Asyncio RuntimeError: Event Loop is Closed

Question

I'm trying to make a bunch of requests (~1000) using Asyncio and the aiohttp library, but I am running into a problem that I can't find much info on.

When I run this code with 10 urls, it runs just fine. When I run it with 100+ urls, it breaks and gives me RuntimeError: Event loop is closed error.

import asyncio
import aiohttp


@asyncio.coroutine
def get_status(url):
    code = '000'
    try:
        res = yield from asyncio.wait_for(aiohttp.request('GET', url), 4)
        code = res.status
        res.close()
    except Exception as e:
        print(e)
    print(code)


if __name__ == "__main__":
    urls = ['https://google.com/'] * 100
    coros = [asyncio.Task(get_status(url)) for url in urls]
    loop = asyncio.get_event_loop()
    loop.run_until_complete(asyncio.wait(coros))
    loop.close()

The stack trace can be found here.

Any help or insight would be greatly appreciated as I've been banging my head over this for a few hours now. Obviously this would suggest that an event loop has been closed that should still be open, but I don't see how that is possible.

Answer 1

The bug is filed as https://github.com/python/asyncio/issues/258 Stay tuned.

As quick workaround I suggest using custom executor, e.g.

loop = asyncio.get_event_loop()
executor = concurrent.futures.ThreadPoolExecutor(5)
loop.set_default_executor(executor)

Before finishing your program please do

executor.shutdown(wait=True)
loop.close()

Answer 2

You're right, loop.getaddrinfo uses a ThreadPoolExecutor to run socket.getaddrinfo in a thread.

You're using asyncio.wait_for with a timeout, which means res = yield from asyncio.wait_for... will raise a asyncio.TimeoutError after 4 seconds. Then the get_status coroutines return None and the loop stops. If a job finishes after that, it will try to schedule a callback in the event loop and raises an exception since it is already closed.