1 files changed, 63 insertions, 0 deletions
diff --git a/third_party/rust/futures-task/src/noop_waker.rs b/third_party/rust/futures-task/src/noop_waker.rs
new file mode 100644
index 0000000000..f76a8a2e95
--- /dev/null
+++ b/third_party/rust/futures-task/src/noop_waker.rs
@@ -0,0 +1,63 @@
+//! Utilities for creating zero-cost wakers that don't do anything.
+
+use core::ptr::null;
+use core::task::{RawWaker, RawWakerVTable, Waker};
+
+unsafe fn noop_clone(_data: *const ()) -> RawWaker {
+    noop_raw_waker()
+}
+
+unsafe fn noop(_data: *const ()) {}
+
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+const fn noop_raw_waker() -> RawWaker {
+    RawWaker::new(null(), &NOOP_WAKER_VTABLE)
+}
+
+/// Create a new [`Waker`] which does
+/// nothing when `wake()` is called on it.
+///
+/// # Examples
+///
+/// ```
+/// use futures::task::noop_waker;
+/// let waker = noop_waker();
+/// waker.wake();
+/// ```
+#[inline]
+pub fn noop_waker() -> Waker {
+    // FIXME: Since 1.46.0 we can use transmute in consts, allowing this function to be const.
+    unsafe { Waker::from_raw(noop_raw_waker()) }
+}
+
+/// Get a static reference to a [`Waker`] which
+/// does nothing when `wake()` is called on it.
+///
+/// # Examples
+///
+/// ```
+/// use futures::task::noop_waker_ref;
+/// let waker = noop_waker_ref();
+/// waker.wake_by_ref();
+/// ```
+#[inline]
+pub fn noop_waker_ref() -> &'static Waker {
+    struct SyncRawWaker(RawWaker);
+    unsafe impl Sync for SyncRawWaker {}
+
+    static NOOP_WAKER_INSTANCE: SyncRawWaker = SyncRawWaker(noop_raw_waker());
+
+    // SAFETY: `Waker` is #[repr(transparent)] over its `RawWaker`.
+    unsafe { &*(&NOOP_WAKER_INSTANCE.0 as *const RawWaker as *const Waker) }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    #[cfg(feature = "std")]
+    fn issue_2091_cross_thread_segfault() {
+        let waker = std::thread::spawn(super::noop_waker_ref).join().unwrap();
+        waker.wake_by_ref();
+    }
+}