| //! Utilities for creating zero-cost wakers that don't do anything. |
| |
| use core::task::{RawWaker, RawWakerVTable, Waker}; |
| use core::ptr::null; |
| #[cfg(feature = "std")] |
| use once_cell::sync::Lazy; |
| |
| 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); |
| |
| 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 { |
| 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] |
| #[cfg(feature = "std")] |
| pub fn noop_waker_ref() -> &'static Waker { |
| static NOOP_WAKER_INSTANCE: Lazy<Waker> = Lazy::new(noop_waker); |
| &*NOOP_WAKER_INSTANCE |
| } |
| |
| #[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(); |
| } |
| } |