Run the actors in this group.

        Parameters:
          delay(int): The minimum amount of time, in milliseconds,
            each message in the group should be delayed by.

def run(self, *, delay=None):
        """Run the actors in this group.

        Parameters:
          delay(int): The minimum amount of time, in milliseconds,
            each message in the group should be delayed by.
        """
        for child in self.children:
            if isinstance(child, (group, pipeline)):
                child.run(delay=delay)
            else:
                self.broker.enqueue(child, delay=delay)

        return self