text: // blocking.cpp
  
  #include <chrono>
  #include <future>
  #include <iostream>
  #include <thread>
  
  int main(){
  
    std::cout << std::endl;
  
    std::async(std::launch::async,[]{
      std::this_thread::sleep_for(std::chrono::seconds(2));
      std::cout << "first thread" << std::endl;
      });
      
    std::async(std::launch::async,[]{
      std::this_thread::sleep_for(std::chrono::seconds(1));  
      std::cout << "second thread" << std::endl;}
      );
    
    std::cout << "main thread" << std::endl;  
  
  }