Спринт 9. Накладные расходы на вызов async.

#include <algorithm>
#include <iostream>
#include <numeric>
#include <random>
#include <vector>
#include <future>
#include <execution>

using namespace std;

template <typename It>
void PrintRange(It range_begin, It range_end) {
    for (auto it = range_begin; it != range_end; ++it) {
        cout << *it << " "s;
    }
    cout << endl;
}

template <typename RandomIt>
void MergeSort(RandomIt range_begin, RandomIt range_end, int async_ = 0) {

    int range_length = range_end - range_begin;
    if (range_length < 2) {
        return;
    }

    vector elements(range_begin, range_end);
    auto mid = elements.begin() + range_length / 2;

    auto right = [mid, end = elements.end(), async_] {
        MergeSort(mid, end, 1 + async_);
    };

    auto left = [begin = elements.begin(), mid, async_] {
        MergeSort(begin, mid, 1 + async_);
    };

    if (2 >= async_) {                                     //max_async
        auto right_async = async(right);
        left();
        right_async.get();
    } else {
        right();
        left();
    }

    merge(execution::par, elements.begin(), mid, mid, elements.end(), range_begin);
}

int main() {
    mt19937 generator;

    vector<int> test_vector(10);

    iota(test_vector.begin(), test_vector.end(), 1);

    shuffle(test_vector.begin(), test_vector.end(), generator);

    PrintRange(test_vector.begin(), test_vector.end());

    MergeSort(test_vector.begin(), test_vector.end());

    PrintRange(test_vector.begin(), test_vector.end());

    MergeSort(test_vector.data(), test_vector.data() + test_vector.size());

    return 0;
}