title: GTK / Glib: how to post message from GUI thread to worker thread?
body: <p>GTK is not thread-safe, but thread-aware - it can be used from multiple threads ensuring that global lock is used to protect GTK API calls. If i need to post a message from worker thread to GTK GUI thread i just call <code>gdk_threads_add_idle()</code> and specified callback will be called in GUI thread after some time.</p>
  
  <p>But what is the easy way to do opposite thing - call specified callback from <code>non-GUI</code> thread as user clicks a button?</p>