<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:
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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