| //! A single-threaded executor where join handles propagate panics from tasks. |
| |
| use std::future::Future; |
| use std::panic::{resume_unwind, AssertUnwindSafe}; |
| use std::pin::Pin; |
| use std::task::{Context, Poll}; |
| use std::thread; |
| |
| use async_task::Task; |
| use crossbeam::channel::{unbounded, Sender}; |
| use futures_lite::{future, FutureExt}; |
| use once_cell::sync::Lazy; |
| |
| /// Spawns a future on the executor. |
| fn spawn<F, R>(future: F) -> JoinHandle<R> |
| where |
| F: Future<Output = R> + Send + 'static, |
| R: Send + 'static, |
| { |
| // A channel that holds scheduled tasks. |
| static QUEUE: Lazy<Sender<Task>> = Lazy::new(|| { |
| let (sender, receiver) = unbounded::<Task>(); |
| |
| // Start the executor thread. |
| thread::spawn(|| { |
| for task in receiver { |
| // No need for `catch_unwind()` here because panics are already caught. |
| task.run(); |
| } |
| }); |
| |
| sender |
| }); |
| |
| // Create a future that catches panics within itself. |
| let future = AssertUnwindSafe(future).catch_unwind(); |
| |
| // Create a task that is scheduled by sending itself into the channel. |
| let schedule = |t| QUEUE.send(t).unwrap(); |
| let (task, handle) = async_task::spawn(future, schedule); |
| |
| // Schedule the task by sending it into the channel. |
| task.schedule(); |
| |
| // Wrap the handle into one that propagates panics. |
| JoinHandle(handle) |
| } |
| |
| /// A join handle that propagates panics inside the task. |
| struct JoinHandle<R>(async_task::JoinHandle<thread::Result<R>>); |
| |
| impl<R> Future for JoinHandle<R> { |
| type Output = Option<R>; |
| |
| fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { |
| match Pin::new(&mut self.0).poll(cx) { |
| Poll::Pending => Poll::Pending, |
| Poll::Ready(None) => Poll::Ready(None), |
| Poll::Ready(Some(Ok(val))) => Poll::Ready(Some(val)), |
| Poll::Ready(Some(Err(err))) => resume_unwind(err), |
| } |
| } |
| } |
| |
| fn main() { |
| // Spawn a future that panics and block on it. |
| let handle = spawn(async { |
| panic!("Ooops!"); |
| }); |
| future::block_on(handle); |
| } |