tokio::time::interval is not working

[rcitsz]

Version

root@6a2e14c7eff5:~/projects/rustprj/rs-proxy/server# cargo version
cargo 1.78.0 (54d8815d0 2024-03-26)

root@6a2e14c7eff5:~/projects/rustprj/rs-proxy/server# cargo tree | grep tokio
│   │   │   │   │   │   ├── tokio v1.37.0
│   │   │   │   │   │   │   └── tokio-macros v2.2.0 (proc-macro)
│   │   │   │   │   │   ├── tokio-util v0.7.10
│   │   │   │   │   │   │   ├── tokio v1.37.0 (*)
│   │   │   │   │   ├── tokio v1.37.0 (*)
│   │   │   │   │   ├── tokio v1.37.0 (*)
│   │   │   │   │   ├── tokio-util v0.7.10 (*)
│   │   │   │   ├── tokio v1.37.0 (*)
│   │   │   │   └── tokio-io-timeout v1.2.0
│   │   │   │       └── tokio v1.37.0 (*)
│   │   │   ├── tokio v1.37.0 (*)
│   │   │   ├── tokio-stream v0.1.15
│   │   │   │   └── tokio v1.37.0 (*)
│   ├── tokio v1.37.0 (*)
│   ├── tokio-stream v0.1.15 (*)
│   │   ├── tokio v1.37.0 (*)
│   │   └── tokio-native-tls v0.3.1
│   │       └── tokio v1.37.0 (*)
│   ├── tokio v1.37.0 (*)
│   ├── tokio-native-tls v0.3.1 (*)
├── tokio v1.37.0 (*)
├── tokio-rustls v0.24.1
│   └── tokio v1.37.0 (*)

Platform

root@6a2e14c7eff5:~/projects/rustprj/rs-proxy/server# uname -a
Linux 6a2e14c7eff5 6.6.16-linuxkit #1 SMP Fri Feb 16 11:54:02 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

Description

Test code is as follows, look at the code comments，thanks.

async fn do_work(s: &mut bool) {
    if *s {
        *s = false;
        tokio::time::sleep(tokio::time::Duration::from_secs(3)).await;
    }
}

#[test]
fn test() {
    tokio::runtime::Runtime::new().unwrap().block_on(async {
        tokio::spawn(async move {
            let mut timer = tokio::time::interval(tokio::time::Duration::from_secs(1));
            let mut s = true; 
            loop {

                 // If add this line, the timer will work properly, otherwise, not woking.
                 // tokio::task::yield_now().await;

                tokio::select! {
                    _= timer.tick() => {
                       println!("----tick");
                    }
                _ = do_work(&mut s) => {}
                }
            }
        })
        .await
        .unwrap();
    });
}

I expect the second timer to output the following content every second, but it doesn't work:
-----tick
-----tick
-----tick
-----tick
-----tick
-----tick
...

[wathenjiang]

This seems to be a slow task poll issue again. Ref: #6315

As for this issue, although it is a multi-thread runtime, there is actually only one worker thread working, and because it is executing the above loop, no one take care of the time driver.

[wathenjiang]

Considering this thread scheduling behavior, should we add an additional time expiration check before reading the state controlled by the driver?

[Darksonn]

This code is blocking the thread because the select! always exists without yielding to the runtime. You must yield to the runtime to have reasonable behavior.

See also #6544.