code: private void onBarrier(int channelIndex) throws IOException {
  		if (!blockedChannels[channelIndex]) {
  			blockedChannels[channelIndex] = true;
  
  			numBarriersReceived++;
  
  			if (LOG.isDebugEnabled()) {
  				LOG.debug("{}: Received barrier from channel {}.",
  					inputGate.getOwningTaskName(),
  					channelIndex);
  			}
  		}
  		else {
  			throw new IOException("Stream corrupt: Repeated barrier for same checkpoint on input " + channelIndex);
  		}
  	}
docs: Blocks the given channel index, from which a barrier has been received.
  
  @param channelIndex The channel index to block.