Re: [PATCH v10 2/2] rust: xarray: Add an abstraction for XArray

[Andreas Hindborg]

"Tamir Duberstein" <tamird@xxxxxxxxx> writes:

> `XArray` is an efficient sparse array of pointers. Add a Rust
> abstraction for this type.
>
> This implementation bounds the element type on `ForeignOwnable` and
> requires explicit locking for all operations. Future work may leverage
> RCU to enable lockless operation.
>
> Inspired-by: Maíra Canal <mcanal@xxxxxxxxxx>
> Inspired-by: Asahi Lina <lina@xxxxxxxxxxxxx>
> Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
> ---

[cut]

> +
> +// SAFETY: It is safe to send `XArray<T>` to another thread when the underlying `T` is `Send`
> +// because XArray is thread-safe and all mutation operations are synchronized.
> +unsafe impl<T: ForeignOwnable + Send> Send for XArray<T> {}
> +
> +// SAFETY: It is safe to send `&XArray<T>` to another thread when the underlying `T` is `Sync`
> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`). Additionally,
> +// `T` is `Send` because XArray is thread-safe and all mutation operations are internally locked.
> +unsafe impl<T: ForeignOwnable + Send + Sync> Sync for XArray<T> {}

I don't understand the sentence: "Additionally, `T` is `Send` because XArray is
 thread-safe and all mutation operations are internally locked.", could
 you elaborate?


Best regards,
Andreas Hindborg