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use super::Signal;
use std::pin::Pin;
use std::marker::Unpin;
use std::sync::{Arc, Weak, Mutex, MutexGuard};
use futures_core::Poll;
use futures_core::task::{LocalWaker, Waker};
#[derive(Debug)]
struct Inner<A> {
value: Option<A>,
waker: Option<Waker>,
dropped: bool,
}
impl<A> Inner<A> {
fn notify(mut lock: MutexGuard<Self>) {
if let Some(waker) = lock.waker.take() {
drop(lock);
waker.wake();
}
}
}
#[derive(Debug)]
pub struct Sender<A> {
inner: Weak<Mutex<Inner<A>>>,
}
impl<A> Sender<A> {
pub fn send(&self, value: A) -> Result<(), A> {
if let Some(inner) = self.inner.upgrade() {
let mut inner = inner.lock().unwrap();
inner.value = Some(value);
Inner::notify(inner);
Ok(())
} else {
Err(value)
}
}
}
impl<A> Drop for Sender<A> {
fn drop(&mut self) {
if let Some(inner) = self.inner.upgrade() {
let mut inner = inner.lock().unwrap();
inner.dropped = true;
Inner::notify(inner);
}
}
}
#[derive(Debug)]
#[must_use = "Signals do nothing unless polled"]
pub struct Receiver<A> {
inner: Arc<Mutex<Inner<A>>>,
}
impl<A> Unpin for Receiver<A> {}
impl<A> Signal for Receiver<A> {
type Item = A;
#[inline]
fn poll_change(self: Pin<&mut Self>, waker: &LocalWaker) -> Poll<Option<Self::Item>> {
let mut inner = self.inner.lock().unwrap();
match inner.value.take() {
None => if inner.dropped {
Poll::Ready(None)
} else {
inner.waker = Some(waker.clone().into_waker());
Poll::Pending
},
a => Poll::Ready(a),
}
}
}
pub fn channel<A>(initial_value: A) -> (Sender<A>, Receiver<A>) {
let inner = Arc::new(Mutex::new(Inner {
value: Some(initial_value),
waker: None,
dropped: false,
}));
let sender = Sender {
inner: Arc::downgrade(&inner),
};
let receiver = Receiver {
inner,
};
(sender, receiver)
}