1use core::pin::Pin;
2use futures_core::future::Future;
3use futures_core::task::{Context, Poll};
4
5/// A macro which yields to the event loop once.
6///
7/// This is equivalent to returning [`Poll::Pending`](futures_core::task::Poll)
8/// from a [`Future::poll`](futures_core::future::Future::poll) implementation.
9/// Similarly, when using this macro, it must be ensured that [`wake`](std::task::Waker::wake)
10/// is called somewhere when further progress can be made.
11///
12/// This macro is only usable inside of async functions, closures, and blocks.
13/// It is also gated behind the `async-await` feature of this library, which is
14/// activated by default.
15#[macro_export]
16macro_rules! pending {
17 () => {
18 $crate::__private::async_await::pending_once().await
19 };
20}
21
22#[doc(hidden)]
23pub fn pending_once() -> PendingOnce {
24 PendingOnce { is_ready: false }
25}
26
27#[allow(missing_debug_implementations)]
28#[doc(hidden)]
29pub struct PendingOnce {
30 is_ready: bool,
31}
32
33impl Future for PendingOnce {
34 type Output = ();
35 fn poll(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Self::Output> {
36 if self.is_ready {
37 Poll::Ready(())
38 } else {
39 self.is_ready = true;
40 Poll::Pending
41 }
42 }
43}
44