RFR: 8273559: Shenandoah: Shenandoah should support multi-threaded heap dump [v3]

[Aleksey Shipilev]

On Mon, 13 Sep 2021 13:34:28 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> At the point when Shenandoah implemented heap dump, there was no ClassLoaderData::_claim_other flag. To avoid CLDG iteration interfering concurrent GC, we chosen single-threaded CLDG iteration with ClassLoaderData::_claim_none and ensured that by asserting calling thread has to be VMThread.
>> 
>>  JDK-8237354 broke the assumption, as it uses safepoint worker to execute heap dump, so that the thread executes CLDG iteration is not necessary VMThread.
>> 
>> Now, with new ClassLoaderData::_claim_other, we can enable multi-threaded CLDG iteration during heap dump.
>> 
>> Test:
>> 
>> - [x] hotspot_gc_shenandoah
>> - [x] tier1 with Shenandoah GC
>
> Zhengyu Gu has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
> 
>  - Merge
>  - Aleksey and Severin's comments
>  - 8273559: Shenandoah: Shenandoah should support multi-threaded heap dump

Marked as reviewed by shade (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/5473