How does deadlocking happen when not updating UI on swing thread?

Question

It looks like the 2 objects that cause the deadlock are the RepaintManager and the JComponent.LOCK object...but I can't really find a scenario where this happens in the code.
Can anybody shed some light on this?

Answer 1

Basic rule of thumb:
If you can't guarantee that your code will run on the AWT-Event thread then wrap your calls in a SwingUtilities.invokeLater() call (or its cousin invokeAndWait()).
Basically this looks like:
SwingUtilities.invokeLater(new Runnable() {
public void run() {
// put your gui updating code here
There are two ways to make something thread safe:
1) Guarantee calls will always come from the same thread
2) Synchronized shared objects.
Swing chose choice 1 since choice 2 would be two big of a performance hit. The thread it uses is the AWT-Event thread. The invokeLater call tosses your Runnable object at the end of the Event Queue. The AWT-Event thread pops a Runnable off the Event Queue processes it and then repeats.
As to specifically whats happening, I can't say without more information. Really you should go back and make sure all your Swing calls are on the AWT-Event thread. That should solve your current problem and prevent future problems.