def windowUpdated(self):
        """
        Called by the L{H2Connection} when this stream's flow control window
        has been opened.
        """
        # If we don't have a producer, we have no-one to tell.
        if not self.producer:
            return

        # If we're not blocked on flow control, we don't care.
        if self._producerProducing:
            return

        # We check whether the stream's flow control window is actually above
        # 0, and then, if a producer is registered and we still have space in
        # the window, we unblock it.
        remainingWindow = self._conn.remainingOutboundWindow(self.streamID)
        if not remainingWindow > 0:
            return

        # We have a producer and space in the window, so that producer can
        # start producing again!
        self._producerProducing = True
        self.producer.resumeProducing()

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