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

Per Liden per.liden at oracle.com
Mon Aug 31 14:15:50 UTC 2015


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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