1use super::arc_wake::ArcWake;
2use super::waker::waker_vtable;
3use alloc::sync::Arc;
4use core::marker::PhantomData;
5use core::mem::ManuallyDrop;
6use core::ops::Deref;
7use core::task::{RawWaker, Waker};
8
9/// A [`Waker`] that is only valid for a given lifetime.
10///
11/// Note: this type implements [`Deref<Target = Waker>`](std::ops::Deref),
12/// so it can be used to get a `&Waker`.
13#[derive(Debug)]
14pub struct WakerRef<'a> {
15 waker: ManuallyDrop<Waker>,
16 _marker: PhantomData<&'a ()>,
17}
18
19impl<'a> WakerRef<'a> {
20 /// Create a new [`WakerRef`] from a [`Waker`] reference.
21 #[inline]
22 pub fn new(waker: &'a Waker) -> Self {
23 // copy the underlying (raw) waker without calling a clone,
24 // as we won't call Waker::drop either.
25 let waker = ManuallyDrop::new(unsafe { core::ptr::read(waker) });
26 Self { waker, _marker: PhantomData }
27 }
28
29 /// Create a new [`WakerRef`] from a [`Waker`] that must not be dropped.
30 ///
31 /// Note: this if for rare cases where the caller created a [`Waker`] in
32 /// an unsafe way (that will be valid only for a lifetime to be determined
33 /// by the caller), and the [`Waker`] doesn't need to or must not be
34 /// destroyed.
35 #[inline]
36 pub fn new_unowned(waker: ManuallyDrop<Waker>) -> Self {
37 Self { waker, _marker: PhantomData }
38 }
39}
40
41impl Deref for WakerRef<'_> {
42 type Target = Waker;
43
44 #[inline]
45 fn deref(&self) -> &Waker {
46 &self.waker
47 }
48}
49
50/// Creates a reference to a [`Waker`] from a reference to `Arc<impl ArcWake>`.
51///
52/// The resulting [`Waker`] will call
53/// [`ArcWake.wake()`](ArcWake::wake) if awoken.
54#[inline]
55pub fn waker_ref<W>(wake: &Arc<W>) -> WakerRef<'_>
56where
57 W: ArcWake,
58{
59 // simply copy the pointer instead of using Arc::into_raw,
60 // as we don't actually keep a refcount by using ManuallyDrop.<
61 let ptr = Arc::as_ptr(wake).cast::<()>();
62
63 let waker =
64 ManuallyDrop::new(unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) });
65 WakerRef::new_unowned(waker)
66}
67