异步select

server coding:

 #!/usr/bin/python
 # -*- coding: utf-8 -*-

 import select
 import socket
 import sys
 import Queue

 # Create a TCP/IP socket
 server = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
 server.setblocking(False)

 # Bind the socket to the port
 server_address = ('localhost',1000)
 print >>sys.stderr, 'starting up on %s port %s'%server_address
 server.bind(server_address)

 # Listen for incoming connections
 server.listen(5)

 # Sockets from which we expect to read
 inputs = [server]

 # Sockets to which we expect to write
 outputs = []

 # Outgoing message queues (socket:Queue)
 message_queues = {}

 while True:
     # Wait for at least one of the sockets to be ready for processing
     print >>sys.stderr, '\nwaiting for the next event'
     #分别筛选出可接收消息的sockets、等待发送消息的sockets、和中途出错的sockets。
     #其中exceptional为了把所有可接收消息的sockets都遍历到，所以要从inputs列表中读取。
     readable, writable, exceptional = select.select(inputs,outputs,inputs)

     # Handle inputs
     for s in readable:
         #第一种情况，创建一个待接收消息的socket放入inputs
         if s is server:
             # A "readable" server socket is ready to accept a connection
             connection, client_address = s.accept()
             print >>sys.stderr, 'new connection from', client_address
             connection.setblocking(0)
             inputs.append(connection)

             # Give the connection a queue for data we want to send
             message_queues[connection] = Queue.Queue()

         #第二种情况，在后续循环中，已经添加到inputs中的sockets已经不是readable了，所以
         #要进行接收消息，消息存在message_queues中，并把该socket添加到outputs。
         else:
             data = s.recv(1024)
             if data:
                 # A readable client socket has data
                 print >>sys.stderr, 'receieved "%s" from %s'%(data.upper(),s.getpeername())
                 message_queues[s].put(data)
                 # Add output channel for response，添加到待发送消息列表
                 if s not in outputs:
                     outputs.append(s)

             #第三种情况就是这个客户端已经断开了，
             #所以你再通过recv()接收到的数据就为空了，
             #所以这个时候你就可以把这个跟客户端的连接关闭了。
             else:
                 print >>sys.stderr, 'closing',client_address,'after reading no data'
                 if s in outputs:
                     outputs.remove(s)#既然客户端都断开了，我就不用再给它返回数据了，所以这时候如果这个客户端的连接对象还在outputs列表中，就把它删掉
                 inputs.remove(s)#inputs中也删除掉
                 s.close()#把这个连接关闭掉

                  # Remove message queue
                 del message_queues[s]

     # Handle outputs
     for s2 in writable:
         try:
             next_msg = message_queues[s2].get_nowait()
         #没有消息了
         except Queue.Empty:
             # No messages waiting so stop checking for writability.
             print >>sys.stderr,'output queue for',s2.getpeername(),'is empty'
             outputs.remove(s2)
         #发送消息
         else:
             print >>sys.stderr, 'sending "%s" to %s'%(next_msg,s2.getpeername())
             s2.send(next_msg)

     # Handle "exceptional conditions"
     for s3 in exceptional:
         print >>sys.stderr, 'handling exceptional condition for ',s3.getpeername()
         # Stop listening for input on the connection
         inputs.remove(s3)
         if s3 in outputs:
             outputs.remove(s3)
         s3.close()

         #Remove message queue
         del message_queues[s3]

client coding

 # -*- coding: utf-8 -*-
 """
 Created on Sun Oct 23 14:49:20 2016

 @author: fuzzier
 """

 import sys
 import socket

 messages = ['This is the message.',
             'It will be sent',
             'in parts.'
             ]
 server_address = ('localhost',1000)

 # Create a TCP/IP socket，创建两个客户端
 socks = [socket.socket(socket.AF_INET,socket.SOCK_STREAM),
          socket.socket(socket.AF_INET,socket.SOCK_STREAM)
          ]

 # Connect the socket to the port where the server is listening
 print >>sys.stderr, 'connecting to %s port %s'%server_address
 for s in socks:
     s.connect(server_address)

 for message in messages:

     # Send messages on both sockets
     for s2 in socks:
         print >>sys.stderr, '%s:sending "%s"'%(s2.getsockname(),message)
         s2.send(message)

     #Read responses on both sockets
     for s3 in socks:
         data = s3.recv(1024)
         print >>sys.stderr, '%s: received "%s"' % (s3.getsockname(), data.upper())
         if not data:
             print >>sys.stderr,'closing socket',s3.getsockname()
             s3.close()

原理图：

运行结果：