code: def active_io(self, iocb):
          
          if _debug: IOController._debug("active_io %r", iocb)
  
          # requests should be idle or pending before coming active
          if (iocb.ioState != IDLE) and (iocb.ioState != PENDING):
              raise RuntimeError("invalid state transition (currently %d)" % (iocb.ioState,))
  
          # change the state
          iocb.ioState = ACTIVE
docs: Called by a handler to notify the controller that a request is
          being processed.