forked from mirror/async-std
ec23632f3e
* Cleanup: replace cfg-if with our macros * Prefix macros with cfg_ * Remove #[macro_export] from internal macros
53 lines
1.3 KiB
Rust
53 lines
1.3 KiB
Rust
use crate::future::Future;
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use crate::task::{Context, Poll};
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use std::pin::Pin;
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/// Cooperatively gives up a timeslice to the task scheduler.
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///
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/// Calling this function will move the currently executing future to the back
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/// of the execution queue, making room for other futures to execute. This is
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/// especially useful after running CPU-intensive operations inside a future.
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///
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/// See also [`task::spawn_blocking`].
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///
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/// [`task::spawn_blocking`]: fn.spawn_blocking.html
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// # fn main() { async_std::task::block_on(async {
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/// #
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/// use async_std::task;
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///
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/// task::yield_now().await;
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/// #
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/// # }) }
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/// ```
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#[cfg(feature = "unstable")]
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#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
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#[inline]
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pub async fn yield_now() {
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YieldNow(false).await
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}
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struct YieldNow(bool);
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impl Future for YieldNow {
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type Output = ();
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// The futures executor is implemented as a FIFO queue, so all this future
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// does is re-schedule the future back to the end of the queue, giving room
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// for other futures to progress.
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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if !self.0 {
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self.0 = true;
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cx.waker().wake_by_ref();
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Poll::Pending
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} else {
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Poll::Ready(())
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}
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}
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}
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