From what I've gathered, in most GTK bindings for most languages, you can't/shouldn't call GTK routines from different threads - in other words: all GUI interactions should be handled by the same thread (but you can probably off-load a lot of non-GUI processing to other threads).

Whether or not threads and the way you're using them is even the right way to go about whatever it is that you're doing is another subject and I'm not going into that. I'm assuming you know what you're doing.