RFR: 8367013: Add Atomic<T> to package/replace idiom of volatile var plus AtomicAccess:: operations [v7]

[Stefan Karlsson]

On Tue, 11 Nov 2025 20:36:38 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
>
> Kim Barrett has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - rename arithmetic operand type from I to Offset
>  - use obviously different test types in HasExchange
>  - remove single-use internal Base type aliases
>  - fix missing order parameter usage

Marked as reviewed by stefank (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27539#pullrequestreview-3451997981