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