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Auto merge of #96875 - SabrinaJewson:noop-waker, r=m-ou-se
Add `task::Waker::noop` I have found myself reimplementing this function many times when I need a `Context` but don't have a runtime or `futures` to hand. Prior art: [`futures::task::noop_waker`](https://docs.rs/futures/0.3/futures/task/fn.noop_waker.html) and [`futures::task::noop_waker_ref`](https://docs.rs/futures/0.3/futures/task/fn.noop_waker_ref.html) Tracking issue: https://github.com/rust-lang/rust/issues/98286 Unresolved questions: 1. Should we also add `RawWaker::noop()`? (I don't think so, I can't think of a use case for it) 2. Should we also add `Context::noop()`? Depending on the future direction `Context` goes a "noop context" might not even make sense in future. 3. Should it be an associated constant instead? That would allow for `let cx = &mut Context::from_waker(&Waker::NOOP);` to work on one line which is pretty nice. I don't really know what the guideline is here. r? rust-lang/libs-api `@rustbot` label +T-libs-api -T-libs
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@ -2,6 +2,7 @@
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use crate::fmt;
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use crate::marker::{PhantomData, Unpin};
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use crate::ptr;
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/// A `RawWaker` allows the implementor of a task executor to create a [`Waker`]
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/// which provides customized wakeup behavior.
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@ -322,6 +323,45 @@ impl Waker {
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Waker { waker }
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}
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/// Creates a new `Waker` that does nothing when `wake` is called.
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///
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/// This is mostly useful for writing tests that need a [`Context`] to poll
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/// some futures, but are not expecting those futures to wake the waker or
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/// do not need to do anything specific if it happens.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(noop_waker)]
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///
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/// use std::future::Future;
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/// use std::task;
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///
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/// let waker = task::Waker::noop();
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/// let mut cx = task::Context::from_waker(&waker);
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///
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/// let mut future = Box::pin(async { 10 });
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/// assert_eq!(future.as_mut().poll(&mut cx), task::Poll::Ready(10));
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/// ```
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#[inline]
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#[must_use]
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#[unstable(feature = "noop_waker", issue = "98286")]
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pub const fn noop() -> Waker {
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const VTABLE: RawWakerVTable = RawWakerVTable::new(
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// Cloning just returns a new no-op raw waker
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|_| RAW,
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// `wake` does nothing
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|_| {},
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// `wake_by_ref` does nothing
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|_| {},
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// Dropping does nothing as we don't allocate anything
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|_| {},
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);
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const RAW: RawWaker = RawWaker::new(ptr::null(), &VTABLE);
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Waker { waker: RAW }
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}
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/// Get a reference to the underlying [`RawWaker`].
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#[inline]
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#[must_use]
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