GNOME applet using threads hangs

Question

I am trying to develop a GNOME applet (put into panel) using python (pyGTK). I've started by following the tutorial suggested in other SO question.

My plan is to let the applet do something in the background in a repetitive fashion (causing its display to be updated). So I thought I am gonna need threads to do it. I've seen several tutorials on how to use threads with pyGTK - most of them follow the pyGTK FAQ. And all of them suggest being cautious.

I tried with the different versions, incl.

#!/usr/bin/python

import pygtk
import sys
pygtk.require('2.0')
import gtk
import gobject
gobject.threads_init()

import gnomeapplet
import time
from threading import Thread

def threadFunction(label):
    gobject.idle_add(label.set_text, 'In the thread')

def factory(applet, iid):
        text = gtk.Label('Start %s' % iid)
        applet.add(text)
        applet.show_all()
        Thread(target=threadFunction, args=(text)).start()
        return True

if __name__ == '__main__':
        print "Starting factory"
        gnomeapplet.bonobo_factory("OAFIID:Gnome_Panel_Example_Factory", gnomeapplet.Applet.__gtype__, "Simple gnome applet example", "1.0", factory)

But it doesn't work. The thread execution seems to hang when trying to update the presentation (gobject.idle_add). I tried:

• replacing gobject.threads_init() with gtk.gdk.threads_init() - because this is what some of the tutorials use,
• subclassing threading.Thread class instead of using Thread(target=)
• using gtk.threads_enter and gtk.threads_leave around any code that is run within a separate thread and updates the widgets,

What is my mistake then?

Is threading imcompatible with applets (as opposed to other pyGTK programs)?

Answer 1

According to several comments on the gtk lists, you shouldn't be trying to update your user interface from threads. It would be better to poll the child threads from your main application. For references see here and here. More can be found by searching the archives. I don't know of any official documentation of this.