Asyncio 不异步执行任务

Question

我正在玩 Python 的 asyncio 模块，我不知道我的简单代码有什么问题。它不会异步执行任务。

#!/usr/bin/env python3    

import asyncio
import string    


async def print_num():
    for x in range(0, 10):
        print('Number: {}'.format(x))
        await asyncio.sleep(1)    

    print('print_num is finished!')    

async def print_alp():
    my_list = string.ascii_uppercase    

    for x in my_list:
        print('Letter: {}'.format(x))
        await asyncio.sleep(1)    

    print('print_alp is finished!')    


async def msg(my_msg):
    print(my_msg)
    await asyncio.sleep(1)    


async def main():
    await msg('Hello World!')
    await print_alp()
    await msg('Hello Again!')
    await print_num()    


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())
    loop.close()

调用脚本时的输出如下：

Hello World!
Letter: A
Letter: B
Letter: C
Letter: D
Letter: E
Letter: F
Letter: G
Letter: H
Letter: I
Letter: J
Letter: K
Letter: L
Letter: M
Letter: N
Letter: O
Letter: P
Letter: Q
Letter: R
Letter: S
Letter: T
Letter: U
Letter: V
Letter: W
Letter: X
Letter: Y
Letter: Z
print_alp is finished!
Hello Again!
Number: 0
Number: 1
Number: 2
Number: 3
Number: 4
Number: 5
Number: 6
Number: 7
Number: 8
Number: 9
print_num is finished!

Answer 1

您按顺序调用函数，因此代码也按顺序执行。请记住，await this 意味着 "do this and wait for it to return"（但与此同时，如果 this 选择暂停执行，其他已经在其他地方开始的任务可能运行）。

如果您想运行异步执行任务，您需要：

async def main():
    await msg('Hello World!')
    task1 = asyncio.ensure_future(print_alp())
    task2 = asyncio.ensure_future(print_num())
    await asyncio.gather(task1, task2)
    await msg('Hello Again!')

另请参阅 asyncio.gather function. Alternatively, you could also use asyncio.wait 的文档。

Answer 2

您遇到了与 await 语句混淆的常见来源，即它们对 'child' coroutines 按顺序运行，但对 'neighbouring' coroutines.

例如：

import asyncio

async def child():
    i = 5
    while i > 0:
        print("Hi, I'm the child coroutine, la la la la la")
        await asyncio.sleep(1)
        i -= 1

async def parent():
    print("Hi, I'm the parent coroutine awaiting the child coroutine")
    await child() # this blocks inside the parent coroutine, but not the neighbour
    print("Hi, I'm the parent, the child coroutine is now done and I can stop waiting")

async def neighbour():
    i = 5
    while i > 0:
        await asyncio.sleep(1)
        print("Hi, I'm your neighbour!")
        i -= 1

async def my_app():
    # start the neighbour and parent coroutines and let them coexist in Task wrappers
    await asyncio.wait([neighbour(), parent()])

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(my_app())

将输出：

Hi, I'm the parent coroutine awaiting the child coroutine
Hi, I'm the child coroutine, la la la la la
Hi, I'm the child coroutine, la la la la la
Hi, I'm your neighbour!
Hi, I'm the child coroutine, la la la la la
Hi, I'm your neighbour!
Hi, I'm the child coroutine, la la la la la
Hi, I'm your neighbour!
Hi, I'm the child coroutine, la la la la la
Hi, I'm your neighbour!
Hi, I'm the parent, the child coroutine is now done and I can stop waiting
Hi, I'm your neighbour!

Process finished with exit code 0

Asyncio 不异步执行任务

Asyncio doesn't execute the tasks asynchronously

python

synchronization

asynchronous

python-asyncio