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

Oleg Pekhovskiy oleg.pekhovskiy at oracle.com
Wed Jul 11 09:08:29 PDT 2012

Thank you for the review, Anthony,

please review the next version of fix:

I followed your suggestions there.
I also added 'volatile' for isFlushing because it could be accessed from 
different threads.


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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