antliscence/src/main/org/apache/tools/ant/taskdefs/ExecuteWatchdog.java

/*
 * The Apache Software License, Version 1.1
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.tools.ant.taskdefs;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.util.TimeoutObserver;
import org.apache.tools.ant.util.Watchdog;

/**
 * Destroys a process running for too long.
 * For example:
 * <pre>
 * ExecuteWatchdog watchdog = new ExecuteWatchdog(30000);
 * Execute exec = new Execute(myloghandler, watchdog);
 * exec.setCommandLine(mycmdline);
 * int exitvalue = exec.execute();
 * if (exitvalue != SUCCESS && watchdog.killedProcess()){
 *              // it was killed on purpose by the watchdog
 * }
 * </pre>
 
 * @author thomas.haas@softwired-inc.com
 * @author <a href="mailto:sbailliez_at_apache.org">Stephane Bailliez</a>
 * @see Execute
 * @see org.apache.tools.ant.util.Watchdog
 * @since Ant 1.2
 */
public class ExecuteWatchdog implements TimeoutObserver {
        
    /** the process to execute and watch for duration */
    private Process process;

    /** say whether or not the watchog is currently monitoring a process */
    private boolean watch = false;
        
    /** exception that might be thrown during the process execution */
    private Exception caught = null;

    /** say whether or not the process was killed due to running overtime */
    private boolean     killedProcess = false;

    /** will tell us whether timeout has occured */
    private Watchdog watchdog;

    /**
     * Creates a new watchdog with a given timeout.
     *
     * @param timeout the timeout for the process in milliseconds. 
     * It must be greather than 0.
     */
    public ExecuteWatchdog(long timeout) {
        watchdog = new Watchdog(timeout);
        watchdog.addTimeoutObserver(this);
    }

    /**
     * @see #ExecuteWatchdog(long)
     * @deprecated Use constructor with a long type instead.
     * (1.4.x compatibility)
     */
    public ExecuteWatchdog(int timeout) {
        this((long)timeout);
    }

    /**
     * Watches the given process and terminates it, if it runs for too long.
     * All information from the previous run are reset.
     * @param process the process to monitor. It cannot be <tt>null</tt>
     * @throws IllegalStateException if a process is still being monitored.
     */
    public synchronized void start(Process process) {
        if (process == null) {
            throw new NullPointerException("process is null.");
        }
        if (this.process != null) {
            throw new IllegalStateException("Already running.");
        }
        this.caught = null;
        this.killedProcess = false;
        this.watch = true;
        this.process = process;
        watchdog.start();
    }

    /**
     * Stops the watcher. It will notify all threads possibly waiting 
     * on this object.
     */
    public synchronized void stop() {
        watchdog.stop();
        watch = false;
        process = null;
    }

    /**
     * Called after watchdog has finished.
     */
    public void timeoutOccured(Watchdog w) {
        try {
            try {
                // We must check if the process was not stopped
                // before being here
                process.exitValue();
            } catch (IllegalThreadStateException itse){
                // the process is not terminated, if this is really
                // a timeout and not a manual stop then kill it.
                if (watch){
                    killedProcess = true;
                    process.destroy();
                }
            }
        } catch (Exception e) {
            caught = e;
        } finally {
            cleanUp();
        }
    }

    /**
     * reset the monitor flag and the process.
     */
    protected void cleanUp() {
        watch = false;
        process = null;
    }

    /**
     * This method will rethrow the exception that was possibly caught during 
     * the run of the process. It will only remains valid once the process has 
     * been terminated either by 'error', timeout or manual intervention. 
     * Information will be discarded once a new process is ran.
     * @throws  BuildException  a wrapped exception over the one that was 
     * silently swallowed and stored during the process run.
     */
    public void checkException() throws BuildException {
        if (caught != null) {
            throw new BuildException("Exception in ExecuteWatchdog.run: "
                                     + caught.getMessage(), caught);
        }
    }

    /**
     * Indicates whether or not the watchdog is still monitoring the process.
     * @return  <tt>true</tt> if the process is still running, otherwise 
     *          <tt>false</tt>.
     */
    public boolean isWatching(){
        return watch;
    }

    /**
     * Indicates whether the last process run was killed on timeout or not.
     * @return  <tt>true</tt> if the process was killed otherwise 
     *          <tt>false</tt>.
     */
    public boolean killedProcess(){
        return killedProcess;
    }
}