RuntimeError: Event loop is closed when following tutorial

[sean-reed]

I get the following error when following the official Channels tutorial at this step (specifically, when checking the channel layer can communicate with Redis using the Django shell):

Task exception was never retrieved
RuntimeError: Event loop is closed

I was using the current channels-redis version (4.0.0) that is installed when following the tutorial. Seems to be related to this issue django/channels_redis#332.

Downgrading to channels-redis version 3.4.1 fixes the issue. I suggest updating the tutorial to

python3 -m pip install channels-redis===3.4.1
until channels-redis fix the issue.

[carltongibson]

Thanks for the report.

You can run the shell with python -m asyncio to give you a concurrent context, and then not use async_to_sync().

That's probably a nicer rewrite to have anyway, if you fancied making that.

Out of interest, what happens if you use asyncio.run() rather than async_to_sync()?

[sean-reed]

Out of interest, what happens if you use asyncio.run() rather than async_to_sync()?

This gives the same error.

You can run the shell with python -m asyncio to give you a concurrent context, and then not use async_to_sync().

Nice! This works. The drawbacks are that you need to manually add the DJANGO_SETTINGS_MODULE environment variable and calling asynchronous functions with await is not introduced until the next part of the tutorial (Part 3). Maybe the small section on using the Django shell to check the channel layer can communicate with Redis can just be removed altogether from the tutorial? I don't see that it adds that much, since if it's not working then you'll find out in the next step anyway and, at the moment, that check is failing when everything is fine.

[carltongibson]

Hi @sean-reed.

I've tracked it down. The move to redis-py requires closing connections explicitly

Utilizing asyncio Redis requires an explicit disconnect of the connection ...

So to get the shell example to pass cleanly we need to do something like this:

>>> import channels.layers
>>> from asgiref.sync import async_to_sync
>>>
>>> channel_layer = channels.layers.get_channel_layer()
>>>
>>> async def closing_send(channel_layer, channel, message):
...     await channel_layer.send(channel, message)
...     await channel_layer.close_pools()
>>>
>>> async_to_sync(closing_send)(channel_layer,'test_channel', {'type': 'hello'})
>>> async_to_sync(channel_layer.receive)('test_channel')
{'type': 'hello'}

Even then we should do the same for the receive call really. (A further call would hit the same issue.)

I'll have a think about the best addition to the docs.

[carltongibson]

This should be resolved by channels-redis 4.1, which will automatically close the redis connection at loop shutdown.

[lunika]

Great news. Do you know when this release will be available ?
Thanks

[carltongibson]

It's already out.

[lunika]

I see no tag nor release on github and on pypi it's still the version 4.0.0: https://pypi.org/project/channels/

Am I missing something ?

[carltongibson]

Channels-redis.

[lunika]

oh my bad. Sorry 🙂