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use nightly waker_getters APIs

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Since https://github.com/rust-lang/rust/issues/96992 has stalled,
to prevent potential unsoundness caused by transmuting to &WakerHack,
we can use nightly waker_getters APIs by gating it behind nightly
feature in embassy-executor without waiting for it to be stablized.
This commit is contained in:
zjp 2024-06-09 11:39:47 +08:00
parent e5495b51b4
commit 3f45ec6ead
2 changed files with 26 additions and 0 deletions
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1
embassy-executor/src/lib.rs
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@ -1,4 +1,5 @@
#![cfg_attr(not(any(feature = "arch-std", feature = "arch-wasm")), no_std)] #![cfg_attr(not(any(feature = "arch-std", feature = "arch-wasm")), no_std)]
#![cfg_attr(feature = "nightly", feature(waker_getters))]
#![allow(clippy::new_without_default)] #![allow(clippy::new_without_default)]
#![doc = include_str!("../README.md")] #![doc = include_str!("../README.md")]
#![warn(missing_docs)] #![warn(missing_docs)]

25
embassy-executor/src/raw/waker.rs
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@ -32,6 +32,7 @@ pub(crate) unsafe fn from_task(p: TaskRef) -> Waker {
/// # Panics /// # Panics
/// ///
/// Panics if the waker is not created by the Embassy executor. /// Panics if the waker is not created by the Embassy executor.
#[cfg(not(feature = "nightly"))]
pub fn task_from_waker(waker: &Waker) -> TaskRef { pub fn task_from_waker(waker: &Waker) -> TaskRef {
// safety: OK because WakerHack has the same layout as Waker. // safety: OK because WakerHack has the same layout as Waker.
// This is not really guaranteed because the structs are `repr(Rust)`, it is // This is not really guaranteed because the structs are `repr(Rust)`, it is
@ -46,7 +47,31 @@ pub fn task_from_waker(waker: &Waker) -> TaskRef {
unsafe { TaskRef::from_ptr(hack.data as *const TaskHeader) } unsafe { TaskRef::from_ptr(hack.data as *const TaskHeader) }
} }
#[cfg(not(feature = "nightly"))]
struct WakerHack { struct WakerHack {
data: *const (), data: *const (),
vtable: &'static RawWakerVTable, vtable: &'static RawWakerVTable,
} }
/// Get a task pointer from a waker.
///
/// This can be used as an optimization in wait queues to store task pointers
/// (1 word) instead of full Wakers (2 words). This saves a bit of RAM and helps
/// avoid dynamic dispatch.
///
/// You can use the returned task pointer to wake the task with [`wake_task`](super::wake_task).
///
/// # Panics
///
/// Panics if the waker is not created by the Embassy executor.
#[cfg(feature = "nightly")]
pub fn task_from_waker(waker: &Waker) -> TaskRef {
let raw_waker = waker.as_raw();
if raw_waker.vtable() != &VTABLE {
panic!("Found waker not created by the Embassy executor. `embassy_time::Timer` only works with the Embassy executor.")
}
// safety: our wakers are always created with `TaskRef::as_ptr`
unsafe { TaskRef::from_ptr(raw_waker.data() as *const TaskHeader) }
}