#32447: ORM query made in `request_finished` signal callback fails in ASGI
-------------------------------------+-------------------------------------
Reporter: Aditya N | Owner: nobody
Type: | Status: new
Uncategorized |
Component: HTTP | Version: 3.0
handling | Keywords: request_finished
Severity: Normal | signal ASGI ORM query
Triage Stage: | Has patch: 1
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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When running Django with an ASGI server, any ORM query that's made inside
a callback connected to the `request_finished` signal fails with an
exception saying:
{{{
SynchronousOnlyOperation: You cannot call this from an async context - use
a thread or sync_to_async
}}}
After inspecting code, I figured out that this was because the
`django.core.handlers.asgi.ASGIHandler` class provides a `send_response`
method which is ''natively async''. This method subsequently fires the
`request_finished` signal and since this happens from within an async
context, Django complains and rightly so.
So the issue here is that this behaviour about the `request_finished`
signal hasn't been documented and so it might come as a surprise to people
when they try to run their code using an ASGI server. Also, any such ORM
queries made from a callback hooked to the `request_started` signal works
just fine without any modifications.
The solution to this problem could be as follows:
1. The synchronous blocking calls made from within the callback hooked to
`request_finished` could be made async using the sync_to_async adapter and
this has to be documented appropriately.
(OR)
2. The `send_response` method could be made natively synchronous and
converted into an async callable using the sync_to_async adapter wherein
it would run in a background thread without blocking the event loop but
this could have performance implications.
If we can finalise on one of the above two or an even better one, I could
send a patch for the same.
--
Ticket URL: <https://code.djangoproject.com/ticket/32447>
Django <https://code.djangoproject.com/>
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