Question

问题： 尽管操作系统时钟分辨率更精确，为什么System.Threading.Timer保持15ms的分辨率？在没有繁忙的CPU等待的情况下，实现1ms定时事件解析的可行方法是什么？

再次压力：系统计时器在我的情况下具有1ms的分辨率（与建议重复的问题相反）。所以这不是系统计时器解析的问题。因此，在所谓的重复问题中没有有用的信息。

背景似乎.NET System.Threading.Timer 没有使用系统时钟分辨率 - 它保持了~15ms的分辨率。尽管OS时钟（例如Sleep分辨率）更精确。

在我的盒子上（几乎空闲且有4个核心可供运行）：

>Clockres.exe

ClockRes v2.0 - View the system clock resolution
Copyright (C) 2009 Mark Russinovich
SysInternals - www.sysinternals.com

Maximum timer interval: 15.625 ms
Minimum timer interval: 0.500 ms
Current timer interval: 1.001 ms

我的快速测试输出：

Sleep test:
Average time delta: 2[ms] (from 993 cases)
System.Threading.Timer test:
Average time delta: 15[ms] (from 985 cases)

测试代码为：

private static void TestSleepVsTimer(long millisecondsDifference, int repetions)
{
    TimingEventsKeeper timingEventsKeeper = new TimingEventsKeeper();
    timingEventsKeeper.Reset((int) millisecondsDifference, repetions);

    while (!timingEventsKeeper.TestDoneEvent.IsSet)
    {
        timingEventsKeeper.CountNextEvent(null);
        Thread.Sleep((int) millisecondsDifference);
    }

    Console.WriteLine("Sleep test: ");
    timingEventsKeeper.Output();

    timingEventsKeeper.Reset((int) millisecondsDifference, repetions);

    Timer t = new Timer(timingEventsKeeper.CountNextEvent, null, TimeSpan.FromMilliseconds(1), TimeSpan.FromMilliseconds(1));
    timingEventsKeeper.TestDoneEvent.Wait();

    Console.WriteLine("System.Threading.Timer test: ");
    timingEventsKeeper.Output();
}

private class TimingEventsKeeper
{
    long _ticksSum = 0;
    long _casesCount = 0;
    long _minTicksDiff;
    long _maxTicksDiff;
    long _lastTicksCount;
    int _repetitons;

    public CountdownEvent TestDoneEvent = new CountdownEvent(0);

    public void Reset(int millisecondsDifference, int repetitions)
    {
        _ticksSum = 0;
        _casesCount = 0;
        _minTicksDiff = millisecondsDifference * 10000;
        _maxTicksDiff = millisecondsDifference * 10000;
        _lastTicksCount = DateTime.UtcNow.Ticks;
        _repetitons = repetitions;
        TestDoneEvent.Reset(repetitions);
    }

    public void CountNextEvent(object unused)
    {
        long currTicksCount = DateTime.UtcNow.Ticks;
        long diff = currTicksCount - _lastTicksCount;
        _lastTicksCount = currTicksCount;

        TestDoneEvent.Signal();

        if (diff >= _maxTicksDiff)
        {
            _maxTicksDiff = diff;
            return;
        }

        if (diff <= _minTicksDiff)
        {
            _minTicksDiff = diff;
            return;
        }

        _casesCount++;
        _ticksSum += diff;

    }

    public void Output()
    {
        if(_casesCount > 0)
            Console.WriteLine("Average time delta: {0}[ms] (from {1} cases)", _ticksSum / _casesCount / 10000, _casesCount);
        else
            Console.WriteLine("No measured cases to calculate average");
    }
}

public static class WinApi
{
    /// <summary>TimeBeginPeriod(). See the Windows API documentation for details.</summary>

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Interoperability", "CA1401:PInvokesShouldNotBeVisible"), System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2118:ReviewSuppressUnmanagedCodeSecurityUsage"), SuppressUnmanagedCodeSecurity]
    [DllImport("winmm.dll", EntryPoint = "timeBeginPeriod", SetLastError = true)]

    public static extern uint TimeBeginPeriod(uint uMilliseconds);

    /// <summary>TimeEndPeriod(). See the Windows API documentation for details.</summary>

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Interoperability", "CA1401:PInvokesShouldNotBeVisible"), System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2118:ReviewSuppressUnmanagedCodeSecurityUsage"), SuppressUnmanagedCodeSecurity]
    [DllImport("winmm.dll", EntryPoint = "timeEndPeriod", SetLastError = true)]

    public static extern uint TimeEndPeriod(uint uMilliseconds);
}

private static void Main(string[] args)
{
    WinApi.TimeBeginPeriod(1);
    TestSleepVsTimer(1, 1000);
    WinApi.TimeEndPeriod(1);
}

EDIT1：

环境： 在.NET 2.0,3.0,3.5（没有CountDownEvent）和4.5下的Build和Release版本上进行了测试在Windows 8（Build 9200），Server 2012（Build 9200），Server 2008（Build 6001 SP1）上 Sleep和Timer之间存在显着差异。

