Merge pull request #7225 from rails/eager_load

Improve eager load on Rails

33 files changed, 215 insertions, 109 deletions

diff --git a/actionmailer/lib/action_mailer.rb b/actionmailer/lib/action_mailer.rb
index 32e6183ff6..cfbe2f1cbd 100644
--- a/actionmailer/lib/action_mailer.rb
+++ b/actionmailer/lib/action_mailer.rb
@@ -35,7 +35,10 @@ require 'active_support/lazy_load_hooks'
 module ActionMailer
   extend ::ActiveSupport::Autoload
 
-  autoload :Collector
+  eager_autoload do
+    autoload :Collector
+  end
+
   autoload :Base
   autoload :DeliveryMethods
   autoload :MailHelper
diff --git a/actionmailer/lib/action_mailer/railtie.rb b/actionmailer/lib/action_mailer/railtie.rb
index 5c03a29f0f..8679096735 100644
--- a/actionmailer/lib/action_mailer/railtie.rb
+++ b/actionmailer/lib/action_mailer/railtie.rb
@@ -5,6 +5,7 @@ require "abstract_controller/railties/routes_helpers"
 module ActionMailer
   class Railtie < Rails::Railtie
     config.action_mailer = ActiveSupport::OrderedOptions.new
+    config.eager_load_namespaces << ActionMailer
 
     initializer "action_mailer.logger" do
       ActiveSupport.on_load(:action_mailer) { self.logger ||= Rails.logger }
diff --git a/actionpack/lib/action_controller.rb b/actionpack/lib/action_controller.rb
index ceb90f8cee..31df9d605c 100644
--- a/actionpack/lib/action_controller.rb
+++ b/actionpack/lib/action_controller.rb
@@ -48,6 +48,12 @@ module ActionController
   eager_autoload do
     autoload :RecordIdentifier
   end
+
+  def self.eager_load!
+    super
+    ActionController::Caching.eager_load!
+    HTML.eager_load!
+  end
 end
 
 # All of these simply register additional autoloads
diff --git a/actionpack/lib/action_controller/railtie.rb b/actionpack/lib/action_controller/railtie.rb
index 851a2c4aee..3ecc105e22 100644
--- a/actionpack/lib/action_controller/railtie.rb
+++ b/actionpack/lib/action_controller/railtie.rb
@@ -9,6 +9,8 @@ module ActionController
   class Railtie < Rails::Railtie #:nodoc:
     config.action_controller = ActiveSupport::OrderedOptions.new
 
+    config.eager_load_namespaces << ActionController
+
     initializer "action_controller.assets_config", :group => :all do |app|
       app.config.action_controller.assets_dir ||= app.config.paths["public"].first
     end
diff --git a/actionpack/lib/action_dispatch.rb b/actionpack/lib/action_dispatch.rb
index b382997052..57b4678add 100644
--- a/actionpack/lib/action_dispatch.rb
+++ b/actionpack/lib/action_dispatch.rb
@@ -38,9 +38,11 @@ module ActionDispatch
   class IllegalStateError < StandardError
   end
 
-  autoload_under 'http' do
-    autoload :Request
-    autoload :Response
+  eager_autoload do
+    autoload_under 'http' do
+      autoload :Request
+      autoload :Response
+    end
   end
 
   autoload_under 'middleware' do
diff --git a/actionpack/lib/action_dispatch/railtie.rb b/actionpack/lib/action_dispatch/railtie.rb
index 5aad8dd23a..ccc0435a39 100644
--- a/actionpack/lib/action_dispatch/railtie.rb
+++ b/actionpack/lib/action_dispatch/railtie.rb
@@ -25,6 +25,8 @@ module ActionDispatch
       'X-Content-Type-Options' => 'nosniff'
     }
 
+    config.eager_load_namespaces << ActionDispatch
+
     initializer "action_dispatch.configure" do |app|
       ActionDispatch::Http::URL.tld_length = app.config.action_dispatch.tld_length
       ActionDispatch::Request.ignore_accept_header = app.config.action_dispatch.ignore_accept_header
diff --git a/actionpack/lib/action_view.rb b/actionpack/lib/action_view.rb
index 4bd72c5520..9d11c284f5 100644
--- a/actionpack/lib/action_view.rb
+++ b/actionpack/lib/action_view.rb
@@ -38,7 +38,6 @@ module ActionView
     autoload :PathSet
     autoload :Template
 
-
     autoload_under "renderer" do
       autoload :Renderer
       autoload :AbstractRenderer
@@ -77,6 +76,11 @@ module ActionView
   autoload :TestCase
 
   ENCODING_FLAG = '#.*coding[:=]\s*(\S+)[ \t]*'
+
+  def self.eager_load!
+    super
+    ActionView::Template.eager_load!
+  end
 end
 
 require 'active_support/core_ext/string/output_safety'
diff --git a/actionpack/lib/action_view/railtie.rb b/actionpack/lib/action_view/railtie.rb
index 9f5e3be454..2d36deaa78 100644
--- a/actionpack/lib/action_view/railtie.rb
+++ b/actionpack/lib/action_view/railtie.rb
@@ -9,6 +9,8 @@ module ActionView
     config.action_view.javascript_expansions = { :defaults => %w(jquery jquery_ujs) }
     config.action_view.embed_authenticity_token_in_remote_forms = false
 
