bug#34138: 27.0.50; Delayed display of PDF file images

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: rudalics@gmx.at,  34138@debbugs.gnu.org,  politza@hochschule-trier.de,  
> tsdh@gnu.org
> Date: Mon, 21 Jan 2019 17:13:05 +0100
> 
> > Still weird: this says that Emacs simply waits for any input to
> > arrive, a.k.a. "is idle".
> >
> > You've mentioned before that one of the two scenarios where you see
> > this problem produces a much longer delay -- could you repeat the same
> > procedure during that long delay, and show the backtrace from that
> > session?  Maybe we will see something more interesting there.
> 
> This (and all the other backtraces I posted or mentioned) was from the
> scenario where I see the long delay, i.e. using pdf-view-mode

So does it mean that during this time Emacs waits for the external
process (is it Ghostscript? ImageMagick?) to complete?  That's all I
see in the backtrace.

Can you establish (e.g., by adding 'message' lines to the Lisp source)
where in the pdf-view-mode's sources this delay starts?  IOW, what is
the last thing pdf-view-mode does before the delay begins?