Re: Bug in new sit-for?

[Chong Yidong]

Lennart Borgman <address@hidden> writes:

> Create a file sit-for-bug.el:
>
>  (message "calling (sit-for 0)")(sit-for 0)
>  (message "calling (sit-for 1)")(sit-for 1)
>  (message "after sit-for")
>
> Evaluate this inside Emacs with eval-buffer. Works fine. Now try instead
>
>  emacs.exe -batch -Q -l sit-for-bug.el
>
> This hangs after the displaying "calling (sit-for 1)". The first
> (sit-for 0) does not hang.

(First off, it isn't hung: press enter, and the sit-for will exit.
The problem is that `read-event' can't be interrupted by the timer in
batch mode).

Anyway, the situation is a little more complicated than that, because
the old sit-for also doesn't work properly.

With the old sit-for, there is no way to interrupt in batch mode: no
matter what key you press, including enter, the sit-for will sit for
the entire duration.

With the new sit-for, the sit-for sits forever.  However, typing in
something + enter (to send the input to Emacs) interrupts it.

Neither behavior is completely satisfactory, and I don't know if
there's a way to do this properly.  I can probably make the new
sit-for mimic the old behavior by not calling read-event in batch
mode.