【Pyhton Network】使用poll()或select()实现非阻塞传输

通常情况下，socket上的I/O会阻塞。即除非操作结束，否则程序不会照常进行。而以下集中情况需要在非阻塞模式下进行：
1. 网络接口在等待数据时是活动的，可以做出相应；
2. 在不使用线程或进程的情况下也可以同时处理多个网络相关任务；
3. 在网络上等待的时候可以执行其它计算
在以上情况中，可以使用两个标准工具解决，poll和select。它们都可以通知操作系统哪个socket对程序感兴趣，当该socket上有事件发生时，操作系统才调用处理程序。
服务器程序每隔5秒向连接对象发送系统当前时间，如下：

#! /usr/bin/env python
# Nonblocking I/O with select() - Chapter 5 - selectclient.py

import socket, sys, select

host = 'localhost'
port = 51423

spinsize = 10
spinpos = 0
spindir = -1

def spin():
global spinsize, spinpos, spindir
spinstr = '.'*spinpos + '|' + '.'*(spinsize-spinpos-1)
sys.stdout.write('\r'+spinstr+' ')
sys.stdout.flush()

spinpos += spindir
if spinpos < 0:
spinpos = 1
spindir = 1
elif spinpos >= spinsize:
spinpos -= 2
spindir = -1

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.connect((host, port))

while 1:
infds, outfds, errfds = select.select([s], [], [s], 0.05) # [s] just the same as[s.fileno()], only need to be a list.
if len(infds):
# Normally, one would use something like "for fd in infds" here.
# We don't bother since there will only ever be a single file
# descriptor here.
data = s.recv(4096)
if not len(data):
print "\rRemote and closed connection; exiting."
break
# Only one item in here -- if there's anything, it's for us.
sys.stdout.write("\rReceived: "+data)
sys.stdout.flush
if len(errfds):
print "\rProblem occurred; exiting."
sys.exit(0)
spin()

View Code
运行截图如下：