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use atomic::{Atomic, Ordering};
use crate::{stream::PollRecv, Context};
use super::{
notifier::Notifier,
oneshot_cell::{OneshotCell, TryRecvError},
};
#[derive(Copy, Clone)]
enum State {
Alive,
Dead,
}
pub struct Transfer<T: Sized> {
sender: Atomic<State>,
receiver: Atomic<State>,
value: OneshotCell<T>,
notify_rx: Notifier,
}
impl<T> Transfer<T> {
pub fn new() -> Self {
Self {
sender: Atomic::new(State::Alive),
receiver: Atomic::new(State::Alive),
value: OneshotCell::new(),
notify_rx: Notifier::new(),
}
}
pub fn send(&self, value: T) -> Result<(), T> {
if let State::Dead = self.receiver.load(Ordering::Acquire) {
return Err(value);
}
self.value.send(value)?;
self.notify_rx.notify();
Ok(())
}
pub fn recv(&self, cx: &Context<'_>) -> PollRecv<T> {
loop {
let guard = self.notify_rx.guard();
match self.value.try_recv() {
Ok(value) => return PollRecv::Ready(value),
Err(TryRecvError::Pending) => {
if let State::Dead = self.sender.load(Ordering::Acquire) {
return match self.value.try_recv() {
Ok(v) => PollRecv::Ready(v),
Err(TryRecvError::Pending) => PollRecv::Closed,
Err(TryRecvError::Closed) => PollRecv::Closed,
};
}
self.notify_rx.subscribe(cx);
if guard.is_expired() {
continue;
}
return PollRecv::Pending;
}
Err(TryRecvError::Closed) => return PollRecv::Closed,
}
}
}
pub fn sender_disconnect(&self) {
self.sender.store(State::Dead, Ordering::Release);
self.notify_rx.notify();
}
pub fn receiver_disconnect(&self) {
self.receiver.store(State::Dead, Ordering::Release);
}
}