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rust: sync: add support for dispatching on Arc and ArcBorrow.
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Trait objects (`dyn T`) require trait `T` to be "object safe". One of
the requirements for "object safety" is that the receiver have one of
the allowed types. This commit adds `Arc<T>` and `ArcBorrow<'_, T>` to
the list of allowed types.

Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Reviewed-by: Vincenzo Palazzo <[email protected]>
Acked-by: Boqun Feng <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
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wedsonaf authored and ojeda committed Jan 16, 2023
1 parent 70e42eb commit 0748424
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Showing 2 changed files with 19 additions and 2 deletions.
1 change: 1 addition & 0 deletions rust/kernel/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
#![feature(allocator_api)]
#![feature(coerce_unsized)]
#![feature(core_ffi_c)]
#![feature(dispatch_from_dyn)]
#![feature(receiver_trait)]
#![feature(unsize)]

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20 changes: 18 additions & 2 deletions rust/kernel/sync/arc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -92,9 +92,15 @@ use core::{
/// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
///
/// ```
/// use kernel::sync::Arc;
/// use kernel::sync::{Arc, ArcBorrow};
///
/// trait MyTrait {
/// // Trait has a function whose `self` type is `Arc<Self>`.
/// fn example1(self: Arc<Self>) {}
///
/// trait MyTrait {}
/// // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
/// fn example2(self: ArcBorrow<'_, Self>) {}
/// }
///
/// struct Example;
/// impl MyTrait for Example {}
Expand Down Expand Up @@ -123,6 +129,9 @@ impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
// dynamically-sized type (DST) `U`.
impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}

// This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}

// 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 an `Arc<T>` may ultimately access `T` directly, for
Expand Down Expand Up @@ -297,6 +306,13 @@ pub struct ArcBorrow<'a, T: ?Sized + 'a> {
// This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}

// This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
// `ArcBorrow<U>`.
impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
for ArcBorrow<'_, T>
{
}

impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
fn clone(&self) -> Self {
*self
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