embassy_sync/waitqueue/
multi_waker.rs

1use core::task::Waker;
2
3use heapless::Vec;
4
5/// Utility struct to register and wake multiple wakers.
6pub struct MultiWakerRegistration<const N: usize> {
7    wakers: Vec<Waker, N>,
8}
9
10impl<const N: usize> MultiWakerRegistration<N> {
11    /// Create a new empty instance
12    pub const fn new() -> Self {
13        Self { wakers: Vec::new() }
14    }
15
16    /// Register a waker. If the buffer is full the function returns it in the error
17    pub fn register(&mut self, w: &Waker) {
18        // If we already have some waker that wakes the same task as `w`, do nothing.
19        // This avoids cloning wakers, and avoids unnecessary mass-wakes.
20        for w2 in &self.wakers {
21            if w.will_wake(w2) {
22                return;
23            }
24        }
25
26        if self.wakers.is_full() {
27            // All waker slots were full. It's a bit inefficient, but we can wake everything.
28            // Any future that is still active will simply reregister.
29            // This won't happen a lot, so it's ok.
30            self.wake();
31        }
32
33        if self.wakers.push(w.clone()).is_err() {
34            // This can't happen unless N=0
35            // (Either `wakers` wasn't full, or it was in which case `wake()` empied it)
36            panic!("tried to push a waker to a zero-length MultiWakerRegistration")
37        }
38    }
39
40    /// Wake all registered wakers. This clears the buffer
41    pub fn wake(&mut self) {
42        // heapless::Vec has no `drain()`, do it unsafely ourselves...
43
44        // First set length to 0, without dropping the contents.
45        // This is necessary for soundness: if wake() panics and we're using panic=unwind.
46        // Setting len=0 upfront ensures other code can't observe the vec in an inconsistent state.
47        // (it'll leak wakers, but that's not UB)
48        let len = self.wakers.len();
49        unsafe { self.wakers.set_len(0) }
50
51        for i in 0..len {
52            // Move a waker out of the vec.
53            let waker = unsafe { self.wakers.as_mut_ptr().add(i).read() };
54            // Wake it by value, which consumes (drops) it.
55            waker.wake();
56        }
57    }
58}
embassy_sync/waitqueue/multi_waker.rs

embassy_sync/waitqueue/
multi_waker.rs
