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@Author： runsen

协程是实现并发编程的一种方式。

https://docs.python.org/zh-cn/3/library/asyncio.html

一说并发，你肯定想到了多线程 ， 多进程模型，没错，多线程 和 多进程，正是解决并发问题的经典模型之一

但是你了解过协程Coroutine吗？

协程：是单线程下的并发，又称微线程。

就是只有一个线程，如何提高速度，解决并发编程

英文名Coroutine。

协程比线程的单位更小——协程

注意协程这个概念完全是程序员自己想出来的东西，它对于操作系统来说根本不存在。操作系统只有进程和线程。

从一个demo学起

import time 

def print_num(num):
    print("Maoli is printing " + str(num) + " nows" )
    time.sleep(1)
    print("Maoli prints" + str(num) + " OK")

def main(nums):
    for num in nums:
        print_num(num)
%time main([i for i in range(1,6)])


Maoli is printing 1 nows
Maoli prints1 OK
Maoli is printing 2 nows
Maoli prints2 OK
Maoli is printing 3 nows
Maoli prints3 OK
Maoli is printing 4 nows
Maoli prints4 OK
Maoli is printing 5 nows
Maoli prints5 OK
Wall time: 5 s

%time 需要在jupyter notebook中运行。

上面代码是从上到下执行的。

下面将上面代码改为协程版

注意py版本3.7以上，主要使用的是asyncio

import asyncio

async def print_num(num):
    print("Maoli is printing " + str(num) + " nows" )
    await asyncio.sleep(1)
    print("Maoli prints" + str(num) + " OK")

async def main(nums):
    for num in nums:
        await print_num(num)
%time asyncio.run(main([i for i in range(1,6)]))


Maoli is printing 1 nows
Maoli prints1 OK
Maoli is printing 2 nows
Maoli prints2 OK
Maoli is printing 3 nows
Maoli prints3 OK
Maoli is printing 4 nows
Maoli prints4 OK
Maoli is printing 5 nows
Maoli prints5 OK
Wall time: 5.01 s

asyncio.run() 函数用来运行最高层级的入口点 "main()" 函数

await 是同步调用等待一个协程。以下代码段会在等待 1 秒后打印 num，速度上没有发生改变。

需要引入asyncio.create_task才可以

可等待对象

如果一个对象可以在 await 语句中使用，那么它就是 可等待 对象

协程中的还一个重要概念，任务（Task）

如果写一个数字是一个任务，那么毛利我要完成5个任务

毛利我写个1-5都这么慢，不行，我要加速写

asyncio.create_task() 函数用来并发运行作为 asyncio 任务 的多个协程。

import asyncio

async def print_num(num):
    print("Maoli is printing " + str(num) + " nows" )
    await asyncio.sleep(1)
    print("Maoli prints" + str(num) + " OK")

async def main(nums):
    tasks = [asyncio.create_task(print_num(num)) for num in nums]
    for task in tasks:
        await task
%time asyncio.run(main([i for i in range(1,6)]))


Maoli is printing 1 nows
Maoli is printing 2 nows
Maoli is printing 3 nows
Maoli is printing 4 nows
Maoli is printing 5 nows
Maoli prints1 OK
Maoli prints3 OK
Maoli prints5 OK
Maoli prints2 OK
Maoli prints4 OK
Wall time: 1.01 s

还可以写成await asyncio.gather(*tasks)这种方法

import asyncio

async def print_num(num):
    print("Maoli is printing " + str(num) + " nows" )
    await asyncio.sleep(1)
    print("Maoli prints" + str(num) + " OK")

async def main(nums):
    tasks = [asyncio.create_task(print_num(num)) for num in nums]
    await asyncio.gather(*tasks)
%time asyncio.run(main([i for i in range(1,6)]))

*tasks 解包列表，将列表变成了函数的参数；与之对应的是， ** dict 将字典变成了函数的参数。

asyncio 队列

asyncio也是只有在Pytohn3.7才有的东西。

asyncio 队列被设计成与 queue 模块类似。

import asyncio
import random

async def consumer(queue, id):
    while True:
        val = await queue.get()
        print('{} get a val: {}'.format(id, val))
        await asyncio.sleep(1)

async def producer(queue, id):
    for i in range(5):
        val = random.randint(1, 10)
        await queue.put(val)
        print('{} put a val: {}'.format(id, val))
        await asyncio.sleep(1)

async def main():
    # 创建队列
    queue = asyncio.Queue()
    # 消费者1号
    consumer_1 = asyncio.create_task(consumer(queue, 'consumer_1'))
    # 消费者2号
    consumer_2 = asyncio.create_task(consumer(queue, 'consumer_2'))
    # 生产者1号
    producer_1 = asyncio.create_task(producer(queue, 'producer_1'))
    # 生产者2号
    producer_2 = asyncio.create_task(producer(queue, 'producer_2'))
    # stop 10秒
    await asyncio.sleep(10)
    consumer_1.cancel()
    consumer_2.cancel()
    
    await asyncio.gather(consumer_1, consumer_2, producer_1, producer_2, return_exceptions=True)

%time asyncio.run(main())

协程的写法简洁清晰，只要把 async / await 语法和 create_task 结合来用，就是Python中比较常见的协程

如果不会多线程，看我之前文章