Request for review (XS): 6662086 6u2+, 7b11+: CMS never clears referents when -XX:+ParallelRefProcEnabled

[John Coomes]

Y Srinivas Ramakrishna (Y.S.Ramakrishna at Sun.COM) wrote:
> Fixed: 6662086 6u2+, 7b11+: CMS never clears referents when -XX:+ParallelRefProcEnabled
> 
> This fixes a regression introduced in 6u2, 7b11, because of which CMS would not
> correctly clear referents when +ParallelRefProcEnabled. This was because
> the CMSIsAliveClosure used during the processing was using an empty span.
> The symptom would typically manifest as a monotonically growing population
> of referents until a stop-world mark-compact collection would reclaim them.
> 
> ...
> 

Looks fine.  One tiny nit relating to the patch hunk below:

> --- old/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Thu May  1 16:05:12 2008
> +++ new/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Thu May  1 16:05:11 2008
> @@ -5531,7 +5532,8 @@
>                                          _mark_bit_map, work_queue(i));
>    CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
>                                                   _mark_bit_map, work_queue(i));
> -  CMSIsAliveClosure is_alive_closure(_mark_bit_map);
> +  assert(_collector->_span.equals(_span), "Inconsistency in _span");
> +  CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
>    _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
>    if (_task.marks_oops_alive()) {
>      do_work_steal(i, &par_drain_stack, &par_keep_alive,

The new assert appears after two other uses of _collector and _span,
one of which is visible above.  Assuming that all uses have the same
requirement, might as well move the assert before the first use.

-John