3

我是 Python 3.5 asyncio 的新手。

在我下面的代码中, asyncio.wait() 不会等待 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:

下面是更新后的函数 display_dt 的代码。现在asyncio.wait工作正常。
但我不明白为什么上面带有 coro 的代码不起作用?

@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 # 需要装饰器吗?

我在这个伟大的章节中找到了答案:

@asyncio.coroutine 装饰器并不神奇。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,那么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 与完全没有用 @asyncio.coroutine 修饰的裸生成器一起使用。↩</p>

4

1 回答 1

7

您必须await使用.wait()协程,而不是传递给await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!
于 2015-11-08T06:31:15.313 回答