code: def unlock(self, session=None):
          
          cmd = SON([("fsyncUnlock", 1)])
          with self._socket_for_writes(session) as sock_info:
              if sock_info.max_wire_version >= 4:
                  try:
                      with self._tmp_session(session) as s:
                          sock_info.command(
                              "admin", cmd, session=s, client=self)
                  except OperationFailure as exc:
                      # Ignore "DB not locked" to replicate old behavior
                      if exc.code != 125:
                          raise
              else:
                  message._first_batch(sock_info, "admin", "$cmd.sys.unlock",
                                       {}, -1, True, self.codec_options,
                                       ReadPreference.PRIMARY, cmd,
                                       self._event_listeners)
docs: Unlock a previously locked server.
  
          :Parameters:
            - `session` (optional): a
              :class:`~pymongo.client_session.ClientSession`.
  
          .. versionchanged:: 3.6
             Added ``session`` parameter.