Use 'preDestruction' method for stopping threads

source/intro.rst

@@ -412,15 +412,14 @@ slot of ``start`` button or another function that should activate
 the periodic task.
 
 Attention!  If this device is killed the ``slotKillDevice`` is called,
-so it is important to re-implement ``slotKillDevice`` method in ``Klass``
-class to stop running our polling loop above
+which calls ``preDestruction`` method in turn.   so it is important to
+re-implement ``preDestruction`` method in ``Klass`` class to stop
+running our polling loop above
 
 .. code-block:: python
 
-    def slotKillDevice(self):
+    def preDestruction(self):
         self.running = False   # stop the loop
-        # call parent version of slotKillDevice method
-        super(Klass, self).slotKillDevice()
 
 Please follow this pattern to allow  ``karabo-stop`` of python server
 working properly. Otherwise the device and server  may hang up!