bug#38807: [Feature request]: Support lisp workers like web workers.

[Eli Zaretskii]

> Date: Fri, 3 Jan 2020 10:52:59 +0800
> From: HaiJun Zhang <netjune@outlook.com>
> Cc: Eli Zaretskii <eliz@gnu.org>, 38807@debbugs.gnu.org
> 
> The threading support introduced in emacs 26 is cool. But it is too complex 
> when every thread can control UI
> and interact with user. While the web worker model is much simpler.

How do you write a useful Lisp application for a thread if you have no
way of displaying any messages?  Besides, some low-level APIs you'd
use in any Lisp will display messages even if your code doesn't.

So some solution for user interaction from threads is still needed, or
else the thread system will not be useful for writing Lisp programs.