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