Inspired by the science fiction novel The Three Body Program.
cradle_system in that novel is used to threaten others: The cradle system will detonate a bomb if no signal is received so as babies will cry if stopping rocking the cradle.
This is a little like watchdog timer in embedded system: if the system is not working properly, the watchdog timer will reset the system. To avoid the reset, the system should periodically feed the watchdog timer.
However, the cradle system is more complex than watchdog timer: it may receive both local and remote signals.
cradle_system will provide LocalCradle and RemoteCradle to simulate the cradle system. And RemoteCradle will work through a p2p network by libp2p(WIP).