Messages in this thread Patch in this message | | | Date | Tue, 23 May 2023 14:44:16 +0000 | Subject | [PATCH v2 2/4] rust: sync: reword the `Arc` safety comment for `Sync` | From | Alice Ryhl <> |
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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> --- rust/kernel/sync/arc.rs | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 87a4c9ed712b..4d10f9868d9e 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -150,9 +150,11 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Ar // mutable reference, for example, when the reference count reaches zero and `T` is dropped. unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {} -// 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> { -- 2.40.1.698.g37aff9b760-goog
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