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

[mikhail cherkasov]

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.
>
> 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
> 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.
>
> 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.
>>
>