docs: def _shutdown(self, cancel, cancel_msg, exc_type=CancelledError):
          ''' Internal shutdown used by 'shutdown' method  above '''
          if cancel:
              # Cancel all in-flight transfers if requested, before waiting
              # for them to complete.
              self._coordinator_controller.cancel(cancel_msg, exc_type)
          try:
              # Wait until there are no more in-progress transfers. This is
              # wrapped in a try statement because this can be interrupted
              # with a KeyboardInterrupt that needs to be caught.
              self._coordinator_controller.wait()
          except KeyboardInterrupt:
              # If not errors were raised in the try block, the cancel should
              # have no coordinators it needs to run cancel on. If there was
              # an error raised in the try statement we want to cancel all of
              # the inflight transfers before shutting down to speed that
              # process up.
              self._coordinator_controller.cancel('KeyboardInterrupt()')
              raise
          finally:
              self._coordinator_controller.cleanup()