Supporting robust on_commit handlers.

[Josh Smeaton]

I recently tracked down an issue in my application where some on_commit handlers didn't execute because one of the previous handlers raised an exception. There appears to be no way to execute on_commit handlers *robustly* as you're able to do with signals [0] using send_robust.

I could sprinkle try/catches around the place, but I'd like to avoid doing so because not all functions that are used as handlers should always swallow exceptions, but could do so when run as on_commit handlers.

Targeting which handlers can be robust or not would be really useful, for example:

def update_search(user):
    # if updating search fails, it's fine, we'll bulk update later anyway
    transaction.on_commit(lambda: search.update(user), robust=True)

def trigger_background_task_one(user):
    # if this task fails, we want to crash
    transaction.on_commit(lambda: mytask.delay(user_id=user.id))

Here if search fails to update it doesn't prevent the background task from being scheduled.

I'm proposing to add a robust kwarg that defaults to False, for backward compatibility, but allows a user to tag specific handlers as such.

[0] ​https://docs.djangoproject.com/en/4.0/topics/signals/#sending-signals

[Mariusz Felisiak]

Sounds reasonable. Please take into account that the current behavior is ​documented.

[Mariusz Felisiak]

Josh, Would you like to prepare a patch?

[Josh Smeaton]

I haven't got the time to put a patch together *right now* but I could do so in the near future. Consider tagging this as "easy pickings" for a budding contributor?

[Josh Smeaton]

I've started an easy pickings thread on -developers ML and would be happy to review and guide someone to make the change: ​https://groups.google.com/g/django-developers/c/Hyqd1Rz6cFs

[Adam Johnson]

Good feature suggestion. The execution in captureOnCommitCallbacks would need extending too :)

[Mariusz Felisiak]

​PR

[Shivan Sivakumaran]

Can this ticket be closed? Seems like the PR was accepted.

[Josh Smeaton]

Replying to Shivan Sivakumaran:

Can this ticket be closed? Seems like the PR was accepted.

Not until the PR is merged, then it'll be closed as fixed

[Sarah Abderemane]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 4a1150b4:

Fixed #33616 -- Allowed registering callbacks that can fail in transaction.on_commit().

Thanks David Wobrock and Mariusz Felisiak for reviews.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 3a08483:

Refs #33616 -- Updated BaseDatabaseWrapper.run_on_commit comment.