bug#5803: 23.1.94; Using tq-enqueue in timer messes with keystroke echoing

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 08 Dec 2020 19:02:51 +0100
> Cc: 5803@debbugs.gnu.org
> 
> (setq proc (start-process "shell" (get-buffer-create "*process*") "/bin/sh"))
> (setq mytq (tq-create proc))
> (defun send-test ()
>   (tq-enqueue mytq "echo TEST\n" "TEST[^0]*" nil 'ignore))
> (setq timer (run-with-timer 1 1 'send-test))
> 
> I'm guessing this somehow interferes with the `echo-timeout' thing?
> (Changing it to something shorter than 1 second makes the C-x-
> appear...  sometimes.)
> 
> Anybody got any insight into what might be happening here?

The sit_for call ends prematurely because output from a subprocess
arrives?