RFR: 8376531: Genshen: Convert ShenandoahOldGeneration to use Atomic<T> [v2]

Wed Jan 28 21:27:09 UTC 2026

On Tue, 27 Jan 2026 23:49:18 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> Came across the source code of ShenandoahOldGeneration, and noticed that we use AtomicAccess to read/write to fields `_promoted_expended`, `_promotion_failure_count`, `_promotion_failure_words` but non of them is declared with volatile modifier.
>> 
>> Given that OpenJDK has introduced `Atomic<T>` to replace the idiom of volatile var plus AtomicAccess:: operations(see details [here](https://bugs.openjdk.org/browse/JDK-8367013), I decided to convert these fields to `Atomic<T>` instead of adding `volatile`.
>> 
>> ### Test
>> - [x] hotshpot_gc_shenandoah
>> - [x] GHA
>
> Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use `1UL` instead of `static_cast<size_t>(1)`

Both PR and JBS bug have been updated, thanks all!

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PR Comment: https://git.openjdk.org/jdk/pull/29456#issuecomment-3814010592