Maintain the number of workers by spawning or killing as required

def stop_actors(self, monitor):
        """Maintain the number of workers by spawning or killing as required
        """
        if monitor.cfg.workers:
            num_to_kill = len(self.managed_actors) - monitor.cfg.workers
            for i in range(num_to_kill, 0, -1):
                w, kage = 0, sys.maxsize
                for worker in self.managed_actors.values():
                    age = worker.impl.age
                    if age < kage:
                        w, kage = worker, age
                self.manage_actor(monitor, w, True)