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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 19:33:14 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 19:33:14 +0000
commit36d22d82aa202bb199967e9512281e9a53db42c9 (patch)
tree105e8c98ddea1c1e4784a60a5a6410fa416be2de /third_party/rust/futures-util/src/future/poll_immediate.rs
parentInitial commit. (diff)
downloadfirefox-esr-36d22d82aa202bb199967e9512281e9a53db42c9.tar.xz
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Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/rust/futures-util/src/future/poll_immediate.rs')
-rw-r--r--third_party/rust/futures-util/src/future/poll_immediate.rs126
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diff --git a/third_party/rust/futures-util/src/future/poll_immediate.rs b/third_party/rust/futures-util/src/future/poll_immediate.rs
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+++ b/third_party/rust/futures-util/src/future/poll_immediate.rs
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+use super::assert_future;
+use core::pin::Pin;
+use futures_core::task::{Context, Poll};
+use futures_core::{FusedFuture, Future, Stream};
+use pin_project_lite::pin_project;
+
+pin_project! {
+ /// Future for the [`poll_immediate`](poll_immediate()) function.
+ ///
+ /// It will never return [Poll::Pending](core::task::Poll::Pending)
+ #[derive(Debug, Clone)]
+ #[must_use = "futures do nothing unless you `.await` or poll them"]
+ pub struct PollImmediate<T> {
+ #[pin]
+ future: Option<T>
+ }
+}
+
+impl<T, F> Future for PollImmediate<F>
+where
+ F: Future<Output = T>,
+{
+ type Output = Option<T>;
+
+ #[inline]
+ fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+ let mut this = self.project();
+ let inner =
+ this.future.as_mut().as_pin_mut().expect("PollImmediate polled after completion");
+ match inner.poll(cx) {
+ Poll::Ready(t) => {
+ this.future.set(None);
+ Poll::Ready(Some(t))
+ }
+ Poll::Pending => Poll::Ready(None),
+ }
+ }
+}
+
+impl<T: Future> FusedFuture for PollImmediate<T> {
+ fn is_terminated(&self) -> bool {
+ self.future.is_none()
+ }
+}
+
+/// A [Stream](crate::stream::Stream) implementation that can be polled repeatedly until the future is done.
+/// The stream will never return [Poll::Pending](core::task::Poll::Pending)
+/// so polling it in a tight loop is worse than using a blocking synchronous function.
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::task::Poll;
+/// use futures::{StreamExt, future, pin_mut};
+/// use future::FusedFuture;
+///
+/// let f = async { 1_u32 };
+/// pin_mut!(f);
+/// let mut r = future::poll_immediate(f);
+/// assert_eq!(r.next().await, Some(Poll::Ready(1)));
+///
+/// let f = async {futures::pending!(); 42_u8};
+/// pin_mut!(f);
+/// let mut p = future::poll_immediate(f);
+/// assert_eq!(p.next().await, Some(Poll::Pending));
+/// assert!(!p.is_terminated());
+/// assert_eq!(p.next().await, Some(Poll::Ready(42)));
+/// assert!(p.is_terminated());
+/// assert_eq!(p.next().await, None);
+/// # });
+/// ```
+impl<T, F> Stream for PollImmediate<F>
+where
+ F: Future<Output = T>,
+{
+ type Item = Poll<T>;
+
+ fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+ let mut this = self.project();
+ match this.future.as_mut().as_pin_mut() {
+ // inner is gone, so we can signal that the stream is closed.
+ None => Poll::Ready(None),
+ Some(fut) => Poll::Ready(Some(fut.poll(cx).map(|t| {
+ this.future.set(None);
+ t
+ }))),
+ }
+ }
+}
+
+/// Creates a future that is immediately ready with an Option of a value.
+/// Specifically this means that [poll](core::future::Future::poll()) always returns [Poll::Ready](core::task::Poll::Ready).
+///
+/// # Caution
+///
+/// When consuming the future by this function, note the following:
+///
+/// - This function does not guarantee that the future will run to completion, so it is generally incompatible with passing the non-cancellation-safe future by value.
+/// - Even if the future is cancellation-safe, creating and dropping new futures frequently may lead to performance problems.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let r = future::poll_immediate(async { 1_u32 });
+/// assert_eq!(r.await, Some(1));
+///
+/// let p = future::poll_immediate(future::pending::<i32>());
+/// assert_eq!(p.await, None);
+/// # });
+/// ```
+///
+/// ### Reusing a future
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::{future, pin_mut};
+/// let f = async {futures::pending!(); 42_u8};
+/// pin_mut!(f);
+/// assert_eq!(None, future::poll_immediate(&mut f).await);
+/// assert_eq!(42, f.await);
+/// # });
+/// ```
+pub fn poll_immediate<F: Future>(f: F) -> PollImmediate<F> {
+ assert_future::<Option<F::Output>, PollImmediate<F>>(PollImmediate { future: Some(f) })
+}