64 lines
2.0 KiB
Rust
64 lines
2.0 KiB
Rust
use super::arc_wake::ArcWake;
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use super::waker::waker_vtable;
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use alloc::sync::Arc;
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use core::marker::PhantomData;
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use core::mem::ManuallyDrop;
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use core::ops::Deref;
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use core::task::{RawWaker, Waker};
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/// A [`Waker`] that is only valid for a given lifetime.
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///
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/// Note: this type implements [`Deref<Target = Waker>`](std::ops::Deref),
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/// so it can be used to get a `&Waker`.
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#[derive(Debug)]
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pub struct WakerRef<'a> {
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waker: ManuallyDrop<Waker>,
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_marker: PhantomData<&'a ()>,
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}
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impl<'a> WakerRef<'a> {
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/// Create a new [`WakerRef`] from a [`Waker`] reference.
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pub fn new(waker: &'a Waker) -> Self {
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// copy the underlying (raw) waker without calling a clone,
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// as we won't call Waker::drop either.
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let waker = ManuallyDrop::new(unsafe { core::ptr::read(waker) });
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Self { waker, _marker: PhantomData }
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}
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/// Create a new [`WakerRef`] from a [`Waker`] that must not be dropped.
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///
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/// Note: this if for rare cases where the caller created a [`Waker`] in
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/// an unsafe way (that will be valid only for a lifetime to be determined
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/// by the caller), and the [`Waker`] doesn't need to or must not be
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/// destroyed.
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pub fn new_unowned(waker: ManuallyDrop<Waker>) -> Self {
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Self { waker, _marker: PhantomData }
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}
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}
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impl Deref for WakerRef<'_> {
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type Target = Waker;
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fn deref(&self) -> &Waker {
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&self.waker
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}
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}
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/// Creates a reference to a [`Waker`] from a reference to `Arc<impl ArcWake>`.
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///
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/// The resulting [`Waker`] will call
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/// [`ArcWake.wake()`](ArcWake::wake) if awoken.
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#[inline]
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pub fn waker_ref<W>(wake: &Arc<W>) -> WakerRef<'_>
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where
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W: ArcWake,
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{
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// simply copy the pointer instead of using Arc::into_raw,
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// as we don't actually keep a refcount by using ManuallyDrop.<
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let ptr = Arc::as_ptr(wake).cast::<()>();
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let waker =
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ManuallyDrop::new(unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) });
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WakerRef::new_unowned(waker)
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}
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