Use after_initialize instead of to_prepare to prevent subscribing multiple times to events in development environment

[benjaminwols]

Context

The current config uses .to_prepare which is run after every code reload in development. This is annoying as subscribers get subscribed multiple times to the save event.

One can easily reproduce the problem in development when using the rails console.
Call reload! from the console and publish an event. After reloading once, the subscriber is executed 3 times.

Related tickets

I think this also addresses issue #6

What's inside

Replace .to_prepare with .after_initialize

Checklist:

• I have added tests
• I have made corresponding changes to the documentation

I had a look to create a failing test, but the current tests don't test the ActiveSupport.on_load("downstream-events") initializer and I'm unsure how to add it.

[benjaminwols]

@palkan Sorry for tagging you, but during Rails World you mentioned that you probably have disabled notifications for this repository.

[palkan]

If we only setup subscribers during the app initialization, we lose code updates on reload—the store would still references previous versions of subscribers.

I think, what we should do here is to reset the store and then trigger the hook to let the app to register fresh versions of the subscribers.

[benjaminwols]

I agree that would be a better solution. I did some digging, but its quite hard to unsubscribe to all downstream-events since we don't keep a list of subscribers. I was able to make it work, but I'm accessing private methods, so it's very fragile.

config.to_prepare do
  ActiveSupport::Notifications.notifier.instance_variable_get(:@string_subscribers).each_key do |key|
    next unless key.is_a?(String) && key.starts_with?("downstream-events")

    ActiveSupport::Notifications.unsubscribe(key)
  end
  ActiveSupport.run_load_hooks("downstream-events", Downstream)
end

@palkan Do you have any suggestions to improve this?

[palkan]

Yeah, dealing with AS internals doesn't look stable. I guess, a better solution would be to add some reset functionality to Downstream (extend the Pubsub interface: https://github.com/palkan/downstream/blob/master/lib/downstream/pubsub_adapters/stateless/pubsub.rb).