Request for Review (M) - 8150994: UseParallelGC fails with UseDynamicNumberOfGCThreads with specjbb2005

Jon Masamitsu jon.masamitsu at oracle.com
Sat Apr 30 01:50:59 UTC 2016


Webrev updated for code review comment.

http://cr.openjdk.java.net/~jmasa/8150994/webrev.01/

Sorry, I muffed the webrev delta but this is the  only change (removal

of the assertion).

src/share/vm/gc/parallel/psParallelCompact.cpp

2249,2250d2248
<           assert(which <= parallel_gc_threads,
<             "Inconsistent number of workers");

Thanks again, Thomas and Kim.

Jon

On 4/12/2016 8:50 PM, Jon Masamitsu wrote:
> The ParallelGC collector compacts by moving live objects from source
> regions to destination regions.  The destination regions are regions 
> that have
> been emptied of live objects and the source regions are regions that hold
> the original locations of the live objects.  When a source region is 
> emptied,
> it becomes a destination region.  At the start of the compaction the
> destination regions are distributed to per thread lists processed by 
> the GC
> workers.   The original implementation had tasks that drain the initial
> destination lists and tasks that steal destination regions from other
> GC workers.  The draining tasks and stealing tasks shared the per thread
> lists of destination regions.  The bug was that the sharing was not
> synchronized correctly.
>
> See [1] for more details.
>
> The fix is to combine the draining tasks and stealing tasks so that
> sharing of the destination lists is not needed.
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8150994
>
> [2] http://cr.openjdk.java.net/~jmasa/8150994/webrev.00/
>
> Thanks.
>
> Jon



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