Question

我试图用以下代码标记将来超时：

import asyncio


@asyncio.coroutine
def greet():
    while True:
        print('Hello World')
        yield from asyncio.sleep(1)

@asyncio.coroutine
def main():
    future = asyncio.async(greet())
    loop.call_later(3, lambda: future.set_result(True))
    yield from future
    print('Ready')

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

＆＃34;定时器＆＃34; loop.call_later在3秒后将结果设置为future。它有效，但我也得到例外：

Hello World
Hello World
Hello World
Ready
Exception in callback <bound method Task._wakeup of Task(<greet>)<result=True>>(Future<result=None>,)
handle: Handle(<bound method Task._wakeup of Task(<greet>)<result=True>>, (Future<result=None>,))
Traceback (most recent call last):
  File "C:\Python33\lib\site-packages\asyncio\events.py", line 39, in _run
    self._callback(*self._args)
  File "C:\Python33\lib\site-packages\asyncio\tasks.py", line 337, in _wakeup
    self._step(value, None)
  File "C:\Python33\lib\site-packages\asyncio\tasks.py", line 267, in _step
    '_step(): already done: {!r}, {!r}, {!r}'.format(self, value, exc)
AssertionError: _step(): already done: Task(<greet>)<result=True>, None, None

这个AssertionError意味着什么？我是否做错了设置loop.call_later完成的未来？

Answer 1

导致异常的原因是：greet即使在future.set_result电话之后仍然继续运行;通过while True更改为if True，您将得到我的意思。

如何使用asyncio.Event？

import asyncio


@asyncio.coroutine
def greet(stop):
    while not stop.is_set():
        print('Hello World')
        yield from asyncio.sleep(1)


@asyncio.coroutine
def main():
    stop = asyncio.Event()
    loop.call_later(3, stop.set)
    yield from asyncio.async(greet(stop))
    print('Ready')

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

Answer 2

您不应该自己致电future.set_result()。事件循环在任务返回后设置未来的结果。

asyncio中的Strange AssertionError

2 个答案: