std::pmr::monotonic_buffer_resource

#include <array>
#include <chrono>
#include <cstddef>
#include <iomanip>
#include <iostream>
#include <list>
#include <memory_resource>
 
template<typename Func>
auto benchmark(Func test_func, int iterations)
{
    const auto start = std::chrono::system_clock::now();
    while (iterations-- > 0)
        test_func();
    const auto stop = std::chrono::system_clock::now();
    const auto secs = std::chrono::duration<double>(stop - start);
    return secs.count();
}
 
int main()
{
    constexpr int iterations{100};
    constexpr int total_nodes{2'00'000};
 
    auto default_std_alloc = [total_nodes]
    {
        std::list<int> list;
        for (int i{}; i != total_nodes; ++i)
            list.push_back(i);
    };
 
    auto default_pmr_alloc = [total_nodes]
    {
        std::pmr::list<int> list;
        for (int i{}; i != total_nodes; ++i)
            list.push_back(i);
    };
 
    auto pmr_alloc_no_buf = [total_nodes]
    {
        std::pmr::monotonic_buffer_resource mbr;
        std::pmr::polymorphic_allocator<int> pa{&mbr};
        std::pmr::list<int> list{pa};
        for (int i{}; i != total_nodes; ++i)
            list.push_back(i);
    };
 
    auto pmr_alloc_and_buf = [total_nodes]
    {
        // достаточно, чтобы поместиться во всех узлах
        std::array<std::byte, total_nodes * 32> buffer;
        std::pmr::monotonic_buffer_resource mbr{buffer.data(), buffer.size()};
        std::pmr::polymorphic_allocator<int> pa{&mbr};
        std::pmr::list<int> list{pa};
        for (int i{}; i != total_nodes; ++i)
            list.push_back(i);
    };
 
    const double t1 = benchmark(default_std_alloc, iterations);
    const double t2 = benchmark(default_pmr_alloc, iterations);
    const double t3 = benchmark(pmr_alloc_no_buf , iterations);
    const double t4 = benchmark(pmr_alloc_and_buf, iterations);
 
    std::cout << std::fixed << std::setprecision(3)
              << "t1 (распределение std по умолчанию): " << t1
              << " секунд; t1/t1: " << t1/t1 << '\n'
              << "t2 (распределение pmr по умолчанию): " << t2
              << " секунд; t1/t2: " << t1/t2 << '\n'
              << "t3 (распределение pmr   без буфера): " << t3
              << " секунд; t1/t3: " << t1/t3 << '\n'
              << "t4 (распределение pmr      и буфер): " << t4
              << " секунд; t1/t4: " << t1/t4 << '\n';
}