Unable to attach listeners

Questions and Help
#1

I’m upgrading an app to Sanic V22.12.0 and the following listeners aren’t been attached anymore.
before_server_start
after_server_start
after_server_stop

The methods attached to these listeners are no longer been called, but I get no error.

I’m using the AppLoader object alongside a factory to create the app and serving with Sanic.serve.

def serve_application(port, interface, ssl_context,) -> None:
   
    app, loader = configure_app()
    app.register_listener(
        partial(load_agent_on_start, model_path, endpoints, remote_storage),
        "before_server_start",
    )

    app.register_listener(
        partial(load_agent_on_start, model_path, endpoints, remote_storage),
        "before_server_start",
    )    
    app.register_listener(close_resources, "after_server_stop")
    app.prepare(
        host=interface,
        port=port,
        ssl=ssl_context,
        backlog=int(os.environ.get(ENV_SANIC_BACKLOG, "100")),
        workers=1,
    )
    Sanic.serve(primary=app, app_loader=loader)

Any help is appreciated, thanks!

#2

Hey @ahopkins,

Following up to my colleague’s @Tawakalt question, I managed to upgrade to v22.12 in our codebase by retaining the previous functionality with registering before_server_start listeners by using the legacy flag in app.run().

I’ve looked closely in the Sanic codebase and noticed that the serve() method triggers only main_process_start, main_process_ready and main_process_stop events such as here and here. I was not able to read in the code where the other 4 events, such as the before_server_start event listener, were being triggered. Is this correct and intended by design?

Since support for _serve_legacy is dropped in version 23.12LTS, could you please recommend how to continue to use before_server_start listeners or how to update our Sanic usage to achieve the same intention with before_server_start, after_server_start, before_server_stop, after_server_stop listeners?

#3

After further digging, I discovered by using a simple Sanic project that if the before_server_start etc listeners are registered within the factory function create_app passed to the factory parameter of AppLoader, then the listeners are correctly attached when running Sanic. However this requires quite a large effort refactoring in our complex codebase to move the listeners to the module where the create_app factory function is defined. Also using if __name__ = "__mp_main__" to register the listeners after instantiation doesn’t seem a viable solution either in our project structure. Is there anything else you recommend to enable an upgrade to Sanic 23.12?