main.rs

use std::convert::Infallible;

mod join_set;

fn background_task1<T>() -> T {
    loop {
        println!("Performing background task 1.");
        std::thread::sleep(std::time::Duration::from_secs(60));
    }
}

fn background_task2() -> Result<Infallible, String> {
    let mut counter = 0;
    loop {
        counter += 1;
        println!("Performing background task 2.");
        std::thread::sleep(std::time::Duration::from_secs(2));
        if counter >= 3 {
            return Err("Background task 2 errored".to_owned());
        }
    }
}

fn main() -> Result<(), String> {
    let mut set = join_set::JoinSet::new();

    set.spawn(background_task1);
    set.spawn(background_task2);

    let res = set
        .join_next()
        .expect("Impossible: received a None from join_next, but there are threads");
    match res {
        Err(e) => Err(format!("Background task panicked: {e:?}")),
        Ok(Err(e)) => Err(format!("Background task errored out: {e}")),
        // Automaticaly understood by the compiler
        // Ok(Ok(())) => panic!("Unexpected background job exit"),
    }
}