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

[Boqun Feng]

On Sun, Jun 16, 2024 at 11:32:31AM -0400, Kent Overstreet wrote:
> 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.

If so, maybe we should do u<Wide> instead of u8, u16, oh, and probably
just Integer<Sign, Wide> instead of i{8,16,32,64) and u{8,16,32,64} ;-)

Regards,
Boqun