一头学Python:gevent美学原理

gevent

greenlet已经实现了协程,不过这些还的人为切换,是不是觉得太难为了,不要捉急,python还有一个比greenlet更强劲的还要可以活动切换任务的模块gevent

其原理是当一个greenlet遭受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,就机关切换来另外的greenlet,等到IO操作完成,再在适当的时候切换回来继续执行。

出于IO操作非常耗时,日常使程序处于等候状态,有了gevent为我们机关切换协程,就确保总有greenlet在运转,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
可以看出,3个greenlet是逐一运行而不是轮番运行

  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()
运作结果

<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

  1. 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”)
])
运作结果

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() #
将次第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”)
])
运转结果

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

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