Re: java.lang.IllegalStateException: Deadlock risk: AWT tree lock acquired on a showing component..

Eric Sosman <>
Thu, 24 May 2007 17:07:04 -0400
Cherukan wrote On 05/24/07 14:45,:


I get this error when trying to popup a Swing dialog from a long-
running background thread.

java.lang.IllegalStateException: Deadlock risk: AWT tree lock acquired
on a
showing component when not on the event dispatch thread. (NOTE: do
*not* use
invokeAndWait to fix this assertion failure; that will increase the
chance of
actual deadlock.)
Thread name: task1-1438375310
       at java.awt.Component.getTreeLock(
       at java.awt.Component.getLocationOnScreen(

I realize this is happening because the current thread is not the
event thread.

But the background thread must get this input from the user to
proceed. Also the input
depends on the processing the thread has done upto this point, so it
cannot be
obtained before the thread has started. After the swing dialog has
closed, the thread
needs to resume its processing picking up where it left off.

As the message says, I cant use invokeAndWait.

Whats the 'safe' approach in such a case?

    (Warning: not tested.) The long-running worker
thread uses invokeLater() to cause the EDT to display
the dialog, and then puts itself to sleep by calling
wait() on some convenient object. When the dialog
gets the desired response, it puts the input into the
aforementioned convenient object and calls notify()
to awaken the sleeping worker thread.


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