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
165

// Take a look at the license at the top of the repository in the LICENSE file.

use futures_channel::oneshot;
use futures_core::task::{Context, Poll};
use std::future::Future;
use std::pin::{self, Pin};

use crate::prelude::*;
use crate::Cancellable;

pub struct GioFuture<F, O, T, E> {
    obj: O,
    schedule_operation: Option<F>,
    cancellable: Option<Cancellable>,
    receiver: Option<oneshot::Receiver<Result<T, E>>>,
}

pub struct GioFutureResult<T, E> {
    sender: ThreadGuard<oneshot::Sender<Result<T, E>>>,
}

unsafe impl<T, E> Send for GioFutureResult<T, E> {}

impl<T, E> GioFutureResult<T, E> {
    pub fn resolve(self, res: Result<T, E>) {
        let _ = self.sender.into_inner().send(res);
    }
}

impl<F, O, T: 'static, E: 'static> GioFuture<F, O, T, E>
where
    O: Clone + 'static,
    F: FnOnce(&O, &Cancellable, GioFutureResult<T, E>) + 'static,
{
    pub fn new(obj: &O, schedule_operation: F) -> GioFuture<F, O, T, E> {
        GioFuture {
            obj: obj.clone(),
            schedule_operation: Some(schedule_operation),
            cancellable: Some(Cancellable::new()),
            receiver: None,
        }
    }
}

impl<F, O, T, E> Future for GioFuture<F, O, T, E>
where
    O: Clone + 'static,
    F: FnOnce(&O, &Cancellable, GioFutureResult<T, E>) + 'static,
{
    type Output = Result<T, E>;

    fn poll(mut self: pin::Pin<&mut Self>, ctx: &mut Context) -> Poll<Result<T, E>> {
        let GioFuture {
            ref obj,
            ref mut schedule_operation,
            ref mut cancellable,
            ref mut receiver,
            ..
        } = *self;

        if let Some(schedule_operation) = schedule_operation.take() {
            let main_context = glib::MainContext::ref_thread_default();
            assert!(
                main_context.is_owner(),
                "Spawning futures only allowed if the thread is owning the MainContext"
            );

            // Channel for sending back the GIO async operation
            // result to our future here.
            //
            // In theory we could directly continue polling the
            // corresponding task from the GIO async operation
            // callback, however this would break at the very
            // least the g_main_current_source() API.
            let (send, recv) = oneshot::channel();

            schedule_operation(
                obj,
                cancellable.as_ref().unwrap(),
                GioFutureResult {
                    sender: ThreadGuard::new(send),
                },
            );

            *receiver = Some(recv);
        }

        // At this point we must have a receiver
        let res = {
            let receiver = receiver.as_mut().unwrap();
            Pin::new(receiver).poll(ctx)
        };

        match res {
            Poll::Pending => Poll::Pending,
            Poll::Ready(Err(_)) => panic!("Async operation sender was unexpectedly closed"),
            Poll::Ready(Ok(v)) => {
                // Get rid of the reference to the cancellable and receiver
                let _ = cancellable.take();
                let _ = receiver.take();
                Poll::Ready(v)
            }
        }
    }
}

impl<F, O, T, E> Drop for GioFuture<F, O, T, E> {
    fn drop(&mut self) {
        if let Some(cancellable) = self.cancellable.take() {
            cancellable.cancel();
        }
        let _ = self.receiver.take();
    }
}

impl<F, O, T, E> Unpin for GioFuture<F, O, T, E> {}

// Actual thread IDs can be reused by the OS once the old thread finished.
// This works around it by using our own counter for threads.
//
// Taken from the fragile crate
use std::sync::atomic::{AtomicUsize, Ordering};
fn next_thread_id() -> usize {
    static mut COUNTER: AtomicUsize = AtomicUsize::new(0);
    unsafe { COUNTER.fetch_add(1, Ordering::SeqCst) }
}

#[doc(alias = "get_thread_id")]
fn thread_id() -> usize {
    thread_local!(static THREAD_ID: usize = next_thread_id());
    THREAD_ID.with(|&x| x)
}

// Taken from glib-rs but we don't want this to be public API
struct ThreadGuard<T> {
    thread_id: usize,
    value: Option<T>,
}

impl<T> ThreadGuard<T> {
    fn new(value: T) -> Self {
        Self {
            thread_id: thread_id(),
            value: Some(value),
        }
    }

    fn into_inner(mut self) -> T {
        if self.thread_id != thread_id() {
            panic!("Value accessed from different thread than where it was created");
        }

        self.value.take().expect("into_inner() called twice")
    }
}

impl<T> Drop for ThreadGuard<T> {
    fn drop(&mut self) {
        if self.thread_id != thread_id() {
            panic!("Value dropped on a different thread than where it was created");
        }
    }
}

unsafe impl<T> Send for ThreadGuard<T> {}