When Reedline may encounter "The cursor position could not be read within a normal duration"?

[tisonkun]

I wonder when Reedline may encounter the internal error "The cursor position could not be read within a normal duration".

I can't stably reproduce it but here is the structure of my code:

    let mut state = Reedline::create()
        .with_validator(Box::new(ScopeQLValidator))
        .with_highlighter(Box::new(ScopeQLHighlighter));

    loop {
        let input = state
            .read_line(&prompt)
            .change_context_lazy(|| Error::Other("failed to read next line".to_string()))?;
        let input = match input {
            Signal::CtrlC | Signal::CtrlD => {
                println!("exit");
                break;
            }
            Signal::Success(input) => input,
        };
        let input = input.trim();

        // other biz code

        state.run_edit_commands(&[EditCommand::InsertString(
            outstanding.trim_start().to_string(),
        )]);
    }

And today in Ubuntu Terminal I encounter:

thread 'main' panicked at cmd/scopeql/src/main.rs:50:78:
called `Result::unwrap()` on an `Err` value: failed to read next line
|- at cmd/scopeql/src/repl/entrypoint.rs:42:14
|
| -> The cursor position could not be read within a normal duration
    | - at cmd/scopeql/src/repl/entrypoint.rs:42:14

I have no idea when this error may occur and find no way to investigate deeper.

[fdncred]

That looks to be a crossterm error message.
https://github.com/crossterm-rs/crossterm/blob/e104a7cb400910609cdde36f322e3905c4baa805/src/cursor/sys/unix.rs#L50

[tisonkun]

@fdncred Yeah.

Do you have some information here to investigate more? Anyway, it's hidden behind reedline's API. I don't know how the error variant can be hit here.

[fdncred]

Not really. It looks to me like crossterm is asking the terminal for the cursor position, waits 2 seconds without a response and then times out with that error.

[tisonkun]

Well. I have no background how "asking for cursor position" can hang or fail :P

[fdncred]

Me either. It may be worth asking on the crossterm repo. I just looks like if crossterm fails to get a lock for the event reader it would fail. I'm not sure what would cause that.