RFR: 8295871: G1: Use different explicit claim marks for CLDs [v2]

[Albert Mingkun Yang]

On Wed, 9 Nov 2022 17:30:47 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi all,
>> 
>>   can I have reviews for this follow-up to [JDK-8295118](https://bugs.openjdk.org/browse/JDK-8295118) that removes the need to clear CLD claim marks for every full gc phase by using different claim values for the different phases.
>> 
>> Some comments:
>> * I used new g1 specific claim values instead of overloading the existing ones, which is imho clearer. I am open to better names, but something like `_claim_strong_2/3` seemed too cryptic. Then again, there is now a collector specific name in the enum. Maybe the enum values should be made collector-specific in some way? Currently they already are (e.g. `_claim_finalizable` is only used in ZGC) as G1 does not need the values except for (multiple) `_claim_strong`.
>> * I moved the CLD mark verification for the mark phase from `prepare_collection` to the constructor of `G1FullGCMarker`; I think this place is more fitting as directly above there is the use in the `CLDToOopClosure`. Also this pattern aligns with the use in the `G1FullGCAdjustTask`.
>> 
>> Testing: tier1-5
>> 
>> Thanks,
>>   Thomas
>
> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   rename claim bits

src/hotspot/share/classfile/classLoaderData.hpp line 209:

> 207:     _claim_strong                   = 3,
> 208:     _claim_strong_stw_fullgc_mark   = 4,
> 209:     _claim_strong_stw_fullgc_adjust = 8,

I feel having `strong` in their names can be misleading -- there are no "finalizable" counterparts for them; IOW, there is only one kind of strength for `*_mark/adjust`. What do others think?

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PR: https://git.openjdk.org/jdk/pull/10989