I think I don't quite understand threading...

Discussion in 'Java' started by OscarC, May 8, 2004.

  1. OscarC

    OscarC Guest


    I'm building a slideshow app and I'd like to be able
    to play some music while viewing the photos. So, I thought
    in using two separate threads, one for the slideshow and
    another for playing the music (I'm using javazoom.net's
    MP3 libraries). Something like this:

    Thread t1 = new Thread(new Slideshow(album));

    Thread t2 = new Thread(new MP3Play());

    The t1 thread opens a new undecorated JFrame and shows
    the photos one after another. The t2 threads starts
    playing some MP3 file.

    Using this I'm not getting what I want. Now, the music
    plays AFTER viewing the photos, not at the same time
    which is the purpose of using threads. What am I doing
    wrong ?

    The code for the MP3Play class is:

    public class MusicPlayer implements Runnable, BasicPlayerListener {

    public void run() {

    // Instantiate BasicPlayer.
    BasicPlayer player = new BasicPlayer();
    // BasicPlayer is a BasicController.
    BasicController control = (BasicController) player;
    // Register BasicPlayerTest to BasicPlayerListener events.
    // It means that this object will be notified on BasicPlayer
    // events such as : opened(...), progress(...), stateUpdated(...)

    try { // Open file, or URL or Stream (shoutcast, icecast) to play.
    control.open(new File("file.mp3"));

    // control.open(new URL("http://yourshoutcastserver.com:8000"));
    // Start playback in a thread. control.play();
    // If you want to pause/resume/pause the played file then
    // write a Swing player and just call control.pause(),
    // control.resume() or control.stop().
    // Use control.seek(bytesToSkip) to seek file
    // (i.e. fast forward and rewind). seek feature will
    // work only if underlying JavaSound SPI implements
    // skip(...). True for MP3SPI (JavaZOOM) and SUN SPI's
    // (WAVE, AU, AIFF).
    // Set Volume (0 to 1.0). control.setGain(0.85);
    // Set Pan (-1.0 to 1.0).
    } catch (BasicPlayerException e) { e.printStackTrace(); }


    public void stateUpdated(BasicPlayerEvent event) {
    // Notification of BasicPlayer states (opened, playing, end of
    media, ...)
    System.out.println("stateUpdated : "+event.toString());

    public void progress(int bytesread, long microseconds, byte[]
    pcmdata, Map properties) {
    // Pay attention to properties. It depends on underlying JavaSound SPI
    // MP3SPI provides mp3.equalizer.
    System.out.println("progress : "+properties.toString());

    public void opened(Object stream, Map properties) {
    // Pay attention to properties. It's useful to get duration,
    // bitrate, channels, even tag such as ID3v2.
    System.out.println("opened : "+properties.toString());

    public void setController(BasicController controller) {
    System.out.println("setController : "+controller);


    Thanks in advance
    OscarC, May 8, 2004
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  2. OscarC

    Ben Wilson Guest

    Have you already tried lowering the priority of the Thread t1, and
    sprinkling a couple of yield() calls around in your code?

    A lot of the Thread functionality in Java is platform-dependent. Which
    platform are you using?

    Ben Wilson, May 8, 2004
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  3. OscarC

    Abs Guest

    No, I haven't tried that. Thanks for the info.
    I'm using winxp. But the app must work in Linux, too.
    Abs, May 8, 2004
  4. OscarC

    xarax Guest


    There is apparently some synchronization issues
    between the two threads, causing the second thread
    to block until the first thread has completed its

    What is the behavior when you change the order
    of starting the threads? Will the music play
    and the pictures wait until the music is finished?
    xarax, May 8, 2004
  5. OscarC

    Abs Guest

    Yes, I've tried to reverse the starting order of
    the threads with the same result, the music starts
    after the slideshow.
    Abs, May 8, 2004
  6. OscarC

    xarax Guest

    You're saying the interposing a Thread.sleep(10000) between
    starting the MP3 player thread (1st thread) and the SlideShow
    thread (2nd thread) won't play the music until after the
    sleep() returns and starts the slide show thread and the
    slide show thread finishes?

    Thread t1 = new Thread(new MP3Play());
    Thread t2 = new Thread(new Slideshow(album));

    You will wait for the sleep(), then see the
    entire slide show before the music starts?
    xarax, May 8, 2004
  7. OscarC

    Abs Guest

    It seems it was a problem of thread priorities. I've reduced
    the priority of the slideshow thread and now the 2 threads
    start at the same time.

    Abs, May 8, 2004
  8. OscarC

    Roedy Green Guest

    Roedy Green, May 9, 2004
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