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// Take a look at the license at the top of the repository in the LICENSE file.
use std::{
fmt::{Debug, Display},
future::Future,
pin::Pin,
task::{Context, Poll},
};
use pin_project_lite::pin_project;
use crate::{cancellable::CancelledHandlerId, prelude::*, Cancellable, IOErrorEnum};
// rustdoc-stripper-ignore-next
/// Indicator that the [`CancellableFuture`] was cancelled.
pub struct Cancelled;
pin_project! {
// rustdoc-stripper-ignore-next
/// A future which can be cancelled via [`Cancellable`].
///
/// # Examples
///
/// ```
/// # use futures::FutureExt;
/// # use gio::prelude::*;
/// # use gio::CancellableFuture;
/// let l = glib::MainLoop::new(None, false);
/// let c = gio::Cancellable::new();
///
/// l.context().spawn_local(CancellableFuture::new(async { 42 }, c.clone()).map(|_| ()));
/// c.cancel();
///
/// ```
pub struct CancellableFuture<F> {
#[pin]
future: F,
#[pin]
waker_handler_cb: Option<CancelledHandlerId>,
cancellable: Cancellable,
}
}
impl<F> CancellableFuture<F> {
// rustdoc-stripper-ignore-next
/// Creates a new `CancellableFuture` using a [`Cancellable`].
///
/// When [`cancel`](CancellableExt::cancel) is called, the future will complete
/// immediately without making any further progress. In such a case, an error
/// will be returned by this future (i.e., [`Cancelled`]).
pub fn new(future: F, cancellable: Cancellable) -> Self {
Self {
future,
waker_handler_cb: None,
cancellable,
}
}
// rustdoc-stripper-ignore-next
/// Checks whether the future has been cancelled.
///
/// This is a shortcut for `self.cancellable().is_cancelled()`
///
/// Note that all this method indicates is whether [`cancel`](CancellableExt::cancel)
/// was called. This means that it will return true even if:
/// * `cancel` was called after the future had completed.
/// * `cancel` was called while the future was being polled.
#[inline]
pub fn is_cancelled(&self) -> bool {
self.cancellable.is_cancelled()
}
// rustdoc-stripper-ignore-next
/// Returns the inner [`Cancellable`] associated during creation.
#[inline]
pub fn cancellable(&self) -> &Cancellable {
&self.cancellable
}
}
impl<F> Future for CancellableFuture<F>
where
F: Future,
{
type Output = Result<<F as Future>::Output, Cancelled>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
if self.is_cancelled() {
return Poll::Ready(Err(Cancelled));
}
let mut this = self.as_mut().project();
match this.future.poll(cx) {
Poll::Ready(out) => Poll::Ready(Ok(out)),
Poll::Pending => {
if let Some(prev_handler) = this.waker_handler_cb.take() {
this.cancellable.disconnect_cancelled(prev_handler);
}
let canceller_handler_id = this.cancellable.connect_cancelled({
let w = cx.waker().clone();
move |_| w.wake()
});
match canceller_handler_id {
Some(canceller_handler_id) => {
*this.waker_handler_cb = Some(canceller_handler_id);
Poll::Pending
}
None => Poll::Ready(Err(Cancelled)),
}
}
}
}
}
impl From<Cancelled> for glib::Error {
fn from(_: Cancelled) -> Self {
glib::Error::new(IOErrorEnum::Cancelled, "Task cancelled")
}
}
impl std::error::Error for Cancelled {}
impl Debug for Cancelled {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "Task cancelled")
}
}
impl Display for Cancelled {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
Debug::fmt(self, f)
}
}
#[cfg(test)]
mod tests {
use futures_channel::oneshot;
use super::{Cancellable, CancellableFuture, Cancelled};
use crate::prelude::*;
#[test]
fn cancellable_future_ok() {
let ctx = glib::MainContext::new();
let c = Cancellable::new();
let (tx, rx) = oneshot::channel();
{
ctx.spawn_local(async {
let cancellable_future = CancellableFuture::new(async { 42 }, c);
assert!(!cancellable_future.is_cancelled());
let result = cancellable_future.await;
assert!(matches!(result, Ok(42)));
tx.send(()).unwrap();
});
}
ctx.block_on(rx).unwrap()
}
#[test]
fn cancellable_future_cancel() {
let ctx = glib::MainContext::new();
let c = Cancellable::new();
let (tx, rx) = oneshot::channel();
{
let c = c.clone();
ctx.spawn_local(async move {
let cancellable_future = CancellableFuture::new(std::future::pending::<()>(), c);
let result = cancellable_future.await;
assert!(matches!(result, Err(Cancelled)));
tx.send(()).unwrap();
});
}
std::thread::spawn(move || c.cancel()).join().unwrap();
ctx.block_on(rx).unwrap();
}
}