Python3 asyncio "Task was destroyed but it is pending" 具有某些特定条件

Question

这里是简化的代码，它使用 python3 协程并为 SIGING 和 SIGTERM 信号设置处理程序以正确停止作业：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import argparse
import asyncio
import signal
import sys


def my_handler(signum, frame):
    print('Stopping')
    asyncio.get_event_loop().stop()
    # Do some staff
    sys.exit()


@asyncio.coroutine
def prob_ip(ip_addr):

    print('Ping ip:%s' % ip_addr)
    proc = yield from asyncio.create_subprocess_exec('ping', '-c', '3', ip_addr)
    ret_code = yield from proc.wait()
    if ret_code != 0:
        print("ip:%s doesn't responding" % ip_addr)
        # Do some staff
        yield from asyncio.sleep(2)
        # Do more staff
        yield from asyncio.sleep(16)


@asyncio.coroutine
def run_probing():

    print('Start probing')
    # Do some staff
    yield from asyncio.sleep(1)

    while True:
        yield from asyncio.wait([prob_ip('192.168.1.3'), prob_ip('192.168.1.2')])
        yield from asyncio.sleep(60)


def main():
    parser = argparse.ArgumentParser()
    parser.description = "Probing ip."
    parser.parse_args()

    signal.signal(signal.SIGINT, my_handler)
    signal.signal(signal.SIGTERM, my_handler)

    asyncio.get_event_loop().run_until_complete(run_probing())


if __name__ == '__main__':
    main()

当我运行它通过：

python3 test1.py

它在没有任何警告的情况下按 Ctrl-C 停止。但是当我运行它通过：

python3 -m test1

它通过 Ctrl-C 打印警告：

$ python3 -m test1 
Start probing
Ping ip:192.168.1.2
Ping ip:192.168.1.3
PING 192.168.1.2 (192.168.1.2): 56 data bytes
PING 192.168.1.3 (192.168.1.3): 56 data bytes
^C--- 192.168.1.2 ping statistics ---
--- 192.168.1.3 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss
1 packets transmitted, 0 packets received, 100% packet loss
Stopping
Task was destroyed but it is pending!
task: <Task pending coro=<prob_ip() running at /tmp/test1.py:22> wait_for=<Future pending cb=[Task._wakeup()]> cb=[_wait.<locals>._on_completion() at /usr/lib/python3.4/asyncio/tasks.py:394]>
Task was destroyed but it is pending!
task: <Task pending coro=<prob_ip() running at /tmp/test1.py:22> wait_for=<Future pending cb=[Task._wakeup()]> cb=[_wait.<locals>._on_completion() at /usr/lib/python3.4/asyncio/tasks.py:394]>

如果我通过以下方式安装此脚本，我会收到同样的警告：

from setuptools import setup

setup(name='some_scripts',
      version='1.0.0.0',
      author='Some Team',
      author_email='team@team.ru',
      url='https://www.todo.ru',
      description='Some scripts',
      packages=['my_package'],
      entry_points={'console_scripts': [
          'test1=my_package.test1:main',
      ]},
      )

我的 python 版本是“3.4.2”

Answer 1

使用asyncio.gather代替asyncio.wait:

Cancellation: if the outer Future is cancelled, all children (that have not completed yet) are also cancelled.

示例：

def handler(future, loop):
    future.cancel()
    loop.stop()

@asyncio.coroutine
def do_some(arg):
    while True:
        print("Do stuff with %s" % arg)
        yield from asyncio.sleep(2)

loop = asyncio.get_event_loop()
future = asyncio.gather(do_some(1), do_some(2))
loop.add_signal_handler(signal.SIGINT, handler, future, loop)
loop.run_forever()

Answer 2

好的。我想我已经弄清楚应该如何停止所有任务了。

首先，据我了解。 BaseEventLoop.stop() is only to stop BaseEventLoop.run_forever(). So one should cancel all tasks via Future.cancel. To get all tasks you can use Task.all_tasks 静态方法。
取消所有任务后 asyncio.CancelledError 将从 run_until_complete 引发异常。所以如果不想将它打印到 stderr，应该抓住它。
而且，在某些情况下，我会收到此错误：TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object。我找到了一些关于这个错误的主题：
- https://bugs.python.org/issue23548
- https://github.com/buildinspace/peru/issues/98
都说退出应用前关闭循环可以解决

所以我们得到这个代码：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import asyncio
import signal


def my_handler():
    print('Stopping')
    for task in asyncio.Task.all_tasks():
        task.cancel()


@asyncio.coroutine
def do_some(some_args):
    while True:
        print("Do staff with %s" % some_args)
        yield from asyncio.sleep(2)


def main():
    loop = asyncio.get_event_loop()

    loop.add_signal_handler(signal.SIGINT, my_handler)

    try:
        loop.run_until_complete(asyncio.wait([do_some(1), do_some(2)]))
    except asyncio.CancelledError:
        print('Tasks has been canceled')
    finally:
        loop.close()


if __name__ == '__main__':
    main()

它也适用于 signal.signal. But as Vincent loop.add_signal_handler 在这种情况下看起来更好。

但我仍然不确定这是停止所有任务的最佳方法。

Python3 asyncio "Task was destroyed but it is pending" 具有某些特定条件

Python3 asyncio "Task was destroyed but it is pending" with some specific condition

coroutine

python-3.x

python-asyncio