爲什麼是最小Threading.Timer間隔爲15ms，儘管timeBeginPeriod（1）

如下片段爲什麼是最小Threading.Timer間隔爲15ms，儘管timeBeginPeriod（1）

[DllImport("winmm.dll", EntryPoint = "timeBeginPeriod")] 
    public static extern uint TimeBeginPeriod(uint uMilliseconds); 

    static void Main(string[] args) 
    { 
     if (TimeBeginPeriod(1) != 0) 
      Console.WriteLine("TimeBeginPeriod failed!"); 

     Console.WriteLine("Sleep"); 
     Stopwatch sw = Stopwatch.StartNew(); 
     for (int i = 0; i < 10; i++) 
     { 
      Thread.Sleep(1); 
      Console.WriteLine(sw.ElapsedTicks * 1000d/Stopwatch.Frequency); 
      sw.Restart(); 
     } 

     Console.WriteLine("Threading.Timer"); 
     sw = null; 
     System.Threading.Timer t = null; 
     int n = 0; 

     t = new Timer(state => 
     { 
      if (sw == null) 
       sw = Stopwatch.StartNew(); 
      else 
      { 
       Console.WriteLine(sw.ElapsedTicks * 1000d/Stopwatch.Frequency); 
       n++; 
       sw.Restart(); 
      } 
      if (n == 10) 
       t.Change(Timeout.Infinite, Timeout.Infinite); 
     }, null, TimeSpan.FromMilliseconds(1), TimeSpan.FromMilliseconds(1)); 
     Console.ReadKey(); 
    }

將例如產生此輸出：

Sleep 
0.151834939915548 
0.757358826331279 
0.786901687225611 
0.712520725399457 
0.715593741662697 
0.798704863327602 
0.5724889615859 
0.648825479215934 
0.436927039609783 
0.517873081634677 
Threading.Timer 
15.5841035662354 
14.8620145856526 
15.1098812837944 
14.4202684978119 
15.3883384620112 
14.7210748852159 
15.307462261265 
15.7125416777831 
14.5991320125882 
15.6035194417168

根據網絡comment by Hans Passant,timeBeginPeriod會影響常規（.net）定時器。那麼爲什麼我的計時器仍然有這個粗粒度？ Thread.Sleep似乎做得很好。

也許相關：它運行在Windows 7，64bit，.net 4，VMWare內部。

來源

2013-04-23 Eugene Beresovsky