如果设计一个服务器程序,每当处理用户请求时,都开始一个线程,将会在一定程序上消耗服务器的资源。为此,一个最好的解决方法就是在服务器启动之前,事先创建一些线程对象,然后,当处理客户端请求时,就从这些建好的线程中获得线程对象,并处理请求。保存这些线程对象的结构就叫做线程池。

    C#中可以通过System.Threading.ThreadPool类来实现,在默认情况下,ThreadPool最大可建立500个工作线程和1000I/O线程(根据机器CPU个数和.net framework版本的不同,这些数据可能会有变化)。下面是一个用C#从线程池获得线程的例子:

private static void execute(object state)
{
     Console.WriteLine(state);      
}
static void Main(string[] args)
{
  
    
int workerThreads;
    
int completionPortThreads;
         
     ThreadPool.GetMaxThreads(
out workerThreads, out completionPortThreads);
     Console.WriteLine(workerThreads);
     Console.WriteLine(completionPortThreads);    
     ThreadPool.QueueUserWorkItem(execute,
"线程1");   // 从线程池中得到一个线程,并运行execute
     ThreadPool.QueueUserWorkItem(execute, "线程2");
     ThreadPool.QueueUserWorkItem(execute,
"线程3");
     Console.ReadLine();
}

 

    下图为上面代码的运行结果。



    要注意的是,使用ThreadPool获得的线程都是后台线程。

    下面的程序是我设计的一个下载文件服务器的例子。这个例子从ThreadPool获得线程,并处理相应的客户端请求。


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Net.Sockets;
using System.IO;

namespace MyThread
{
    
class FileServer
     {
        
private String root;
        
private Thread listenerThread;

        
private void worker(object state)
         {
              TcpClient client
= state as TcpClient;
             
try
              {

                  client.ReceiveTimeout
= 2000;
                  Stream stream
= client.GetStream();
                  System.IO.StreamReader sr
= new StreamReader(stream);
                  String line
= sr.ReadLine();
                  String[] array
= line.Split(' ');
                  String path
= array[1].Replace('/', '\\');
                  String filename
= root + path;
                 
if (File.Exists(filename))  // 如果下载文件存在,开始下载这个文件
                  {
                      FileStream fileStream
= new FileStream(filename, FileMode.Open, FileAccess.Read,
                                                           FileShare.Read);
                     
byte[] buffer = new byte[8192]; // 每次下载8K
                     int count = 0;
                      String responseHeader
= "HTTP/1.1 200 OK\r\n" +
                                             
"Content-Type:application/octet-stream\r\n" +
                                             
"Content-Disposition:attachment;filename=" +
                                                   filename.Substring(filename.LastIndexOf("\\") + 1) + "\r\n\r\n";
                     
byte[] header = ASCIIEncoding.ASCII.GetBytes(responseHeader);
                      stream.Write(header,
0, header.Length);
                     
while ((count = fileStream.Read(buffer, 0, buffer.Count())) > 0)
                      {
                          stream.Write(buffer,
0, count);
                      }
                      Console.WriteLine(filename
+ "下载完成");
                  }
                 
else  // 文件不存在,输出提示信息
                  {
                      String response
= "HTTP/1.1 200 OK\r\nContent-Type:text/plain;charset=utf-8\r\n\r\n文件不存在";
                     
byte[] buffer = ASCIIEncoding.UTF8.GetBytes(response);
                      stream.Write(buffer,
0, buffer.Length);
                  }

              }
             
catch (Exception e)
              {
                  Console.WriteLine(e.Message);
              }
             
finally
              {
                 
if (client != null)
                  {
                      client.Close();
                  }
              }
         }

        
private void listener()
         {
             TcpListener listener
= new TcpListener(1234);
             listener.Start();  
// 开始监听客户端请求
             TcpClient client = null;

            
while (true)
             {
                 client
= listener.AcceptTcpClient();
                 client.ReceiveTimeout
=2000;
                 ThreadPool.QueueUserWorkItem(worker, client);  
// 从线程池中获得一个线程来处理客户端请求
             }
         }
        
public FileServer(String root)
         {
            
this.root= root;        
         }
        
public void start()
         {
             listenerThread
= new Thread(listener);
             listenerThread.Start();  
// 开始运行监听线程
         }
     }
}


    FileServer类的使用方法:

    FileServer fs = new FileServer(“d:\\download”);

fs.start(); // 端口为1234

如果d:"download目录中有一个叫aa.exe的文件,在浏览器中输入如下的地址可下载:
    http://localhost:1234/aa.exe

下图为下载对话框:

要注意的是,本程序并没有处理含有中文和其他特殊字符(如空格)的url,因为,文件名要为英文名(不能有空格等特殊字符)。