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

Jon Masamitsu jon.masamitsu at oracle.com
Mon Aug 31 18:20:58 UTC 2015


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.

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



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