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Thread: Getting Image reader to change source

  1. #1
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    Default Getting Image reader to change source

    I'm building an image gallery type program. I want to be able to abort the loading of an image and start loading another. Here's some of the code I've got so far.

    ImageReader reader = null;
    File image1 = "myFile.jpg";
    File image2 = "myFile2.jpg;
    ImagePanel imgPnl = new ImagePanel();
     
    public void loadImage(File f) {
        if(reader != null) reader.abort();
     
        //get file extention
        String filename = f.getName();
        int pos = filename.lastIndexOf('.');
        String ext = filename.substring(pos+1);
     
        Iterator readers = ImageIO.getImageReadersByFormatName(ext);
        ImageInputStream iis = null;
     
        try { 
            iis = ImageIO.createImageInputStream(f);
        } catch (IOException ex) { 
            ex.printStackTrace();
        }
     
        reader = (ImageReader) readers.next();
        reader.setInput(iis);
        reader.addIIOReadProgressListener(new MyProgressListener());
        reader.addIIOReadUpdateListener(new MyUpdateListener());
     
        Thread thread = new Thread(new Runnable() {
            public void run() {
                try {
                    reader.read(0);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
     
        thread.start();
    }
     
    // Component that draw a BufferedImage
    class ImagePanel extends JPanel {
        private BufferedImage img;
     
        public void setImage(BufferedImage img) {
            this.img = img;
            this.repaint();
        }
     
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            if(img != null)
                g.drawImage(img, 0, 0, null);
        }
    }
     
    class MyProgressListener implements IIOReadProgressListener {
        ...
    }
     
    class MyUpdateListener implements IIOReadUpdateListener {
        ...
        public void imageUpdate(ImageReader source, BufferedImage theImage, int minX, int minY, int width, int height, int periodX, int periodY, int[] bands) {
            imgPnl.setImage(theImage);
        }
        ...
    }

    So, if the image is still loading (from the new thread) I can call loadImage() with a different file and it aborts and then begins to work on the new file. This does work, but pretty quickly I run into errors like this:

    Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Attempt to use instance of com.sun.imageio.plugins.jpeg.JPEGImageReader@6c1989b5 locked on thread Thread[Thread-10,6,main] from thread Thread[AWT-EventQueue-0,6,main]

    What's causing this and how do I fix it?


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Getting Image reader to change source

    The message says you are trying to use the same instance of a class on two threads.
    Perhaps the class is not thread safe in some way.
    Can you make a new instance for each thread?
    Or synchronize the method that uses it.

  3. #3
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    Default Re: Getting Image reader to change source

    I thought about using only one instance, but if my next file is in a different format, I need a new ImageReader.

    I was just looking into Thread.join() and I thought the problem could be that I'm not waiting for the thread using the ImageReader to terminate properly. I now store a reference to the reader thread and interrupt() + join() on it when trying to load a different image. I also put an interrupted check in one of the frequently called methods in the IIORead listeners.

    So far so good, no errors yet. Hope this is a decent way of handling this situation; I'm new to thread programming.

    ImageReader reader = null;
    File image1 = "myFile.jpg";
    File image2 = "myFile2.jpg;
    ImagePanel imgPnl = new ImagePanel();
    Thread activeThread = null;
     
    public void loadImage(File f) {
     
        if(activeThread != null) {
            if(activeThread.getState() != Thread.State.TERMINATED) {
                try {
                    activeThread.interrupt();
                    activeThread.join();
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
            }
        }
     
        //get file extention
        String filename = f.getName();
        int pos = filename.lastIndexOf('.');
        String ext = filename.substring(pos+1);
     
        Iterator readers = ImageIO.getImageReadersByFormatName(ext);
        ImageInputStream iis = null;
     
        try { 
            iis = ImageIO.createImageInputStream(f);
        } catch (IOException ex) { 
            ex.printStackTrace();
        }
     
        reader = (ImageReader) readers.next();
        reader.setInput(iis);
        reader.addIIOReadProgressListener(new MyProgressListener());
        reader.addIIOReadUpdateListener(new MyUpdateListener());
     
        activeThread = new Thread(new Runnable() {
            public void run() {
                try {
                    reader.read(0);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
     
        activeThread.start();
    }
     
    // Component that draw a BufferedImage
    class ImagePanel extends JPanel {
        private BufferedImage img;
     
        public void setImage(BufferedImage img) {
            this.img = img;
            this.repaint();
        }
     
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            if(img != null)
                g.drawImage(img, 0, 0, null);
        }
    }
     
    class MyProgressListener implements IIOReadProgressListener {
        ...
    }
     
    class MyUpdateListener implements IIOReadUpdateListener {
        ...
        public void imageUpdate(ImageReader source, BufferedImage theImage, int minX, int minY, int width, int height, int periodX, int periodY, int[] bands) {
            if(Thread.interrupted()) {
                source.abort();
                return;
            }
            imgPnl.setImage(theImage);
     
        }
        ...
    }

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