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SubjectRe: [PATCH 2/2] rust: sync: add `CondVar::wait_timeout`
On Fri, Dec 8, 2023 at 8:04 PM Benno Lossin <benno.lossin@proton.me> wrote:
>
> On 12/6/23 11:09, Alice Ryhl wrote:
> > + /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
> > + /// thread to sleep. It wakes up when notified by [`CondVar::notify_one`] or
> > + /// [`CondVar::notify_all`], or when the thread receives a signal.
> > + ///
> > + /// Returns whether there is a signal pending.
> > + fn wait_internal_timeout<T, B>(
> > + &self,
> > + wait_state: u32,
> > + guard: &mut Guard<'_, T, B>,
> > + timeout: u64,
> > + ) -> u64
> > + where
> > + T: ?Sized,
> > + B: Backend,
> > + {
> > + let wait = Opaque::<bindings::wait_queue_entry>::uninit();
> > +
> > + // SAFETY: `wait` points to valid memory.
> > + unsafe { bindings::init_wait(wait.get()) };
> > +
> > + // SAFETY: Both `wait` and `wait_list` point to valid memory.
> > + unsafe {
> > + bindings::prepare_to_wait_exclusive(self.wait_list.get(), wait.get(), wait_state as _)
>
> Does `.into()` work here? If for some reason the type here changes, we
> probably want to know about it.

I think we may be able to eliminate this cast by using c_int for the
integer type.

> > + };
> > +
> > + // SAFETY: Switches to another thread.
> > + let timeout =
> > + guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout as _) as _ });
>
> Ditto.

Here, we're casting u64->long and then long->u64. How about this?

u64->long - Use timeout.try_into().unwrap_or(MAX_SCHEDULE_TIMEOUT),
since MAX_SCHEDULE_TIMEOUT is LONG_MAX.

long->u64 - This value is guaranteed to be less than the argument
passed to schedule_timeout. Use .into() for infallible cast.

Alice

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