1 use pin_project_lite::pin_project;
2 use std::future::Future;
3 use std::pin::Pin;
4 use std::task::{Context, Poll};
5 
6 pin_project! {
7     /// Future for the [`unconstrained`](unconstrained) method.
8     #[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
9     #[must_use = "Unconstrained does nothing unless polled"]
10     pub struct Unconstrained<F> {
11         #[pin]
12         inner: F,
13     }
14 }
15 
16 impl<F> Future for Unconstrained<F>
17 where
18     F: Future,
19 {
20     type Output = <F as Future>::Output;
21 
22     cfg_coop! {
23         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
24             let inner = self.project().inner;
25             crate::coop::with_unconstrained(|| inner.poll(cx))
26         }
27     }
28 
29     cfg_not_coop! {
30         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
31             let inner = self.project().inner;
32             inner.poll(cx)
33         }
34     }
35 }
36 
37 /// Turn off cooperative scheduling for a future. The future will never be forced to yield by
38 /// Tokio. Using this exposes your service to starvation if the unconstrained future never yields
39 /// otherwise.
40 ///
41 /// See also the usage example in the [task module](index.html#unconstrained).
42 #[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
unconstrained<F>(inner: F) -> Unconstrained<F>43 pub fn unconstrained<F>(inner: F) -> Unconstrained<F> {
44     Unconstrained { inner }
45 }
46