Autoload race condition: uninitialized constant errors

[f-mer]

This is more like a hypothesis than a straight bug report.

Expected behavior vs actual behavior

Using ActiveModelSerializers with a threaded web server (in my case puma) I get infrequent uninitialized constant errors. I think it's caused by the use of autoload. I guess that ActiveSupports autoload is not threadsafe and on application boot not all modules / classes are necessarily implicitly loaded.

Steps to reproduce

I'm not sure there is a way to reproduce. I think it's a race condition which only emerges under load.

Environment

ActiveModelSerializers Version (commit ref if not on tag): 0-10-stable

Output of ruby -e "puts RUBY_DESCRIPTION": ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]

Rails Version: 5.1.4

Errors

NameError: uninitialized constant ActiveModelSerializers::Adapter::JsonApi::ResourceIdentifier

NameError: uninitialized constant ActiveModelSerializers::Adapter::JsonApi::Relationship

NameError: uninitialized constant ActiveModelSerializers::Adapter::JsonApi::Deserialization

Additonal helpful information

I'm trying to solve the problem in this fork. Adding ActiveModelSerializers::Adapter::JsonApi to eager_load_namespaces in application.rb.

class Application < Rails::Application
  config.eager_load_namespaces << ActiveModelSerializers::Adapter::JsonApi
end

This problem might also be cause by the deactivation of dependency loading in rails 5?

[bf4]

Interesting. I haven't run on Rails 5 yet.

In the past I have used an initializer with

ActiveSupport.on_load(:action_controller) do
  require 'active_model_serializers/register_jsonapi_renderer'
  ActiveModelSerializers.eager_load! if Rails.env.production?
  ActiveModelSerializers::Adapter::JsonApi.eager_load! if Rails.env.production?
  require 'active_model/serializer/null'
  ActiveModel::Serializer::Null
end

[bf4]

How come you're not using a release?

[f-mer]

From the ActiveSupport::Autoload source I draw the conclusion that calling eager_load! will have no effect without wrapping autoload calls inside eager_autoload blocks.

Went also with an initializer but loading the constants explicitly on boot:

ActiveModelSerializers::Deserialization
ActiveModelSerializers::Adapter::JsonApi::Relationship
ActiveModelSerializers::Adapter::JsonApi::ResourceIdentifier

Haven't seen the errors again since deployed.

Platformatec's blog post Eager loading for greater good is a good read on this topic.
But I'm not entirely sure what needs to go into eager_autoload blocks.

How come you're not using a release?

Oh, we are using 0.10.7. Got confused by the part in braces.

[bf4]

Looks like we can add this to the docs as an FAQ of some sort, if you'd like to make a PR

[GeminPatel]

facing a similar issue:

uninitialized constant ActiveModelSerializers::Adapter::JsonApi::Meta
Did you mean? ActiveModelSerializers::Adapter::JsonApi::Meta

So what is the work around here? From what I understand, we can write all the constants in an initializer. Is a list or some way with which we can do this for all in a well-practiced manner?

Rails is 5.1.6
Ruby is 2.3.1
AMS is 0.10.7
Puma is 3.11.4 with 2 workers and 25 threads on each worker on each machine.

[bf4]

@GeminPatel I'm not sure how Rails 5 would differ, but have you tried an initializer like what I described #2255 (comment)

[f-mer]

Rails 5 unhooks autoloading (#a71350c) after the application has booted. I suspect the error originates from this gem not explicitly loading all deps during application boot.

The initializer is a workaround which actually forces autoloading during application boot.

@bf4 #3f65eba fixes the issue. Would you be interesetd in a pull request?

[bf4]

Yup, also generally help not leaving ams completely abandoned :)

…

On Mon, Oct 8, 2018, 2:46 AM Fabian Mersch ***@***.***> wrote: Rails 5 unhooks autoloading (#a71350c <rails/rails@a71350c#diff-bf85cfa3d5f11bd1db1c97843818351b>) after the application has booted. I suspect the error originates from this gem not explicitly loading all deps during application boot. The initializer is a workaround which actually forces autoloading during application boot. @bf4 <https://github.com/bf4> #3f65eba <f-mer/active_model_serializers@3f65eba> fixes the issue. Would you be interesetd in a pull request? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#2255 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAIuQsgs07DTOqEeqUDrc_9BuDM1pAZUks5uiwLagaJpZM4UJ8aH> .