1 //! Utilities for creating zero-cost wakers that don't do anything. 2 3 use core::ptr::null; 4 use core::task::{RawWaker, RawWakerVTable, Waker}; 5 noop_clone(_data: *const ()) -> RawWaker6unsafe fn noop_clone(_data: *const ()) -> RawWaker { 7 noop_raw_waker() 8 } 9 noop(_data: *const ())10unsafe fn noop(_data: *const ()) {} 11 12 const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop); 13 noop_raw_waker() -> RawWaker14const fn noop_raw_waker() -> RawWaker { 15 RawWaker::new(null(), &NOOP_WAKER_VTABLE) 16 } 17 18 /// Create a new [`Waker`] which does 19 /// nothing when `wake()` is called on it. 20 /// 21 /// # Examples 22 /// 23 /// ``` 24 /// use futures::task::noop_waker; 25 /// let waker = noop_waker(); 26 /// waker.wake(); 27 /// ``` 28 #[inline] noop_waker() -> Waker29pub fn noop_waker() -> Waker { 30 // FIXME: Since 1.46.0 we can use transmute in consts, allowing this function to be const. 31 unsafe { Waker::from_raw(noop_raw_waker()) } 32 } 33 34 /// Get a static reference to a [`Waker`] which 35 /// does nothing when `wake()` is called on it. 36 /// 37 /// # Examples 38 /// 39 /// ``` 40 /// use futures::task::noop_waker_ref; 41 /// let waker = noop_waker_ref(); 42 /// waker.wake_by_ref(); 43 /// ``` 44 #[inline] noop_waker_ref() -> &'static Waker45pub fn noop_waker_ref() -> &'static Waker { 46 struct SyncRawWaker(RawWaker); 47 unsafe impl Sync for SyncRawWaker {} 48 49 static NOOP_WAKER_INSTANCE: SyncRawWaker = SyncRawWaker(noop_raw_waker()); 50 51 // SAFETY: `Waker` is #[repr(transparent)] over its `RawWaker`. 52 unsafe { &*(&NOOP_WAKER_INSTANCE.0 as *const RawWaker as *const Waker) } 53 } 54 55 #[cfg(test)] 56 mod tests { 57 #[test] 58 #[cfg(feature = "std")] issue_2091_cross_thread_segfault()59 fn issue_2091_cross_thread_segfault() { 60 let waker = std::thread::spawn(super::noop_waker_ref).join().unwrap(); 61 waker.wake_by_ref(); 62 } 63 } 64