6.线程、进程、协程基础篇

1.进程是资源分配的最小单位，拥有自己独立的栈和堆，进程间资源不共享，进程是由操作系统调度，一个进程可以开启多个线程；

在python中multiprocess模块提供了Process类，实现进程相关功能。

简单实现：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

from multiprocessing import Process

def func(index):
    print('Process %d' % index)
if __name__ == '__main__':
    for i in range(4):
        p = Process(target=func, args=(i,))
        p.start()

2.线程是cpu调度的最小单位，拥有自己独立的栈和共享的堆，也是由操作系统调度；

python中的 GIL（Global Interpreter Lock），全局解释器锁，首先需要明确的是：GIL并不是python这门语言的特性，它是在CPython解释器引入的一个概念，而python又有很多解释器，CPython解释器是其中最流行的一个，看下图，当python解释器是 CPython时，执行流程为：

（1）线程1获得GIL，线程2没有获得GIL则不能继续执行；

（2）线程1往下走经过操作系统，操作系统经过调度，让cpu1执行；

（3）线程1释放GIL，线程2获得，则线程2按照上面步骤走，循环往复。

结论：当python解释器是CPython时，由于GIL的存在，所以只会有一个线程在执行，不能利用多核cpu，CPython的GIL是历史遗留的一个问题。

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　python代码执行流程图

python中的threading模块实现了Thread类

简单实现：

方式一：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

import threading
import time

def func(index):
    time.sleep(1)
    print('Thread %d' % index)

for i in range(10):
    t = threading.Thread(target=func, args=(i,))
    t.start()

方式二：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

import threading
class MyThreading(threading.Thread):

    def __init__(self,func,arg):
        super(MyThreading,self).__init__()
        self.func = func
        self.arg = arg

    def run(self):
        self.func(self.arg)

def func(index):
    print('Threading %d' % index)

for i in range(10):
    obj = MyThreading(func, i)
    obj.start()

3.协程拥有独立的栈和共享的堆，由程序员在代码中自己调度，通过2的讲解，知道了在CPython解释器中每一时刻只会有一个线程在跑，利用不了多核cpu，但是还存在多线程切换的消耗，所以就出了协程，协程是在一个线程上跑，把一个线程分解成多个“微线程”，实现类似多线程的效果，并且节省了多线程时线程切换的时间。

第三方模块greenlet和gevent实现协程

greenlet实现：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

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()

输出为：
12
56
34
78

gevent实现:

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

from gevent import monkey
monkey.patch_all() #windows下提升io阻塞敏感度,碰到io阻塞快速切换
import gevent
import requests
import time

def func(url):
    print('url: %s' % url)
    resp = requests.get(url)
    data = resp.text
    print('%d bytes received from %s.' % (len(data), url))

start_time = time.time()
gevent.joinall([
        gevent.spawn(func, 'http://www.cnblogs.com/jiangjing/'),
        gevent.spawn(func, 'https://www.cnblogs.com/'),
        gevent.spawn(func, 'https://www.cnblogs.com/f-ck-need-u/p/8409723.html'),
        gevent.spawn(func, 'http://www.cnblogs.com/f-ck-need-u/p/7048359.html'),
        gevent.spawn(func, 'https://www.python.org/'),
])
end_time = time.time()
print('consume time is %d' % (end_time - start_time))

输出为：
url: http://www.cnblogs.com/jiangjing/
url: https://www.cnblogs.com/
url: https://www.cnblogs.com/f-ck-need-u/p/8409723.html
url: http://www.cnblogs.com/f-ck-need-u/p/7048359.html
url: https://www.python.org/
11658 bytes received from http://www.cnblogs.com/jiangjing/.
40828 bytes received from https://www.cnblogs.com/.
30753 bytes received from https://www.cnblogs.com/f-ck-need-u/p/8409723.html.
33181 bytes received from http://www.cnblogs.com/f-ck-need-u/p/7048359.html.
48890 bytes received from https://www.python.org/.
consume time is 1

不使用协程，使用单线程串行执行对比：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/2/3

from gevent import monkey
monkey.patch_all() #windows下提升io阻塞敏感度,碰到io阻塞快速切换
import gevent
import requests
import time

def func(url):
    print('url: %s' % url)
    resp = requests.get(url)
    data = resp.text
    print('%d bytes received from %s.' % (len(data), url))

start_time = time.time()
urls = ['http://www.cnblogs.com/jiangjing/', 'https://www.cnblogs.com/',
        'https://www.cnblogs.com/f-ck-need-u/p/8409723.html',
        'http://www.cnblogs.com/f-ck-need-u/p/7048359.html',
        'https://www.python.org/']
for url in urls:
    func(url)
end_time = time.time()
print('consume time is %d' % (end_time - start_time))

输出为：
url: http://www.cnblogs.com/jiangjing/
11658 bytes received from http://www.cnblogs.com/jiangjing/.
url: https://www.cnblogs.com/
40822 bytes received from https://www.cnblogs.com/.
url: https://www.cnblogs.com/f-ck-need-u/p/8409723.html
30753 bytes received from https://www.cnblogs.com/f-ck-need-u/p/8409723.html.
url: http://www.cnblogs.com/f-ck-need-u/p/7048359.html
33181 bytes received from http://www.cnblogs.com/f-ck-need-u/p/7048359.html.
url: https://www.python.org/
48890 bytes received from https://www.python.org/.
consume time is 2

结论：使用协程执行速度更快