How to handle graceful shutdown inside of aiohttp coroutines?

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I want to save state into the database of a background aiohttp coroutine before server is shut down. I was thinking of creating a global array of coroutine jobs that need to be finished and do an await asyncio.gather(*global_jobs) in the shutdown handler.

Is this the proper approach?

aiohttp python-asyncio python
1 Answers

I'm not sure I understand what you mean by "the database of a background aiohttp coroutine" but, as far as cleanup actions at shutdown go, you can:

Use a signal handler

import asyncio
import signal


loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGINT, my_signal_handler, *additional_args_list)

In a Unix setting, if you know that the application is going to be interrupted with a specific signal, you can perform cleanup actions selectively for that signal. See loop.add_signal_handler(signum, callback, *args) for further information.

Note: you can employ a callable class rather than a function as callback, so that the class instance can hold a reference to any resource you wish to interact with during shutdown, e.g. the coroutines you mentioned in your question.

Catch asyncio.CancelledError

import asyncio


async def my_coro():
    try:
        # Normal interaction with aiohttp
        while True:
            pass
    except asyncio.CancelledError:
        cleanup_actions()

If you can assume that, at shutdown, the event loop will be stopped cleanly, you can count on your running coroutines to be thrown an asyncio.CancelledError before the loop is closed.

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