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From: Andreas Hindborg <a.hindborg@kernel.org>
To: "Tamir Duberstein" <tamird@gmail.com>
Cc: "Danilo Krummrich" <dakr@kernel.org>,  "Miguel Ojeda"
 <ojeda@kernel.org>,  "Alex Gaynor" <alex.gaynor@gmail.com>,  "Boqun Feng"
 <boqun.feng@gmail.com>,  "Gary Guo" <gary@garyguo.net>,  =?utf-8?Q?Bj?=
 =?utf-8?Q?=C3=B6rn?= Roy Baron
 <bjorn3_gh@protonmail.com>,  "Benno Lossin" <benno.lossin@proton.me>,
  "Alice Ryhl" <aliceryhl@google.com>,  "Trevor Gross" <tmgross@umich.edu>,
  =?utf-8?Q?Ma=C3=ADra?= Canal <mcanal@igalia.com>,  "Asahi Lina"
 <lina@asahilina.net>,
  <rust-for-linux@vger.kernel.org>,  <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v10 2/2] rust: xarray: Add an abstraction for XArray
In-Reply-To: <20241120-rust-xarray-bindings-v10-2-a25b2b0bf582@gmail.com>
	(Tamir Duberstein's message of "Wed, 20 Nov 2024 06:48:18 -0500")
References: <20241120-rust-xarray-bindings-v10-0-a25b2b0bf582@gmail.com>
	<6-QAwX1sgFm2t2PaGbx9Vw6zd35JfTSAuPp7yhzHZwErXXnBaRrz2lr-ACxVU1VnDQdEuDeN8Lv1PZjT6b13UQ==@protonmail.internalid>
	<20241120-rust-xarray-bindings-v10-2-a25b2b0bf582@gmail.com>
Date: Tue, 03 Dec 2024 13:16:15 +0100
Message-ID: <87h67lezcg.fsf@kernel.org>
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"Tamir Duberstein" <tamird@gmail.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: Ma=C3=ADra Canal <mcanal@igalia.com>
> Inspired-by: Asahi Lina <lina@asahilina.net>
> Signed-off-by: Tamir Duberstein <tamird@gmail.com>
> ---

[cut]

> +
> +// SAFETY: It is safe to send `XArray<T>` to another thread when the und=
erlying `T` is `Send`
> +// because XArray is thread-safe and all mutation operations are synchro=
nized.
> +unsafe impl<T: ForeignOwnable + Send> Send for XArray<T> {}
> +
> +// SAFETY: It is safe to send `&XArray<T>` to another thread when the un=
derlying `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 operatio=
ns are internally locked.
> +unsafe impl<T: ForeignOwnable + Send + Sync> Sync for XArray<T> {}

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


Best regards,
Andreas Hindborg