为什么 asyncio.wait 不等待 FIRST_COMPLETED

Question

我是 Python 3.5 asyncio 的新手。

在我下面的代码中，asyncio.wait() 不等待 stop_future 完成：

import asyncio
import datetime
from concurrent.futures import FIRST_COMPLETED


def stop():  # callback after 12 seconds

    print('stop', datetime.datetime.now())
    stop_future.set_result('Done!')


async def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        # sleep 5 seconds or stop_future done
        asyncio.wait([await asyncio.sleep(5), stop_future],  return_when=FIRST_COMPLETED)
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())


loop = asyncio.get_event_loop()
stop_future = asyncio.Future()
loop.call_later(12, stop)
loop.run_until_complete(display_dt())
loop.close()

结果：

dt-1 2015-11-08 00:49:37.324582
dt-2 2015-11-08 00:49:42.325503
dt-1 2015-11-08 00:49:42.325503
dt-2 2015-11-08 00:49:47.326423
dt-1 2015-11-08 00:49:47.326423
stop 2015-11-08 00:49:49.327192  # async.wait stop_future not triggered
dt-2 2015-11-08 00:49:52.327343  # while loop finishes here
>>> Done!

更新：

下面是更新函数的代码 display_dt。现在 asyncio.wait 工作正常。
但是我不明白为什么上面的coro代码不起作用？？

@asyncio.coroutine    # decorator necessary? It works fine without 
def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        yield from asyncio.wait([asyncio.sleep(5), stop_future], return_when=FIRST_COMPLETED)
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())

结果：

dt-1 2015-11-08 01:19:06.289915
dt-2 2015-11-08 01:19:11.290836
dt-1 2015-11-08 01:19:11.290836
dt-2 2015-11-08 01:19:16.291757
dt-1 2015-11-08 01:19:16.291757
stop 2015-11-08 01:19:18.292525
dt-2 2015-11-08 01:19:18.292525  # async wait stop_future triggered
Done!

更新： @asyncio.coroutine # 是否需要装饰器？

我在this great chapter中找到了答案：

@asyncio.coroutine 装饰器并不神奇。事实上，如果它装饰了一个生成器函数并且没有设置 PYTHONASYNCIODEBUG 环境变量，装饰器实际上什么都不做。它只是设置了一个属性，_is_coroutine，以方便框架的其他部分。可以将 asyncio 与根本没有用 @asyncio.coroutine 修饰的裸生成器一起使用。↩

Answer 1

您必须 await .wait() 协程，而不是 await 您 传递给 的协程 .wait():

async def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        # sleep 5 seconds or stop_future done
        await asyncio.wait([asyncio.sleep(5), stop_future], return_when=FIRST_COMPLETED) # <----
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())

现在这等同于您的编辑，但使用的是 原生协程 （即 async/await 语法）。

更新显示结果：

dt-1 2015-11-08 13:14:21.910399
dt-2 2015-11-08 13:14:26.911320
dt-1 2015-11-08 13:14:26.911320
dt-2 2015-11-08 13:14:31.912240
dt-1 2015-11-08 13:14:31.912240
stop 2015-11-08 13:14:33.913009
dt-2 2015-11-08 13:14:33.913009
Done!

为什么 asyncio.wait 不等待 FIRST_COMPLETED

Why asyncio.wait does not wait for the FIRST_COMPLETED

python

future

event-loop

python-asyncio

python-3.5