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

[Philip Race]

Ok, approved

phil.

On 4/12/20, 4:05 AM, Sergey Bylokhov wrote:
> 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):
>    
> http://cr.openjdk.java.net/~pchelko/9/7185258/webrev.01/src/macosx/native/sun/osxapp/NSApplicationAWT.m.sdiff.html
>    That was already fixed as part of JDK-8080504, and this is why I 
> cannot reproduce it now:
>    http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/e06161762a72
>
>  - The part which tried to tweak the default timeout and had some code 
> to stop waiting:
>    
> http://cr.openjdk.java.net/~pchelko/9/7185258/webrev.01/src/macosx/classes/sun/lwawt/macosx/LWCToolkit.java.sdiff.html
>    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:
>
> http://cr.openjdk.java.net/~serb/7185258/webrev.02/
>
>
> 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.
>>>
>>>
>
>