day10---异步I/O，gevent协程

协程

协程，又称微线程，纤程。英文名Coroutine。一句话说明什么是线程：协程是一种用户态的轻量级线程。

协程拥有自己的寄存器上下文和栈。协程调度切换时，将寄存器上下文和栈保存到其他地方，在切回来的时候，恢复先前保存的寄存器上下文和栈。因此：

协程能保留上一次调用时的状态（即所有局部状态的一个特定组合），每次过程重入时，就相当于进入上一次调用的状态，换种说法：进入上一次离开时所处逻辑流的位置。

协程的好处：

• 无需线程上下文切换的开销
• 无需原子操作锁定及同步的开销
• 方便切换控制流，简化编程模型
• 高并发+高扩展性+低成本：一个CPU支持上万的协程都不是问题。所以很适合用于高并发处理。

缺点：

• 无法利用多核资源：协程的本质是个单线程,它不能同时将 单个CPU 的多个核用上,协程需要和进程配合才能运行在多CPU上.当然我们日常所编写的绝大部分应用都没有这个必要，除非是cpu密集型应用。
• 进行阻塞（Blocking）操作（如IO时）会阻塞掉整个程序

使用yield实现协程操作例子　　　　

import time
import queue
def consumer(name):
    print("--->starting eating baozi...")
    while True:
        new_baozi = yield
        print("[%s] is eating baozi %s" % (name,new_baozi))
        #time.sleep(1)

def producer():

    r = con.__next__()
    r = con2.__next__()
    n = 0
    while n < 5:
        n +=1
        con.send(n)
        con2.send(n)
        print("\033[32;1m[producer]\033[0m is making baozi %s" %n )

if __name__ == '__main__':
    con = consumer("c1")
    con2 = consumer("c2")
    p = producer()

#!/usr/bin/env python
#-*- coding:utf-8 -*-
# Author:DCC
from greenlet import greenlet
import gevent
'''
def test1():
    print(12)
    gr2.switch()
    print(34)
    gr2.switch()
def test2():
    print(56)
    gr1.switch()
    print(78)
gr1 = greenlet(test1)
gr2 = greenlet(test2)
gr1.switch()
'''
def foo():
    print("Running in foo")
    gevent.sleep(4)
    print("switch to foo")
def bar():
    print("Running in bar")
    gevent.sleep(1)
    print("已经调到bar")
def func3():
    print("Running in func3")
    gevent.sleep(2)
    print("func3 again")

gevent.joinall([
    gevent.spawn(foo),
    gevent.spawn(bar),
    gevent.spawn(func3),
])

遇到IO阻塞时会自动切换任务

爬虫

#!/usr/bin/env python
#-*- coding:utf-8 -*-
# Author:DCC
from urllib import request
import  gevent,time
from gevent import monkey
monkey.patch_all()#把当前程序的所有的IO操作单独做上标记
#之前 gevent是不是捕获 urllib的IO操作的，所有，无法进行切换
def f(url):
    print("GET: %s" % url)
    resp = request.urlopen(url)
    data = resp.read()
    print("%d bytes received from %s." % (len(data),url))

urls = [
    "https://www.python.org/",
    "https://www.yahoo.com/",
    "https://github.com/"
]
start_time = time.time()
for url in urls:
    f(url)
print("同步cost",time.time()-start_time)
async_start_time = time.time()
gevent.joinall([
    gevent.spawn(f,"https://www.python.org/"),
    gevent.spawn(f,"https://www.yahoo.com/"),
    gevent.spawn(f,"https://github.com/"),
])
print("异步cost",time.time()-async_start_time)

通过gevent实现单线程下的多socket并发

server side

import sys
import socket
import time
import gevent

from gevent import socket,monkey
monkey.patch_all()

def server(port):
    s = socket.socket()
    s.bind(('0.0.0.0', port))
    s.listen(500)
    while True:
        cli, addr = s.accept()
        gevent.spawn(handle_request, cli)

def handle_request(conn):
    try:
        while True:
            data = conn.recv(1024)
            print("recv:", data)
            conn.send(data)
            if not data:
                conn.shutdown(socket.SHUT_WR)

    except Exception as  ex:
        print(ex)
    finally:
        conn.close()
if __name__ == '__main__':
    server(8001)

client side 

import socket

HOST = 'localhost'    # The remote host
PORT = 8001           # The same port as used by the server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
while True:
    msg = bytes(input(">>:"),encoding="utf8")
    s.sendall(msg)
    data = s.recv(1024)
    #print(data)

    print('Received', repr(data))
s.close()