Name: md23716 Date: 08/23/2001

A paint() method invocation of an awt Component from a synchronized block can result in a deadlock.

The deadlock occurs between the AWT-EventQueue-0 and the user thread(in this case, ProxyEventQueue). The AWT-EventQueue-0 acquires the class instance and waits for the AWT Tree lock. The user thread acquires the AWT tree lock (may be through a validate() call) and waits for the lock on the class instance.

The AWT tree lock was introduced in 1.3 and which was not present in 1.2.

Source code that demonstrates the problem:
synchronized void clearScreen(){
       changeCursor(OFF,false);
       offscreen.setColor(color_bg);
       offscreen.fillRect(0, 0, screenWidth, screenHeight);
       changeCursor(ON,false);
       if (dragBox)
         drawDragBox();
       repaint();
    }

Suggested solution is to change the documentation for the paint() method regarding the AWT tree lock, if the method is being called from inside a synchronized block.

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