为什么这不重复： 正如我发布的那样 - 操作系统计时器分辨率设置为1毫秒（并且Sleep也没有表现出这种行为）。 因此，这不是OS定时器分辨率（中断频率）的错误 - 这是System.Threading.Timer特有的。

EDIT2： （添加了TimeBeginPeriod和TimeEndPeriod对代码的调用 - 强制更改OS计时器分辨率）

Answer 1

使用从WaitHandle派生的其中一个同步类，例如AutoResetEvent或ManualResetEvent，在调用WaitOne（）方法时设置timeout参数。

通过循环调用WaitOne，您可以实现计时器。

您可以发出等待句柄派生类的信号，以打断或中断计时器。

注意，要更改分辨率，最好使用实现IDisposable的帮助程序类：

internal sealed class TimePeriod : IDisposable
{
    private const string WINMM = "winmm.dll";

    private static TIMECAPS timeCapabilities;

    private static int inTimePeriod;

    private readonly int period;

    private int disposed;

    [DllImport(WINMM, ExactSpelling = true)]
    private static extern int timeGetDevCaps(ref TIMECAPS ptc, int cbtc);

    [DllImport(WINMM, ExactSpelling = true)]
    private static extern int timeBeginPeriod(int uPeriod);

    [DllImport(WINMM, ExactSpelling = true)]
    private static extern int timeEndPeriod(int uPeriod);

    static TimePeriod()
    {
        int result = timeGetDevCaps(ref timeCapabilities, Marshal.SizeOf(typeof(TIMECAPS)));
        if (result != 0)
        {
            throw new InvalidOperationException("The request to get time capabilities was not completed because an unexpected error with code " + result + " occured.");
        }
    }

    internal TimePeriod(int period)
    {
        if (Interlocked.Increment(ref inTimePeriod) != 1)
        {
            Interlocked.Decrement(ref inTimePeriod);
            throw new NotSupportedException("The process is already within a time period. Nested time periods are not supported.");
        }

        if (period < timeCapabilities.wPeriodMin || period > timeCapabilities.wPeriodMax)
        {
            throw new ArgumentOutOfRangeException("period", "The request to begin a time period was not completed because the resolution specified is out of range.");
        }

        int result = timeBeginPeriod(period);
        if (result != 0)
        {
            throw new InvalidOperationException("The request to begin a time period was not completed because an unexpected error with code " + result + " occured.");
        }

        this.period = period;
    }

    internal static int MinimumPeriod
    {
        get
        {
            return timeCapabilities.wPeriodMin;
        }
    }

    internal static int MaximumPeriod
    {
        get
        {
            return timeCapabilities.wPeriodMax;
        }
    }

    internal int Period
    {
        get
        {
            if (this.disposed > 0)
            {
                throw new ObjectDisposedException("The time period instance has been disposed.");
            }

            return this.period;
        }
    }

    public void Dispose()
    {
        if (Interlocked.Increment(ref this.disposed) == 1)
        {
            timeEndPeriod(this.period);
            Interlocked.Decrement(ref inTimePeriod);
        }
        else
        {
            Interlocked.Decrement(ref this.disposed);
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct TIMECAPS
    {
        internal int wPeriodMin;

        internal int wPeriodMax;
    }
}

然后您可以使用：

using (new TimePeriod(1))
{
    ////...
}

尼克

Answer 2

为什么System.Threading.Timer可以保持15ms的分辨率，而OS时钟的分辨率却要精确得多？

显然是由于实施。 System.Threading.Timer（因此Task.Delay）使用.NET运行时计时器队列，该队列不遵守系统计时器的分辨率。此外，我运行了（.net 4.x）Windows（7、10；服务器2012、2016）测试，发现WaitHandle.WaitOne（）和Monitor.Wait（）不尊重 WinForms上的系统计时器解析度GUI线程（（answer above使用WaitHandle）。因此，只有Thread.Sleep在GUI线程上尊重它。

在不忙于等待CPU的情况下实现1ms定时事件分辨率的推荐方法是什么？

Jim Mischel指出的一种方法。但是，它有以下缺点：
在 windows 线程池线程上执行回调。
时间间隔与当前时间相对。
时间间隔为整数 ms，因此理论上最大精度为1 ms。
根据许多报告， 1.5-2毫秒精度几乎是您可以达到的，并且只能通过timeBeginPeriod（1）来。

另一种方法是：NtSetTimerResolution和Waitable Timer Objects。您可以获得0.5毫秒的分辨率（取决于硬件和Windows版本）。
对于c＃示例（这不是您的计时器类的示例，而是在c＃中使用此函数的示例），您可以选中此article。

您也可以尝试Nick's的建议，但要记住GUI线程的问题。

System.Threading.Timer vs System.Threading.Thread.Sleep resolution - .NET Timer不使用系统时钟分辨率

2 个答案: