[samples][async_subscribe] Connect or disconnect command ignored When systemctl restart mosquitto.service

[YeahhhhLi]

I git clone paho.mqtt.cpp v1.2.0, build example and run async_subscibe, everything is ok

$ git status
HEAD detached at v1.2.0

$ ./src/samples/async_subscribe 
\Connecting to the MQTT server...
Connection success

Subscribing to topic 'hello'
	for client paho_cpp_async_subcribe using QoS1

Press Q<Enter> to quit

Subscription success for token: [1]
	token topic: 'hello', ...

And then I test the reconnect function

systemctl restart mosquitto.service 

the error happened:

Connection lost
Reconnecting...
Connection attempt failed
Error: MQTT error [-18]: Connect or disconnect command ignored

Isn't it better to report errors through on_failure here?

At present, when I introduce the reconnection function, I must use try catch to catch the exception.

So, is there a better solution?

Similar problems also occur in the async client publish interface:

    paho_mqtt::message_ptr message = paho_mqtt::make_message(topic, data, size);
    client_->publish(message, /*user context*/nullptr, *iaction_cb_);

it will throw exception when client is disconneted