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 | |
6 | unsafe fn noop_clone(_data: *const ()) -> RawWaker { |
7 | noop_raw_waker() |
8 | } |
9 | |
10 | unsafe fn noop(_data: *const ()) {} |
11 | |
12 | const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop); |
13 | |
14 | const 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 ] |
29 | pub 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 ] |
45 | pub 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" )] |
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 | |