code: def __request_mark_sent(self, requestId):
          
          with self.__requests:
              try:
                  req = self.__requests[requestId]
              except KeyError:
                  # request might have had a response already have been removed by receiving thread
                  pass
              else:
                  req.exception = None
                  req._send_time = monotonic()
docs: Set send time & clear exception from request if set, ignoring non-existent requests