ex-21-07

来自「Programming Csharp Source Code(代码) Prog」· 代码 · 共 90 行

// Example 21-07: Implementing asynchronous I/O 

namespace Programming_CSharp
{
   using System;
   using System.IO;
   using System.Threading;
   using System.Text;

   public class AsynchIOTester
   {
      private Stream inputStream;   
    
      // delegated method
      private AsyncCallback myCallBack; 

      // buffer to hold the read data
      private byte[] buffer;         
 
      // the size of the buffer
      const int BufferSize = 256;

      // constructor
      AsynchIOTester()
      {
         // open the input stream
         inputStream = 
            File.OpenRead(
            @"C:\test\source\AskTim.txt");

         // allocate a buffer
         buffer = new byte[BufferSize];

         // assign the call back
         myCallBack = 
            new AsyncCallback(this.OnCompletedRead);
      }

      public static void Main()
      {
         // create an instance of AsynchIOTester
         // which invokes the constructor
         AsynchIOTester theApp = 
            new AsynchIOTester();           

         // call the instance method
         theApp.Run();
      }

      void Run()
      {
         inputStream.BeginRead(
            buffer,             // holds the results
            0,                  // offset
            buffer.Length,      // (BufferSize)
            myCallBack,         // call back delegate
            null);              // local state object

         // do some work while data is read
         for (long i = 0; i < 500000; i++)        
         {
            if (i%1000 == 0)
            {
               Console.WriteLine("i: {0}", i);
            }
         }
            
      }

      // call back method
      void OnCompletedRead(IAsyncResult asyncResult)
      {
         int bytesRead = 
            inputStream.EndRead(asyncResult);

         // if we got bytes, make them a string 
         // and display them, then start up again. 
         // Otherwise, we're done.
         if (bytesRead > 0)
         {
            String s = 
               Encoding.ASCII.GetString(buffer, 0, bytesRead);
            Console.WriteLine(s);
            inputStream.BeginRead(
               buffer, 0, buffer.Length, myCallBack, null);
         }
      }
   }
}