RFR: 8377713: Shenandoah: Convert ShenandoahReferenceProcessor to use Atomic<T> [v2]

[William Kemper]

On Tue, 24 Feb 2026 18:00:17 GMT, Ben Taylor <btaylor at openjdk.org> wrote:

>> Modernizes the code as has been done in other areas of Shenandoah and G1 GCs.
>> 
>> The same tier1 tests pass before and after this change on x86_64 and aarch64 linux when run with -XX:+UseShenandoahGC
>
> Ben Taylor has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Change add_then_fetch - 1 to fetch_then_add

Marked as reviewed by wkemper (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29767#pullrequestreview-3863822275