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有许多封装好的异步非阻塞IO多路复用框架，底层在linux基于最新的epoll实现，为了更好的使用，了解其底层原理还是有必要的。
下面记录下分别基于Select/Poll/Epoll的echo server实现。
Python Select Server，可监控事件数量有限制：

#!/usr/bin/python
# -*- coding: utf-8 -*-
import select
import socket</span>
import Queueserver = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
server.setblocking(False)
server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR  , 1)
server_address= ('192.168.1.5',8080)
server.bind(server_address)
server.listen(10)#select轮询等待读socket集合
inputs = [server]
#select轮询等待写socket集合
outputs = []
message_queues = {}
#select超时时间
timeout = 20while True:print "等待活动连接......"readable , writable , exceptional = select.select(inputs, outputs, inputs, timeout)if not (readable or writable or exceptional) :print "select超时无活动连接，重新select...... "continue;   #循环可读事件for s in readable :#如果是server监听的socketif s is server:#同意连接connection, client_address = s.accept()print "新连接： ", client_addressconnection.setblocking(0)#将连接加入到select可读事件队列inputs.append(connection)#新建连接为key的字典，写回读取到的消息message_queues[connection] = Queue.Queue()else:#不是本机监听就是客户端发来的消息data = s.recv(1024)if data :print "收到数据：" , data , "客户端：",s.getpeername()message_queues[s].put(data)if s not in outputs:#将读取到的socket加入到可写事件队列outputs.append(s)else:#空白消息，关闭连接print "关闭连接：", client_addressif s in outputs :outputs.remove(s)inputs.remove(s)s.close()del message_queues[s]for s in writable:try:msg = message_queues[s].get_nowait()except Queue.Empty:print "连接：" , s.getpeername() , '消息队列为空'outputs.remove(s)else:print "发送数据：" , msg , "到", s.getpeername()s.send(msg)for s in exceptional:print "异常连接：", s.getpeername()inputs.remove(s)if s in outputs:outputs.remove(s)s.close()del message_queues[s]

Python Poll Server，Select升级版，无可监控事件数量限制，还是要轮询所有事件：

#!/usr/bin/python
# -*- coding: utf-8 -*-
import socket
import select
import Queueserver = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.setblocking(False)
server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_address = ("192.168.1.5", 8080)
server.bind(server_address)
server.listen(5)
print  "服务器启动成功，监听IP：" , server_address
message_queues = {}
#超时，毫秒
timeout = 5000
#监听哪些事件
READ_ONLY = ( select.POLLIN | select.POLLPRI | select.POLLHUP | select.POLLERR)
READ_WRITE = (READ_ONLY|select.POLLOUT)
#新建轮询事件对象
poller = select.poll()
#注册本机监听socket到等待可读事件事件集合
poller.register(server,READ_ONLY)
#文件描述符到socket映射
fd_to_socket = {server.fileno():server,}
while True:print "等待活动连接......"#轮询注册的事件集合events = poller.poll(timeout)if not events:print "poll超时，无活动连接，重新poll......"continueprint "有" , len(events), "个新事件，开始处理......"for fd ,flag in events:s = fd_to_socket[fd]#可读事件if flag & (select.POLLIN | select.POLLPRI) :if s is server :#如果socket是监听的server代表有新连接connection , client_address = s.accept()print "新连接：" , client_addressconnection.setblocking(False)fd_to_socket[connection.fileno()] = connection#加入到等待读事件集合poller.register(connection,READ_ONLY)message_queues[connection]  = Queue.Queue()else :#接收客户端发送的数据data = s.recv(1024)if data:print "收到数据：" , data , "客户端：" , s.getpeername()message_queues[s].put(data)#修改读取到消息的连接到等待写事件集合poller.modify(s,READ_WRITE)else :# Close the connectionprint "  closing" , s.getpeername()# Stop listening for input on the connectionpoller.unregister(s)s.close()del message_queues[s]#连接关闭事件elif flag & select.POLLHUP :print " Closing ", s.getpeername() ,"(HUP)"poller.unregister(s)s.close()#可写事件elif flag & select.POLLOUT :try:msg = message_queues[s].get_nowait()except Queue.Empty:print s.getpeername() , " queue empty"poller.modify(s,READ_ONLY)else :print "发送数据：" , data , "客户端：" , s.getpeername()s.send(msg)#异常事件elif flag & select.POLLERR:print "  exception on" , s.getpeername()poller.unregister(s)s.close()del message_queues[s]</span>

Python Epoll Server，基于回调的事件通知模式，轻松管理大量连接：

#!/usr/bin/python
# -*- coding: utf-8 -*-
import socket, select
import Queueserversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_address = ("192.168.1.5", 8080)
serversocket.bind(server_address)
serversocket.listen(1)
print  "服务器启动成功，监听IP：" , server_address
serversocket.setblocking(0)
timeout = 10
#新建epoll事件对象，后续要监控的事件添加到其中
epoll = select.epoll()
#添加服务器监听fd到等待读事件集合
epoll.register(serversocket.fileno(), select.EPOLLIN)
message_queues = {}fd_to_socket = {serversocket.fileno():serversocket,}
while True:print "等待活动连接......"#轮询注册的事件集合events = epoll.poll(timeout)if not events:print "epoll超时无活动连接，重新轮询......"continueprint "有" , len(events), "个新事件，开始处理......"for fd, event in events:socket = fd_to_socket[fd]#可读事件if event & select.EPOLLIN:#如果活动socket为服务器所监听，有新连接if socket == serversocket:connection, address = serversocket.accept()print "新连接：" , addressconnection.setblocking(0)#注册新连接fd到待读事件集合epoll.register(connection.fileno(), select.EPOLLIN)fd_to_socket[connection.fileno()] = connectionmessage_queues[connection]  = Queue.Queue()#否则为客户端发送的数据else:data = socket.recv(1024)if data:print "收到数据：" , data , "客户端：" , socket.getpeername()message_queues[socket].put(data)#修改读取到消息的连接到等待写事件集合epoll.modify(fd, select.EPOLLOUT)#可写事件elif event & select.EPOLLOUT:try:msg = message_queues[socket].get_nowait()except Queue.Empty:print socket.getpeername() , " queue empty"epoll.modify(fd, select.EPOLLIN)else :print "发送数据：" , data , "客户端：" , socket.getpeername()socket.send(msg)#关闭事件elif event & select.EPOLLHUP:epoll.unregister(fd)fd_to_socket[fd].close()del fd_to_socket[fd]
epoll.unregister(serversocket.fileno())
epoll.close()
serversocket.close()