RFR: 8372650: Convert GenericWaitBarrier to use Atomic<T>

[Aleksey Shipilev]

On Thu, 27 Nov 2025 08:36:41 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to GenericWaitBarrier to use Atomic rather than
> directly applying AtomicAccess to volatile members.
> 
> Testing: mach5 tier1-5

Looks right, except one place:

src/hotspot/share/utilities/waitBarrier_generic.cpp line 199:

> 197:     }
> 198:   }
> 199:   assert(_outstanding_wakeups.load_acquire() == 0, "Post disarm: Should not have outstanding wakeups");

Does not have to be `_acquire`, original load is relaxed.

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PR Review: https://git.openjdk.org/jdk/pull/28527#pullrequestreview-3514487147
PR Review Comment: https://git.openjdk.org/jdk/pull/28527#discussion_r2567965169