Home Backend Development Python Tutorial Python中使用select模块实现非阻塞的IO

Python中使用select模块实现非阻塞的IO

Jun 06, 2016 am 11:21 AM
io python non-blocking

Socket的英文原义是“孔”或“插座”。作为BSD UNIX的进程通信机制,取后一种意思。通常也称作”套接字”,用于描述IP地址和端口,是一个通信链的句柄。在Internet上的主机一般运行了多个服务软件,同时提供几种服务。每种服务都打开一个Socket,并绑定到一个端口上,不同的端口对应于不同的服务。Socket正如其英文原意那样,像一个多孔插座。一台主机犹如布满各种插座的房间,每个插座有一个编号,有的插座提供220伏交流电, 有的提供110伏交流电,有的则提供有线电视节目。 客户软件将插头插到不同编号的插座,就可以得到不同的服务。–百度百科

socket如此重要,现在的网络编程几乎都是用的它,它起源于Unix,而Unix/Linux基本哲学之一就是“一切皆文件”,都可以用打开,读写,关闭的模式来操作。然而,对于网络服务来说,往往针对大量的客户群体,例如web,对于这类服务,必须要保证既能并行处理请求,又能保证服务的稳定。但传统的socket在处理并发方面有所欠缺,借助与select模块,能够较好的是要非阻塞的IO。

Python中的select模块以列表形式接受四个参数,分别是需要监控的可读文件对象,可写文件对象,产生异常的文件对象和超时设置,当监控的对象发生变化时,select会返回发生变化的对象列表。下面是用select实现一个简单的聊天室:

#!/usr/bin/env python
#*-* coding:utf-8 *-*
import socket
import select
import sys
import signal
class ChatServer():
  def __init__(self,host,port,timeout=10,backlog=5):
    #记录连接的客户端数量
    self.clients =0
    #存储连接的客户端socket和地址对应的字典
    self.clientmap={}
    #存储连接的客户端socket
    self.outputs = []
    #建立socket
    self.server=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
    self.server.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
    self.server.bind((host,port))
    self.server.listen(backlog)
    #增加信号处理
    signal.signal(signal.SIGINT,self.sighandler) 
  def sighandler(self):
    sys.stdout.write("Shutdown Server......\n")
    #向已经连接客户端发送关系信息,并主动关闭socket
    for output in self.outputs:
      output.send("Shutdown Server")
      output.close()
    #关闭listen
    self.server.close()
    sys.stdout.flush()
  #主函数,用来启动服务器
  def run(self):
    #需要监听的可读对象
    inputs=[self.server]
    
    runing=True
    #添加监听主循环
    while runing:
      try:
        readable,writeable,exceptional = select.select(inputs,self.outputs,[])
        #此处会被select模块阻塞,只有当监听的三个参数发生变化时,select才会返回
      except select.error,e:
        break
      #当返回的readable中含有本地socket的信息时,表示有客户端正在请求连接
      if self.server in readable:
        #接受客户端连接请求
        client,addr=self.server.accept()
        sys.stdout.write("New Connection from %s\n"%str(addr))
        sys.stdout.flush()
        #更新服务器上客户端连接情况
        #1,数量加1
        #2,self.outputs增加一列
        #3,self.clientmap增加一对
        #4, 给input添加可读监控
        self.clients += 1
        self.outputs.append(client)
        self.clientmap[client]=addr
        inputs.append(client)
      
      #readable中含有已经添加的客户端socket,并且可读
      #说明 1,客户端有数据发送过来或者 2,客户端请求关闭
      elif len(readable) != 0:
        #1, 取出这个列表中的socket
        csock=readable[0]
        #2, 根据这个socket,在事先存放的clientmap中,去除客户端的地址,端口的详细信息
        host,port = self.clientmap[csock]
        #3,取数据, 或接受关闭请求,并处理
        #注意,这个操作是阻塞的,但是由于数据是在本地缓存之后,所以速度会非常快
        try:
          data = csock.recv(1024).strip()
          for cs in self.outputs:
            if cs != csock:
              cs.send("%s\n"%data)
        except socket.error,e:
          self.clients -= 1
          inputs.remove(csock)
          self.outputs.remove(csock)
          del self.clientmap[csock]
      #print self.outputs
    self.server.close()
        
if __name__ == "__main__":
  chat=ChatServer("",8008)
  chat.run()

Copy after login

运行这个脚本,然后用任意客户端如telnet或netcat连接8008端口,多个客户端之间就可以进行对话。

其实select模块本身是阻塞的,当需要监控的socket发生变化时,select作出返回,下面的程序会继续执行,程序根据select的返回值,对各种情况作出处理。

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