<AWT Dev> RFR: 7185258 [macosx] Deadlock in SunToolKit.realSync()

Sergey Bylokhov Sergey.Bylokhov at oracle.com
Sun Apr 12 11:05:34 UTC 2020

Hi, Phil.

I completely forgot about that version of the fix, here are my thoughts about it.
It does not fix the test in question, it is still executed too slow, and fails by the
timeout, the reason is that it does not take into account the blocked events when DnD
is active.

That version had two parts:
  - The code which avoids the deadlock(actually it avoid an infinite waiting):
    That was already fixed as part of JDK-8080504, and this is why I cannot reproduce it now:

  - The part which tried to tweak the default timeout and had some code to stop waiting:
    If I understand the code above correctly then on EDT it will wait no more than 500 ms,
    and in other cases will wait till the timeout, the same could be achieved w/o the loop by the:
         if (EventQueue.isDispatchThread()) {
             // do not block EDT for a long time
             timeout = XX;
         return nativeSyncQueue(timeout);

I think that it could be useful to minimize blocking EDT, so decided to merge this part to the current fix:


On 4/7/20 3:04 pm, Philip Race wrote:
> There were previous attempts to fix this on mac :
> https://mail.openjdk.java.net/pipermail/awt-dev/2013-December/006719.html
> https://mail.openjdk.java.net/pipermail/awt-dev/2014-January/006809.html
> https://mail.openjdk.java.net/pipermail/awt-dev/2014-February/007047.html
> which you reviewed. Can you comment on how the current proposal avoids
> the problems raised there ?
> -phil.
> On 4/6/20, 12:20 AM, Sergey Bylokhov wrote:
>> Hello.
>> Please review the fix for jdk/client.
>> Bug: https://bugs.openjdk.java.net/browse/JDK-7185258
>> Fix: http://cr.openjdk.java.net/~serb/7185258/webrev.01
>> The Robot.waitForIdle and SunToolKit.realSync() may hang if executed when DnD is
>> in progress, because they posts native events to the application and waits when
>> these event will be dispatched. During DnD this events are blocked, so every call
>> to waitForIdle will hang for a timeout(which is 10 seconds) per native event check.
>> This may appear as a deadlock.
>> The similar bug was fixed on windows:
>> http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/7658a78a93de
>> Solution on macOS is similar, skips the native checks when the DnD is in progress.

Best regards, Sergey.

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