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use std::{cell::UnsafeCell, pin::Pin};
use atomic::{Atomic, Ordering};
use crate::stream::{PollRecv, Stream};
use crate::Context;
#[derive(Copy, Clone)]
enum State {
Ready,
Taken,
}
pub struct OnceStream<T> {
state: Atomic<State>,
data: UnsafeCell<Option<T>>,
}
impl<T> OnceStream<T> {
pub fn new(item: T) -> Self {
Self {
state: Atomic::new(State::Ready),
data: UnsafeCell::new(Some(item)),
}
}
}
impl<T> Stream for OnceStream<T> {
type Item = T;
fn poll_recv(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> PollRecv<Self::Item> {
if self
.state
.compare_exchange(
State::Ready,
State::Taken,
Ordering::AcqRel,
Ordering::Relaxed,
)
.is_ok()
{
let value = unsafe {
let reference = self.data.get().as_mut().unwrap();
reference.take().unwrap()
};
return PollRecv::Ready(value);
}
PollRecv::Closed
}
}
#[cfg(test)]
mod tests {
use std::pin::Pin;
use crate::{
stream::{PollRecv, Stream},
Context,
};
#[test]
fn test() {
let mut repeat = crate::stream::once(1usize);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut repeat).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut repeat).poll_recv(&mut cx));
}
}