Re: [PATCH] rust: sync: add lazy initialization methods to SetOnce

[Andreas Hindborg]

"Alice Ryhl" <aliceryhl@xxxxxxxxxx> writes:

> On Sun, Feb 15, 2026 at 09:27:17PM +0100, Andreas Hindborg wrote:
>> Add methods to get a reference to the contained value or populate the
>> SetOnce if empty. The new `as_ref_or_populate` method accepts a value
>> directly, while `as_ref_or_populate_with` accepts a fallible closure,
>> allowing for lazy initialization that may fail. Both methods spin-wait
>> if another thread is concurrently initializing the container.
>>
>> Also add `populate_with` which takes a fallible closure and serves as
>> the implementation basis for the other populate methods.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
>
>> +    /// Get a reference to the contained object, or populate the [`SetOnce`]
>> +    /// with the value returned by `callable` and return a reference to that
>> +    /// object.
>> +    pub fn as_ref_or_populate_with(&self, callable: impl FnOnce() -> Result<T>) -> Result<&T> {
>> +        if !self.populate_with(callable)? {
>> +            while self.init.load(Acquire) != 2 {
>> +                core::hint::spin_loop();
>> +            }
>
> We should not be implementing our own spinlocks.

That is a great proverb. I'd be happy to receive a suggestion on an
alternate approach for this particular context.


Best regards,
Andreas Hindborg