Resource shutdown ignores dependencies between resources

First of all, thank you for the great library.

I have encountered an issue with a bit of an unusual case of having dependencies between resources where both of them have cleanup, and the order of the cleanup matters. This is the container we are using:

class Container(containers.DeclarativeContainer):
    config = providers.Configuration()

    engine = providers.Singleton(...)

    session = providers.Resource(create_session, engine)
    token = providers.Resource(locked_token, session)

def create_session(engine):
    db_session = Session(engine)
    try:
        yield db_session
    finally:
        db_session.close()

def locked_token(session):
    token = session.query(...)
    session.commit()
    try:
        yield token
    finally:
        session.refresh(token)
        ...
        session.commit()

Resource initialization works completely fine, the session gets initialized before the token. But at shutdown of the application, we tried calling container.shutdown(), and what happened was that it closed the session first, thus making the token cleanup crash (since it got a new session - SQLAlchemy sessions create a new one on close()).

In other words, the change requested here is that the container shuts down resources in reverse order of starting them.

[saulbein]

Hi again @rmk135,

The workaround has been fine for a while now.

We have a different framework that is responsible for application lifetime (Prefect) and we had the container integrated with it’s tasks, so that we can easily provide external dependencies. Since we have multiple projects using this setup, I would like to factor out the code linking these two frameworks, but I can’t do that unless container.shutdown() respects the shutdown order - the linker code can’t know about what the container has, just that it is a container.

Not trying to rush you or anything, just expanding on the use case.

[saulbein]

No worries, we all make mistakes sometimes 😃 Thanks for the fix!