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

[Eli Zaretskii]

> Date: Fri, 3 Jan 2020 11:45:51 +0800
> From: HaiJun Zhang <netjune@outlook.com>
> Cc: michael.albinus@gmx.de, arthur.miller@live.com, 
>  38807@debbugs.gnu.org
> 
>  2. the display engine prepares the glyph matrix
>  3. convert the glyph matrix to bitmap and display it
> 
>  I think lots of work are in 2.
> 
>  Actually, 3 is also a lot of work. 
> 
> Then 3 can be done in a separate thread from 2 and 1?

How would that help?  Until 3 is done, the user doesn't see the
display updated.  And if you think 3 doesn't touch any Lisp, then
thats not true, just see how many times you find "Lisp_Object" in,
say, xterm.c.