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use core::pin::Pin;
use futures_core::future::Future;
use futures_core::task::{Context, Poll};
/// A macro which yields to the event loop once.
///
/// This is equivalent to returning [`Poll::Pending`](futures_core::task::Poll)
/// from a [`Future::poll`](futures_core::future::Future::poll) implementation.
/// Similarly, when using this macro, it must be ensured that [`wake`](std::task::Waker::wake)
/// is called somewhere when further progress can be made.
///
/// This macro is only usable inside of async functions, closures, and blocks.
/// It is also gated behind the `async-await` feature of this library, which is
/// activated by default.
#[macro_export]
macro_rules! pending {
() => {
$crate::__private::async_await::pending_once().await
};
}
#[doc(hidden)]
pub fn pending_once() -> PendingOnce {
PendingOnce { is_ready: false }
}
#[allow(missing_debug_implementations)]
#[doc(hidden)]
pub struct PendingOnce {
is_ready: bool,
}
impl Future for PendingOnce {
type Output = ();
fn poll(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Self::Output> {
if self.is_ready {
Poll::Ready(())
} else {
self.is_ready = true;
Poll::Pending
}
}
}