C++ 시간함수 성능비교 #1

#include <iostream>
#include <thread>
#include <chrono>
#include <mutex>
#include <atomic>
#include <windows.h>

auto main() -> int
{
    std::cout << "start" << std::endl;
    constexpr int COUNT = 10000000;
    
    {
        auto startTime = std::chrono::steady_clock::now();
        long long accCount = 0;

        for (int i = 0; i < COUNT; i++)
        {
            volatile auto now = std::chrono::steady_clock::now();
        }
        auto endTime = std::chrono::steady_clock::now();

        std::cout << "std std::chrono steady clock : "
            << std::chrono::duration_cast<std::chrono::milliseconds>(endTime - startTime).count()
            << "ms" 
            << ", accCount : " << accCount << std::endl;
    }

    {
        auto startTime = std::chrono::steady_clock::now();
        auto initTime = std::chrono::system_clock::now();
        long long accCount = 0;

        for (int i = 0; i < COUNT; i++)
        {
            volatile auto now = std::chrono::system_clock::now();
        }

        auto endTime = std::chrono::steady_clock::now();
        std::cout << "std std::chrono system clock : "
            << std::chrono::duration_cast<std::chrono::milliseconds>(endTime - startTime).count()
            << "ms" << std::endl;
    }

    {
        auto startTime = std::chrono::steady_clock::now();
        
        SYSTEMTIME stInit;
        GetSystemTime(&stInit);
        long long accCount = 0;

        for (int i = 0; i < COUNT; i++)
        {
            SYSTEMTIME stNow;
            GetSystemTime(&stNow);
            volatile WORD sec = stNow.wSecond;
        }

        auto endTime = std::chrono::steady_clock::now();
        std::cout << "windows  : "
            << std::chrono::duration_cast<std::chrono::milliseconds>(endTime - startTime).count()
            << "ms" 
            << ", accCount : " << accCount << std::endl;
    }

    {
        auto startTime = std::chrono::steady_clock::now();

        bool isShutdown = false;
        std::atomic<SYSTEMTIME> stNow;
        auto timer = std::thread([&isShutdown, &stNow]() {
            while (isShutdown == false)
            {
                {
                    SYSTEMTIME now;
                    GetSystemTime(&now);
                    stNow = now;
                }
                ::Sleep(0);
            }
            });

        for (int i = 0; i < COUNT/10; i++)
        {
            SYSTEMTIME now = stNow;
            for (int i = 0; i < 10; i++)
            {
                volatile WORD sec = now.wSecond;
            }
        }

        auto endTime = std::chrono::steady_clock::now();
        std::cout << "Threading windows  : "
            << std::chrono::duration_cast<std::chrono::milliseconds>(endTime - startTime).count()
            << "ms" << std::endl;

        isShutdown = true;
        timer.join();
    }
}