RFR: Utilize parallel workers for GC tasks during safepoints

[Zhengyu Gu]

>> I fail to see any benefit, can you explain? or we can drain satb buffer at
>> the very beginning?
> This is a concurrent marking loop, which is ran concurrently with
> mutator, right? If so, delaying SATB processing to handle excess queues
> might fill up SATB queue prematurely, since all GC workers are busy
> draining the excess queues and not processing SATB at the beginning? I'd
> think draining SATB during the excess queue processing is safer in this
> regard.

Ah, yes.

Thanks,

-Zhengyu


> Thanks,
> -Aleksey
>