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

[Boqun Feng]

On Sun, Jun 16, 2024 at 05:51:07AM -0400, Kent Overstreet wrote:
> On Sat, Jun 15, 2024 at 03:12:33PM -0700, Boqun Feng wrote:
> > What's the issue of having AtomicI32 and AtomicI64 first then? We don't
> > need to do 1 or 2 until the real users show up.
> > 
> > And I'd like also to point out that there are a few more trait bound
> > designs needed for Atomic<T>, for example, Atomic<u32> and Atomic<i32>
> > have different sets of API (no inc_unless_negative() for u32).
> > 
> > Don't make me wrong, I have no doubt we can handle this in the type
> > system, but given the design work need, won't it make sense that we take
> > baby steps on this? We can first introduce AtomicI32 and AtomicI64 which
> > already have real users, and then if there are some values of generic
> > atomics, we introduce them and have proper discussion on design.
> > 
> > To me, it's perfectly fine that Atomic{I32,I64} co-exist with Atomic<T>.
> > What's the downside? A bit specific example would help me understand
> > the real concern here.
> 
> Err, what?
> 
> Of course we want generic atomics, and we need that for properly
> supporting cmpxchg.
> 

Nope. Note this series only introduces the atomic types (atomic_ C
APIs), but cmpxchg C APIs (no atomic_ prefix) are probably presented via
a different API, where we need to make it easier to interact with normal
types, and we may use generic there.

> Bogun, you've got all the rust guys pushing for doing this with
> generics, I'm not sure why you're being stubborn here?

Hmm? Have you seen the email I replied to John, a broader Rust community
seems doesn't appreciate the idea of generic atomics.

Regards,
Boqun