<AWT Dev> Review Request for 8065709: Deadlock in awt/logging apparently introduced by 8019623

mikhail cherkasov mikhail.cherkasov at oracle.com
Thu Jan 22 10:42:45 UTC 2015

Hi Anton, Sergey,

Anton advised today to implement eager initialization of  EQ's logger 
instead of lazy initialization of EQ's logger.
So now it will be initialized out of any AppContext's lock and I thinks 
it's definitely better solution because
no ugly getLogger methods, less changes and now we know when and where 
logger will be initialized.

Could you please review a new version:
http://cr.openjdk.java.net/~mcherkas/8065709/webrev.03/ ?


On 1/20/2015 8:14 PM, Sergey Bylokhov wrote:
> On 20.01.2015 19:08, Anton V. Tarasov wrote:
>> Hi Mikhail,
>> Ok, you removed the new lock at least. Looks better now (no more 
>> comments from me). Thank you!
> Personally I prefered to remove this logging, but this version looks 
> fine also.
>> Regards,
>> Anton.
>> On 20.01.2015 17:26, mikhail cherkasov wrote:
>>> Hi Anton,
>>> please check new version: 
>>> http://cr.openjdk.java.net/~mcherkas/8065709/webrev.01/src/share/classes/java/awt/EventQueue.java.udiff.html
>>> I applied changes advised by your in offline, the synchronization 
>>> and second check for null was removed.
>>> PlatformLogger.getLogger is already synchronized and can be treated 
>>> as sync block and second check.
>>> Thanks,
>>> Mikhail.
>>> On 1/19/2015 10:38 PM, Anton Tarasov wrote:
>>>> On 19/01/15 19:15, mikhail cherkasov wrote:
>>>>> On 1/19/2015 5:59 PM, Anton V. Tarasov wrote:
>>>>>> Hi Mikhail,
>>>>>> It seems the problem is not limited to EventQueue only. Even if 
>>>>>> you solve it for EventQueue, the EventQueue ctor may cause a 
>>>>>> chain of calls where some other AWT class is first accessed and 
>>>>>> initialized. What if it contains the same getLogger() call in a 
>>>>>> static block?
>>>>> it can, but currently EventQueue doesn't do such things.
>>>> I guess that it's nearly impossible to guarantee that AppContext 
>>>> ctor will never ever call anything containing uninitialized loggers.
>>>>>> If you agree with this, then there should be a generic solution 
>>>>>> for the deadlock.
>>>>>> What comes to my mind is the following. The deadlock happens due 
>>>>>> to a reverse lock taking order. Can we change it?
>>>>>> In LogManager.getUserContext() it seems like the javaAwtAccess 
>>>>>> lock scope can be narrowed down. Namely, we can move the 
>>>>>> javaAwtAccess.getAppletContext() line out of it.
>>>>> it's already done:
>>>>> http://hg.openjdk.java.net/jdk9/dev/jdk/rev/83f20d8bc13a
>>>> Oh, thanks, I didn't read all the discussion the first time. Well, 
>>>> I see there's another deadlock involving the 
>>>> sun.util.logging.PlatformLogger class...
>>>>>> In which case the method implementation should be additionally 
>>>>>> synchronized. For instance, we can use the getAppContextLock for 
>>>>>> the whole body of the method. Is the method implemented somewhere 
>>>>>> else except the AppContext class?
>>>>>> Will it work from your point of view? (Probably, I didn't take 
>>>>>> into account all the details.)
>>>>> All this tricky synchronizations was done on purpose, I believe it 
>>>>> was done for performance sake.
>>>>> So I want to make as less changes as possible, it's better to 
>>>>> still miss couple cases then introduce a
>>>>> new big issue in the last public update. Anyway, this fix plus 
>>>>> http://hg.openjdk.java.net/jdk9/dev/jdk/rev/83f20d8bc13a
>>>>> should cover all cases, the only possible if EQ ctor will lead to 
>>>>> javaAwtAccess, but it doesn't.
>>>> Ok, I'm fine with the fix (it looks harmless). However, I can't say 
>>>> I like it because it introduses new lock and breaks consistency (in 
>>>> all the other cases we get loggers directly)...
>>>> I'd look for any better solution in an appropriate time slot.
>>>> Reagards,
>>>> Anton.
>>>>>> Regards,
>>>>>> Anton.
>>>>>> On 16.01.2015 17:18, mikhail cherkasov wrote:
>>>>>>> Hi all,
>>>>>>> JBS: https://bugs.openjdk.java.net/browse/JDK-8065709
>>>>>>> Webrev: http://cr.openjdk.java.net/~mcherkas/8065709/webrev.00/
>>>>>>> AppContext creation is guarder by getAppContextLockand, but 
>>>>>>> during AppContext creation
>>>>>>> we also call EventQueue initialization, during EQ initialization 
>>>>>>> logger initialization happens
>>>>>>> it acquires "javaAwtAccess".  if "javaAwtAccess" is acquired by 
>>>>>>> other it can lead to deadlock:
>>>>>>> T1 T2
>>>>>>> start AppContext  creation
>>>>>>> acquire javaAwtAccess
>>>>>>> acquire getAppContextLock
>>>>>>> init EQ                                         call getAppContext
>>>>>>> init Logger                                   waiting for 
>>>>>>> getAppContextLock
>>>>>>> waiting for javaAwtAccess
>>>>>>> I applied the fix suggested in jbs comments by Petr.
>>>>>>> I replaced eager logger initialization in EQ with lazy, so we 
>>>>>>> won't invoke Logger
>>>>>>> during EQ initialization as result no deadlock.
>>>>>>> Thanks,
>>>>>>> Mikhail.

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