blocking and block_on tasks have false positive lints

[hds]

What crate(s) in this repo are involved in the problem?

tokio-console

What is the issue?

When using the #[tokio::main] macro, some non-async tasks are missed because the console-subscriber is initialized after the runtime has already started. Specifically

• block_on task
• blocking tasks for the workers in a multi-thread runtime

This hides a problem which is only visible if the console-susbcriber is started before the runtime. Both these types of tasks trigger false-positive warnings from lints.

• block_on triggers the lost waker lint
• blocking tasks trigger the never yielded lint

How can the bug be reproduced?

The following code reproduces both false positives:

fn main() {
    console_subscriber::init();

    let rt = tokio::runtime::Builder::new_multi_thread()
        .enable_all()
        .build()
        .unwrap();

    rt.block_on(async {
        _ = tokio::spawn(async {
            tokio::time::sleep(std::time::Duration::from_secs(6000)).await;
        })
        .await;
    });
}

Logs, error output, etc

The view in Tokio Console is:

Versions

• tokio-console 0.1.10 (also on main at the time of reporting)

Possible solution

• Modify the lints to first check the kind (added in feat(console): replace target column with kind column in tasks view #478) of the task being checked.

Only if the kind is task or local should the actual check be performed, if the kind is block_on or blocking then Warning::Ok should be returned.

For the current 3 lints that have been written, block_on and blocking tasks should always return Warning::Ok as the lints only make sense for true async tasks that are polled.

[javihernant]

Hi! I'd like to work on this. It looks like a great issue to get started in tokio-console contributions, which is exactly my idea.