std::launch

// launch::async vs launch::deferred
#include <iostream>     // std::cout
#include <future>       // std::async, std::future, std::launch
#include <chrono>       // std::chrono::milliseconds
#include <thread>       // std::this_thread::sleep_for
void print_ten (char c, int ms) {
  for (int i=0; i<10; ++i) {
    std::this_thread::sleep_for (std::chrono::milliseconds(ms));
    std::cout << c;
  }
}
int main ()
{
  std::cout << "with launch::async:\n";
  std::future<void> foo = std::async (std::launch::async,print_ten,'*',100);
  std::future<void> bar = std::async (std::launch::async,print_ten,'@',200);
  // async "get" (wait for foo and bar to be ready):
  foo.get();
  bar.get();
  std::cout << "\n\n";
  std::cout << "with launch::deferred:\n";
  foo = std::async (std::launch::deferred,print_ten,'*',100);
  bar = std::async (std::launch::deferred,print_ten,'@',200);
  // deferred "get" (perform the actual calls):
  foo.get();
  bar.get();
  std::cout << '\n';
  return 0;
}