docs: def initialize(self, runtime):
          """Initialize this listener. Finds most recent timestamp"""
          if self.is_alive():
              raise IllegalState('notification thread is already initialized')
          if not JSON_CLIENT.is_json_client_set() and runtime is not None:
              JSON_CLIENT.set_json_client(runtime)
          try:
              cursor = JSON_CLIENT.json_client['local']['oplog.rs'].find().sort('ts', DESCENDING).limit(-1)
          except TypeError:
              # filesystem, so .json_client is a bool and not iterable
              pass
          else:
              try:
                  self.last_timestamp = cursor.next()['ts']
              except StopIteration:
                  self.last_timestamp = Timestamp(0, 0)