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