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//! A single-threaded executor where join handles catch panics inside tasks.
#![feature(async_await)]
use std::future::Future;
use std::panic::AssertUnwindSafe;
use std::thread;
use crossbeam::channel::{unbounded, Sender};
use futures::executor;
use futures::future::FutureExt;
use lazy_static::lazy_static;
/// Spawns a future on the executor.
fn spawn<F, R>(future: F) -> async_task::JoinHandle<thread::Result<R>, ()>
where
F: Future<Output = R> + Send + 'static,
R: Send + 'static,
{
lazy_static! {
// A channel that holds scheduled tasks.
static ref QUEUE: Sender<async_task::Task<()>> = {
let (sender, receiver) = unbounded::<async_task::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();
handle
}
fn main() {
// Spawn a future that completes succesfully.
let handle = spawn(async {
println!("Hello, world!");
});
// Block on the future and report its result.
match executor::block_on(handle) {
None => println!("The task was cancelled."),
Some(Ok(val)) => println!("The task completed with {:?}", val),
Some(Err(_)) => println!("The task has panicked"),
}
// Spawn a future that panics.
let handle = spawn(async {
panic!("Ooops!");
});
// Block on the future and report its result.
match executor::block_on(handle) {
None => println!("The task was cancelled."),
Some(Ok(val)) => println!("The task completed with {:?}", val),
Some(Err(_)) => println!("The task has panicked"),
}
}
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