RFR: Concurrent partial should fix up roots only on cancel

[Zhengyu Gu]

This is actually what I am testing :-) Good.

-Zhengyu

On 10/10/2017 09:33 AM, Aleksey Shipilev wrote:
> Actually, the change in Verifier path in incorrect, correct change is:
> 
> diff -r 5722209e1105 src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp
> --- a/src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp	Tue Oct 10 13:24:55 2017 +0200
> +++ b/src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp	Tue Oct 10 15:33:05 2017 +0200
> @@ -527,7 +527,9 @@
>       if (ShenandoahVerify && ! _heap->cancelled_concgc()) {
>         _heap->verifier()->verify_after_partial();
>       }
> -  } else {
> +  }
> +
> +  if (_heap->cancelled_concgc()) {
>       // Fixup roots to make them consistent
>       _heap->fixup_roots();
>     }
> 
> -Aleksey
> 
> On 10/10/2017 03:30 PM, Zhengyu Gu wrote:
>> Good to me.
>>
>> -Zhengyu
>>
>> On 10/10/2017 09:04 AM, Aleksey Shipilev wrote:
>>> http://cr.openjdk.java.net/~shade/shenandoah/concpartial-fixroots-cancel/webrev.01/
>>>
>>> Obvious when you stare into assert like:
>>>
>>> #  assert(cancelled_concgc()) failed: Only after concurrent cycle failed
>>>
>>> ...because the condition in final_partial_collection is cunning:
>>>
>>>    476   if (_has_work && ! _heap->cancelled_concgc()) {
>>>
>>> ...can call into "else" branch, and thus call heap->fixup_roots() without cancelled GC, when
>>> _has_work=false. This will fail the assert inside fixup_roots(). We should just do that on
>>> cancellation path only.
>>>
>>> Testing: hotspot_gc_shenandoah
>>>
>>> Thanks,
>>> -Aleksey
>>>
> 
>