80972f1e0e
This is a `core` patch to make wakers 1 word (the task pointer) instead of 2 (task pointer + vtable). It allows having the "waker optimization" we had a while back on `WakerRegistration/AtomicWaker`, but EVERYWHERE, without patching all crates. Advantages: - Less memory usage. - Faster. - `AtomicWaker` can actually use atomics to load/store the waker, No critical section needed. - No `dyn` call, which means `cargo-call-stack` can now see through wakes. Disadvantages: - You have to patch `core`... - Breaks all executors and other things that create wakers, unless they opt in to using the new `from_ptr` API. How to use: - Run this shell script to patch `core`. https://gist.github.com/Dirbaio/c67da7cf318515181539122c9d32b395 - Enable `build-std` - Enable `build-std-features = core/turbowakers` - Enable feature `turbowakers` in `embassy-executor`, `embassy-sync`. - Make sure you have no other crate creating wakers other than `embassy-executor`. These will panic at runtime. Note that the patched `core` is equivalent to the unpached one when the `turbowakers` feature is not enabled, so it should be fine to leave it there.
53 lines
1.9 KiB
Rust
53 lines
1.9 KiB
Rust
use core::mem;
|
|
use core::task::Waker;
|
|
|
|
/// Utility struct to register and wake a waker.
|
|
#[derive(Debug, Default)]
|
|
pub struct WakerRegistration {
|
|
waker: Option<Waker>,
|
|
}
|
|
|
|
impl WakerRegistration {
|
|
/// Create a new `WakerRegistration`.
|
|
pub const fn new() -> Self {
|
|
Self { waker: None }
|
|
}
|
|
|
|
/// Register a waker. Overwrites the previous waker, if any.
|
|
pub fn register(&mut self, w: &Waker) {
|
|
match self.waker {
|
|
// Optimization: If both the old and new Wakers wake the same task, we can simply
|
|
// 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)) => {}
|
|
_ => {
|
|
// 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()
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Wake the registered waker, if any.
|
|
pub fn wake(&mut self) {
|
|
if let Some(w) = self.waker.take() {
|
|
w.wake()
|
|
}
|
|
}
|
|
|
|
/// Returns true if a waker is currently registered
|
|
pub fn occupied(&self) -> bool {
|
|
self.waker.is_some()
|
|
}
|
|
}
|