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// 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::{ffi, 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)
}
}
mod sealed {
pub trait Sealed {}
impl<T: super::IsA<super::Cancellable>> Sealed for T {}
}
pub trait CancellableExtManual: sealed::Sealed + IsA<Cancellable> {
// 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> {
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::<*const (), unsafe extern "C" fn()>(
connect_trampoline::<Self, F> as *const (),
)),
Box::into_raw(callback) as *mut _,
Some(destroy_closure::<F>),
))
}
}
// 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> {
let callback = glib::thread_guard::ThreadGuard::new(callback);
self.connect_cancelled(move |obj| (callback.into_inner())(obj))
}
// 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) {
unsafe { ffi::g_cancellable_disconnect(self.as_ptr() as *mut _, id.as_raw()) };
}
// 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>> {
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);
}
})
}
// rustdoc-stripper-ignore-next
/// Set an error if the cancellable is already cancelled.
#[doc(alias = "g_cancellable_set_error_if_cancelled")]
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))
}
}
}
}
impl<O: IsA<Cancellable>> CancellableExtManual for O {}
#[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();
}
}