1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
use std::pin::Pin;
use std::task::{Poll, Context};
use futures::{Future, FutureExt, channel::oneshot, future::{select, Either, Shared, FusedFuture}, executor::block_on};

/// Future that resolves when the exit signal has fired.
#[derive(Clone)]
pub struct Exit(Shared<oneshot::Receiver<()>>);

impl Future for Exit {
    type Output = ();

    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
        let receiver = &mut Pin::into_inner(self).0;

        if receiver.is_terminated() {
            Poll::Ready(())
        } else {
            Pin::new(receiver).poll(cx).map(drop)
        }
    }
}

impl Exit {
     /// Perform given work until complete.
    pub fn until<F: Future + Unpin>(self, future: F) -> impl Future<Output = Option<F::Output>> {
        select(self, future)
            .map(|either| match either {
                Either::Left(_) => None,
                Either::Right((output, _)) => Some(output)
            })
    }

    /// Block the current thread until complete.
    pub fn wait(self) {
        block_on(self)
    }
}

/// Exit signal that fires either manually or on drop.
pub struct Signal(oneshot::Sender<()>);

impl Signal {
    /// Fire the signal manually.
    pub fn fire(self) -> Result<(), ()> {
        self.0.send(())
    }
}

/// Create a signal and exit pair. `Exit` is a future that resolves when the `Signal` object is
/// either dropped or has `fire` called on it.
pub fn signal() -> (Signal, Exit) {
    let (sender, receiver) = oneshot::channel();
    (Signal(sender), Exit(receiver.shared()))
}

#[cfg(test)]
mod tests {
    use futures::future::{join3, ready, pending, lazy};
    use std::thread::{spawn, sleep};
    use std::time::Duration;
    use std::sync::Arc;
    use super::*;

    #[test]
    fn it_works() {
        let (signal, exit_a) = signal();
        let exit_b = exit_a.clone();
        let exit_c = exit_b.clone();

        let barrier = Arc::new(::std::sync::Barrier::new(2));
        let thread_barrier = barrier.clone();
        let handle = spawn(move || {
            let barrier = ::futures::future::lazy(move |_| {
                thread_barrier.wait();
            });

            block_on(join3(exit_a, exit_b, barrier));
        });

        barrier.wait();
        signal.fire().unwrap();

        let _ = handle.join();
        exit_c.wait()
    }

    #[test]
    fn drop_signal() {
        let (signal, exit) = signal();

        let thread = spawn(move || {
            sleep(Duration::from_secs(1));
            drop(signal)
        });

        thread.join().unwrap();
        exit.wait()
    }

    #[test]
    fn many_exit_signals() {
        let mut handles = Vec::new();
        let (signal, exit) = signal();

        for _ in 0 .. 100 {
            let exit = exit.clone();
            handles.push(spawn(move || {
                sleep(Duration::from_secs(1));
                exit.wait();
            }));
        }

        signal.fire().unwrap();

        for handle in handles {
            handle.join().unwrap();
        }
    }

    #[test]
    fn exit_signal_are_send_and_sync() {
        fn is_send_and_sync<T: Send + Sync>() {}

        is_send_and_sync::<Exit>();
        is_send_and_sync::<Signal>();
    }

    #[test]
    fn work_until() {
        let (signal, exit) = signal();
        let work_a = exit.clone().until(ready(5));
        assert_eq!(block_on(work_a), Some(5));

        signal.fire().unwrap();
        let work_b = exit.until(pending::<()>());
        assert_eq!(block_on(work_b), None);
    }

    #[test]
    fn works_from_other_thread() {
        let (signal, exit) = signal();

        ::std::thread::spawn(move || {
            ::std::thread::sleep(::std::time::Duration::from_millis(2500));
            signal.fire().unwrap();
        });

        block_on(exit);
    }

    #[test]
    fn clone_works() {
        let (_signal, mut exit) = signal();

        let future = lazy(move |cx| {
            let _ = Pin::new(&mut exit).poll(cx);

            let mut exit2 = exit.clone();
            let _ = Pin::new(&mut exit2).poll(cx);
        });

        block_on(future)
    }
}