Question

greenlet已经实现了协程，但是这个还的人工切换，是不是觉得太麻烦了，不要捉急，python还有一个比greenlet更强大的并且能够自动切换任务的模块gevent

其原理是当一个greenlet遇到IO(指的是input output 输入输出，比如网络、文件操作等)操作时，比如访问网络，就自动切换到其他的greenlet，等到IO操作完成，再在适当的时候切换回来继续执行。

由于IO操作非常耗时，经常使程序处于等待状态，有了gevent为我们自动切换协程，就保证总有greenlet在运行，而不是等待IO

安装

pip3 install gevent

1. gevent的使用

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()

运行结果

<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

可以看到，3个greenlet是依次运行而不是交替运行

2. 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

3. 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")
])

运行结果

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