when the windowing system shuts down, how does Gnome/X tell an application to quit?

[Anna <christiana hipointcoffee com>]

Hi.

I was assuming my application would get a POSIX SIGTERM when I did a
logout of my Gnome session.  Looks like that's not happening though.
The main loop doesn't terminate either.  Does GTK+ call _exit() or
something without returning from the main loop?  And, how does GTK+ know
that Gnome/X11 is shutting down?  I don't know where to look in the
docs, and searches have only turned up stuff written for an audience
that seems to already know the answers.  I'm hoping someone can shed a
whole bunch of light on this for me.

Thanks,

- Anna