Alex, we don't have much to go on, particularly since you do not
indicate how you're blocking the thread.  I'm betting you're waiting on
a synchronized class.  But some extra stuff:

        - Swing calls must occur from the event thread, but construction etc.
of Swing objects can be done in the main thread no problem.
        - You can force something to be done from within Swing's event thread
with SwingUtilities.invokeLater(...)

Sean