RFR: 8367013: Add Atomic<T> to package/replace idiom of volatile var plus AtomicAccess:: operations [v5]

[Kim Barrett]

On Wed, 22 Oct 2025 14:48:44 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> The name "xchg" is pretty generic (it could just as easily be used for a
>> non-atomic exchange in some other class). The explicit `Atomic::` (now
>> `AtomicAccess::`) qualifier made for easy disambiguation. Similarly for the
>> others, like "inc" and "dec", and not providing short forms for "add" and
>> "sub". (And remember that we mostly eschew operator overloading, though I
>> think not always to our benefit. If not for that, such other classes probably
>> would be doing that rather than named operations for arithmetic.) I think
>> "cmpxchg" is pretty well understood to be atomic; I think if one tried to use
>> that name for a non-atomic operation in some other class one might well get
>> some push-back.
>> 
>> Personally, I also find the short names are harder to spot in the middle of
>> other code, and I liked that `AtomicAccess::foo` (formerly `Atomic::foo` was
>> easy to spot.
>> 
>> I think updating AtomicAccess to be consistent with what we decide for
>> Atomic<T> should be done, but only after Atomic<T> has been fully adopted, so
>> we're only dealing the the remaining resudue. This has already been discussed
>> with regard to explicit "relaxed" load/store qualifiers.
>
> I don't know if I've said it here or only offline, so I post it here. I would have preferred if this patch retained the names from `AtomicAccess`. I don't think it would be problematic to understand that `var.xchg()` requires you to understand what `var` is. And if you know that `var` is an `Atomic` then you know what `var` is then this is no more confusing than a call to `AtomicAccess::xchg`. The same for `inc` and `dec`.

Obviously, I disagree. I think using those names would be strictly (and
noticeably) worse that what is currently proposed, and have explained why I
think that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27539#discussion_r2453224169