两个异步操作，一个超时

Question

基本上我想要：

await action1()
await action2()
return result

两个操作都有一个超时，并且 - 这很重要 - 有一条错误消息告诉哪个操作超时。

为了比较，只需一个操作：

try:
    await asyncio.wait_for(action(), timeout=1.0)
except asyncio.TimeoutError:
    raise RuntimeError("Problem")

现在有两个动作我有这个但不喜欢它。

import asyncio

async def a2():
    try:
        await asyncio.sleep(1.0)
    except asyncio.CancelledError:
        raise RuntimeError("Problem 1") from None
    try:
        await asyncio.sleep(1.0)
    except asyncio.CancelledError:
        raise RuntimeError("Problem 2") from None
    return True


async def test():
    loop = asyncio.get_event_loop()
    action_task = loop.create_task(a2())
    # timeouts: 0.5 -> Problem1 exc; 1.5 -> Problem2 exc; 2.5 -> OK
    try:
        await asyncio.wait_for(action_task, timeout=0.5)
    except asyncio.TimeoutError:
        pass
    result = await action_task

asyncio.get_event_loop().run_until_complete(test())

我觉得拥有以下内容真的违反直觉：

except asyncio.TimeoutError:
     pass

超时处理是主要功能。你能推荐一个更好的方法吗？

Answer 1

你能推荐一个更好的方法吗？

您的代码是正确的，但如果您正在寻找更优雅的东西，也许上下文管理器会适合您的使用：

class Timeout:
    def __init__(self, tmout):
        self.tmout = tmout
        self._timed_out = False
        self._section = None

    async def __aenter__(self):
        loop = asyncio.get_event_loop()
        self._timer = loop.call_later(self.tmout, self._cancel_task,
                                      asyncio.current_task())
        return self

    def set_section(self, section):
        self._section = section

    def _cancel_task(self, task):
        self._timed_out = True
        task.cancel()

    async def __aexit__(self, t, v, tb):
        if self._timed_out:
            assert t is asyncio.CancelledError
            raise RuntimeError(self._section) from None
        else:
            self._timer.cancel()

人们会这样使用它：

async def main():
    # raises RuntimeError("second sleep")
    async with Timeout(1) as tmout:
        tmout.set_section("first sleep")
        # increase above 1.0 and "first sleep" is raised
        await asyncio.sleep(0.8)
        tmout.set_section("second sleep")
        await asyncio.sleep(0.5)

asyncio.get_event_loop().run_until_complete(main())

Answer 2

最初为aiohttp 开发的async_timeout 模块可能正是您需要的。它的回溯包含导致超时的行。

安装：

pip install async_timeout

用法：

import asyncio
from async_timeout import timeout


async def main():
    with timeout(1.5) as t:

        await asyncio.sleep(1)  # first

        await asyncio.sleep(1)  # second

        await asyncio.sleep(1)  # third

        print('not timeout')


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

输出：

Traceback (most recent call last):
  File "C:\Users\gmn\main.py", line 74, in main
    await asyncio.sleep(1)  # second
  File "C:\Users\gmn\AppData\Local\Programs\Python\Python37\lib\asyncio\tasks.py", line 564, in sleep
    return await future
concurrent.futures._base.CancelledError

During handling of the above exception, another exception occurred:
  ...

这里的第二行和第三行告诉你发生超时的地方：

  File "C:\Users\gmn\main.py", line 74, in main
    await asyncio.sleep(1)  # second