tokio 0.2.19

An event-driven, non-blocking I/O platform for writing asynchronous I/O backed applications.
Documentation 
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use crate::sync::oneshot;

use futures::future::poll_fn;
use loom::future::block_on;
use loom::thread;
use std::task::Poll::{Pending, Ready};

#[test]
fn smoke() {
    loom::model(|| {
        let (tx, rx) = oneshot::channel();

        thread::spawn(move || {
            tx.send(1).unwrap();
        });

        let value = block_on(rx).unwrap();
        assert_eq!(1, value);
    });
}

#[test]
fn changing_rx_task() {
    loom::model(|| {
        let (tx, mut rx) = oneshot::channel();

        thread::spawn(move || {
            tx.send(1).unwrap();
        });

        let rx = thread::spawn(move || {
            let ready = block_on(poll_fn(|cx| match Pin::new(&mut rx).poll(cx) {
                Ready(Ok(value)) => {
                    assert_eq!(1, value);
                    Ready(true)
                }
                Ready(Err(_)) => unimplemented!(),
                Pending => Ready(false),
            }));

            if ready {
                None
            } else {
                Some(rx)
            }
        })
        .join()
        .unwrap();

        if let Some(rx) = rx {
            // Previous task parked, use a new task...
            let value = block_on(rx).unwrap();
            assert_eq!(1, value);
        }
    });
}

// TODO: Move this into `oneshot` proper.

use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

struct OnClose<'a> {
    tx: &'a mut oneshot::Sender<i32>,
}

impl<'a> OnClose<'a> {
    fn new(tx: &'a mut oneshot::Sender<i32>) -> Self {
        OnClose { tx }
    }
}

impl Future for OnClose<'_> {
    type Output = bool;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<bool> {
        let res = self.get_mut().tx.poll_closed(cx);
        Ready(res.is_ready())
    }
}

#[test]
fn changing_tx_task() {
    loom::model(|| {
        let (mut tx, rx) = oneshot::channel::<i32>();

        thread::spawn(move || {
            drop(rx);
        });

        let tx = thread::spawn(move || {
            let t1 = block_on(OnClose::new(&mut tx));

            if t1 {
                None
            } else {
                Some(tx)
            }
        })
        .join()
        .unwrap();

        if let Some(mut tx) = tx {
            // Previous task parked, use a new task...
            block_on(OnClose::new(&mut tx));
        }
    });
}