receiver … time passes… 74 Some senders have stop sources. “I’ll do my best!” They pass stop tokens to the operation state. Cancellation details are internal to algorithms. “Hey, receiver! I’ve THREE-WAY HANDSHAKE OpState Caller Receiver “Please stop.” “I’ve stopped.”76 SENDERS PASS STOP TOKENS TO CHILDREN VIA RECEIVERS when_all then then then schedule schedule schedule connect X 3 stop_source

request a thread to stop execution  Stop requests are visible to all associated stop_sources and stop_tokens  std::stop_callback  Callback is called when stop is requested on associated stop_token  std::stop_callback