[RFC 2/2] rust: sync: Add atomic support

[Kent Overstreet]

On Sun, Jun 16, 2024 at 05:14:56PM +0200, Miguel Ojeda wrote:
> On Sun, Jun 16, 2024 at 4:16 PM Boqun Feng <boqun.feng at gmail.com> wrote:
> >
> > Hmm? Have you seen the email I replied to John, a broader Rust community
> > seems doesn't appreciate the idea of generic atomics.
> 
> I don't think we can easily draw that conclusion from those download
> numbers / dependent crates.
> 
> portable-atomic may be more popular simply because it provides
> features for platforms the standard library does not. The interface
> being generic or not may have nothing to do with it. Or perhaps
> because it has a 1.x version, while the other doesn't, etc.
> 
> In fact, the atomic crate is essentially about providing `Atomic<T>`,
> so one could argue that all those downloads are precisely from people
> that want a generic atomic.
> 
> Moreover, I noticed portable-atomic's issue #1 in GitHub is,
> precisely, adding `Atomic<T>` support. The maintainer has a PR for
> that updated over time, most recently a few hours ago.
> 
> There is also `AtomicCell<T>` from crossbeam, which is the first
> feature listed in its docs.
> 
> Anyway...
> 
> The way I see it, both approaches seem similar (i.e. for what we are
> going to use them for today, at least) and neither apparently has a
> major downside today for those use cases (apart from needed refactors
> later to go to another approach).
> 
> (By the "generic approach", by the way, I mean just providing
> `Atomic<{i32,i64}>`, not a complex design)
> 
> So it is up to you on what you send for the non-RFC patches, of
> course, and if nobody has the time / wants to do the work for the
> "simple" generic approach, then we can just go ahead with this for the
> moment. But I think it would be nice to at least consider the "simple"
> generic approach to see how much worse it would be.
> 
> Other bits to consider, that perhaps give you arguments for one or the
> other: consequences on the compilation time, on inlining, on the error
> messages for new users, on the generated documentation, on how easy to
> grep they are, etc.

Yeah, rereading the thread - I'm with Miguel and Gary.

Generics are simply the correct way to do it, if the wider rust
community didn't do it that way I think that can be chalked up more to
historical baggage or needlessly copying the base integer type scheme.

Let's please do it right here, and generics are the correct approach.