RFR: 8377045: Shenandoah: Convert ShenandoahLock related code to use Atomic<T>

[William Kemper]

On Tue, 10 Feb 2026 17:59:56 GMT, Ben Taylor <btaylor at openjdk.org> wrote:

> Modernizes ShenandoahLock code by replacing AtomicAccess methods with Atomic types.
> 
> Tier1 test results on x86_64 linux are the same before and after this change when running with TEST_VM_OPTS=-XX:+UseShenandoahGC.

Looks good to me, but we should give @pengxiaolong a heads up because this will likely cause merge conflicts with https://github.com/openjdk/jdk/pull/29543.

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Marked as reviewed by wkemper (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29658#pullrequestreview-3782165251