Messages in this thread | | | Date | Tue, 23 May 2023 13:29:07 -0300 | Subject | Re: [PATCH v2 2/4] rust: sync: reword the `Arc` safety comment for `Sync` | From | Martin Rodriguez Reboredo <> |
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On 5/23/23 11:44, Alice Ryhl wrote: > The safety comment on `impl Sync for Arc` references the Send safety > comment. This commit avoids that in case the two comments drift apart in > the future. > > Suggested-by: Andreas Hindborg <a.hindborg@samsung.com> > 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 `&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. > unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {} > > impl<T> Arc<T> {
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
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