Jason Macnak | ea22e81 | 2020-03-18 01:29:19 +0000 | [diff] [blame] | 1 | use super::arc_wake::{ArcWake}; |
| 2 | use super::waker::waker_vtable; |
| 3 | use alloc::sync::Arc; |
| 4 | use core::mem::ManuallyDrop; |
| 5 | use core::marker::PhantomData; |
| 6 | use core::ops::Deref; |
| 7 | use core::task::{Waker, RawWaker}; |
| 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)] |
| 14 | pub struct WakerRef<'a> { |
| 15 | waker: ManuallyDrop<Waker>, |
| 16 | _marker: PhantomData<&'a ()>, |
| 17 | } |
| 18 | |
| 19 | impl<'a> WakerRef<'a> { |
| 20 | /// Create a new [`WakerRef`] from a [`Waker`] reference. |
| 21 | pub fn new(waker: &'a Waker) -> Self { |
| 22 | // copy the underlying (raw) waker without calling a clone, |
| 23 | // as we won't call Waker::drop either. |
| 24 | let waker = ManuallyDrop::new(unsafe { core::ptr::read(waker) }); |
| 25 | WakerRef { |
| 26 | waker, |
| 27 | _marker: PhantomData, |
| 28 | } |
| 29 | } |
| 30 | |
| 31 | /// Create a new [`WakerRef`] from a [`Waker`] that must not be dropped. |
| 32 | /// |
| 33 | /// Note: this if for rare cases where the caller created a [`Waker`] in |
| 34 | /// an unsafe way (that will be valid only for a lifetime to be determined |
| 35 | /// by the caller), and the [`Waker`] doesn't need to or must not be |
| 36 | /// destroyed. |
| 37 | pub fn new_unowned(waker: ManuallyDrop<Waker>) -> Self { |
| 38 | WakerRef { |
| 39 | waker, |
| 40 | _marker: PhantomData, |
| 41 | } |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | impl Deref for WakerRef<'_> { |
| 46 | type Target = Waker; |
| 47 | |
| 48 | fn deref(&self) -> &Waker { |
| 49 | &self.waker |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | /// Creates a reference to a [`Waker`] from a reference to `Arc<impl ArcWake>`. |
| 54 | /// |
| 55 | /// The resulting [`Waker`] will call |
| 56 | /// [`ArcWake.wake()`](ArcWake::wake) if awoken. |
| 57 | #[inline] |
| 58 | pub fn waker_ref<W>(wake: &Arc<W>) -> WakerRef<'_> |
| 59 | where |
| 60 | W: ArcWake |
| 61 | { |
| 62 | // simply copy the pointer instead of using Arc::into_raw, |
| 63 | // as we don't actually keep a refcount by using ManuallyDrop.< |
| 64 | let ptr = (&**wake as *const W) as *const (); |
| 65 | |
| 66 | let waker = ManuallyDrop::new(unsafe { |
| 67 | Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) |
| 68 | }); |
| 69 | WakerRef::new_unowned(waker) |
| 70 | } |