bug#35961: 27.0.50; Sometimes frame freezes and stops updating (almost entirely)

[Eli Zaretskii]

> Cc: 35961@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Thu, 30 May 2019 19:37:26 +0300
> 
> > Emacs's
> > display engine updates all the frames one after the other, in a single
> > thread, so the situation where one frame is updated, but another
> > isn't, is simply impossible, as far as the Emacs code is concerned.
> 
> Having said the above, surely there is also some code that passes the 
> rendered frame contents to the windowing system, or the graphical toolkit?

Yes, but if you are thinking about some thread in that
toolkit/windowing library getting stuck while others continue working,
you can try starting Emacs in X synchronous mode (etc/DEBUG has the
details), then Emacs will wait for each X call to return, and X will
not return until the request completes.  If you see the same problem
in that case, i.e. some frame(s) become not responsive while others
don't, it is almost certainly not an Emacs problem.