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use pin_project_lite::pin_project;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
pin_project! {
/// Future for the [`unconstrained`](unconstrained) method.
#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
#[must_use = "Unconstrained does nothing unless polled"]
pub struct Unconstrained<F> {
#[pin]
inner: F,
}
}
impl<F> Future for Unconstrained<F>
where
F: Future,
{
type Output = <F as Future>::Output;
cfg_coop! {
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let inner = self.project().inner;
crate::runtime::coop::with_unconstrained(|| inner.poll(cx))
}
}
cfg_not_coop! {
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let inner = self.project().inner;
inner.poll(cx)
}
}
}
/// Turn off cooperative scheduling for a future. The future will never be forced to yield by
/// Tokio. Using this exposes your service to starvation if the unconstrained future never yields
/// otherwise.
///
/// See also the usage example in the [task module](index.html#unconstrained).
#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
pub fn unconstrained<F>(inner: F) -> Unconstrained<F> {
Unconstrained { inner }
}