Name: dk106046 Date: 07/12/2002

1.4.0-rc-b91

Problem found running the IBM Host On Demand application. The problem is occasional, on NT 4 operating system. The stack dump shows that the volatile image is in the process of going away, and the code is designed to handle this case by creating a new one. However the failure is not the expected one, but an earlier null pointer exception caused by the image being present, but the graphicsconfig within it being null.

java.lang.NullPointerException
       at sun/awt/windows/WVolatileImage.getDeviceColorModel(WVolatileImage.java:161)
       at sun/awt/windows/WVolatileImage.createHWData(WVolatileImage.java:116)
       at sun/awt/windows/WVolatileImage.initAcceleratedBackground(WVolatileImage.java:129)
       at sun/awt/image/SunVolatileImage.validate(SunVolatileImage.java:291)
       at javax/swing/JComponent.paintDoubleBuffered(JComponent.java:4730)

The proposed solution is to add code in WVolatileImage to handle the null pointer exception, and allow the expected failure to happen later:

   protected ColorModel getDeviceColorModel() {
       if (comp != null) {
           Win32GraphicsConfig gc =
              (Win32GraphicsConfig)comp.getGraphicsConfiguration();
            if (gc != null) { /*ibm@52938*/
                try { /*ibm@52938*/
                    return gc.getDeviceColorModel();
                } /*ibm@52938*/
                catch (NullPointerException e) { /*ibm@52938*/
                  /* fall through to return the default */ /*ibm@52938*/
                } /*ibm@52938*/
            } /*ibm@52938*/
        }
        return ((Win32GraphicsConfig)graphicsConfig).getDeviceColorModel();
    }


In this 'belt and braces' approach we are testing both for a null gc, and any failure in getDeviceColorModel - this is probably overkill, as the error found is gc being null.

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