Eager load modules on boot

Using ActiveModelSerializers with a threaded web server eg. Puma
uninitialized constant errors are thrown. Leaving this article for
reference:
http://blog.plataformatec.com.br/2012/08/eager-loading-for-greater-good/.

lib/active_model/serializer.rb

@@ -18,6 +18,7 @@ module ActiveModel
     # @see #serializable_hash for more details on these valid keys.
     SERIALIZABLE_HASH_VALID_KEYS = [:only, :except, :methods, :include, :root].freeze
     extend ActiveSupport::Autoload
+    eager_autoload do
       autoload :Adapter
       autoload :Null
       autoload :Attribute
@@ -28,6 +29,7 @@ module ActiveModel
       autoload :BelongsToReflection
       autoload :HasOneReflection
       autoload :HasManyReflection
+    end
     include ActiveSupport::Configurable
     include Caching
 

lib/active_model_serializers.rb

@@ -5,16 +5,19 @@ require 'active_support/core_ext/string/inflections'
 require 'active_support/json'
 module ActiveModelSerializers
   extend ActiveSupport::Autoload
+  eager_autoload do
     autoload :Model
     autoload :Callbacks
-  autoload :Deserialization
     autoload :SerializableResource
+    autoload :SerializationContext
     autoload :Logging
     autoload :Test
     autoload :Adapter
     autoload :JsonPointer
     autoload :Deprecate
     autoload :LookupChain
+    autoload :Deserialization
+  end
 
   class << self; attr_accessor :logger; end
   self.logger = ActiveSupport::TaggedLogging.new(ActiveSupport::Logger.new(STDOUT))
@@ -46,6 +49,11 @@ module ActiveModelSerializers
     $VERBOSE = original_verbose
   end
 
+  def self.eager_load!
+    super
+    ActiveModel::Serializer.eager_load!
+  end
+
   require 'active_model/serializer/version'
   require 'active_model/serializer'
   require 'active_model/serializable_resource'

lib/active_model_serializers/adapter/json_api.rb

@@ -22,14 +22,16 @@ module ActiveModelSerializers
   module Adapter
     class JsonApi < Base
       extend ActiveSupport::Autoload
+      eager_autoload do
         autoload :Jsonapi
         autoload :ResourceIdentifier
-      autoload :Relationship
         autoload :Link
         autoload :PaginationLinks
         autoload :Meta
         autoload :Error
         autoload :Deserialization
+        autoload :Relationship
+      end
 
       def self.default_key_transform
         :dash

lib/active_model_serializers/railtie.rb

@@ -5,6 +5,8 @@ require 'action_controller/serialization'
 
 module ActiveModelSerializers
   class Railtie < Rails::Railtie
+    config.eager_load_namespaces << ActiveModelSerializers
+
     config.to_prepare do
       ActiveModel::Serializer.serializers_cache.clear
     end