Example of usage of std::future and std::async for multithreaded computation.

future_example.cpp

#include <future>
#include <iostream>
#include <numeric>
#include <vector>

// Returns the sum of all integers between [1, n]
int sum(const unsigned int n) {
  std::vector<int> numbers(n);
  std::iota(numbers.begin(), numbers.end(), 1);
  return std::accumulate(numbers.begin(), numbers.end(), 0);
}

// Performs some arbitrary task
void task() {
  std::cout << "Executing task...\n";
  constexpr int num_tasks = 500;
  std::vector<int> result;

  for (int i = 0; i < num_tasks; ++i) {
    result.push_back(i);
  }
}

int main() {
  // Spawns two threads to complete the calculations, storing the result in a
  // future. Uses std::launch::async to launch the thread right now
  std::future<int> a = std::async(std::launch::async, sum, 500);
  std::future<int> b = std::async(std::launch::async, sum, 750);

  // Run some arbitrary task on the main thread while the multithreaded
  // computations are running
  task();

  std::cout << "Computation result: " << a.get() + b.get() << '\n';
  return 0;
}