Analysis on JDK-8022321 java/lang/ref/ fails intermittently

srikalyan chandrashekar srikalyan.chandrashekar at
Tue Jan 7 02:15:12 UTC 2014

Sure David will give that a try, we have so far attempted to
1. Print state data(as per the test creator peter.levart's inputs),
2. Use UEH(uncaught exception handler per Mandy's inputs)


On 1/6/14 4:40 PM, David Holmes wrote:
> Back from vacation ...
> On 20/12/2013 4:49 PM, David Holmes wrote:
>> On 20/12/2013 12:57 PM, srikalyan chandrashekar wrote:
>>> Hi David Thanks for your comments, the unguarded part(clean and 
>>> enqueue)
>>> in the Reference Handler thread does not seem to create any new 
>>> objects,
>>> so it is the application(the test in this case) which is adding objects
>>> to heap and causing the Reference Handler to die with OOME.
>> The ReferenceHandler thread can only get OOME if it allocates (directly
>> or indirectly) - so there has to be something in the unguarded part that
>> causes this. Again it may be an implicit action in the VM - similar to
>> the class load issue for InterruptedException.
> Run a debug VM with -XX:+TraceExceptions to see where the OOME is 
> triggered.
> David
> -----
>> David
>> I am still
>>> unsure about the side effects of the code change and agree with your
>>> thoughts(on memory exhaustion test's reliability).
>>> PS: hotspot dev alias removed from CC.
>>> -- 
>>> Thanks
>>> kalyan
>>> On 12/19/13 5:08 PM, David Holmes wrote:
>>>> Hi Kalyan,
>>>> This is not a hotspot issue so I'm moving this to core-libs, please
>>>> drop hotspot from any replies.
>>>> On 20/12/2013 6:26 AM, srikalyan wrote:
>>>>> Hi all,  I have been working on the bug JDK-8022321
>>>>> <> , this is a 
>>>>> sporadic
>>>>> failure and the webrev is available here
>>>> I'm really not sure what to make of this. We have a test that triggers
>>>> an out-of-memory condition but the OOME can actually turn up in the
>>>> ReferenceHandler thread causing it to terminate and the test to fail.
>>>> We previously accounted for the non-obvious occurrences of OOME due to
>>>> the Object.wait and the possible need to load the InterruptedException
>>>> class - but still the OOME can appear where we don't want it. So
>>>> finally you have just placed the whole for(;;) loop in a
>>>> try/catch(OOME) that ignores the OOME. I'm certain that makes the test
>>>> happy, but I'm not sure it is really what we want for the
>>>> ReferenceHandler thread. If the OOME occurs while cleaning, or
>>>> enqueuing then we will fail to clean and/or enqueue but there would be
>>>> no indication that has occurred and I think that is a bigger problem
>>>> than this test failing.
>>>> There may be no way to make this test 100% reliable. In fact I'd
>>>> suggest that no memory exhaustion test can be 100% reliable.
>>>> David
>>>>> *
>>>>> **"Root Cause:Still not known"*
>>>>> 2 places where there is a possibility for OOME
>>>>> 1) Cleaner.clean()
>>>>> 2) ReferenceQueue.enqueue()
>>>>> 1)  The cleanup code in turn has 2 places where there is potential 
>>>>> for
>>>>> throwing OOME,
>>>>>      a) thunk Thread which is run from clean() method. This 
>>>>> Runnable is
>>>>> passed to Cleaner and appears in the following classes
>>>>>          java/nio/
>>>>>          sun/misc/
>>>>>          sun/nio/fs/
>>>>>          sun/nio/ch/
>>>>>          sun/misc/Cleaner/
>>>>> However none of the above overridden implementations ever create an
>>>>> object in the clean() code.
>>>>>      b) new PrivilegedAction created in try catch Exception block of
>>>>> clean() method but for this object to be created and to be held
>>>>> responsible for OOME an Exception(other than OOME) has to be thrown.
>>>>> 2) No new heap objects are created in the enqueue method nor
>>>>> anywhere in
>>>>> the deep call stack (VM.addFinalRefCount() etc) so this cannot be a
>>>>> potential cause.
>>>>> *Experimental change to* :
>>>>> - Put one more guard (try catch with OOME block) in the Reference
>>>>> Handler Thread which may give the Reference Handler a chance to
>>>>> cleanup.
>>>>> This is fixing the test failure (several 1000 runs with 0 failures)
>>>>> - Without the above change the test fails atleast 3-5 times for every
>>>>> 1000 run.
>>>>> *PS*: The code change is to a very critical part of JDK and i am 
>>>>> fully
>>>>> not aware of the consequences of the change, hence seeking expert 
>>>>> help
>>>>> here. Appreciate your time and inputs towards this.

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