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use crate::loom::sync::Arc;
use std::marker::PhantomData;
use std::mem::ManuallyDrop;
use std::ops::Deref;
use std::task::{RawWaker, RawWakerVTable, Waker};
/// Simplified waking interface based on Arcs.
pub(crate) trait Wake: Send + Sync + Sized + 'static {
/// Wake by value.
fn wake(arc_self: Arc<Self>);
/// Wake by reference.
fn wake_by_ref(arc_self: &Arc<Self>);
}
/// A `Waker` that is only valid for a given lifetime.
#[derive(Debug)]
pub(crate) struct WakerRef<'a> {
waker: ManuallyDrop<Waker>,
_p: PhantomData<&'a ()>,
}
impl Deref for WakerRef<'_> {
type Target = Waker;
fn deref(&self) -> &Waker {
&self.waker
}
}
/// Creates a reference to a `Waker` from a reference to `Arc<impl Wake>`.
pub(crate) fn waker_ref<W: Wake>(wake: &Arc<W>) -> WakerRef<'_> {
let ptr = Arc::as_ptr(wake) as *const ();
let waker = unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) };
WakerRef {
waker: ManuallyDrop::new(waker),
_p: PhantomData,
}
}
fn waker_vtable<W: Wake>() -> &'static RawWakerVTable {
&RawWakerVTable::new(
clone_arc_raw::<W>,
wake_arc_raw::<W>,
wake_by_ref_arc_raw::<W>,
drop_arc_raw::<W>,
)
}
unsafe fn inc_ref_count<T: Wake>(data: *const ()) {
// Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
let arc = ManuallyDrop::new(Arc::<T>::from_raw(data as *const T));
// Now increase refcount, but don't drop new refcount either
let _arc_clone: ManuallyDrop<_> = arc.clone();
}
unsafe fn clone_arc_raw<T: Wake>(data: *const ()) -> RawWaker {
inc_ref_count::<T>(data);
RawWaker::new(data, waker_vtable::<T>())
}
unsafe fn wake_arc_raw<T: Wake>(data: *const ()) {
let arc: Arc<T> = Arc::from_raw(data as *const T);
Wake::wake(arc);
}
// used by `waker_ref`
unsafe fn wake_by_ref_arc_raw<T: Wake>(data: *const ()) {
// Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
let arc = ManuallyDrop::new(Arc::<T>::from_raw(data as *const T));
Wake::wake_by_ref(&arc);
}
unsafe fn drop_arc_raw<T: Wake>(data: *const ()) {
drop(Arc::<T>::from_raw(data as *const T))
}