Unable to use positional arguments in the decorator for database_sync_to_async

[Kevv-J]

Hi,
I've been using the sync_to_async wrapper from asgiref but wanted a method that would cleanly close old connections and was redirected to use the database_sync_to_async.

Earlier

@sync_to_async(thread_sensitive=settings.THREAD_SENSITIVE)
def foo():

Now

@database_sync_to_async(thread_sensitive=settings.THREAD_SENSITIVE)
def foo():
It gives me the following error:

File "[file-path]", line 27, in [class-name]
@database_sync_to_async(thread_sensitive=settings.THREAD_SENSITIVE)
TypeError: init() missing 1 required positional argument: 'func'

using the following versions:
asgiref==3.4.1
channels==3.0.4

Are positional arguments supported in the decorator?

[carltongibson]

Perhaps not with the decorator syntax... — but I'd have to dig in to look.

I'd imagine it would work as:

def foo():
    ...

foo = @database_sync_to_async(foo, thread_sensitive=settings.THREAD_SENSITIVE)

BUT thread_sensitive is specifically for database connections... AFAICS it should never be False.

[carltongibson]

That's not (exactly) what thread_sensitive means… Rather, it requires that database queries are made on the same thread as the DB connection was created on. It'll break otherwise.

[Kevv-J]

We are using Django with channels and running the application with ASGI (Daphne). As the application is using the ASYNC approach, essentially it runs as a single-threaded application and with thread_sensitive=true, pretty much only one DB connection is ever created. with the application having to server large number of requests, reusing just one DB connection might be a bottleneck and that’s why we were experimenting with thread_sensitive=false. If thread_sensitive=true is the way to go, can you suggest how to have a bit more parallelism when running this application?

[carltongibson]

Upgrade to Django 4.0, which introduced per-request contexts for thread sensitive actions.

[Kevv-J]

Hey, @carltongibson. I'd like to explore this feature in Django 4.0 and looked into documentation for the same but couldn't find anything related to per-request contexts for thread sensitive actions in 4.0 that are different from 3.2. Could you point me in the right direction?

[carltongibson]

@Kevv-J It's an implementation detail... But see django/django@36fa071