Messages in this thread Patch in this message | | | Date | Thu, 18 May 2023 14:24:05 -0700 | From | Boqun Feng <> | Subject | Re: [PATCH v1 1/2] rust: specify when `ARef` is thread safe |
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On Wed, May 17, 2023 at 09:59:04AM +0000, 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> > --- > rust/kernel/types.rs | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 29db59d6119a..9c8d94c04deb 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -321,6 +321,17 @@ pub struct ARef<T: AlwaysRefCounted> { > _p: PhantomData<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 an `ARef<T>` may ultimately access `T` directly, for
Does the "ultimately access `T` directly" here imply mutably or exclusively? If so, it makes sense to me to call it out. I'm trying to make sure we can agree on some "common terminologies" ;-)
Regards, Boqun
> +// 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` for the > +// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&ARef<T>` > +// into an `ARef<T>`, which may lead to `T` being accessed by the same reasoning as above. > +unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {} > + > impl<T: AlwaysRefCounted> ARef<T> { > /// Creates a new instance of [`ARef`]. > /// > > base-commit: ac9a78681b921877518763ba0e89202254349d1b > -- > 2.40.1.606.ga4b1b128d6-goog >
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