RFR: 8229044: G1RedirtyCardsQueueSet should be local to a collection

[Kim Barrett]

> On Aug 3, 2019, at 3:10 PM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi,
> 
> On 03.08.19 01:43, Kim Barrett wrote:
>> Please review this change to the use of G1RedirtyCardsQueueSet.
>> Rather than a singleton instance in the G1CollectedHeap that is reused
>> by each collection pause, we now (stack) allocate one for use by the
>> current collection pause.
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8229044
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8229044/open.00/
>> Testing:
>> mach5 tier1-5
> 
>  looks good. Thanks.
> 
> I was wondering whether at some point we should extract all transient GC state coupled with the actual algorithms applied into a separate class. But that's probably something for the future :)
> 
> Thomas

Thanks.

I thought about putting the redirty set directly in the ParScanThreadStateSet with an
accessor and passing that set to more places, but that seemed like it would make it
more difficult to understand the usage of the ParScanThreadState[Set].

I also thought about putting it in the EvacuationInfo, but what’s there seems to be
accounting stuff and not otherwise interesting data structures.  And again, I’d probably
prefer to extract the redirty set to pass into call trees that need it and not all the other
stuff.

I think part of the problem is that there’s just a lot of varied state shared between various
largish pieces of the collector.  Finding ways to reduce that would be nice, but detangling
is often hard work.