为什么DateTime.Now DateTime.UtcNow这么慢/太贵

我意识到这对于微观优化领域来说太远了,但是我很好奇为什么对DateTime.Now和DateTime.UtcNow的调用如此“昂贵”。我有一个示例程序,它运行两个场景来执行一些“工作”(添加到计数器),并尝试执行此操作1秒。我有好几种办法使它在有限的时间内完成这项工作。示例显示,DateTime.Now和DateTime.UtcNow的速度明显慢于Environment.TickCount,但与只让单独的线程休眠1秒,然后设置一个值来指示要停止的工作线程相比,这甚至慢得多。

所以我的问题是:

• 为什么读取布尔值比读取int值快?
• 处理这些类型的场景的理想方法是什么?在这些场景中,您需要允许某些东西在有限的时间内运行,但是您不想浪费更多的时间检查时间而不是实际执行工作?

class Program
{
    private static volatile bool done = false;
    private static volatile int doneInt = 0;
    private static UInt64 doneLong = 0;

    private static ManualResetEvent readyEvent = new ManualResetEvent(false);

    static void Main(string[] args)
    {
        MethodA_PrecalcEndTime();
        MethodB_CalcEndTimeEachTime();
        MethodC_PrecalcEndTimeUsingUtcNow();

        MethodD_EnvironmentTickCount();

        MethodX_SeperateThreadBool();
        MethodY_SeperateThreadInt();
        MethodZ_SeperateThreadLong();

        Console.WriteLine("Done...");
        Console.ReadLine();
    }

    private static void MethodA_PrecalcEndTime()
    {
        int cnt = 0;
        var doneTime = DateTime.Now.AddSeconds(1);
        var startDT = DateTime.Now;
        while (DateTime.Now <= doneTime)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void MethodB_CalcEndTimeEachTime()
    {
        int cnt = 0;
        var startDT = DateTime.Now;
        while (DateTime.Now <= startDT.AddSeconds(1))
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void MethodC_PrecalcEndTimeUsingUtcNow()
    {
        int cnt = 0;
        var doneTime = DateTime.UtcNow.AddSeconds(1);
        var startDT = DateTime.Now;
        while (DateTime.UtcNow <= doneTime)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }


    private static void MethodD_EnvironmentTickCount()
    {
        int cnt = 0;
        int doneTick = Environment.TickCount + 1000; // <-- should be sane near where the counter clocks...
        var startDT = DateTime.Now;
        while (Environment.TickCount <= doneTick)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void MethodX_SeperateThreadBool()
    {
        readyEvent.Reset();
        Thread counter = new Thread(CountBool);
        Thread waiter = new Thread(WaitBool);
        counter.Start();
        waiter.Start();
        waiter.Join();
        counter.Join();
    }

    private static void CountBool()
    {
        int cnt = 0;
        readyEvent.WaitOne();
        var startDT = DateTime.Now;
        while (!done)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void WaitBool()
    {
        readyEvent.Set();
        Thread.Sleep(TimeSpan.FromSeconds(1));
        done = true;
    }

    private static void MethodY_SeperateThreadInt()
    {
        readyEvent.Reset();
        Thread counter = new Thread(CountInt);
        Thread waiter = new Thread(WaitInt);
        counter.Start();
        waiter.Start();
        waiter.Join();
        counter.Join();
    }

    private static void CountInt()
    {
        int cnt = 0;
        readyEvent.WaitOne();
        var startDT = DateTime.Now;
        while (doneInt<1)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void WaitInt()
    {
        readyEvent.Set();
        Thread.Sleep(TimeSpan.FromSeconds(1));
        doneInt = 1;
    }

    private static void MethodZ_SeperateThreadLong()
    {
        readyEvent.Reset();
        Thread counter = new Thread(CountLong);
        Thread waiter = new Thread(WaitLong);
        counter.Start();
        waiter.Start();
        waiter.Join();
        counter.Join();
    }

    private static void CountLong()
    {
        int cnt = 0;
        readyEvent.WaitOne();
        var startDT = DateTime.Now;
        while (doneLong < 1)
        {
            cnt++;
        }
        var endDT = DateTime.Now;
        Console.WriteLine("Time Taken: {0,30} Total Counted: {1,20}", endDT.Subtract(startDT), cnt);
    }

    private static void WaitLong()
    {
        readyEvent.Set();
        Thread.Sleep(TimeSpan.FromSeconds(1));
        doneLong = 1;
    }

}