bug#58634: Long delay with blank screen whilst loading desktop at emacs startup

[Eli Zaretskii]

> Date: Wed, 19 Oct 2022 19:58:36 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>, 58634@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> I have a theory.  The function desktop-restore-file-buffer visits a file
> with find-file-noselect, then calls switch-to-buffer on it.  (This is the
> interactive command on C-x b.)  In earlier times, there would be a delay
> in visiting the next file, and in this delay redisplay would happen.  The
> user would thus see a sequence of short displays of his files being
> loaded.  Nowadays, the time to visit a file is so short that redisplay
> never registers a delay, and so doesn't redisplay.  But with something
> slowing the processing down a little (outputting "Restoring
> desktop......", for example), the OS's file system goes to sleep, and
> takes long enough to wake up for redisplay to trigger.  Or something like
> that.
> 
> What do you think?

Does this happen with Emacs 28 as well in your configuration?  Because
with Emacs 28 I use desktop.el all the time, and I do see the frame
displaying some files and messages in the echo-area.  If the same
happens for you with Emacs 28, I guess it's somehow related to your
init files and/or what exactly is in your session.  For example, my
sessions always include some buffers under Text mode or its
descendants, and those turn on Flyspell mode in my configuration;
starting Flyspell mode launches the speller as a sub-process, and that
usually triggers some form of redisplay.  In addition, I have
garbage-collection-messages turned on, so GC-related messages are
shown in the echo-area, which also is a kind of redisplay.  Restoring
file buffers sometimes produces prompts, e.g. if the file is too large
or there are local variables there that require confirmation -- and
those prompts trigger redisplay as well.

If you have none of that in your configuration, perhaps desktop.el can
indeed produce a completely blank frame.  Although it sounds strange
to me, since I never saw anything like that.  But it could be because
I'm used to starting Emacs with my configuration.