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

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 19 Oct 2022 13:28:42 +0000
> From: Alan Mackenzie <acm@muc.de>
> 
> In my current desktop file, I have 166 buffers.  I'm using an up to date
> Emacs 29.
> 
> On loading this desktop into emacs -nw on X Windows, or into a linux
> console, it takes a long time to load, around 28 seconds.  Of that time,
> my terminal window/screen is entirely blank for around 18 seconds, with
> not even a mode line being displayed.

And nothing in the echo-area, either?

> Doing the same in a GUI run on X also takes around 28 seconds to load,
> but during that time, random buffers are displayed on the screen,
> complete with mode line.
> 
> I think the native compiler is running in the background during this 28
> seconds, and thus contributes to the relatively long start up time.

To test this hypothesis, leave Emacs alone running until
list-processes shows an empty list, then restart Emacs.  This time,
you should not see the delay due to native compilation, so if there
still is a delay, it is unlikely to be due to native compilation.

In any case, you should be able to see whether it's native compilation
by watching the emacs --batch processes that run on your system during
that time.

In general, even if the native compilation is running at startup, it
should not delay the startup (barring some bug), because Emacs loads
the *.elc files when *.eln are unavailable, without waiting for the
compilation to complete.

> This ~18 seconds of blank screen is likely to be disconcerting to some
> users, and thus surely should be reckoned as a bug.

So please help us understand what causes this, so we could fix it.

Thanks.