学步园

// StopWatch.cs
using System;
using System.ComponentModel;
using System.Runtime.InteropServices;

public class StopWatch
{
 [DllImport("Kernel32.dll")]
 static extern bool QueryPerformanceCounter(out long lpPerformanceCount);

 [DllImport("Kernel32.dll")]
 static extern bool QueryPerformanceFrequency(out long lpFrequency);

 long start;
 long stop;
 long frequency;
 const decimal multiplier = 1.0e9M;

 public StopWatch()
 {
  if (QueryPerformanceFrequency(out frequency) == false)
  {
   // Frequency not supported
   throw new Win32Exception();
  }
 }

 public void Start()
 {
  QueryPerformanceCounter(out start);
 }

 public void Stop()
 {
  QueryPerformanceCounter(out stop);
 }

 public double Duration(int iterations)
 {
  return ((((double)(stop - start) * (double)multiplier) / (double)frequency) / iterations);
 }
}

它的使用比DateTime.Now还要简单，如下所示：

StopWatch myTimer = new StopWatch();
// Measure without boxing
myTimer.Start();
for(int i = 0; i < iterations; i++)
{
  // do some work to time
}
myTimer.Stop();
// 计算每次循环所花的平均时间（单位：十亿分之一秒）
double result = myTimer.Duration(iterations);