C#中精确计算运行时间的类

using System;
using System.Threading;
using System.ComponentModel;
using System.Runtime.InteropServices;

namespace TestEntity
{
    ///   <summary> 
    ///   进行精确操作计时的类。 
    ///   </summary> 
    public sealed class RunTime
    {
        //   -----   私有对象 
        [DllImport("Kernel32.dll ")]
        private static extern bool QueryPerformanceFrequency(out   long lpFrequency);

        [DllImport("Kernel32.dll ")]
        private static extern bool QueryPerformanceCounter(out   long lpPerformanceCount);

        private long startTime, stopTime;
        private long freq;

        ///   <summary> 
        ///   初始化   <see   cref= "RunTime "/>   类的新实例。 
        ///   </summary> 
        public RunTime()
        {
            this.startTime = 0;
            this.stopTime = 0;

            if (QueryPerformanceFrequency(out   freq) == false)
                throw new Win32Exception();
        }

        ///   <summary> 
        ///   开始执行计时。 
        ///   </summary> 
        public void Start()
        {
            Thread.Sleep(0);
            QueryPerformanceCounter(out   startTime);
        }

        ///   <summary> 
        ///   停止计时。 
        ///   </summary> 
        public void Stop()
        {
            QueryPerformanceCounter(out   stopTime);
        }

        ///   <summary> 
        ///   获取计时后得到的计时时间。（单位为秒） 
        ///   </summary> 
        public double DurationSecs
        {
            get
            {
                //   判断是否执行了开始和结束 
                if (startTime == 0 || stopTime == 0)
                    throw new InvalidOperationException("Unit_TimeVariableIsNull ");
                return (double)(stopTime - startTime) / (double)freq;
            }
        }

        ///   <summary> 
        ///   获取计时后的计时时间。（单位为毫秒） 
        ///   </summary> 
        public float DurationMsel
        {
            get
            {
                if (startTime == 0 || stopTime == 0)
                    throw new InvalidOperationException("Unit_TimeVariableIsNull");
                return float.Parse((this.DurationSecs * 1000).ToString("##0.### "));
            }
        }
    }
}