gistfile1.cpp

/* You could have an actor base class with a protected `receive` and a public `send` function,
 * which pull and push (respectively) messages out of and into the message queue. Each actor
 * has a message queue. You then inherit that class and override a virtual function `run`,
 * which is on a separate thread.
 */
 
// abstract actor base class
template<class Message>
class actor {
public:
    actor() {
        /* Because of C++, we are fucked; we cannot call a virtual function from ctor. This
         * needs to be done in some other way.
         */
        std::thread thread{[this] {
            run(); // whoops
        }};
    }
    virtual ~actor() = default;
 
    void send(Message message) {
        msg_queue.push(message);
    }
 
    void join() {
        // FIXME: Join thread.
    }
 
protected:
    virtual void run() = 0;
    
    Message receive() {
        // this function is blocking
        return msg_queue.pull(); // removes front object and returns it
    }
 
private:
    atomic_queue<Message> msg_queue;
};

struct car {
    car() {
        age = rand<unsigned>();
        weight = random<unsigned>();
    }
    unsigned age, weight;
};

// example: car server
class car_server : public actor<std::pair<actor&, std::string>> {
protected:
    virtual void run() override {
        car c;
        for (;;) {
            // read message and respond to it
            auto message = receive();
            switch (message.second) {
                case "get_age": message.first.send(car.age; break;
                case "get_weight": message.first.send(car.weight); break;
                case "buy_new_car": c = car{}; break;
                default: break; // probably log error or send an error back to the consumer
            }
        }
    }
};

// example: car server client
class car_consumer : public actor<unsigned> {
protected:
    virtual void run() override {
        car_server srvr;
        
        actr.send("get_age");
        std::cout << "Car age is " << receive() << '\n';
        
        actr.send("get_weight");
        std::cout << "Car weight is " << receive() << '\n';
        
        actr.send("buy_new_car");
        std::cout << "Buying a new car...\n";
        
        actr.send("get_age");
        std::cout << "Car age is " << receive() << '\n';
        
        actr.send("get_weight");
        std::cout << "Car weight is " << receive() << '\n';
        
        // now, consumer is done and exits
    }
}
 
// example: using logger
int main() {
    car_consumer consumer;
    car_consumer.join();
}