43 lines
1.2 KiB
Rust
43 lines
1.2 KiB
Rust
use core::future::Future;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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/// Yield from the current task once, allowing other tasks to run.
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///
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/// This can be used to easily and quickly implement simple async primitives
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/// without using wakers. The following snippet will wait for a condition to
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/// hold, while still allowing other tasks to run concurrently (not monopolizing
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/// the executor thread).
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///
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/// ```rust,no_run
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/// while !some_condition() {
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/// yield_now().await;
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/// }
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/// ```
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///
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/// The downside is this will spin in a busy loop, using 100% of the CPU, while
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/// using wakers correctly would allow the CPU to sleep while waiting.
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///
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/// The internal implementation is: on first poll the future wakes itself and
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/// returns `Poll::Pending`. On second poll, it returns `Poll::Ready`.
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pub fn yield_now() -> impl Future<Output = ()> {
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YieldNowFuture { yielded: false }
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}
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struct YieldNowFuture {
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yielded: bool,
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}
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impl Future for YieldNowFuture {
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type Output = ();
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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if self.yielded {
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Poll::Ready(())
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} else {
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self.yielded = true;
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cx.waker().wake_by_ref();
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Poll::Pending
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}
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}
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}
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