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

[Eli Zaretskii]

> Date: Thu, 20 Oct 2022 15:28:48 +0000
> Cc: akrl@sdf.org, 58634@debbugs.gnu.org, acm@muc.de
> From: Alan Mackenzie <acm@muc.de>
> 
> > Because once redisplay is triggered, it runs to completion, whether
> > it's "slow" or not.  So if redisplay doesn't happen in one case it
> > means it wasn't triggered.  Things that trigger redisplay are calls to
> > 'message', to 'sit-for', explicit call to 'redisplay', and some others.
> 
> I am puzzled by what is triggering the redisplay at all.  Redisplay will
> happen when "Emacs is waiting for input"

Or when triggered by specific API calls I mentioned above.

> but that means solely keyboard and mouse input, doesn't it?

Also window-system events.

> It doesn't mean file system input, does it?

No, not if you mean "normal" file I/O (as opposed to, say, inotify).

> So once Emacs starts the desktop loading with a call to `load', there
> would appear to be nothing (in my setup, not yours) to trigger redisplay
> until the load is complete.  But it happens in a GUI Emacs and sometimes
> in a tty Emacs.  It happened for me on the linux console when I rebuilt
> my Emacs 29 without native compilation; I got, IIRC, two buffers
> displayed.

That's exactly what needs to be explained: what triggers redisplay in
the GUI session and why doesn't it happen in the -nw session?

> > > If you agree with me that this needs fixing (I think you do), I have two
> > > ideas on how to fix it:
> 
> > I don't yet see what is the problem we are supposed to fix here.  Even
> > if, after we dig deeper into this and understand why the frame stays
> > blank in the console case, why is that a problem that needs fixing?
> 
> Because it looks, for an extended period of time, like Emacs has hung
> completely.

That just takes getting used to.

And anyway, let's postpone this part of the discussion until we
understand what happens in the -nw session that makes it behave
differently.  because we are talking about a phenomenon we don't
understand well enough.

> This is going to irritate people, and might prompt some users to
> abort Emacs.  If it can be 18 seconds blank screen for me, it could
> easily be 2 minutes for somebody else with a larger desktop file or
> a slower machine.

I don't see why it should irritate: you cannot do anything with Emacs
during that time anyway.