On Wed Jul 9, 2025 at 12:34 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@xxxxxxxxxx> writes:
>> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
>>> "Boqun Feng" <boqun.feng@xxxxxxxxx> 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 <a.hindborg@xxxxxxxxxx> 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 <a.hindborg@xxxxxxxxxx>
>>>>>
>>>>> LGTM:
>>>>> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>>>>>
>>>>> > +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
