RFR: 8361099: Shenandoah: Improve heap lock contention by using CAS for memory allocation [v20]

[Xiaolong Peng]

On Tue, 6 Jan 2026 21:32:30 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Xiaolong Peng has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 265 commits:
>> 
>>  - Merge branch 'openjdk:master' into cas-alloc-1
>>  - Fix build error after merging from tip
>>  - Merge branch 'master' into cas-alloc-1
>>  - Merge branch 'master' into cas-alloc-1
>>  - Some comments updates as suggested in PR review
>>  - Fix build failure after merge
>>  - Expend promoted from ShenandoahOldCollectorAllocator
>>  - Merge branch 'master' into cas-alloc-1
>>  - Address PR comments
>>  - Merge branch 'openjdk:master' into cas-alloc-1
>>  - ... and 255 more: https://git.openjdk.org/jdk/compare/de81d389...cf13b7b5
>
> src/hotspot/share/gc/shenandoah/shenandoahAllocator.cpp line 254:
> 
>> 252:   // Step 1: find out the alloc regions which are ready to refresh.
>> 253:   for (uint i = 0; i < _alloc_region_count; i++) {
>> 254:     ShenandoahAllocRegion* alloc_region = &_alloc_regions[i];
> 
> We've got the heap lock here.  why does this need to be atomic?  Comments in the code should make this clear.

I believe AtomicAccess::load here is not needed, I'll remove it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26171#discussion_r2670262454