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    
019    package org.apache.commons.exec;
020    
021    import 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     */
048    public 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        /**
072         * Creates a new watchdog with a given timeout.
073         * 
074         * @param timeout
075         *            the timeout for the process in milliseconds. It must be
076         *            greater than 0 or 'INFINITE_TIMEOUT'
077         */
078        public ExecuteWatchdog(final long timeout) {
079            this.killedProcess = false;
080            this.watch = false;
081            this.hasWatchdog = (timeout != INFINITE_TIMEOUT);
082            if(this.hasWatchdog) {
083                this.watchdog = new Watchdog(timeout);
084                this.watchdog.addTimeoutObserver(this);
085            }
086            else {
087                this.watchdog = null;
088            }
089        }
090    
091        /**
092         * Watches the given process and terminates it, if it runs for too long. All
093         * information from the previous run are reset.
094         * 
095         * @param process
096         *            the process to monitor. It cannot be <tt>null</tt>
097         * @throws IllegalStateException
098         *             if a process is still being monitored.
099         */
100        public synchronized void start(final Process process) {
101            if (process == null) {
102                throw new NullPointerException("process is null.");
103            }
104            if (this.process != null) {
105                throw new IllegalStateException("Already running.");
106            }
107            this.caught = null;
108            this.killedProcess = false;
109            this.watch = true;
110            this.process = process;
111            if(this.hasWatchdog) {
112                watchdog.start();
113            }
114        }
115    
116        /**
117         * Stops the watcher. It will notify all threads possibly waiting on this
118         * object.
119         */
120        public synchronized void stop() {
121            if(hasWatchdog) {
122                watchdog.stop();
123            }
124            watch = false;
125            process = null;
126        }
127    
128        /**
129         * Destroys the running process manually.
130         */
131        public synchronized void destroyProcess() {
132            this.timeoutOccured(null);
133            this.stop();
134        }
135    
136        /**
137         * Called after watchdog has finished.
138         */
139        public synchronized void timeoutOccured(final Watchdog w) {
140            try {
141                try {
142                    // We must check if the process was not stopped
143                    // before being here
144                    if(process != null) {
145                        process.exitValue();
146                    }
147                } catch (IllegalThreadStateException itse) {
148                    // the process is not terminated, if this is really
149                    // a timeout and not a manual stop then destroy it.
150                    if (watch) {
151                        killedProcess = true;
152                        process.destroy();
153                    }
154                }
155            } catch (Exception e) {
156                caught = e;
157                DebugUtils.handleException("Getting the exit value of the process failed", e);
158            } finally {
159                cleanUp();
160            }
161        }
162    
163    
164        /**
165         * This method will rethrow the exception that was possibly caught during
166         * the run of the process. It will only remains valid once the process has
167         * been terminated either by 'error', timeout or manual intervention.
168         * Information will be discarded once a new process is ran.
169         * 
170         * @throws Exception
171         *             a wrapped exception over the one that was silently swallowed
172         *             and stored during the process run.
173         */
174        public synchronized void checkException() throws Exception {
175            if (caught != null) {
176                throw caught;
177            }
178        }
179    
180        /**
181         * Indicates whether or not the watchdog is still monitoring the process.
182         * 
183         * @return <tt>true</tt> if the process is still running, otherwise
184         *         <tt>false</tt>.
185         */
186        public synchronized boolean isWatching() {
187            return watch;
188        }
189    
190        /**
191         * Indicates whether the last process run was killed.
192         * 
193         * @return <tt>true</tt> if the process was killed
194         *         <tt>false</tt>.
195         */
196        public synchronized boolean killedProcess() {
197            return killedProcess;
198        }
199    
200        /**
201         * reset the monitor flag and the process.
202         */
203        protected synchronized void cleanUp() {
204            watch = false;
205            process = null;
206        }    
207    }