RFR: Utilize parallel workers for GC tasks during safepoints

[Roman Kennke]

Hi Zhengyu,

I like it!

For going from N par threads to M conc threads, you let the conc
threads claim the extra queues. For the other direction (i.e. final-
mark), are you relying on stealing to see the extra par queues?

Fine to commit.

/Roman

Am Freitag, den 18.11.2016, 14:27 -0500 schrieb Zhengyu Gu:
> The change allows Shenandoah GC to utilize parallel GC workers during
> STW safepoints, without the restriction imposed by the number of
> concurrent GC threads.
> 
> The main purpose of the change is to allow us scale up/down GC
> concurrent and parallel workers independently.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/workers/webrev.00/
> 
> 
> Tests:
> 
> - jcstress (fastdebug)
> - Shenandoah GC test (fastdebug and release)
> - SPECjbb (fastdebug and release)
> - SPECjvm (fastdebug)
> 
> 
> Thanks,
> 
> -Zhengyu
>