On Wed Jul 9, 2025 at 12:34 PM CEST, Andreas Hindborg wrote: > "Benno Lossin" <[email protected]> writes: >> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote: >>> "Boqun Feng" <[email protected]> writes: >>>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote: >>>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <[email protected]> >>>>> wrote: >>>>> > >>>>> > Introduce the `SetOnce` type, a container that can only be written once. >>>>> > The container uses an internal atomic to synchronize writes to the >>>>> > internal >>>>> > value. >>>>> > >>>>> > Signed-off-by: Andreas Hindborg <[email protected]> >>>>> >>>>> LGTM: >>>>> Reviewed-by: Alice Ryhl <[email protected]> >>>>> >>>>> > +impl<T> Drop for SetOnce<T> { >>>>> > + fn drop(&mut self) { >>>>> > + if self.init.load(Acquire) == 2 { >>>>> > + // SAFETY: By the type invariants of `Self`, `self.init == >>>>> > 2` means that `self.value` >>>>> > + // contains a valid value. We have exclusive access, as we >>>>> > hold a `mut` reference to >>>>> > + // `self`. >>>>> > + unsafe { drop_in_place(self.value.get()) }; >>>>> >>>>> This load does not need to be Acquire. It can be a Relaxed load or >>>>> even an unsynchronized one since the access is exclusive. >>>> >>>> Right, I think we can do the similar as Revocable here: >>>> >>>> if *self.init.get_mut() == 2 { } > > Ok, now I got it. You are saying I don't need to use the atomic load > method, because I have mutable access. Sounds good. > > But I guess a relaxed load and access through a mutable reference should > result in the same code generation on most (all?) platforms?
AFAIK it is not the same on arm. --- Cheers, Benno
