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Date:   Wed, 24 May 2023 14:52:50 +0000
To:     Alice Ryhl <aliceryhl@google.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     rust-for-linux@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH v1 7/7] rust: workqueue: add `try_spawn` helper method
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On Wednesday, May 17th, 2023 at 22:31, Alice Ryhl <aliceryhl@google.com> wr=
ote:
> This adds a convenience method that lets you spawn a closure for
> execution on a workqueue. This will be the most convenient way to use
> workqueues, but it is fallible because it needs to allocate memory.
>=20
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/workqueue.rs | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>=20
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index 007005ddcaf0..303b72efd95f 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -57,6 +57,42 @@ impl Queue {
>              })
>          }
>      }
> +
> +    /// Tries to spawn the given function or closure as a work item.
> +    ///
> +    /// This method can fail because it allocates memory to store the wo=
rk item.
> +    pub fn try_spawn<T: 'static + Send + Fn()>(&self, func: T) -> Result=
 {

Why is this `Fn()` instead of `FnOnce()`?

> +        let init =3D pin_init!(ClosureWork {
> +            work <- Work::new(),
> +            func: Some(func),
> +        });
> +
> +        self.enqueue(Box::pin_init(init)?);
> +        Ok(())
> +    }
> +}
> +
> +/// A helper type used in `try_spawn`.
> +#[pin_data]
> +struct ClosureWork<T> {
> +    #[pin]
> +    work: Work<Pin<Box<ClosureWork<T>>>>,
> +    func: Option<T>,
> +}
> +
> +impl<T> ClosureWork<T> {
> +    fn project(self: Pin<&mut Self>) -> &mut Option<T> {
> +        // SAFETY: The `func` field is not structurally pinned.
> +        unsafe { &mut self.get_unchecked_mut().func }
> +    }
> +}
> +
> +impl<T: FnOnce()> BoxWorkItem for ClosureWork<T> {
> +    fn run(mut self: Pin<Box<Self>>) {
> +        if let Some(func) =3D self.as_mut().project().take() {
> +            (func)()
> +        }
> +    }
>  }
>=20
>  /// A work item.
> @@ -280,6 +316,10 @@ macro_rules! impl_has_work {
>      )*};
>  }
>=20
> +impl_has_work! {
> +    impl<T> HasWork<Pin<Box<Self>>> for ClosureWork<T> { self.work }
> +}
> +
>  /// Declares that [`Arc<Self>`] should implement [`WorkItem`].
>  ///
>  /// # Examples
> --
> 2.40.1.606.ga4b1b128d6-goog
>=20

--
Cheers,
Benno