1use pin_project_lite::pin_project;
2use std::future::Future;
3use std::pin::Pin;
4use std::task::{Context, Poll};
5
6pin_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
16impl<F> Future for Unconstrained<F>
17where
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::task::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")))]
43pub fn unconstrained<F>(inner: F) -> Unconstrained<F> {
44 Unconstrained { inner }
45}
46