RFR: 8367013: Add Atomic<T> to package/replace idiom of volatile var plus AtomicAccess:: operations

[Francesco Andreuzzi]

On Sun, 28 Sep 2025 11:10:41 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change that adds the type Atomic<T>, to use as the type
> of a variable that is accessed (including writes) concurrently by multiple
> threads. This is intended to replace (most) uses of the current HotSpot idiom
> of declaring a variable volatile and accessing that variable using functions
> from the AtomicAccess class.
> https://github.com/openjdk/jdk/blame/528f93f8cb9f1fb9c19f31ab80c8a546f47beed2/doc/hotspot-style.md#L138-L147
> 
> This change replaces https://github.com/openjdk/jdk/pull/27462. Differences are
> 
> * Substantially restructured `Atomic<T>`, to be IDE friendly. It's
> operationally the same, with the same API, hence uses and gtests didn't need
> to change in that respect. Thanks to @stefank for raising this issue, and for
> some suggestions toward improvements.
> 
> * Changed how fetch_then_set for atomic translated types is handled, to avoid
> having the function there at all if it isn't usable, rather than just removing
> it via SFINAE, leaving an empty overload set.
> 
> * Added more gtests.
> 
> Testing: mach5 tier1-6, GHA sanity tests

src/hotspot/share/runtime/atomic.hpp line 517:

> 515:   using ValueType = T;
> 516: 
> 517:   // If T is default constructible, construct from a a default constructed T.

Suggestion:

  // If T is default constructible, construct from a default constructed T.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27539#discussion_r2385750050