Re: [PATCH v1 1/2] rust: sync: add `Arc::ptr_eq`

[Benno Lossin]

On 5/17/23 22:08, Alice Ryhl wrote:
> Add a method for comparing whether two `Arc` pointers reference the same
> underlying object.
> 
> This comparison can already be done by getting a reference to the inner
> values and comparing whether the references have the same address.
> However, writing `Arc::ptr_eq(a, b)` is generally less error-prone than
> doing the same check on the references, since you might otherwise
> accidentally compare the two `&Arc<T>` references instead, which wont
> work because those are pointers to pointers to the inner value, when you
> just want to compare the pointers to the inner value.
> 
> Also, this method might optimize better because getting a reference to
> the inner value involves offsetting the pointer, which this method does
> not need to do.
> 
> Co-developed-by: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
> Signed-off-by: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>

> ---
>   rust/kernel/sync/arc.rs | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index e6d206242465..274febe3bb06 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -221,6 +221,11 @@ impl<T: ?Sized> Arc<T> {
>           // reference can be created.
>           unsafe { ArcBorrow::new(self.ptr) }
>       }
> +
> +    /// Compare whether two [`Arc`] pointers reference the same underlying object.
> +    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
> +        core::ptr::eq(this.ptr.as_ptr(), other.ptr.as_ptr())
> +    }
>   }
> 
>   impl<T: 'static> ForeignOwnable for Arc<T> {
> 
> base-commit: ac9a78681b921877518763ba0e89202254349d1b
> --
> 2.40.1.606.ga4b1b128d6-goog
> 

-- 
Cheers,
Benno