parallel features of C++11

x.cpp

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

template<typename Ran>
int parallel_sum(Ran b, Ran e)
{
    typename Ran::difference_type len = e - b;
    if (len < 10000000)
        return std::accumulate(b, e, 0);

    Ran m = b + len/2;
    auto handle = std::async(std::launch::async, parallel_sum<Ran>, m, e);
    const int sum = parallel_sum(b, m);
    return sum + handle.get();
}

template<typename Cont>
void run(const Cont& vs, std::function<int()> f)
{
    using namespace std::chrono;
    time_point<system_clock> start, end;

    start = system_clock::now();
    const int result = f();
    end = system_clock::now();

    const int elapsed_ms = duration_cast<milliseconds>(end-start).count();
    std::cout << "result=" << result << " (" << elapsed_ms << "ms)\n";
}

int main(int argc, char** argv)
{
    const int n = argc>1 ? std::stoi(argv[1]) : 100;
    std::vector<int> v(n, 1);

    run(v, [&v] { return parallel_sum(v.begin(), v.end()); });
    run(v, [&v] { return std::accumulate(v.begin(), v.end(), 0); });
}