44 lines
1.3 KiB
Rust
44 lines
1.3 KiB
Rust
use core::future::Future;
|
|
use core::pin::Pin;
|
|
use core::task::{Context, Poll};
|
|
|
|
/// Yield from the current task once, allowing other tasks to run.
|
|
///
|
|
/// This can be used to easily and quickly implement simple async primitives
|
|
/// without using wakers. The following snippet will wait for a condition to
|
|
/// hold, while still allowing other tasks to run concurrently (not monopolizing
|
|
/// the executor thread).
|
|
///
|
|
/// ```rust,no_run
|
|
/// while !some_condition() {
|
|
/// yield_now().await;
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// The downside is this will spin in a busy loop, using 100% of the CPU, while
|
|
/// using wakers correctly would allow the CPU to sleep while waiting.
|
|
///
|
|
/// The internal implementation is: on first poll the future wakes itself and
|
|
/// returns `Poll::Pending`. On second poll, it returns `Poll::Ready`.
|
|
pub fn yield_now() -> impl Future<Output = ()> {
|
|
YieldNowFuture { yielded: false }
|
|
}
|
|
|
|
#[must_use = "futures do nothing unless you `.await` or poll them"]
|
|
struct YieldNowFuture {
|
|
yielded: bool,
|
|
}
|
|
|
|
impl Future for YieldNowFuture {
|
|
type Output = ();
|
|
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
|
|
if self.yielded {
|
|
Poll::Ready(())
|
|
} else {
|
|
self.yielded = true;
|
|
cx.waker().wake_by_ref();
|
|
Poll::Pending
|
|
}
|
|
}
|
|
}
|