@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
