bug#41646: Startup in Windows is very slow when load-path contains many

[Eli Zaretskii <eliz@gnu.org>]

> From: Lin Sun <sunlin7.mail@gmail.com>
> Date: Fri, 1 Nov 2024 18:15:23 +0000
> Cc: monnier@iro.umontreal.ca, stefankangas@gmail.com, acorallo@gnu.org, 
> 	41646@debbugs.gnu.org, monnier@gnu.org
> 
> How about this: I write some windows specific code only available on
> the windows to cache the files for the load-path. It will NOT affect
> other platforms. Like a flag "load-path-cache-expired 60" (nil/t) for
> windows users who won't change path/files a lot, then Emacs can cache
> the files list for path entries for 60 seconds.  As I pasted, with the
> files cache, it can reduce the startup time from ~16s to ~5s, and also
> improve the running time performance. That will save a lot of emacs
> windows users.

I'd like us first to have a good understanding of the problems, their
aspects, and the goals of the proposed changes.  I'd also would like
to have some agreed-upon timing of searching load-path, including its
dependence on the number of directories in load-path, and the relative
part of the startup that this particular aspect explains.  (Are you
really saying that it takes Emacs 16 sec to search 300 directories for
300 files?)  Only then we will have enough information to discuss
potential solutions and their effects on the startup time.

In general, a Windows-only feature is something I'd prefer not to
have, because quite a few users use Emacs on both Windows and
GNU/Linux, so having OS specific features should be avoided.  But it
can be acceptable if no better alternative exists.  But this is
something we should talk about much later, not now.