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Message-Id: <DBPMYTZSIEQ5.3NPJM1CYVO3CK@kernel.org>
Date: Wed, 30 Jul 2025 21:28:05 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, <rust-for-linux@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Cc: "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 Wed Jul 30, 2025 at 6:34 PM CEST, Boqun Feng wrote:
> `try_spawn()` could use an example to demonstrate the usage, and
> arguably it's the most simple usage of workqueue in case someone needs a
> deferred work, so add it.
>
> Cc: Joel Fernandes <joelagnelf@...dia.com>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
> Miguel, Alice and Tejun, while I'm at it, should we also rename the
> function to `spawn()` because of the motivation mentioned here [1]?
>
> [1]: https://rust-for-linux.zulipchat.com/#narrow/channel/291566-Library/topic/.60new.60.20or.20.60try_new.60.3F/near/529533317
>
> Also I find the `{ <clone> || { } }` is really good if I only need to
> clone the Arc for passing to a callback closure, but I'm not sure how
> people feel about it, so criticism is welcome ;-)
I'm not so sure, see below :)
> rust/kernel/workqueue.rs | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index b9343d5bc00f..59c1a5e14d12 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -331,6 +331,33 @@ pub fn enqueue_delayed<W, const ID: u64>(&self, w: W, delay: Jiffies) -> W::Enqu
> /// Tries to spawn the given function or closure as a work item.
> ///
> /// This method can fail because it allocates memory to store the work item.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// use kernel::{alloc::flags, sync::{Arc, Completion, new_spinlock}, workqueue};
> + ///
> + /// let work_done = Arc::pin_init(Completion::new(), flags::GFP_KERNEL)?;
> + /// let data = Arc::pin_init(new_spinlock!(0), flags::GFP_KERNEL)?;
> + ///
> + /// 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();
workqueue::system().try_spawn(flags::GFP_KERNEL, move || {
*data2.lock() = 42;
work_done2.complete_all();
})?;
There are some discussions of introducing some better syntax for (cheap)
cloning, so maybe we can use that in the future.
---
Cheers,
Benno
> + ///
> + /// work_done.wait_for_completion();
> + ///
> + /// // `work_done` being completed implies the observation of the write of `data` in the work.
> + /// assert_eq!(*data.lock(), 42);
> + /// # Ok::<(), Error>(())
> + /// ```
> pub fn try_spawn<T: 'static + Send + FnOnce()>(
> &self,
> flags: Flags,
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