Messages in this thread | | | Date | Thu, 25 May 2023 13:45:12 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v2 3/4] rust: specify when `ARef` is thread safe |
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On 5/23/23 16:44, 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>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> --- > rust/kernel/types.rs | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 29db59d6119a..1e5380b16ed5 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -321,6 +321,19 @@ 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` 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`]. > /// > -- > 2.40.1.698.g37aff9b760-goog >
-- Cheers, Benno
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