System.Threading.Timer与System.Threading.Thread.Sleep解析-.NET计
本文关键字：System Threading 解析 NET Thread Timer Sleep | 更新日期: 2023-09-27 17:59:29
问题：为什么System.Threading.Timer在操作系统时钟分辨率更精确的情况下仍保持15ms的分辨率？在没有繁忙CPU等待的情况下，实现1ms定时事件分辨率的推荐方法是什么？
再次强调：在我的情况下，系统计时器有1ms的分辨率（与建议的重复问题相反）。因此这不是系统计时器分辨率的问题因此，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-它保持了约15ms的分辨率。尽管OS时钟（以及例如Sleep分辨率）要精确得多。
在我的盒子上（当几乎空闲并且有4个核心可供运行时）：
>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)
测试代码所在位置：
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);
}
第1版：
环境：在.NET 2.0、3.0、3.5（不含CountDownEvent）和4.5下的构建和发布版本上进行了测试在Windows 8（内部版本9200）、Server 2012（内部版本6200）和Server 2008（内部版本6001 SP1）上CCD_ 4与CCD_。
为什么不重复：正如我发布的那样，操作系统计时器的分辨率设置为1ms（而且Sleep没有表现出这种行为）因此，这不是操作系统计时器分辨率（中断频率）的故障-这是System.Threading.Timer特有的问题。
第2版：（添加了对代码的TimeBeginPeriod和TimeEndPeriod调用-以强制更改操作系统计时器分辨率）
使用从WaitHandle派生的同步类之一，如AutoResetEvent或ManualResetEvent，在调用WaitOne（）方法时设置超时参数。
通过在循环中调用WaitOne，您可以实现一个定时器。
您可以向等待句柄派生类发出信号以中断计时器。
注意，要更改分辨率，最好使用实现IDisposable:的助手类
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))
{
////...
}
Nick
为什么System.Threading.Timer在操作系统时钟分辨率更精确的情况下仍保持15ms的分辨率？
显然是由于实施。System.Threading.Timer（以及Task.Delay）使用.NET运行时计时器队列，该队列不尊重系统计时器解析。此外，我运行了测试（.net 4.x）窗口（7，10；服务器20122016），发现WaitHandle.WaitOne（）和Monitor.Wait（）也不尊重WinForms GUI线程上的系统计时器分辨率（使用WaitHandle是上面的答案）。所以，只有Thread.Sleep在GUI线程上尊重它。
在没有繁忙CPU等待的情况下，实现1ms定时事件分辨率的推荐方法是什么？
Jim Mischel指出的一种方式。但是，它也有缺点，比如：
在窗口线程池线程上执行回调
时间间隔是相对于当前时间的
时间间隔为整数毫秒，因此理论上最大精度为1毫秒。
根据许多报告，1.5-2ms精度实际上是您可以达到的最大值，并且仅使用timeBeginPeriod（1）调用。
另一种方法是：NtSetTimerResolution和Waitable Timer对象。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（它不是您的定时器类的示例，而是在c#中使用这些函数的示例），您可以查看本文。
您也可以尝试Nick的建议，但需要记住GUI线程的问题。