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

Kim Barrett kim.barrett at
Fri Apr 29 21:41:19 UTC 2016

> On Apr 12, 2016, at 11:50 PM, Jon Masamitsu <jon.masamitsu at> 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]
> [2]
> Thanks.
> Jon

Looks good.

2248         if (++which == parallel_gc_threads) {
2249           assert(which <= parallel_gc_threads,

The comparison on 2248 was changed from task_count (which no longer
exists) to parallel_gc_threads, thereby guaranteeing the asserted


More information about the hotspot-gc-dev mailing list