Trigger callback change event and triggering corresponding streams.

def process_on_event(self):
        """
        Trigger callback change event and triggering corresponding streams.
        """
        if not self._queue:
            self._active = False
            return
        # Get unique event types in the queue
        events = list(OrderedDict([(event.event_name, event)
                                   for event in self._queue]).values())
        self._queue = []

        # Process event types
        for event in events:
            msg = {}
            for attr, path in self.attributes.items():
                model_obj = self.plot_handles.get(self.models[0])
                msg[attr] = self.resolve_attr_spec(path, event, model_obj)
            self.on_msg(msg)
        self.plot.document.add_timeout_callback(self.process_on_event, 50)