`ActiveSupport::LogSubscriber` example and code reloads about rails

[rafaelfranca]

Subscribers, including LogSubscribers, like most other registries in the Rails frameworks, are not expected to handle reloads.

Now that lib can be autoloaded, makes this situation difficult. Either we change most of those registries to be reload aware, perhaps making them less performant or we document what can't be reloaded, which is probably everything that was made to be used in libraries, like the mentioned feature.

[fxn]

Stuff that is cached cannot be reloadable. Middleware is an example, this section of the autoloading guide explains this (but I see there is an obsolete mention to lib).

If you still want lib to be reloadable, one way to organize this would be to create lib/log_subscribers and ignore that subdirectory in the autoload_lib call.

[fxn]

@josegomezr where in the application is the log subscriber loaded?

[josegomezr]

I had something like this:

module Namespace
  extend ActiveSupport::Autoload

  autoload :MyService
end

and in the soruce of namespace/my_service.rb.

require_relative ./log_subscriber.rb

Then I saw the repeating messages and blamed the #attach_to, and with the
results of this research I ended up with:

module Namespace
  extend ActiveSupport::Autoload

  autoload :MyService # this is the class emitting `xxx.namespace` events.

  eager_autoload do
    autoload :LogSubscriber
  end

  # LogSubscriber.attach_to :namespace
  LogSubscriber.reaload_capable_attach_to :namespace
end

[fxn]

And namespace/my_service.rb, where was it stored? How was Namespace loaded?

Subscribers are typically defined while the application boots, because you want them to be ready, when is yours effectively defined?

Are any of those files in the autoload paths?

[josegomezr]

Are any of those files in the autoload paths?

I believe that's the case. Files are in rails-root/lib/, and application.rb has:

config.autoload_lib(ignore: %w[tasks])

[fxn]

But, who loads these files, and when? Is loading them triggered from config/initializers?

[josegomezr]

I triggered the behavior from the console by:

Namespace::MyService.new().call()

That should be Zeitwerk loading them (?). I didn't do any require call other than what application.rb already had.

The way I was intending to use the service [and in turn the subscriber] was in a rake task like:

namespace :ns do
  task import_all: :environment do
    Namespace::MyService.new().call()
  end
end

and just bin/rake ns:import_all

p.s: This is a bit far away from my ruby understanding, I apologize if I can't answer clearly 😅

[fxn]

No prob at all :D, I believe I have an idea of your setup now.

About to fly to RailsConf right now, I'll followup if there's anything else worth sharing. Thank you!

[fxn]

Stuff that is cached cannot be reloadable. Middleware is an example, this section of the autoloading guide explains this (but I see there is an obsolete mention to lib).

I revised that obsolete paragraph in dcbd6b0. That patch has been backported to 7-1-stable too.