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WakerRegistration: Wake previous task if any

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This commit is contained in:
Dario Nieuwenhuis 2021-01-11 10:38:25 +01:00
parent 60df9e0d38
commit 877fc0321a
1 changed files with 17 additions and 6 deletions
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23
embassy/src/util/waker.rs
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@ -1,3 +1,4 @@
use core::mem;
use core::task::Context;
use core::task::Waker;
@ -19,11 +20,21 @@ impl WakerRegistration {
// keep the old waker, skipping the clone. (In most executor implementations,
// cloning a waker is somewhat expensive, comparable to cloning an Arc).
Some(ref w2) if (w2.will_wake(w)) => {}
// In all other cases
// - we have no waker registered
// - we have a waker registered but it's for a different task.
// then clone the new waker and store it
_ => self.waker = Some(w.clone()),
_ => {
// clone the new waker and store it
if let Some(old_waker) = mem::replace(&mut self.waker, Some(w.clone())) {
// We had a waker registered for another task. Wake it, so the other task can
// reregister itself if it's still interested.
//
// If two tasks are waiting on the same thing concurrently, this will cause them
// to wake each other in a loop fighting over this WakerRegistration. This wastes
// CPU but things will still work.
//
// If the user wants to have two tasks waiting on the same thing they should use
// a more appropriate primitive that can store multiple wakers.
old_waker.wake()
}
}
}
}
@ -35,4 +46,4 @@ impl WakerRegistration {
pub fn context(&self) -> Option<Context<'_>> {
self.waker.as_ref().map(|w| Context::from_waker(w))
}
}
}