RFR(xs): 8134749: SoftReferences declared dead too early

[Per Liden]

Hi Jon,

On 2015-08-31 20:20, Jon Masamitsu wrote:
> Per,
>
> Change looks good.
>
> Could you please run some tests with your fix and
> -XX:+UseDynamicNumberOfGCThreads and
> -XX:+UseParallelGC threads?  UseDynamicNumberOfGCThreads sometimes moves
> work among the queues to get them into queues that will be processed by
> an active
> GC worker.  Thanks.
>

Thanks for looking at the patch. I'll do some test runs with those options.

cheers,
/Per


> Jon
>
>
> On 08/31/2015 07:15 AM, Per Liden wrote:
>>
>> Hi,
>>
>> While preparing a different patch I looked through the
>> ReferenceProcessor and noticed what looks like a silent mistreatment
>> of SoftReferences.
>>
>> Summary: RefProcPhase1Task uses WorkerThread::id() to select the list
>> to process. After the recent changes to how WorkGang works[1], this no
>> longer guarantees that all reference lists are processed. This in turn
>> means we might kill SoftReferences even when the policy says they
>> should be kept alive.
>>
>> The fix here would be to use the worker_id (named "i" in this code)
>> passed into the Task's work() function instead of using
>> WorkerThread::id().
>>
>>
>> [1] There's no longer any guarantee that all GangWorker threads will
>> execute the Task's work() function, since a quick-to-wakeup worker
>> thread might steal the work intended for a slow-to-wakeup worker thread.
>>
>>
>> Webrev: http://cr.openjdk.java.net/~pliden/8134749/webrev.0/
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8134749
>>
>> Testing: jprt
>>
>>
>> Btw, I'll to send out a follow-up patch (JDK-8134744) which makes sure
>> WorkerThread::id() and the worker_id always match to avoid this type
>> of bugs in the future.
>>
>> /Per
>