Re: [PATCH v6 4/9] rust: sync: atomic: Add generic atomics

Boqun Feng
2025-07-14T07:09:01Z

On Fri, Jul 11, 2025 at 08:35:25PM +0200, Benno Lossin wrote:
[..]
> >> > +///
> >> > +/// # Guarantees
> >> > +///
> >> > +/// Doing an atomic operation while holding a reference of [`Self`] won't cause a data race,
> >> > +/// this is guaranteed by the safety requirement of [`Self::from_ptr()`] and the extra safety
> >> > +/// requirement of the usage on pointers returned by [`Self::as_ptr()`].
> >>
> >> I'd rather think we turn this into an invariant that says any operations
> >> on `self.0` through a shared reference is atomic.
> >>
[...]
> > [...]
> >> > + let a = self.as_ptr().cast::<T::Repr>();
> >> > +
> >> > + // SAFETY:
> >> > + // - For calling the atomic_read*() function:
> >> > + // - `a` is a valid pointer for the function per the CAST justification above.
> >> > + // - Per the type guarantees, the following atomic operation won't cause data races.
> >>
> >> Which type guarantees? `Self`?
> >>
> >
> > The above "# Guarantees" of `Atomic<T>`, but yeah I think it should be
> > "# Invariants".
>
> Yeah and if we use invariants/guarantees always mention the type that
> they are of and don't assume the reader will "know" :)
>

Just FYI, I ended dropping the "# Invariants" (or Guarantees) of
`Atomic<T>` because I don't need them any more. Instead I add a
guarantee for Atoimc::as_ptr(): always returns a properly aligned
pointer, which I actually need for calling C functions.

Regards,
Boqun

> ---
> Cheers,
> Benno