Oh my gosh. Now I have this particular problem with Emacs that when I
use it in daemon mode, sometimes my X11 connection to Emacs is buggy,
and in particular, sometimes when I control-click for a popup menu,
somehow I loose focus to the X window and cannot get it back, Emacs is
frozen and locked up in a loop that it thinks it can get out of but
will never get out, so what can I do? Okay, here’s my experience.
You have to open up GDB and manually jump out of the problematic code.
This will cause a segmentation violation in the offending thread. At
this point, you probably want to restart your Emacs server, but before
you do, you can safely re-attach with emacsclient -t and do whatever
you want to do to wrap up and close down for a restart. But don’t use
emacsclient -c, because that is highly risky and may cause the
server to crash.
So what do you do in GDB? This is what I did:
(gdb) jump XSync