1use super::arc_wake::ArcWake;
2use alloc::sync::Arc;
3use core::mem;
4use core::task::{RawWaker, RawWakerVTable, Waker};
5
6pub(super) fn waker_vtable<W: ArcWake + 'static>() -> &'static RawWakerVTable {
7 &RawWakerVTable::new(
8 clone_arc_raw::<W>,
9 wake_arc_raw::<W>,
10 wake_by_ref_arc_raw::<W>,
11 drop_arc_raw::<W>,
12 )
13}
14
15/// Creates a [`Waker`] from an `Arc<impl ArcWake>`.
16///
17/// The returned [`Waker`] will call
18/// [`ArcWake.wake()`](ArcWake::wake) if awoken.
19pub fn waker<W>(wake: Arc<W>) -> Waker
20where
21 W: ArcWake + 'static,
22{
23 let ptr: *const () = Arc::into_raw(this:wake).cast::<()>();
24
25 unsafe { Waker::from_raw(waker:RawWaker::new(data:ptr, waker_vtable::<W>())) }
26}
27
28// FIXME: panics on Arc::clone / refcount changes could wreak havoc on the
29// code here. We should guard against this by aborting.
30
31#[allow(clippy::redundant_clone)] // The clone here isn't actually redundant.
32unsafe fn increase_refcount<T: ArcWake + 'static>(data: *const ()) {
33 // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
34 let arc: ManuallyDrop> = mem::ManuallyDrop::new(unsafe { Arc::<T>::from_raw(ptr:data.cast::<T>()) });
35 // Now increase refcount, but don't drop new refcount either
36 let _arc_clone: mem::ManuallyDrop<_> = arc.clone();
37}
38
39// used by `waker_ref`
40#[inline(always)]
41unsafe fn clone_arc_raw<T: ArcWake + 'static>(data: *const ()) -> RawWaker {
42 unsafe { increase_refcount::<T>(data) }
43 RawWaker::new(data, waker_vtable::<T>())
44}
45
46unsafe fn wake_arc_raw<T: ArcWake + 'static>(data: *const ()) {
47 let arc: Arc<T> = unsafe { Arc::from_raw(ptr:data.cast::<T>()) };
48 ArcWake::wake(self:arc);
49}
50
51// used by `waker_ref`
52unsafe fn wake_by_ref_arc_raw<T: ArcWake + 'static>(data: *const ()) {
53 // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
54 let arc: ManuallyDrop> = mem::ManuallyDrop::new(unsafe { Arc::<T>::from_raw(ptr:data.cast::<T>()) });
55 ArcWake::wake_by_ref(&arc);
56}
57
58unsafe fn drop_arc_raw<T: ArcWake + 'static>(data: *const ()) {
59 drop(unsafe { Arc::<T>::from_raw(ptr:data.cast::<T>()) })
60}
61