basic thread example from modern cpp concurrency in depth

s1e13-exercise.hpp

#include <iostream>
#include <queue>
#include <thread>
#include <atomic>
#include <string>
#include <chrono>

int main() {
  std::queue<int> qth1, qth2;
  std::thread th1, th2;
  std::atomic<bool> doneFlag{false};

  th1 = std::thread([&](){
    while(!doneFlag){
      if(qth1.empty()){
        std::this_thread::sleep_for(std::chrono::seconds(2));
      }else{
        int cmd = qth1.front();
        std::cerr<<"Thread1:"<<cmd<<std::endl;
        qth1.pop();
        std::this_thread::sleep_for(std::chrono::seconds(2));
      }
    }
  });

   th2 = std::thread([&](){
    while(!doneFlag){
      if(qth2.empty()){
        std::this_thread::sleep_for(std::chrono::seconds(2));
      }else{
        int cmd = qth2.front();
        std::cerr<<"Thread2:"<<cmd<<std::endl;
        qth2.pop();
        std::this_thread::sleep_for(std::chrono::seconds(2));
      }
    }
  });


  int cmd;
  while(!doneFlag){
    std::cout<<"Enter command:"<<std::endl;
    std::cin >> cmd;

    if(cmd==0){
      qth1.push(cmd);
    }else if(cmd==1){
      qth2.push(cmd);
    }else if(cmd==2){
      doneFlag=true;
    }else{
      std::cerr<<"Wrong Command."<<std::endl;
    }
    std::this_thread::sleep_for(std::chrono::seconds(1));
  }

  th1.join();
  th2.join();
  std::cout<<"All threads were joined. Program finished."<<std::endl;

}