def _fetchBlock(self):
        """ internal use only.
	 get a block of rows from the server and put in standby block.
         future enhancements:
         (1) locks for multithreaded access (protect from multiple calls)
         (2) allow for prefetch by use of separate thread
        """
        # make sure that another block request is not standing
        if self._blockRequestInProgress :
           # need to wait here before returning... (TODO)
           return

        # make sure another block request has not completed meanwhile
        if self._standbyBlock is not None: 
           return

        self._blockRequestInProgress = True
        fetchReq = TFetchResultsReq(operationHandle=self.operationHandle,
                                    orientation=TFetchOrientation.FETCH_NEXT,
                                    maxRows=self.arraysize)
        self._standbyBlock = self._fetch([],fetchReq)
        self._blockRequestInProgress = False
        return
internal use only.
	 get a block of rows from the server and put in standby block.
         future enhancements:
         (1) locks for multithreaded access (protect from multiple calls)
         (2) allow for prefetch by use of separate thread