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

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Message-ID: <CAJ-ks9mvAvRoRd+zncGU7RG7a_=X_mgvmU8BWZanOcF4tddbPQ@mail.gmail.com>
Date: Tue, 3 Dec 2024 10:00:04 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
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

On Tue, Dec 3, 2024 at 7:16 AM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> "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?

This comment came from the original series, I'll reword it in the next version.