为什么asyncio.wait不等待FIRST_COMPLETED

Question

我是Python 3.5 asyncio的新手.

在下面的代码中,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:

下面是更新的函数display_dt的代码.现在asyncio.wait工作正常.
但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#decorator必要吗？

我在这个伟大的章节中找到了答案:

@ asyncio.coroutine装饰器并不神奇.实际上,如果它设置了一个生成器函数并且没有设置PYTHONASYNCIODEBUG环境变量,那么装饰器几乎什么都不做.它只是设置一个属性_is_coroutine,以方便框架的其他部分.可以将asyncio与没有使用@ asyncio.coroutine装饰的裸发生器一起使用

Answer 1

您必须await是.wait()协程,而不是await您传递给 协程的协同程序.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())

现在这相当于您的编辑,但使用本机协程(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!