def process_default(self, event):
        """
        Processes |event|.
        """
        self._stats_lock.acquire()
        try:
            events = event.maskname.split('|')
            for event_name in events:
                count = self._stats.get(event_name, 0)
                self._stats[event_name] = count + 1
        finally:
            self._stats_lock.release()
Processes |event|.