学步园

参考： http://www.cnblogs.com/snailrun/p/3805188.html

异步网络据说能极大的提高网络server的连接速度,所以打算写一个专题,来学习和了解异步网络.因为Python有个非常出名的异步Lib:Twisted,所以就用Python来完成. 

OK,首先写一个pythone socket的server段,对开放三个端口:10000,10001,10002.krondo的例子中是每个server绑定一个端口,测试的时候需要分别开3个shell,分别运行.这太麻烦了,就分别用三个Thread来运行这些services. 

import optparse
import os
import socket
import time
from threading import Thread
from io import StringIO

txt = '''1111
2222
3333
4444
'''

# 服务端程序处理过程
def server(listen_socket):
	while True:
		buf = StringIO(txt)
		sock, addr = listen_socket.accept()
		print('Somebody at %s wants poetry!' %(addr,))
		while True:
			try:
				line = buf.readline().strip()
				if not line:
					sock.close()
					break
				sock.sendall(line.encode('utf8')) # this is a blocking call
				print('send bytes to client: %s' %line)
			except socket.error:
				sock.close()
				break
			time.sleep(0.5) # server每发送一个单词后等待一会
		sock.close()
		print('\n')

# 同时开启三个服务端线程，分别在三个端口监听
# 服务端程序为阻塞方式，只能一次服务于一个客户端
def main():
	ports = [10000, 10001, 10002]
	for port in ports:
		listen_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
		listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
		addres = ('127.0.0.1', port)
		listen_socket.bind(addres)
		listen_socket.listen(5)
		print("start listen at: %d" %port)
		worker = Thread(target = server, args = [listen_socket])
		worker.setDaemon(True)
		worker.start()

if __name__ == '__main__':
	main()
	while True:
		time.sleep(0.1) # 如果不sleep的话, CPU会被Python完全占用了

下面是一个client, 用阻塞方式，先后连接这个三个端口的server: 

from socket import *

# 建立三个客户端，分别连接三个不同的服务端程序, 接收服务端传过来的数据并打印
# 这三个客户端是阻塞方式通信的
if __name__ == '__main__':
	ports = [10000, 10001, 10002]
	for port in ports:
		address = ('127.0.0.1', port)
		sock = socket(AF_INET, SOCK_STREAM)
		sock.connect(address)
		poem = ''
		while True:
			data = sock.recv(4)
			if not data:
				sock.close()
				break
			poem += data.decode('utf8')
		print(poem)
		sock.close()

下面用异步的client来读取，代码如下：

import datetime, errno, optparse, select, socket

def connect(port):
	"""Connect to the given server and return a non-blocking socket."""
	address = ('127.0.0.1', port)
	sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
	sock.connect(address)
	sock.setblocking(0)		# 设置为非阻塞模式
	return sock

def format_address(address):
	host, port = address
	return '%s:%s' % (host or '127.0.0.1', port)

if __name__ == '__main__':
	ports = [10000, 10001, 10002]
	start = datetime.datetime.now()

	sockets = list(map(connect, ports))
	poems = dict.fromkeys(sockets, '') # socket -> accumulated poem
	sock2task = dict([(s, i + 1) for i, s in enumerate(sockets)])

	while sockets:
		#运用select来确保那些可读取的异步socket可以立即开始读取IO
		#OS不停的搜索目前可以read的socket，有的话就返回rlist
		rlist, _, _ = select.select(sockets, [], [])
		for sock in rlist:
			data = ''
			while True:
				try:
					new_data = sock.recv(1024)
					new_data = new_data.decode('utf8')
				except socket.error as e:
					if e.args[0] == errno.EWOULDBLOCK:
						break
					raise
				else:
					if not new_data:
						break
					else:
						print(new_data)
						data += new_data

			task_num = sock2task[sock]
			if not data:
				print(poems[sock])	# 打印sock接收到的数据
				sockets.remove(sock)
				sock.close()
				print('Task %d finished\n' % task_num)
			else:
				addr_fmt = format_address(sock.getpeername())
				msg = 'Task %d: got %d bytes of poetry from %s\n'
				print(msg % (task_num, len(data), addr_fmt))

			poems[sock] += data		# 保存每个sock接收到的数据

	elapsed = datetime.datetime.now() - start
	print('Got poems in %s' %elapsed)

结果只需要2秒就完成了读取任务。效率非常明显啊。对客户端的异步改造主要有两点： 

• 同步模式下，客户端分别创建socket；而在异步模式下，client开始就创建了所有的socket。
• 通过“sock.setblocking(0)”设置socket为异步模式。
• 通过Unix系统的select来返回可读取socket信息
• 最为核心的是8行和26行。尤其是26行的select操作返回待读取socket的列表。