Comment 4 for bug 908618

straight from the documentation.. http://developer.gnome.org/gdk/stable/gdk-Threads.html

"Idles, timeouts, and input functions from GLib, such as g_idle_add(), are executed outside of the main GTK+ lock. So, if you need to call GTK+ inside of such a callback, you must surround the callback with a gdk_threads_enter()/gdk_threads_leave() pair or use gdk_threads_add_idle_full() which does this for you. However, event dispatching from the mainloop is still executed within the main GTK+ lock, so callback functions connected to event signals like GtkWidget::button-press-event, do not need thread protection.

In particular, this means, if you are writing widgets that might be used in threaded programs, you must surround timeouts and idle functions in this matter."