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

[Alice Ryhl <aliceryhl@google.com>]

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@kernel.org>

> +    /// 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.

Alice