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SubjectRe: [PATCH v2 3/4] rust: specify when `ARef` is thread safe
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On 5/23/23 11:44, Alice Ryhl wrote:
> An `ARef` behaves just like the `Arc` when it comes to thread safety, so
> we can reuse the thread safety comments from `Arc` here.
>
> This is necessary because without this change, the Rust compiler will
> assume that things are not thread safe even though they are.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> ---
> [...]
>
> +// SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because
> +// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
> +// `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a
> +// mutable reference, for example, when the reference count reaches zero and `T` is dropped.
> +unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
> +
> +// SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`
> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
> +// it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an
> +// `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
> +// example, when the reference count reaches zero and `T` is dropped.
> +unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
> +
> impl<T: AlwaysRefCounted> ARef<T> {
> /// Creates a new instance of [`ARef`].
> ///

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

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