Re: [RFC PATCH] rust: workqueue: Add an example for try_spawn()

[Boqun Feng <boqun.feng@gmail.com>]

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 ;-)

> & my instinct is to move the let bindings out (which would produce code
> that doesn't compile).
> 
> > That said, I'm not really against using `work_done2` and `data2`, just
> > I'm afraid that may be more confusing.
> 
> I don't think that's a problem.
> 
> >>     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.
> >
> > Do you have links to these discussions.
> 
> It's an RFC:
> 
>     https://github.com/rust-lang/rfcs/pull/368
> 
> There probably are more discussions on zulip, but I haven't read those.
> The RFC also has a project goal:
> 
>     https://rust-lang.github.io/rust-project-goals/2025h2/ergonomic-rc.html

Thanks for the pointer.

Regards,
Boqun

> 
> ---
> Cheers,
> Benno