RFR: Cherry-pick upstream parallel safepoint cleanup (JDK-8180932 and JDK-8185102)

[Zhengyu Gu]

runtime/sweeper.hpp:
only diff is an extra line

Otherwise, looks good to me.

-Zhengyu



On 07/25/2017 09:34 AM, Roman Kennke wrote:
> This change brings Shenandoah repos to what I've pushed upstream
> regarding parallel safepoint cleanup, and reverts the parts that have
> changed during review. Since the upstream patch does not actually
> provide parallel workers (only a GC interface), I added some code to
> Shenandoah that provides workers when specifying
> -XX:ParallelSafepointCleanupThreads=2 or more.
>
> There are some small diffs between upstream and Shenandoah still, but
> this involves the merging of deflation and nmethod marking into GC
> passes. I left them alone for now, until this is upstreamed too.
>
> http://cr.openjdk.java.net/~rkennke/par-safepoint-cleanup-upstream/webrev.00/
> <http://cr.openjdk.java.net/%7Erkennke/par-safepoint-cleanup-upstream/webrev.00/>
>
> Good to go?
>
> Roman
>