Re: [PATCH v2 2/4] rust: sync: reword the `Arc` safety comment for `Sync`

[Alice Ryhl]

On 5/23/23 17:50, Gary Guo wrote:
> > -// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
> > -// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
> > -// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
> > +// SAFETY: It is safe to send `&Arc<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 `&Arc<T>` may clone it and get an
> > +// `Arc<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.
>
> "for example" here implies that there are other case to get a mutable
> reference? I don't think that's true for our `Arc` since we don't
> provide a `get_mut` method.

Ah, yes, that's true. Good point.