socket之IO多路复用

概述

　　目的：同一个线程同时处理多个IO请求。

　　本文以python的select模块来实现socket编程中一个server同时处理多个client请求的问题。

　　web框架tornado就是以此实现多客户端连接问题的。以下为select源码说明：

def select(rlist, wlist, xlist, timeout=None): # real signature unknown; restored from __doc__
    """
    select(rlist, wlist, xlist[, timeout]) -> (rlist, wlist, xlist)

    Wait until one or more file descriptors are ready for some kind of I/O.
    The first three arguments are sequences of file descriptors to be waited for:
    rlist -- wait until ready for reading
    wlist -- wait until ready for writing
    xlist -- wait for an ``exceptional condition''
    If only one kind of condition is required, pass [] for the other lists.
    A file descriptor is either a socket or file object, or a small integer
    gotten from a fileno() method call on one of those.

    The optional 4th argument specifies a timeout in seconds; it may be
    a floating point number to specify fractions of seconds.  If it is absent
    or None, the call will never time out.

    The return value is a tuple of three lists corresponding to the first three
    arguments; each contains the subset of the corresponding file descriptors
    that are ready.

    *** IMPORTANT NOTICE ***
    On Windows and OpenVMS, only sockets are supported; on Unix, all file
    descriptors can be used.
    """
    pass

# classes

实例1

server端

#!/usr/bin/env python
#-*- coding:utf-8 -*-
import socket
import select
ss = socket.socket()
ss.bind(("localhost",8000))
ss.listen(5)
ss.setblocking(False)

inputs = [ss]
while True:
    rList,wList,e = select.select(inputs,[],[],2)
    print "inputs:", inputs
    print "resaults:", rList
    for r in rList:
        if r == ss:
            con,addr = r.accept()
            inputs.append(con)
        else:

            try:
                data = r.recv(1024)
            except socket.error,e:
                inputs.remove(r)
            else:
                r.send(data)

server

client端

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

sc = socket.socket()
sc.connect(("localhost",8000))
while True:
    data = raw_input("Input:")
    sc.sendall(data)
    print sc.recv(1024)
sc.close()

client

操作步骤

1. 启动server
2. 启动client，并输入：123
3. 再次启动client，并输入：345

操作结果：

• client1

Input:123
123
Input:

• client2

Input:345
345
Input:

• server端

#启动server，不启动client，select监听的句柄为：ss_70,无变化，select监听结果：resaults = []
inputs: [<socket._socketobject object at 0x0241FC70>]
resaults: []
#启动client，句柄ss_FC70连接了客户端，select将监听到的变化的句柄返回，rList=[ss_70]
inputs: [<socket._socketobject object at 0x0241FC70>]
resaults: [<socket._socketobject object at 0x0241FC70>]
#将ss.accept()得到的客户端句柄conn_A8追加至监听列表,inputs = [ss_70,conn_A8,]，当client不发送请求时，select监听的inputs列表中的句柄没有发生变化，返回列表resaults=[]
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>]
resaults: []
#client发送信息时，server端select监听的inputs列表中conn_A8句柄发生变化，select返回监听结果：rList = [conn_A8]
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>]
resaults: [<socket._socketobject object at 0x0241FCA8>]
#在无client连接和没有已连接的客户端发送消息，select所监听的inputs列表无增加，返回列表rList为空
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>]
resaults: []
#client项server发送消息，select监听列表中客户端句柄conn_A8发生变化，select监听返回结果rList=[conn_A8]
inputs: [<socket._socketobject object at 0x024DFC70>, <socket._socketobject object at 0x024DFCA8>]
resaults: [<socket._socketobject object at 0x024DFCA8>]

#接下来就有意思了，保持第一个客户端不断开，再打开第二个客户端client2，句柄ss_70发生变化（我们在服务端只创建了一个socket实例），又会产生一个新的client2的回话句柄conn_E0,追加至select监听列表inputs中
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>]
resaults: [<socket._socketobject object at 0x0241FC70>]
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>, <socket._socketobject object at 0x0241FCE0>]
resaults: []
#client2向server端发送消息，client2的回话句柄conn_E0发生变化，被返回，rList=[conn_E0]
inputs: [<socket._socketobject object at 0x0241FC70>, <socket._socketobject object at 0x0241FCA8>, <socket._socketobject object at 0x0241FCE0>]
resaults: [<socket._socketobject object at 0x0241FCE0>]

实例2

#!/usr/bin/env python
#-*- coding:utf-8 -*-
import socket
import select
import Queue
ss = socket.socket()
ss.bind(("localhost",8000))
ss.listen(5)
#设置为False，accept接受消息时为非阻塞
ss.setblocking(False)
#selec监听列表，若列表中哪个句柄发生变化，返回个readAble，否则readAble列表为空
rList = [ss]
#写列表，writeAble == wList，二者相等，select返回值即wList的值
wList = []
#定义一个字典，key:客户端句柄，value：接收和发送的消息队列；用于收和发之间共享数据
msg_queues = {}
while True:
    readAble,writeAble,e = select.select(rList,wList,[],2)
    for r in readAble:
        if r == ss:
            conn,addr = r.accept()
            rList.append(conn)
        else:
            #创建接收的消息队列
            msg_queues[r] = Queue.Queue()
            try:
                data = r.recv(1024)
            #客户端断开连接会抛出：socket.error 10054异常，将此客户端连接句柄从select监听列表中移除
            except socket.error,e:
                rList.remove(r)
            else:
                #将接收到的消息加入句柄所对应的队列中
                msg_queues[r].put(data)
                #如果此client句柄wList列表不存在，就加入wList列表
                if r not in wList:
                    wList.append(r)
    for w in wList:
        try:
            w.sendall(msg_queues[w].get_nowait())
        except Queue.Empty:
            pass
        #因为select监听wList时，只要wList列表中有，就返回wList中所有的句柄，所以使用完后需要删除
        wList.remove(w)
        del msg_queues[w]

select