Python—–笑谈协程

Python—–笑谈协程
1. 协程
​ 协程又称微线程,迁程。Coroutine

​ 协程是python中另外一种实现多任务的方式,只不过比线程占用更小的执行单元。

​ 在一个线程中的某个函数,可以在任何地方保存当前函数的一些临时变量等信息,然后切换到另外一个函数中执行,注意不是通过调用函数的方式做到的,并且切换的次数以及什么时候再切换到原来的函数都由开发者自己确定

2. 协程和线程的差异
​ 实现多任务时,线程切换从系统层面远不止保存和恢复CPU上下文这么简单。操作系统为了程序运行的高效性,每个线程都有自己缓存Cache等数据,操作系统还会帮你做这些数据的恢复工作。所以线程的切换非常耗性能。

​ 但是,协程的切换只是单纯的操作CPU的上下文,一秒钟切换个上百万次系统都可以

import time
def work1():
while True:
print(“—-work1—“)
yield
time.sleep(0.5)
def work2():
while True:
print(“—-work2—“)
yield
time.sleep(0.5)
def main():
w1 = work1()
w2 = work2()
while True:
next(w1)
next(w2)
if __name__ == “__main__”:
main()

—-work1—
—-work2—
—-work1—
—-work2—
—-work1—
—-work2—
—-work1—
—-work2—
—-work1—
—-work2—
—-work1—
—-work2—
…省略…

3. greenlet
from greenlet import greenlet
import time
def test1():
while True:
print “—A–”
gr2.switch()
time.sleep(0.5)
def test2():
while True:
print “—B–”
gr1.switch()
time.sleep(0.5)
gr1 = greenlet(test1)
gr2 = greenlet(test2)
#切换到gr1中运⾏
gr1.switch()

4. gevent
​ greenlet已经实现了协程,但是还是需要人工切换。

​ gevent模块可以实现自动切换

import gevent
def f(n):
for i in range(n):
print(gevent.getcurrent(), i)
g1 = gevent.spawn(f, 5)
g2 = gevent.spawn(f, 5)
g3 = gevent.spawn(f, 5)
g1.join()
g2.join()
g3.join()

实现结果:
<Greenlet at 0x10e49f550: f(5)> 0
<Greenlet at 0x10e49f550: f(5)> 1
<Greenlet at 0x10e49f550: f(5)> 2
<Greenlet at 0x10e49f550: f(5)> 3
<Greenlet at 0x10e49f550: f(5)> 4
<Greenlet at 0x10e49f910: f(5)> 0
<Greenlet at 0x10e49f910: f(5)> 1
<Greenlet at 0x10e49f910: f(5)> 2
<Greenlet at 0x10e49f910: f(5)> 3
<Greenlet at 0x10e49f910: f(5)> 4
<Greenlet at 0x10e49f4b0: f(5)> 0
<Greenlet at 0x10e49f4b0: f(5)> 1
<Greenlet at 0x10e49f4b0: f(5)> 2
<Greenlet at 0x10e49f4b0: f(5)> 3
<Greenlet at 0x10e49f4b0: f(5)> 4

4.1 gevent切换执行
import gevent
def f(n):
for i in range(n):
print(gevent.getcurrent(), i)
#⽤来模拟⼀个耗时操作, 注意不是time模块中的sleep
gevent.sleep(1)
g1 = gevent.spawn(f, 5)
g2 = gevent.spawn(f, 5)
g3 = gevent.spawn(f, 5)
g1.join()
g2.join()
g3.join()

运行结果:
<Greenlet at 0x7fa70ffa1c30: f(5)> 0
<Greenlet at 0x7fa70ffa1870: f(5)> 0
<Greenlet at 0x7fa70ffa1eb0: f(5)> 0
<Greenlet at 0x7fa70ffa1c30: f(5)> 1
<Greenlet at 0x7fa70ffa1870: f(5)> 1
<Greenlet at 0x7fa70ffa1eb0: f(5)> 1
<Greenlet at 0x7fa70ffa1c30: f(5)> 2
<Greenlet at 0x7fa70ffa1870: f(5)> 2
<Greenlet at 0x7fa70ffa1eb0: f(5)> 2
<Greenlet at 0x7fa70ffa1c30: f(5)> 3
<Greenlet at 0x7fa70ffa1870: f(5)> 3
<Greenlet at 0x7fa70ffa1eb0: f(5)> 3
<Greenlet at 0x7fa70ffa1c30: f(5)> 4
<Greenlet at 0x7fa70ffa1870: f(5)> 4
<Greenlet at 0x7fa70ffa1eb0: f(5)> 4

4.2 给程序打补丁
from gevent import monkey
import gevent
import random
import time

def coroutine_work(coroutine_name):
for i in range(10):
print(coroutine_name, i)
time.sleep(random.random())
gevent.joinall([
gevent.spawn(coroutine_work, “work1”),
gevent.spawn(coroutine_work, “work2”)
])

运行结果
work1 0
work1 1
work1 2
work1 3
work1 4
work1 5
work1 6
work1 7
work1 8
work1 9
work2 0
work2 1
work2 2
work2 3
work2 4
work2 5
work2 6
work2 7
work2 8
work2 9

from gevent import monkey
import gevent
import random
import time
# 有耗时操作时需要
monkey.patch_all() # 将程序中⽤到的耗时操作的代码, 换为gevent中⾃⼰实现的模块
def coroutine_work(coroutine_name):
for i in range(10):
print(coroutine_name, i)
time.sleep(random.random())
gevent.joinall([
gevent.spawn(coroutine_work, “work1”),
gevent.spawn(coroutine_work, “work2”)
])

实现结果:
work1 0
work2 0
work1 1
work1 2
work1 3
work2 1
work1 4
work2 2
work1 5
work2 3
work1 6
work1 7
work1 8
work2 4
work2 5
work1 9
work2 6
work2 7
work2 8
work2 9

5. 总结
进程是资源分配的单位
线程是操作系统调度的单位
进程切换需要的资源很*大,效率很低
线程切换需要的资源一般,效率一般
协程切换任务资源很小,效率高
多进程、多线程根据CPU核数不一样可能是并行的,也可能是并发的。
协程的本质就是使用当前进程在不同的函数代码中切换执行,可以理解为并行。
协程是一个用户层面的概念,不同协程的模型实现可能是单线程也就可能是多线程