bug#43177: Bug: Emacs 27.1 hangs forever in `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1'

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Robert Pluim <rpluim@gmail.com>,  43177@debbugs.gnu.org,
>   emacs@Alexander.Shukaev.name
> Date: Thu, 03 Sep 2020 19:51:17 +0200
> 
> On Sep 03 2020, Eli Zaretskii wrote:
> 
> > Do we understand why including the x backend produces such a huge
> > delay?  Where is most of that time spent, and why?
> 
> My guess would be that probing fonts via the x backend is expensive due
> to round trips to the X server (and the X server is quite busy during
> that time).

If that is the reason, I guess we should try to minimize the number of
fonts for which this is done.  Like, for example, set up some data
structure to be consulted when a deciding whether a given font should
be used with the x backend.  After all, the number of fonts for which
that backend is needed is quite small, basically bitmapped fonts.