准确计算时间差

简单地使用 beginDate - endDate 不精确，总是某个值的倍数，比如 0.015625 秒的倍数，值比较小时，干脆就是个0 (0 倍)。

.NET Framework v2.0 中新增了一个 System.Diagnostics.Stopwatch 对象，本文就是说用它来计算时间差，.NET 2.0 中是现成的，因此对 2.0 来说，这文章没什么意义，只要知道有这个对象就可以了，用法也相当简单，举例：

public   void  SomeMethod()
{
    Stopwatch stopwatch  =  Stopwatch.StartNew();
     //  do something 
     //  仅仅简单举例, Stopwatch 还提供了其他更为详细的属性和方法。
    Console.WriteLine( " Elapsed Seconds: {0} " , stopwatch.Elapsed.TotalSeconds);
}

在 1.1 里没有提供，但只需把该对象完整的反编译代码 Copy 出来自建一个 Stopwatch 对象，再做一点小改动就 OK 了。 代码与举例：

using  System;
using  System.Runtime.InteropServices;
using  System.Security;
using  System.Security.Permissions;

namespace  Zealot.Framework.Web.Utils
{
     ///   <summary>
     ///  v1.1 没有 Stopwatch，从 v2.0 复制出来
     ///   </summary>
     public   class  Stopwatch
    {
         //  Fields
         private   long  elapsed;
         public   static   readonly   long  Frequency;
         public   static   readonly   bool  IsHighResolution;
         private   bool  isRunning;
         private   long  startTimeStamp;
         private   static   readonly   double  tickFrequency;
         private   const   long  TicksPerMillisecond  =   0x2710 ;
         private   const   long  TicksPerSecond  =   0x989680 ;

         //  Methods
         static  Stopwatch()
        {
             if  ( ! SafeNativeMethods.QueryPerformanceFrequency( out  Frequency))
            {
                IsHighResolution  =   false ;
                Frequency  =   0x989680 ;
                tickFrequency  =   1 ;
            }
             else
            {
                IsHighResolution  =   true ;
                tickFrequency  =   10000000 ;
                tickFrequency  /=  ( double )Frequency;
            }
        }

         public  Stopwatch()
        {
             this .Reset();
        }

         private   long  GetElapsedDateTimeTicks()
        {
             long  rawElapsedTicks  =   this .GetRawElapsedTicks();
             if  (IsHighResolution)
            {
                 double  num2  =  rawElapsedTicks;
                num2  *=  tickFrequency;
                 return  ( long )num2;
            }
             return  rawElapsedTicks;
        }

         private   long  GetRawElapsedTicks()
        {
             long  elapsed  =   this .elapsed;
             if  ( this .isRunning)
            {
                 long  num3  =  GetTimestamp()  -   this .startTimeStamp;
                elapsed  +=  num3;
            }
             return  elapsed;
        }

         public   static   long  GetTimestamp()
        {
             if  (IsHighResolution)
            {
                 long  num  =   0 ;
                SafeNativeMethods.QueryPerformanceCounter( out  num);
                 return  num;
            }
             return  DateTime.UtcNow.Ticks;
        }

         public   void  Reset()
        {
             this .elapsed  =   0 ;
             this .isRunning  =   false ;
             this .startTimeStamp  =   0 ;
        }

         public   void  Start()
        {
             if  ( ! this .isRunning)
            {
                 this .startTimeStamp  =  GetTimestamp();
                 this .isRunning  =   true ;
            }
        }

         public   static  Stopwatch StartNew()
        {
            Stopwatch stopwatch  =   new  Stopwatch();
            stopwatch.Start();
             return  stopwatch;
        }

         public   void  Stop()
        {
             if  ( this .isRunning)
            {
                 long  num2  =  GetTimestamp()  -   this .startTimeStamp;
                 this .elapsed  +=  num2;
                 this .isRunning  =   false ;
            }
        }

         //  Properties
         public  TimeSpan Elapsed
        {
             get
            {
                 return   new  TimeSpan( this .GetElapsedDateTimeTicks());
            }
        }

         public   long  ElapsedMilliseconds
        {
             get
            {
                 return  ( this .GetElapsedDateTimeTicks()  /  (( long ) 0x2710 ));
            }
        }

         public   long  ElapsedTicks
        {
             get
            {
                 return   this .GetRawElapsedTicks();
            }
        }

         public   bool  IsRunning
        {
             get
            {
                 return   this .isRunning;
            }
        }
    }
}

编译时发现有 2 处错误，无法找到 SafeNativeMethods 对象，因为它是 internal 访问限制的。 而 在这个类里用到了 SafeNativeMethods 中的两个方法，QueryPerformanceFrequency 和 QueryPerformanceCounter，把他们也反编译出来，直接加入自建的 Stopwatch 类当中，或者在与 Stopwatch 相同的命名空间下同样自建一个 SafeNativeMethods 类就可以了。

using  System;
using  System.Runtime.InteropServices;
using  System.Security;
using  System.Security.Permissions;

namespace  Zealot.Framework.Web.Utils
{
    [SuppressUnmanagedCodeSecurity]
     internal   class  SafeNativeMethods
    {
        [DllImport( " kernel32.dll " )]
         internal   static   extern   bool  QueryPerformanceCounter( out   long  value);

        [DllImport( " kernel32.dll " )]
         internal   static   extern   bool  QueryPerformanceFrequency( out   long  value);
    }
}

转自：http://www.zealotforce.net/reply-638.aspx