<AWT Dev> [7u6] Review request for 7177040: Deadlock between PostEventQueue.noEvents, EventQueue.isDispatchThread and SwingUtilities.invokeLater

Anton V. Tarasov anton.tarasov at oracle.com
Thu Jul 12 06:27:14 PDT 2012

Hi Oleg,

I see nothing wrong in the fix. Hope you've run all the tests related.


On 11.07.2012 20:08, Oleg Pekhovskiy wrote:
> Thank you for the review, Anthony,
> please review the next version of fix:
> http://cr.openjdk.java.net/~bagiras/7u6/7177040.2
> I followed your suggestions there.
> I also added 'volatile' for isFlushing because it could be accessed from different threads.
> Thanks,
> Oleg
> 7/11/2012 7:35 PM, Anthony Petrov wrote:
>> Hi Oleg,
>> 1. I suggest to rename isPending to isFlushing, as it reflects the current state of the 
>> PostEventQueue more precisely.
>> 2. I suggest to use the try{}finally{} pattern to set/reset the new flag in the flush() method to 
>> ensure the flag is reset even if the while() loop throws an exception.
>> Otherwise the fix looks good.
>> -- 
>> best regards,
>> Anthony
>> On 7/11/2012 7:24 PM, Oleg Pekhovskiy wrote:
>>> Hi!
>>> Please review the fix for CR:
>>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7177040
>>> Webrev:
>>> http://cr.openjdk.java.net/~bagiras/7u6/7177040.1
>>> The idea of the fix is that there are two concurrent threads that try to get two synchronization 
>>> objects EventQueue.pushPopLock and PostEventQueue itself.
>>> For NetBeans these threads are (EDT & WarmUp) or (EDT & TimerQueue).
>>> Problem happens when EDT is interrupted and goes to EventQueue.detachDispatchThread() where 
>>> EventQueue.pushPopLock is owned and
>>> EDT is waiting to own PostEventQueue when calling SunToolkit.isPostEventQueueEmpty() -> 
>>> PostEventQueue.noEvents().
>>> At the same time another thread calls EventQueue.postEvent() that calls 
>>> EventQueue.flushPendingEvents() -> PostEventQueue.flush() where PostEventQueue is owned
>>> and another thread is waiting to own EventQueue.pushPopLock when calling EventQueue.postEvent() 
>>> -> EventQueue.postEventPrivate().
>>> To avoid potential deadlock I moved synchronization out of postEvent()'s cycle in 
>>> PostEventQueue.flush(),
>>> but to be clear about the existence of Events that are not posted to EventQueue yet I added 
>>> PostEventQueue.isPending flag that is true until the end of the cycle.
>>> There are only two classes that utilize PostEventQueue.flush() method: 
>>> SunToolkit.flushPendingEvents() and SunToolkitSubclass.flushPendingEvents().
>>> They are both synchronized by static SunToolkit.flushLock. That eliminates the situation when we 
>>> have overlapped calls of PostEventQueue.flush().
>>> Thanks,
>>> Oleg

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