RFR: 8376350: Convert ReferenceProcessorPhaseTimes to use Atomic<T>

[Stefan Karlsson]

On Mon, 26 Jan 2026 15:52:10 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this change to convert `ReferenceProcessorPhaseTimes` to use `Atomic<T>`.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Changes requested by stefank (Reviewer).

src/hotspot/share/gc/shared/referenceProcessorPhaseTimes.cpp line 199:

> 197: 
> 198:   for (int i = 0; i < number_of_subclasses_of_ref; i++) {
> 199:     ::new (&_ref_dropped[i]) Atomic<size_t>{};

I had some offline discussions with @jdksjolen and @walulyai about if we really should be using placement new to reset `Atomic`s, and if this is the correct way, should we also call the destructor on the old object?

That discussion ended up with suggesting the following instead:
Suggestion:

    _ref_dropped[i].store_relaxed(0);

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PR Review: https://git.openjdk.org/jdk/pull/29423#pullrequestreview-3710905054
PR Review Comment: https://git.openjdk.org/jdk/pull/29423#discussion_r2731775781