RFR: Parallel verification

[Roman Kennke]

Am 03.07.2017 um 12:56 schrieb Aleksey Shipilev:
> Hi,
>
> Verification takes a while now, since we are verifying lots of floating garbage
> (still marked, and can be walked by GC). I think we can trivially parallelize it:
>   http://cr.openjdk.java.net/~shade/shenandoah/verifier-parallel/webrev.01/
>
> We are deliberately not using work-stealing, because we don't want to rely on
> ShTQ correctness, and not using usual ShHeap region iterators for the similar
> reason.
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
>
I am undecided. On the one hand, it is nice to verify stuff fast. On the
other side, the verifier should be as simple as possible, such that we
can trivially see that it's doing the right thing. Parallelization goes
against that IMO. I think this patch is still ok (but maybe that's just
me, because I have done this so often, I can tell that it's correct),
but I wouldn't introduce more complexity into the verifier unless really
necessary. There's not much point in making that code superfast, but
there's the whole point of making it work correctly... Up to you!

Roman