select

服务器端

#!/usr/bin/env 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(0)#设置0就是非阻塞模式，1就是阻塞模式

# Bind the socket to the port
server_address = ('localhost', 10000)
print >> sys.stderr, 'starting up on %s port %s' % server_address
server.bind(server_address)

# Listen for incoming connections
server.listen(5)#最大允许的连接数是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 inputs:#死循环

    # Wait for at least one of the sockets to be ready for processing
    print >>sys.stderr, '
waiting for the next event'
    readable, writable, exceptional = select.select(inputs, outputs, inputs)#第三个是错误信息，这个select就是要检测是否有就绪的文件描述符


    # Handle inputs
    for s in readable:#找出已经就绪的连接

        if s is server:#如果此时是一个新链接
            # 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()#每个连接一个q,保证独立不乱

        else:#此时是老连接，开始接收数据
            data = s.recv(1024)
            if data:
                # A readable client socket has data
                print >> sys.stderr, 'received "%s" from %s' % (data, s.getpeername())
                message_queues[s].put(data)
                # Add output channel for response
                if s not in outputs:
                    outputs.append(s)
                else:
                    # Interpret empty result as closed connection
                    print >> sys.stderr, 'closing', client_address, 'after reading no data'
                    # Stop listening for input on the connection
                    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 s in writable:
        try:
            next_msg = message_queues[s].get_nowait()
        except Queue.Empty:
            # No messages waiting so stop checking for writability.
            print >>sys.stderr, 'output queue for', s.getpeername(), 'is empty'
            outputs.remove(s)
        else:
            print >>sys.stderr, 'sending "%s" to %s' % (next_msg, s.getpeername())
            s.send(next_msg)

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

        # Remove message queue
        del message_queues[s]

客户端

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

import socket
import sys

messages = ['This is the message. ',
            'It will be sent ',
            'in parts.',
            ]
server_address = ('localhost', 10000)

# Create a TCP/IP socket
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 s in socks:
        print >> sys.stderr, '%s: sending "%s"' % (s.getsockname(), message)
        s.send(message)

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