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Override Waker::clone_from to avoid cloning Wakers unnecessarily

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SabrinaJewson 2023-07-27 16:29:13 +01:00
parent 49a16b64b0
commit 6cdb7df443
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1 changed files with 14 additions and 1 deletions
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15
library/core/src/task/wake.rs
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@ -231,6 +231,10 @@ impl fmt::Debug for Context<'_> {
/// this might be done to wake a future when a blocking function call completes on another
/// thread.
///
/// Note that it is preferable to use `waker.clone_from(&new_waker)` instead
/// of `*waker = new_waker.clone()`, as the former will avoid cloning the waker
/// unnecessarily if the two wakers [wake the same task](Self::will_wake).
///
/// [`Future::poll()`]: core::future::Future::poll
/// [`Poll::Pending`]: core::task::Poll::Pending
#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/66401
@ -302,7 +306,9 @@ impl Waker {
/// when the `Waker`s would awaken the same task. However, if this function
/// returns `true`, it is guaranteed that the `Waker`s will awaken the same task.
///
/// This function is primarily used for optimization purposes.
/// This function is primarily used for optimization purposes — for example,
/// this type's [`clone_from`](Self::clone_from) implementation uses it to
/// avoid cloning the waker when they would wake the same task anyway.
#[inline]
#[must_use]
#[stable(feature = "futures_api", since = "1.36.0")]
@ -382,6 +388,13 @@ impl Clone for Waker {
waker: unsafe { (self.waker.vtable.clone)(self.waker.data) },
}
}
#[inline]
fn clone_from(&mut self, source: &Self) {
if !self.will_wake(source) {
*self = source.clone();
}
}
}
#[stable(feature = "futures_api", since = "1.36.0")]