Re: Possible bug with transaction.on_commit

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Hi Bart,

On 05/16/2016 02:10 PM, barthelemy@infobart.com wrote:
> I believe that I encountered a bug or at least a serious limitation with
> transaction.on_commit in Django 1.9.x. Essentially, the on_commit hooks
> seem to be tied to the database connection instead of the transaction.
> This means that unrelated transactions may trigger on_commit hooks,
> which results in undesired execution order.
[...]
> I wanted to know if someone encountered this issue or if I am
> misunderstanding on_commit before opening a ticket.

I am the author of on_commit, and I think the behavior you have
encountered is a bug that should be fixed. Doing additional database
work in `on_commit` callbacks wasn't really a use case I had in mind in
the design; I made sure it basically worked, but clearly didn't explore
it sufficiently in cases of multiple registered hooks.

Storing the on_commit state on the connection is not really optional,
since that's where _all_ transaction-related state is stored, but I
think it should still be possible to fix this. Perhaps by having
`run_and_clear_commit_hooks` copy the list of hooks into a local
variable and immediately clear the state on the connection before it
calls any of the hooks? Not entirely sure, need to add a failing test
and play with it a bit.

Thanks for catching and reporting this. If you'd be willing to file a
ticket in Trac, that'd be great.

Carl

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