How tokio timeout cancel works?

[gxxxh]

If i create a handle by tokio::spawn, how does tokio timeout works to cancel that handle?
Like if I see tokio task as a thread, will tokio send a sigkill to stop that thread?

[Darksonn]

Cancellation works by running the destructor of the future. This causes the future to stop running next time it yields at an .await, at which point all local variables are cleaned up.

However, be aware that using timeout on a JoinHandle does not cancel the task! When the timeout triggers, that drops the JoinHandle, which does not stop the task. So to implement a timeout on a task, you must explicitly call abort.

let task = tokio::spawn(...);
timeout(&mut task, duration).await;
task.abort(); // <-- this causes cancellation

[gxxxh]

are you sure? the example in the doc doesn't say anything about abort https://docs.rs/tokio/latest/tokio/time/fn.timeout.html

[Darksonn]

Yes, but the thing about abort only applies to the JoinHandle type that you get when using tokio::spawn. For any other future, it is not needed.

[gxxxh]

Yes, but the thing about abort only applies to the JoinHandle type that you get when using tokio::spawn. For any other future, it is not needed.

If, in my tokio task, I using command line to start another process,
when it comes to timeout, what will happen to that process?

[gxxxh]

Yes, but the thing about abort only applies to the JoinHandle type that you get when using tokio::spawn. For any other future, it is not needed.

what will happend when JoinHandle is dropped?

[Darksonn]

Dropping a JoinHandle doesn't do anything.

[NABIL207]

Hello All,
@Darksonn
this solution is not applicable if I have a function called for example launch_task, and I want it to simply launch the task and return.

async fn launch_task () ->() {
    let task = tokio::spawn(...);
    timeout(&mut task, duration).await;
    task.abort(); // <-- this causes cancellation
}

If I understand correctly, launch_task() never returns until the timeout is reached and the task is aborted. isn't ??

[Darksonn]

You can use tokio::spawn(timeout(..., duration)) to spawn the task. This will cause the task to exit after duration if necessary.