72 lines
1.3 KiB
Rust
72 lines
1.3 KiB
Rust
//! A flag that can be raised to wake a task.
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//!
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//! Copied wholesale from <https://docs.rs/futures/latest/futures/task/struct.AtomicWaker.html>
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//! unfortunately not aware of crated version!
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use std::{
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pin::Pin,
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sync::{
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atomic::{AtomicBool, Ordering::Relaxed},
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Arc,
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},
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};
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use futures::{
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future::Future,
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task::{AtomicWaker, Context, Poll},
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};
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#[derive(Debug)]
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struct Inner {
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waker: AtomicWaker,
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set: AtomicBool,
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}
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#[derive(Clone, Debug)]
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pub struct Flag(Arc<Inner>);
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impl Default for Flag {
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fn default() -> Self {
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Self::new(false)
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}
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}
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impl Flag {
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pub fn new(value: bool) -> Self {
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Self(Arc::new(Inner {
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waker: AtomicWaker::new(),
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set: AtomicBool::new(value),
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}))
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}
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pub fn raised(&self) -> bool {
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self.0.set.load(Relaxed)
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}
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pub fn raise(&self) {
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self.0.set.store(true, Relaxed);
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self.0.waker.wake();
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}
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}
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impl Future for Flag {
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type Output = ();
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
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// quick check to avoid registration if already done.
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if self.0.set.load(Relaxed) {
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return Poll::Ready(());
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}
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self.0.waker.register(cx.waker());
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// Need to check condition **after** `register` to avoid a race
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// condition that would result in lost notifications.
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if self.0.set.load(Relaxed) {
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Poll::Ready(())
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} else {
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Poll::Pending
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}
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}
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}
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