code: def cancel(self, message=None):
          
          if not self.is_alive():
              return
          if message is None:
              message = 'cancelled by Fiber.cancel()'
          self._hub.run_callback(self.throw, Cancelled, Cancelled(message))
docs: Schedule the fiber to be cancelled in the next iteration of the
          event loop.
  
          Cancellation works by throwing a :class:`~gruvi.Cancelled` exception
          into the fiber. If *message* is provided, it will be set as the value
          of the exception.