// communicating data using std::promise and std::future
#include <future>
#include <iostream>
#include <thread>
using data_t = double;

void prod(std::promise<data_t >&& prom, data_t a, data_t b){
  prom.set_value(a*b);
}

int main(){

  
  // promises
  std::promise<data_t> prom1, prom2;
  // futures
  auto fu_res1 = prom1.get_future();
  auto fu_res2 = prom2.get_future();
  // calculate the result in two threads
  data_t a, b;
  a = 1.0;
  b = 2.0;
  std::thread th1(prod,std::move(prom1),a,b);
  a = 10.0;
  b = 20.0;
  std::thread th2(prod,std::move(prom2),a,b);

  // retreive the result
  std::cout << fu_res1.get() << "\n";
  std::cout << fu_res2.get() << "\n";
  
  th1.join();  
  th2.join();
}