[Performance Tip]StreamReader Or File.ReadAllLines

在我们使用文件读取时，往往会看到StreamReader或者File.ReadAllLInes这样的方法，有时候我就想这两个有什么差别呢？于是写个小程序比较下

   1: using System;

   2: using System.Collections.Generic;

   3: using System.Linq;

   4: using System.Text;

   5: using System.IO;

   6: using System.Diagnostics;

   7:  

   8: namespace PerformanceTips

   9: {

  10:     class Program

  11:     {

  12:         static void Main(string[] args)

  13:         {

  14:             string path = Path.Combine(Environment.CurrentDirectory, "Test.txt");

  15:             Stopwatch sw = new Stopwatch();

  16:             sw.Start();

  17:             using (StreamReader sr = new StreamReader(path))

  18:             {

  19:                 sr.ReadToEnd();

  20:             }

  21:             sw.Stop();

  22:             Console.WriteLine("StreamReader.ReadToEnd(), Time Cost: {0}", sw.ElapsedTicks);

  23:  

  24:             sw.Reset();

  25:             sw.Start();

  26:             File.ReadAllText(path);

  27:             sw.Stop();

  28:             Console.WriteLine("File.ReadAllText(), Time Cost: {0}", sw.ElapsedTicks);

  29:  

  30:             Console.Read();

  31:         }

  32:     }

  33: }

测试环境: Visual Studio 2008 SP1 + .Net 3.5 SP1

test.txt

格式: ASCII

大小: 59KB

结果

结果差别比较惊人

去查看下File.ReadAllText的源代码 

   1: public static string ReadAllText(string path)

   2: {

   3:     return ReadAllText(path, Encoding.UTF8);

   4: }

   5:  

   6: public static string ReadAllText(string path, Encoding encoding)

   7: {

   8:     using (StreamReader reader = new StreamReader(path, encoding))

   9:     {

  10:         return reader.ReadToEnd();

  11:     }

  12: }

这下把我搞郁闷了, 都是一样的东西要差距这么大，无奈，给StreamReader加上UTF8

   1: using (StreamReader sr = new StreamReader(path, Encoding.UTF8))

   2:             {

   3:                 sr.ReadToEnd();

   4:             }

   5:             sw.Stop();

结果:

这样就比较正常了，然而还是有点差距，我们让打开编译器优化， 将模式改到Release

再看结果

没有办法了，暂时解释为File.ReadAllLines的方法存在于mscorlib中，默认CLR对存在于该程序集中的调用有优化.

无证据，等日后证明或者推翻