Active Object Pattern

ActiveObject.cpp

#include <functional>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <iostream>

class Active {
public:
    using Message = std::function<void()>;
    
    Active():keep_running(true){
       thd = std::thread([this]{ // mainline: dispatch loop {}
         while(keep_running){
             Message m;
             bool is_valid{false};
             {//pop message
                std::lock_guard<std::mutex> lg(qmut);
                if(!mq.empty()){
                    m = mq.front();
                    mq.pop();
                    is_valid =true;
                }
             }
             //execute
             if(is_valid){
                m(); 
             }
             {//wait for more
                std::unique_lock<std::mutex> lk(qmut);
                cv.wait(lk,[&]{return !mq.empty();});
             }
         }
       });
    }

    ~Active() { // shut down
        keep_running = false;
        Send( [=]{ ; } );// send sentinel and
        if(thd.joinable()){
          thd.join();// wait for msgs to drain
        }
    }
    
    Active(const Active&)=delete;
    Active& operator=(const Active& other)=delete;
    void Send(const Message m) { // enqueue a message
        {
            std::lock_guard<std::mutex> lg(qmut);
            mq.push(std::move(m)); 
        }
        cv.notify_one();
    }
private:
    bool keep_running;
    std::queue<Message> mq; 
    std::mutex qmut;
    std::thread thd;
    std::condition_variable cv;

};

int main(){
  Active a;
  a.Send([](){
    std::cout << "Hello from Active object" << std::endl;
  });
}