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Freedom for Media in Java
There is a newer version: 1.0.2-jitsi
package net.sf.fmj.media.util;

/**
 * LoopThread A looping thread that implements a safe way of pausing and
 * restarting. Instead of using suspend() and resume() from the thread class, a
 * pause() and start() method is provided. To use it, you will: - subclass from
 * it; - overwrite the process() callback; - call start() to initiate the
 * thread.
 *
 * @version 1.9, 98/09/28
 */
public abstract class LoopThread extends MediaThread
{
    protected boolean paused = false, started = false;
    protected boolean killed = false;
    private boolean waitingAtPaused = false;

    /**
     * The pause flag determines the initial state.
     */
    public LoopThread()
    {
        setName("Loop thread");
    }

    /**
     * Same as pause except that it blocks until the loop has actually paused
     * (at waitHereIfPaused).
     */
    public synchronized void blockingPause()
    {
        if (waitingAtPaused || killed)
            return;
        paused = true;
        waitForCompleteStop();
    }

    public boolean isPaused()
    {
        return paused;
    }

    public synchronized void kill()
    {
        killed = true;
        notifyAll();
    }

    /**
     * Set the paused state to true. The thread will halt at the beginning of
     * the loop at the next iteration. i.e., unlike suspend(), the thread will
     * NOT pause immediately. It will execute until the next waitHereIfPaused()
     * is encountered.
     */
    public synchronized void pause()
    {
        paused = true;
    }

    /**
     * process callback function.
     */
    protected abstract boolean process();

    /**
     * The run method for the Thread class.
     */
    @Override
    public void run()
    {
        /*
         * Let the super MediaThread do whatever it has been designed to do. For
         * example, it may set the priority of this thread.
         */
        super.run();

        for (;;)
        {
            // Wait here if pause() was invoked. Until start() is called,
            // the thread will wait here indefinitely.
            if (!waitHereIfPaused())
                break;

            // Invoke the callback function.
            if (!process())
                break;
        }
    }

    /**
     * Resume the loop at the beginning of the loop where waitHereIfPaused() is
     * called.
     */
    @Override
    public synchronized void start()
    {
        if (!started)
        {
            super.start();
            started = true;
        }
        paused = false;
        notifyAll();
    }

    /**
     * Wait until the loop has come to a complete stop.
     */
    public synchronized void waitForCompleteStop()
    {
        try
        {
            while (!killed && !waitingAtPaused && paused)
                wait();
        } catch (InterruptedException e)
        {
        }
    }

    /**
     * Wait until the loop has come to a complete stop. Time out after the given
     * milli seconds.
     */
    public synchronized void waitForCompleteStop(int millis)
    {
        try
        {
            if (!killed && !waitingAtPaused && paused)
                wait(millis);
        } catch (InterruptedException e)
        {
        }
    }

    /**
     * Put the thread in a wait() if the paused state is on. Otherwise, it will
     * just proceed.
     */
    public synchronized boolean waitHereIfPaused()
    {
        if (killed)
            return false;
        waitingAtPaused = true;
        if (paused)
            notifyAll(); // notify the blocking pause.
        try
        {
            while (!killed && paused)
                wait();
        } catch (InterruptedException e)
        {
            System.err.println("Timer: timeLoop() wait interrupted " + e);
        }
        waitingAtPaused = false;
        if (killed)
            return false;
        return true;
    }

}