HELP: Using MediaTracker causes OutOfMemoryError

[K Duke]

Hello everyone:
I am trying to create a simple JApplet animation sequence using (about) 129 JPEG images. I am using a MediaTracker object to keep track of image loading.
--------------------------------------------------------------

tracker = new MediaTracker(this);
for(int i=0; i<images.length; i++) {    
 tracker.addImage(images[i], 0);    
 isLoadError = tracker.isErrorAny();}
try {    
 tracker.waitForAll(); // Causes OutOfMemoryError here}  
catch(InterruptedException ie) { }

-------------------------------------------------------------------
After adding all images to a Mediatracker object, I call the waitForAll() method to ensure all images are loaded before I call paint. I am using a Swing Timer object that fires every 100 ms, and calls repaint(). Decreasing the number of images to 10 or so obviously prevents the OutOfMemoryError.
However, I MUST to be able to load all 129 images before I render the animation sequence.
Any suggestions? Thanks in advance.

[Joe Ess]

Use smaller images?

[K Duke]

Originally posted by Joe Ess:
Use smaller images?

Assuming that is *NOT* an option, Is there any other way?

[K Duke]

By the way, the images are around 70 KB each.

[Joe Ess]

The only thing I can think of, if indeed loading the images is the problem, is that the VM is so busy loading all 129 images, it doesn't get a chance to request more memory from the system and that's what causes it to run out of memory. Try loading the images in blocks of 10 or 20. Call Thread.yield() at the end of each loop to let the system catch up. It's not the most efficient thing, but it's better than hitting the wall when running out of memory.

[Nathan Pruett]

That's not going to stop an OutOfMemoryError... that actually means you have used up all the available JVM heap memory. There are commands to configure the maximum heap sizes of the JVM, but none of these are going to be available to you if you're running as an Applet. You're going to have to cut down on the number of images you're loading or their size ( very, very drastically... because I'm getting OutOfMemoryErrors with as few as *7* 50K images...) or use some kind of actual video package (i.e. JMF or Quicktime for Java ) for this.
[ October 23, 2003: Message edited by: Nathan Pruett ]

[K Duke]

I am trying to add each image to a MediaTracker object using a loop:
for(int i=imgFirst, j=0; i<=imgLast; i++, j++) {
images[j] = getImage(getCodeBase(), imgDir + separator + imgName
+ i + imgExt);
tracker.addImage(images[j], j+1);
}
Once I am done displaying the image, will the call:

tracker.removeImage(image[j], j+1);

followed by a call:

System.gc();

free memory used to load images that have been displayed already.
I was thinking of freeing memory in a separate thread while the main thread displays the image. I am having some problems synchronizing the two threads.
Do you think this is a good idea?

[Nathan Pruett]

Doh! I forgot about removeImage!

Yes, it looks like the reason MediaTracker is causing an OutOfMemoryException is because the MediaTracker saves an extra copy. Calling removeImage() must null this copy out.

Here's the code I was using to test it out... it might help you -

package test.mediatracker;
 
import java.awt.Graphics;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.Toolkit;
 
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
 
public class MTTest extends JFrame {
    
    private ImagePanel p;
    private Loader loader;
    
    public MTTest() {
        super( "MediaTrackerTest" );
        p = new ImagePanel();
        getContentPane().add( p );
        
        loader = new Loader( p );
        Thread t = new Thread( loader );
        t.start();
    }
    
    public void setVisible( boolean b ) {
        super.setVisible( b );
        loader.isVisible( b );
    }
    
    public static void main(String[] args) {
        JFrame f = new MTTest();
        f.setBounds( 300, 300, 300, 300 );
        f.setDefaultCloseOperation( EXIT_ON_CLOSE );
        f.setVisible( true );
    }
    
    private static class ImagePanel extends JComponent {
        private Image i;
        private int count;
        
        public void paintComponent( Graphics g ) {
            if ( i != null ) {
                g.drawImage( i, 0, 0, this );
            }
            g.drawString( Integer.toString( count ), 50, 50 );
        }
        
        public void setImage( Image i ) {
            this.i = i;
            count+=1;
            this.repaint();
        }
    }
    
    private static class Loader implements Runnable {
        
        private volatile boolean visible = false;
        private volatile boolean alive = true;
        private MediaTracker tracker;
        private Image current;
        private Image buffer;
        private int index = 0;
        private int last = 12;
        private boolean isLoadError = false;
        private ImagePanel p;
        
        public Loader( ImagePanel p ) {
            this.p = p;
            tracker = new MediaTracker( p );
        }
        
        public void run() {
            while ( alive ) {
                if ( visible ) {
                    try {
                        tracker.removeImage( buffer );
                        buffer = Toolkit.getDefaultToolkit().getImage( "image" + index + ".jpg" );
                        index++;
                        if ( index >= last ) {
                            index = 0;
                        }
                        tracker.addImage( buffer, 0 );
                        tracker.waitForID( 0 );
                        current = buffer;
                        System.gc();
                        SwingUtilities.invokeAndWait( new Runnable() {
                            public void run() {
                                p.setImage( current );
                            }
                        } );
                        Thread.sleep( 100 );
                    } catch ( Exception x ) {
                        x.printStackTrace();
                    }
                }
            }
        }
        
        public void isVisible( boolean b ) {
            visible = b;
        }
    }
}

[K Duke]

Hi Nathan,
Thanks a lot. It does work. I was initially using a Timer to fire events every X msec, and loading the images in a separate thread. I faced some synchronization problems.
Your approach works fine. The problem is that I am trying to simulate a movie effect by displaying about 10 fps or more. So the time delay between slices is about 100 ms or less. The thread loop takes more than 100 ms to remove the old image, load the new image and call the garbage collector. So the time between 2 images is now > 100 ms (on an average about 200 ms). I am trying to get the delay between images down to 50 ms.
I call System.currentMillis() before image display, and the second time after it does the remove-load-gc sequence, and this difference is about 200 ms.
Thanks.