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
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
// Take a look at the license at the top of the repository in the LICENSE file.

use std::num::NonZeroU64;

use futures_channel::oneshot;
use futures_core::Future;
use glib::{prelude::*, translate::*};

use crate::Cancellable;

// rustdoc-stripper-ignore-next
/// The id of a cancelled handler that is returned by `CancellableExtManual::connect`. This type is
/// analogous to [`glib::SignalHandlerId`].
#[derive(Debug, Eq, PartialEq)]
#[repr(transparent)]
pub struct CancelledHandlerId(NonZeroU64);

impl CancelledHandlerId {
    // rustdoc-stripper-ignore-next
    /// Returns the internal signal handler ID.
    #[allow(clippy::missing_safety_doc)]
    pub unsafe fn as_raw(&self) -> libc::c_ulong {
        self.0.get() as libc::c_ulong
    }
}

impl TryFromGlib<libc::c_ulong> for CancelledHandlerId {
    type Error = GlibNoneError;
    #[inline]
    unsafe fn try_from_glib(val: libc::c_ulong) -> Result<Self, GlibNoneError> {
        NonZeroU64::new(val as _).map(Self).ok_or(GlibNoneError)
    }
}

pub trait CancellableExtManual {
    // rustdoc-stripper-ignore-next
    /// Convenience function to connect to the `signal::Cancellable::cancelled` signal. Also
    /// handles the race condition that may happen if the cancellable is cancelled right before
    /// connecting. If the operation is cancelled from another thread, `callback` will be called
    /// in the thread that cancelled the operation, not the thread that is running the operation.
    /// This may be the main thread, so the callback should not do something that can block.
    ///
    /// `callback` is called at most once, either directly at the time of the connect if `self` is
    /// already cancelled, or when `self` is cancelled in some thread.
    ///
    /// Since GLib 2.40, the lock protecting `self` is not held when `callback` is invoked. This
    /// lifts a restriction in place for earlier GLib versions which now makes it easier to write
    /// cleanup code that unconditionally invokes e.g.
    /// [`CancellableExt::cancel()`][crate::prelude::CancellableExt::cancel()].
    ///
    /// # Returns
    ///
    /// The id of the signal handler or `None` if `self` has already been cancelled.
    #[doc(alias = "g_cancellable_connect")]
    fn connect_cancelled<F: FnOnce(&Self) + Send + 'static>(
        &self,
        callback: F,
    ) -> Option<CancelledHandlerId>;
    // rustdoc-stripper-ignore-next
    /// Local variant of [`Self::connect_cancelled`].
    #[doc(alias = "g_cancellable_connect")]
    fn connect_cancelled_local<F: FnOnce(&Self) + 'static>(
        &self,
        callback: F,
    ) -> Option<CancelledHandlerId>;
    // rustdoc-stripper-ignore-next
    /// Disconnects a handler from a cancellable instance. Additionally, in the event that a signal
    /// handler is currently running, this call will block until the handler has finished. Calling
    /// this function from a callback registered with [`Self::connect_cancelled`] will therefore
    /// result in a deadlock.
    ///
    /// This avoids a race condition where a thread cancels at the same time as the cancellable
    /// operation is finished and the signal handler is removed.
    #[doc(alias = "g_cancellable_disconnect")]
    fn disconnect_cancelled(&self, id: CancelledHandlerId);
    // rustdoc-stripper-ignore-next
    /// Returns a `Future` that completes when the cancellable becomes cancelled. Completes
    /// immediately if the cancellable is already cancelled.
    fn future(&self) -> std::pin::Pin<Box<dyn Future<Output = ()> + Send + Sync + 'static>>;
    // rustdoc-stripper-ignore-next
    /// Set an error if the cancellable is already cancelled.
    // rustdoc-stripper-ignore-next-stop
    /// If the `self` is cancelled, sets the error to notify
    /// that the operation was cancelled.
    ///
    /// # Returns
    ///
    /// [`true`] if `self` was cancelled, [`false`] if it was not
    #[doc(alias = "g_cancellable_set_error_if_cancelled")]
    fn set_error_if_cancelled(&self) -> Result<(), glib::Error>;
}

