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

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Message-ID: <87h67lezcg.fsf@kernel.org>
Date: Tue, 03 Dec 2024 13:16:15 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Tamir Duberstein" <tamird@...il.com>
Cc: "Danilo Krummrich" <dakr@...nel.org>,  "Miguel Ojeda"
 <ojeda@...nel.org>,  "Alex Gaynor" <alex.gaynor@...il.com>,  "Boqun Feng"
 <boqun.feng@...il.com>,  "Gary Guo" <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno Lossin" <benno.lossin@...ton.me>,
  "Alice Ryhl" <aliceryhl@...gle.com>,  "Trevor Gross" <tmgross@...ch.edu>,
  Maíra Canal <mcanal@...lia.com>,  "Asahi Lina"
 <lina@...hilina.net>,
  <rust-for-linux@...r.kernel.org>,  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 2/2] rust: xarray: Add an abstraction for XArray

"Tamir Duberstein" <tamird@...il.com> 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@...lia.com>
> Inspired-by: Asahi Lina <lina@...hilina.net>
> Signed-off-by: Tamir Duberstein <tamird@...il.com>
> ---

[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