Spawned task panics instead of returning error in JoinHandle

[kevin-june]

Hi all,

One of the doc examples isn't behaving how I expect: it panics when I expect it to return a JoinError.

Here is the example code:

use tokio::task;
use std::io;
use std::panic;

#[tokio::main]
async fn main() -> io::Result<()> {
    let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        panic!("boom");
    });

    let err = join_handle.await.unwrap_err();
    assert!(err.is_panic());
    Ok(())
}

The docs state that:

If the task panics, the error is a JoinError that contains the panic

However, when I run the example code locally or in the Rust playground, I see the panic crash the entire program.

Am I misunderstanding the docs? Perhaps there is some configuration that I am missing? Here is a link to a playground that illustrates this behavior.

Thanks!

[Darksonn]

The panic message is printed even if you catch it. Try this:

use tokio::task;
use std::io;
use std::panic;

#[tokio::main]
async fn main() -> io::Result<()> {
    let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        panic!("boom");
    });

    let err = join_handle.await.unwrap_err();
    assert!(err.is_panic());

    println!("at the end");

    Ok(())
}

[kevin-june]

Oh! Thank you. That is true.

I didn't notice that the program ran to completion, but now that I look more closely I see that the exit code is 0 (success).

Thank you for your time!