Message-ID: <CANiq72mz=OzzHJJyOPeWcxEtppP+v0KUq63_u5NB7-R84avaPg@mail.gmail.com>
Date: Sun, 16 Jun 2024 17:14:56 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>, Benno Lossin <benno.lossin@...ton.me>, 
	Gary Guo <gary@...yguo.net>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
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	Alan Stern <stern@...land.harvard.edu>, Andrea Parri <parri.andrea@...il.com>, 
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	Jade Alglave <j.alglave@....ac.uk>, Luc Maranget <luc.maranget@...ia.fr>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Akira Yokosawa <akiyks@...il.com>, 
	Daniel Lustig <dlustig@...dia.com>, Joel Fernandes <joel@...lfernandes.org>, 
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	"H. Peter Anvin" <hpa@...or.com>, Catalin Marinas <catalin.marinas@....com>, torvalds@...ux-foundation.org, 
	linux-arm-kernel@...ts.infradead.org, linux-fsdevel@...r.kernel.org, 
	Trevor Gross <tmgross@...ch.edu>, dakr@...hat.com
Subject: Re: [RFC 2/2] rust: sync: Add atomic support

On Sun, Jun 16, 2024 at 4:16 PM Boqun Feng <boqun.feng@...il.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.

Cheers,
Miguel

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