def flowControlBlocked(self):
        """
        Called by the L{H2Connection} when this stream's flow control window
        has been exhausted.
        """
        if not self.producer:
            return

        if self._producerProducing:
            self.producer.pauseProducing()
            self._producerProducing = False

        Called by the L{H2Connection} when this stream's flow control window
        has been exhausted.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/_http2.py