code: def add(self, id, ttl_secs):
          
          ttl_secs = min(ttl_secs + self.ttl_offset_secs, self.max_ttl_secs)
          self._tombstones[id] = IOLoop.current().call_later(
              ttl_secs, self.forget, id,
          )
docs: Adds a new request to the Cemetery that is known to have timed out.
  
          The request will be forgotten after ``ttl_secs + ttl_offset_secs``
          seconds.
  
          :param id:
              ID of the request
          :param ttl_secs:
              TTL of the request (in seconds)