1 files changed, 66 insertions, 0 deletions
diff --git a/third_party/rust/futures-task/src/waker_ref.rs b/third_party/rust/futures-task/src/waker_ref.rs
new file mode 100644
index 0000000000..aac4109577
--- /dev/null
+++ b/third_party/rust/futures-task/src/waker_ref.rs
@@ -0,0 +1,66 @@
+use super::arc_wake::ArcWake;
+use super::waker::waker_vtable;
+use alloc::sync::Arc;
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::ops::Deref;
+use core::task::{RawWaker, Waker};
+
+/// A [`Waker`] that is only valid for a given lifetime.
+///
+/// Note: this type implements [`Deref<Target = Waker>`](std::ops::Deref),
+/// so it can be used to get a `&Waker`.
+#[derive(Debug)]
+pub struct WakerRef<'a> {
+    waker: ManuallyDrop<Waker>,
+    _marker: PhantomData<&'a ()>,
+}
+
+impl<'a> WakerRef<'a> {
+    /// Create a new [`WakerRef`] from a [`Waker`] reference.
+    #[inline]
+    pub fn new(waker: &'a Waker) -> Self {
+        // copy the underlying (raw) waker without calling a clone,
+        // as we won't call Waker::drop either.
+        let waker = ManuallyDrop::new(unsafe { core::ptr::read(waker) });
+        Self { waker, _marker: PhantomData }
+    }
+
+    /// Create a new [`WakerRef`] from a [`Waker`] that must not be dropped.
+    ///
+    /// Note: this if for rare cases where the caller created a [`Waker`] in
+    /// an unsafe way (that will be valid only for a lifetime to be determined
+    /// by the caller), and the [`Waker`] doesn't need to or must not be
+    /// destroyed.
+    #[inline]
+    pub fn new_unowned(waker: ManuallyDrop<Waker>) -> Self {
+        Self { waker, _marker: PhantomData }
+    }
+}
+
+impl Deref for WakerRef<'_> {
+    type Target = Waker;
+
+    #[inline]
+    fn deref(&self) -> &Waker {
+        &self.waker
+    }
+}
+
+/// Creates a reference to a [`Waker`] from a reference to `Arc<impl ArcWake>`.
+///
+/// The resulting [`Waker`] will call
+/// [`ArcWake.wake()`](ArcWake::wake) if awoken.
+#[inline]
+pub fn waker_ref<W>(wake: &Arc<W>) -> WakerRef<'_>
+where
+    W: ArcWake,
+{
+    // simply copy the pointer instead of using Arc::into_raw,
+    // as we don't actually keep a refcount by using ManuallyDrop.<
+    let ptr = Arc::as_ptr(wake).cast::<()>();
+
+    let waker =
+        ManuallyDrop::new(unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) });
+    WakerRef::new_unowned(waker)
+}