impl<O: IsA<Cancellable>> CancellableExtManual for O {
    #[doc(alias = "g_cancellable_connect")]
    fn connect_cancelled<F: FnOnce(&Self) + Send + 'static>(
        &self,
        callback: F,
    ) -> Option<CancelledHandlerId> {
        unsafe extern "C" fn connect_trampoline<P: IsA<Cancellable>, F: FnOnce(&P)>(
            this: *mut ffi::GCancellable,
            callback: glib::ffi::gpointer,
        ) {
            let callback: &mut Option<F> = &mut *(callback as *mut Option<F>);
            let callback = callback
                .take()
                .expect("Cancellable::cancel() closure called multiple times");
            callback(Cancellable::from_glib_borrow(this).unsafe_cast_ref())
        }

        unsafe extern "C" fn destroy_closure<F>(ptr: glib::ffi::gpointer) {
            let _ = Box::<Option<F>>::from_raw(ptr as *mut _);
        }

        let callback: Box<Option<F>> = Box::new(Some(callback));
        unsafe {
            from_glib(ffi::g_cancellable_connect(
                self.as_ptr() as *mut _,
                Some(std::mem::transmute::<_, unsafe extern "C" fn()>(
                    connect_trampoline::<Self, F> as *const (),
                )),
                Box::into_raw(callback) as *mut _,
                Some(destroy_closure::<F>),
            ))
        }
    }
    #[doc(alias = "g_cancellable_connect")]
    fn connect_cancelled_local<F: FnOnce(&Self) + 'static>(
        &self,
        callback: F,
    ) -> Option<CancelledHandlerId> {
        let callback = glib::thread_guard::ThreadGuard::new(callback);

        self.connect_cancelled(move |obj| (callback.into_inner())(obj))
    }
    #[doc(alias = "g_cancellable_disconnect")]
    fn disconnect_cancelled(&self, id: CancelledHandlerId) {
        unsafe { ffi::g_cancellable_disconnect(self.as_ptr() as *mut _, id.as_raw()) };
    }
    fn future(&self) -> std::pin::Pin<Box<dyn Future<Output = ()> + Send + Sync + 'static>> {
        let cancellable = self.as_ref().clone();
        let (tx, rx) = oneshot::channel();
        let id = cancellable.connect_cancelled(move |_| {
            let _ = tx.send(());
        });
        Box::pin(async move {
            rx.await.unwrap();
            if let Some(id) = id {
                cancellable.disconnect_cancelled(id);
            }
        })
    }

    fn set_error_if_cancelled(&self) -> Result<(), glib::Error> {
        unsafe {
            let mut error = std::ptr::null_mut();
            let is_ok = ffi::g_cancellable_set_error_if_cancelled(
                self.as_ref().to_glib_none().0,
                &mut error,
            );
            // Here's the special case, this function has an inverted
            // return value for the error case.
            debug_assert_eq!(is_ok == glib::ffi::GFALSE, error.is_null());
            if error.is_null() {
                Ok(())
            } else {
                Err(from_glib_full(error))
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::prelude::*;

    #[test]
    fn cancellable_callback() {
        let c = Cancellable::new();
        let id = c.connect_cancelled(|_| {});
        c.cancel(); // if it doesn't crash at this point, then we're good to go!
        c.disconnect_cancelled(id.unwrap());
    }

    #[test]
    fn cancellable_callback_local() {
        let c = Cancellable::new();
        let id = c.connect_cancelled_local(|_| {});
        c.cancel(); // if it doesn't crash at this point, then we're good to go!
        c.disconnect_cancelled(id.unwrap());
    }

    #[test]
    fn cancellable_error_if_cancelled() {
        let c = Cancellable::new();
        c.cancel();
        assert!(c.set_error_if_cancelled().is_err());
    }

    #[test]
    fn cancellable_future() {
        let c = Cancellable::new();
        c.cancel();
        glib::MainContext::new().block_on(c.future());
    }

    #[test]
    fn cancellable_future_thread() {
        let cancellable = Cancellable::new();
        let c = cancellable.clone();
        std::thread::spawn(move || c.cancel()).join().unwrap();
        glib::MainContext::new().block_on(cancellable.future());
    }

    #[test]
    fn cancellable_future_delayed() {
        let ctx = glib::MainContext::new();
        let c = Cancellable::new();
        let (tx, rx) = oneshot::channel();
        {
            let c = c.clone();
            ctx.spawn_local(async move {
                c.future().await;
                tx.send(()).unwrap();
            });
        }
        std::thread::spawn(move || c.cancel()).join().unwrap();
        ctx.block_on(rx).unwrap();
    }
}