C#线程处理系列之线程池中的I/O线程

从运行结果可以看出，此时是调用线程池中的I/O线程去执行回调函数的，同时在工程所的的binDebug文件目录下有生成一个text.txt文件，打开文件可以知道里面的内容正是你写入的。

下面演示如何从刚才的文件中异步读取我们写入的内容：

using System;
using System.IO;
using System.Text;
using System.Threading;

namespace AsyncFileRead
{
  class Program
  {
    const int maxsize = 1024;
    static byte[] readbytes = new byte[maxsize];
    static void Main(string[] args)
    {
      ThreadPool.SetMaxThreads(1000, 1000);
      PrintMessage("Main Thread start");

      // 初始化FileStream对象
      FileStream filestream = new FileStream("test.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite, 100, false);

      // 异步读取文件内容
      filestream.BeginRead(readbytes, 0, readbytes.Length, new AsyncCallback(EndReadCallback), filestream);
      Console.Read();
    }

    private static void EndReadCallback(IAsyncResult asyncResult)
    {
      Thread.Sleep(1000);
      PrintMessage("Asynchronous Method start");

      // 把AsyncResult.AsyncState转换为State对象
      FileStream readstream = (FileStream)asyncResult.AsyncState;
      int readlength = readstream.EndRead(asyncResult);
      if (readlength <=0)
      {
        Console.WriteLine("Read error");
        return;
      }

      string readmessage = Encoding.Unicode.GetString(readbytes, 0, readlength);
      Console.WriteLine("Read Message is :" + readmessage);
      readstream.Close();
    }

    // 打印线程池信息
    private static void PrintMessage(String data)
    {
      int workthreadnumber;
      int iothreadnumber;

      // 获得线程池中可用的线程，把获得的可用工作者线程数量赋给workthreadnumber变量
      // 获得的可用I/O线程数量给iothreadnumber变量
      ThreadPool.GetAvailableThreads(out workthreadnumber, out iothreadnumber);

      Console.WriteLine("{0}n CurrentThreadId is {1}n CurrentThread is background :{2}n WorkerThreadNumber is:{3}n IOThreadNumbers is: {4}n",
        data,
        Thread.CurrentThread.ManagedThreadId,
        Thread.CurrentThread.IsBackground.ToString(),
        workthreadnumber.ToString(),
        iothreadnumber.ToString());
    }
  }
}