spin with threads

edit

Hi. I'm having problems with spin and multiples subscriptions. I want to subscribe to two topic and going on with my program. Something like:

X_callback(){something};
Y_callback(){something};


int main(){
thread(subscribe to topic X with callback X_callback)
thread(subscribe to topic Y_callback)
more things to do...
}

I don't know what to do with spin() if I've threads. I've used Multithread spin but doesn't work. Doing something like:

MultiThreadSping s(4);

X_callback(){s.spin()};
Y_callback(){s.spin()};

int main(){
some code
}

EDIT. This was my first idea:

void alivesCallback(const std_msgs::String::ConstPtr &msg){
    //control new connection
}

void temperatureCallback(const std_msgs::String::ConstPtr &msg){
    temperature = msg->data;
}


void subscriptionAliveTopic(){
    ros::NodeHandle n;
    ros::Subscriber sub = n.subscribe("alive", 1000, alivesCallback);
    ros::spin();
}


void subscriptionTemperatureTopic(){
    ros::NodeHandle n;
    ros::Subscriber sub = n.subscribe("temperature", 1000, temperatureCallback);
    ros::spin();
}


int main(){

    boos::thread t1(boost::bind(subscriptionAliveTopic));
    boos::thread t2(boost::bind(subscriptionTemperatureTopic));

    //more things to do
}