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use core::mem;
use core::ptr::NonNull;
use core::task::{RawWaker, RawWakerVTable, Waker};
use super::{wake_task, TaskHeader};
const VTABLE: RawWakerVTable = RawWakerVTable::new(clone, wake, wake, drop);
unsafe fn clone(p: *const ()) -> RawWaker {
RawWaker::new(p, &VTABLE)
}
unsafe fn wake(p: *const ()) {
wake_task(NonNull::new_unchecked(p as *mut TaskHeader))
}
unsafe fn drop(_: *const ()) {
// nop
}
pub(crate) unsafe fn from_task(p: NonNull<TaskHeader>) -> Waker {
Waker::from_raw(RawWaker::new(p.as_ptr() as _, &VTABLE))
}
/// 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.
pub fn task_from_waker(waker: &Waker) -> NonNull<TaskHeader> {
// safety: OK because WakerHack has the same layout as Waker.
// This is not really guaranteed because the structs are `repr(Rust)`, it is
// indeed the case in the current implementation.
// TODO use waker_getters when stable. https://github.com/rust-lang/rust/issues/96992
let hack: &WakerHack = unsafe { mem::transmute(waker) };
if hack.vtable != &VTABLE {
panic!("Found waker not created by the Embassy executor. `embassy_executor::time::Timer` only works with the Embassy executor.")
}
// safety: we never create a waker with a null data pointer.
unsafe { NonNull::new_unchecked(hack.data as *mut TaskHeader) }
}
struct WakerHack {
data: *const (),
vtable: &'static RawWakerVTable,
}
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