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.
35 lines
1.1 KiB
Rust
35 lines
1.1 KiB
Rust
use core::ptr::NonNull;
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use core::task::Waker;
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use super::{wake_task, TaskHeader, TaskRef};
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pub(crate) unsafe fn from_task(p: TaskRef) -> Waker {
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Waker::from_turbo_ptr(NonNull::new_unchecked(p.as_ptr() as _))
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}
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/// Get a task pointer from a waker.
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///
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/// This can be used as an optimization in wait queues to store task pointers
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/// (1 word) instead of full Wakers (2 words). This saves a bit of RAM and helps
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/// avoid dynamic dispatch.
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///
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/// You can use the returned task pointer to wake the task with [`wake_task`](super::wake_task).
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///
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/// # Panics
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///
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/// Panics if the waker is not created by the Embassy executor.
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pub fn task_from_waker(waker: &Waker) -> TaskRef {
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let ptr = waker.as_turbo_ptr().as_ptr();
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// safety: our wakers are always created with `TaskRef::as_ptr`
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unsafe { TaskRef::from_ptr(ptr as *const TaskHeader) }
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}
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#[inline(never)]
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#[no_mangle]
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fn _turbo_wake(ptr: NonNull<()>) {
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// safety: our wakers are always created with `TaskRef::as_ptr`
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let task = unsafe { TaskRef::from_ptr(ptr.as_ptr() as *const TaskHeader) };
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wake_task(task)
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}
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