揭秘 Python 协程

Python笔记本
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知识点

  • 协程和多线程的区别,主要在于两点,一是协程为单线程;二是协程由用户决定,在哪些地方交出控制权,切换到下一个任务。
  • 协程的写法更加简洁清晰,把 async / await 语法和 create_task 结合来用,对于中小级别的并发需求已经毫无压力。
  • 写协程程序的时候,你的脑海中要有清晰的事件循环概念,知道程序在什么时候需要暂停、等待 I/O,什么时候需要一并执行到底。

代码示例

协程的底层原理

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import asyncio

async def worker_1():
    print('worker_1 start')
    await asyncio.sleep(1)
    print('worker_1 done')

async def worker_2():
    print('worker_2 start')
    await asyncio.sleep(2)
    print('worker_2 done')

async def main():
    task1 = asyncio.create_task(worker_1())
    task2 = asyncio.create_task(worker_2())
    print('before await')
    await task1
    print('awaited worker_1')
    await task2
    print('awaited worker_2')

%time asyncio.run(main())

########## 输出 ##########

before await
worker_1 start
worker_2 start
worker_1 done
awaited worker_1
worker_2 done
awaited worker_2
Wall time: 2.01 s

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到底发生了什么呢?

生产者消费者模型

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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():
    queue = asyncio.Queue()

    consumer_1 = asyncio.create_task(consumer(queue, 'consumer_1'))
    consumer_2 = asyncio.create_task(consumer(queue, 'consumer_2'))

    producer_1 = asyncio.create_task(producer(queue, 'producer_1'))
    producer_2 = asyncio.create_task(producer(queue, 'producer_2'))

    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())

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最后更新 2019-11-28
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