linux-kernel - Re: [RFC PATCH] rust: workqueue: Add an example for try

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Message-Id: <DBQYQR7BPKQA.2UVOPCU6LXXAY@kernel.org>
Date: Fri, 01 Aug 2025 10:54:26 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>,
 "Gary Guo" <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "Danilo Krummrich" <dakr@...nel.org>, "Tejun Heo" <tj@...nel.org>, "Tamir
 Duberstein" <tamird@...il.com>, "Hamza Mahfooz"
 <hamzamahfooz@...ux.microsoft.com>, "Alban Kurti" <kurti@...icto.ai>, "Joel
 Fernandes" <joelagnelf@...dia.com>, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH] rust: workqueue: Add an example for try_spawn()

On Fri Aug 1, 2025 at 3:15 AM CEST, Boqun Feng wrote:
> On Thu, Jul 31, 2025 at 11:30:10AM +0200, Benno Lossin wrote:
>> On Wed Jul 30, 2025 at 9:38 PM CEST, Boqun Feng wrote:
>> > On Wed, Jul 30, 2025 at 09:28:05PM +0200, Benno Lossin wrote:
>> >> On Wed Jul 30, 2025 at 6:34 PM CEST, Boqun Feng wrote:
>> >> > +    /// workqueue::system().try_spawn(
>> >> > +    ///     flags::GFP_KERNEL,
>> >> > +    ///     {
>> >> > +    ///         let work_done = work_done.clone();
>> >> > +    ///         let data = data.clone();
>> >> > +    ///         move || {
>> >> > +    ///             *data.lock() = 42;
>> >> > +    ///             work_done.complete_all();
>> >> > +    ///         }
>> >> > +    ///     }
>> >> > +    /// )?;
>> >> 
>> >> Not doing your pattern and instead adding a `2` postfix we get:
>> >> 
>> >>     let work_done2 = work_done.clone();
>> >>     let data2 = data.clone();
>> >> 
>> >
>> > Yeah, the thing I want to achieve with my pattern is: make it clear that
>> > the work and the task that queues the work are sharing the same
>> > `work_done` and `data` (well, no the same `Arc` exactly, but the `Arc`s
>> > that are pointing to the same object). This pattern here doesn't show
>> > that clearly imo.
>> 
>> I think it's fine, that pattern is often used for that. Not heavily
>> opposed to doing it your way, but I feel like the code looks a bit weird
>
> Ok, I will drop my style and use work_done2 and data2, because it'll be
> at the general documentation, but I might keep using my pattern in other
> code because it looks reasonable to me ;-)

It is reasonable :) If you do want to use the same name for them, then I
personally think this looks better than moving the let bindings inside
of the expression:

    {
        let work_done = work_done.clone();
        let data = data.clone();
        workqueue::system().try_spawn(flags::GFP_KERNEL, move || {
            *data.lock() = 42;
            work_done.complete_all();
        })?;
    }

But that gives the `try_spawn` call extra indentation which also isn't
ideal... I'd be best for the language feature to exist :)

---
Cheers,
Benno