynchronous process than 'ExecuteWatchdog' is the
037 * keeper of the process handle. In some cases it is useful not to define
038 * a timeout (and pass 'INFINITE_TIMEOUT') and to kill the process explicitly
039 * using 'destroyProcess()'.
040 * <p>
041 * Please note that ExecuteWatchdog is processed asynchronously, e.g. it might
042 * be still attached to a process even after the DefaultExecutor.execute 
043 * has returned.
044 *
045 * @see org.apache.commons.exec.Executor
046 * @see org.apache.commons.exec.Watchdog
047 */
048public class ExecuteWatchdog implements TimeoutObserver {
049
050    /** The marker for an infinite timeout */
051    public static final long INFINITE_TIMEOUT = -1;
052    
053    /** The process to execute and watch for duration. */
054    private Process process;
055
056    /** Is a user-supplied timeout in use */
057    private final boolean hasWatchdog;
058
059    /** Say whether or not the watchdog is currently monitoring a process. */
060    private boolean watch;
061
062    /** Exception that might be thrown during the process execution. */
063    private Exception caught;
064
065    /** Say whether or not the process was killed due to running overtime. */
066    private boolean killedProcess;
067
068    /** Will tell us whether timeout has occurred. */
069    private final Watchdog watchdog;
070
071    /** Indicates that the process is verified as started */
072    private volatile boolean processStarted;
073
074    /**
075     * Creates a new watchdog with a given timeout.
076     * 
077     * @param timeout
078     *            the timeout for the process in milliseconds. It must be
079     *            greater than 0 or 'INFINITE_TIMEOUT'
080     */
081    public ExecuteWatchdog(final long timeout) {
082        this.killedProcess = false;
083        this.watch = false;
084        this.hasWatchdog = (timeout != INFINITE_TIMEOUT);
085        this.processStarted = false;
086        if(this.hasWatchdog) {
087            this.watchdog = new Watchdog(timeout);
088            this.watchdog.addTimeoutObserver(this);
089        }
090        else {
091            this.watchdog = null;
092        }
093    }
094
095    /**
096     * Watches the given process and terminates it, if it runs for too long. All
097     * information from the previous run are reset.
098     * 
099     * @param process
100     *            the process to monitor. It cannot be <tt>null</tt>
101     * @throws IllegalStateException
102     *             if a process is still being monitored.
103     */
104    public synchronized void start(final Process process) {
105        if (process == null) {
106            throw new NullPointerException("process is null.");
107        }
108        if (this.process != null) {
109            throw new IllegalStateException("Already running.");
110        }
111        this.caught = null;
112        this.killedProcess = false;
113        this.watch = true;
114        this.process = process;
115        this.processStarted = true;
116        this.notifyAll();
117        if(this.hasWatchdog) {
118            watchdog.start();
119        }
120    }
121
122    /**
123     * Stops the watcher. It will notify all threads possibly waiting on this
124     * object.
125     */
126    public synchronized void stop() {
127        if(hasWatchdog) {
128            watchdog.stop();
129        }
130        watch = false;
131        process = null;
132    }
133
134    /**
135     * Destroys the running process manually.
136     */
137    public synchronized void destroyProcess() {
138        ensureStarted();
139        this.timeoutOccured(null);
140        this.stop();
141    }
142
143    /**
144     * Called after watchdog has finished.
145     */
146    public synchronized void timeoutOccured(final Watchdog w) {
147        try {
148            try {
149                // We must check if the process was not stopped
150                // before being here
151                if(process != null) {
152                    process.exitValue();
153                }
154            } catch (IllegalThreadStateException itse) {
155                // the process is not terminated, if this is really
156                // a timeout and not a manual stop then destroy it.
157                if (watch) {
158                    killedProcess = true;
159                    process.destroy();
160                }
161            }
162        } catch (Exception e) {
163            caught = e;
164            DebugUtils.handleException("Getting the exit value of the process failed", e);
165        } finally {
166            cleanUp();
167        }
168    }
169
170
171    /**
172     * This method will rethrow the exception that was possibly caught during
173     * the run of the process. It will only remains valid once the process has
174     * been terminated either by 'error', timeout or manual intervention.
175     * Information will be discarded once a new process is ran.
176     * 
177     * @throws Exception
178     *             a wrapped exception over the one that was silently swallowed
179     *             and stored during the process run.
180     */
181    public synchronized void checkException() throws Exception {
182        if (caught != null) {
183            throw caught;
184        }
185    }
186
187    /**
188     * Indicates whether or not the watchdog is still monitoring the process.
189     * 
190     * @return <tt>true</tt> if the process is still running, otherwise
191     *         <tt>false</tt>.
192     */
193    public synchronized boolean isWatching() {
194        ensureStarted();
195        return watch;
196    }
197
198    /**
199     * Indicates whether the last process run was killed.
200     * 
201     * @return <tt>true</tt> if the process was killed
202     *         <tt>false</tt>.
203     */
204    public synchronized boolean killedProcess() {
205        return killedProcess;
206    }
207
208    /**
209     * reset the monitor flag and the process.
210     */
211    protected synchronized void cleanUp() {
212        watch = false;
213        process = null;
214    }
215
216    void setProcessNotStarted(){
217        processStarted = false;
218    }
219
220    /**
221     * Ensures that the process is started, so we do not race with asynch execution.
222     * The caller of this method must be holding the lock on this
223     */
224    private void ensureStarted(){
225        while (!processStarted){
226            try {
227                this.wait();
228            } catch (InterruptedException e) {
229                throw new RuntimeException(e.getMessage());
230            }
231        }
232    }
233}