Hooking into Gtk's iteration

[Hrvoje Niksic <hniksic srce hr>]

Is there a way to hook a function of mine into every iteration of the
main loop?  Specifically, I want something to happen every time Gtk's
poll() is, for whatever reason, interrupted.

I think I saw code that achieved that with strategic use of
g_source_add(), but it tried to do other things as well, which made it 
hard to understand.

(I know I can write my own loop using gtk_main_iteration() in blocking
mode, but that is not a good solution because it makes gtk_main_quit() 
useless.)