RFR: 8231672: Simplify the reference processing parallelization framework [v5]

[Leo Korinth]

On Sat, 24 Apr 2021 09:32:44 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Leo Korinth has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:
>> 
>>  - make RefProcTask a StackObj
>>  - Merge branch 'master' into _8231672
>>  - using proxies instead of ClosureContexts
>>  - remove maybe prefix, change in one place to nullable
>>  - Merge branch 'master' into _8231672
>>  - Changes after first review
>>  - 8231672: Simplify the reference processing parallelization framework
>
> src/hotspot/share/gc/parallel/psCompactionManager.hpp line 42:
> 
>> 40: 
>> 41: class ParCompactionManager : public CHeapObj<mtGC> {
>> 42:   friend class CompactionWithStealingTask;
> 
> `CompactionWithStealingTask` and `UpdateAndFillClosure` are dead code.

I will remove them.

> src/hotspot/share/gc/shared/referenceProcessor.hpp line 591:
> 
>> 589: enum class RefProcThreadModel { Multi, Single };
>> 590: 
>> 591: class RefProcTask : StackObj {
> 
> Maybe put some comments here, explaining what `RefProcTask` and `RefProcProxyTask` are, their interaction/relation.

I will try to do that.

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PR: https://git.openjdk.java.net/jdk/pull/2782