+    config.eager_load_namespaces << ActionView
+
     initializer "action_view.embed_authenticity_token_in_remote_forms" do |app|
       ActiveSupport.on_load(:action_view) do
         ActionView::Helpers::FormTagHelper.embed_authenticity_token_in_remote_forms =
diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index ec2d734647..d1cc19ec6b 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -34,7 +34,6 @@ module ActiveModel
   autoload :Conversion
   autoload :Dirty
   autoload :EachValidator, 'active_model/validator'
-  autoload :Errors
   autoload :Lint
   autoload :MassAssignmentSecurity
   autoload :Model
@@ -49,11 +48,22 @@ module ActiveModel
   autoload :Validations
   autoload :Validator
 
+  eager_autoload do
+    autoload :Errors
+  end
+
   module Serializers
     extend ActiveSupport::Autoload
 
-    autoload :JSON
-    autoload :Xml
+    eager_autoload do
+      autoload :JSON
+      autoload :Xml
+    end
+  end
+
+  def eager_load!
+    super
+    ActiveModel::Serializer.eager_load!
   end
 end
 
diff --git a/activemodel/lib/active_model/railtie.rb b/activemodel/lib/active_model/railtie.rb
index 63ffe5db63..f239758b35 100644
--- a/activemodel/lib/active_model/railtie.rb
+++ b/activemodel/lib/active_model/railtie.rb
@@ -1,2 +1,8 @@
 require "active_model"
-require "rails"
\ No newline at end of file
+require "rails"
+
+module ActiveModel
+  class Railtie < Rails::Railtie
+    config.eager_load_namespaces << ActiveModel
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 39427bc296..fa94f6a941 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -160,6 +160,15 @@ module ActiveRecord
 
   autoload :TestCase
   autoload :TestFixtures, 'active_record/fixtures'
+
+  def self.eager_load!
+    super
+    ActiveRecord::Locking.eager_load!
+    ActiveRecord::Scoping.eager_load!
+    ActiveRecord::Associations.eager_load!
+    ActiveRecord::AttributeMethods.eager_load!
+    ActiveRecord::ConnectionAdapters.eager_load!
+  end
 end
 
 ActiveSupport.on_load(:active_record) do
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 672d9a4246..ecf8547e67 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -29,8 +29,11 @@ module ActiveRecord
       'ActiveRecord::RecordNotSaved'   => :unprocessable_entity
     )
 
+
     config.active_record.use_schema_cache_dump = true
 
+    config.eager_load_namespaces << ActiveRecord
+
     rake_tasks do
       require "active_record/base"
       load "active_record/railties/databases.rake"
diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index 56d6676961..41d77ab6c1 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -37,7 +37,6 @@ module ActiveSupport
   autoload :LogSubscriber
   autoload :Notifications
 
-  # TODO: Narrow this list down
   eager_autoload do
     autoload :BacktraceCleaner
     autoload :BasicObject
@@ -55,12 +54,12 @@ module ActiveSupport
     autoload :OptionMerger
     autoload :OrderedHash
     autoload :OrderedOptions
-    autoload :Rescuable
     autoload :StringInquirer
     autoload :TaggedLogging
     autoload :XmlMini
   end
 
+  autoload :Rescuable
   autoload :SafeBuffer, "active_support/core_ext/string/output_safety"
   autoload :TestCase
 end
diff --git a/activesupport/lib/active_support/dependencies/autoload.rb b/activesupport/lib/active_support/dependencies/autoload.rb
index 4045db3232..df490ae298 100644
--- a/activesupport/lib/active_support/dependencies/autoload.rb
+++ b/activesupport/lib/active_support/dependencies/autoload.rb
@@ -1,52 +1,78 @@
 require "active_support/inflector/methods"
 
 module ActiveSupport
+  # Autoload and eager load conveniences for your library.
+  #
+  # This module allows you to define autoloads based on
+  # Rails conventions (i.e. no need to define the path
+  # it is automatically guessed based on the filename)
+  # and also define a set of constants that needs to be
+  # eager loaded:
+  #
+  #   module MyLib
+  #     extend ActiveSupport::Autoload
+  #
+  #     autoload :Model
+  #
+  #     eager_autoload do
+  #       autoload :Cache
+  #     end
+  #   end
+  #
+  # Then your library can be eager loaded by simply calling:
+  #
+  #   MyLib.eager_load!
+  #
   module Autoload
-    @@autoloads = {}
-    @@under_path = nil
-    @@at_path = nil
-    @@eager_autoload = false
+    def self.extended(base)
+      base.class_eval do
+        @_autoloads = {}
+        @_under_path = nil
+        @_at_path = nil
+        @_eager_autoload = false
+      end
+    end
 
-    def autoload(const_name, path = @@at_path)
+    def autoload(const_name, path = @_at_path)
       unless path
-        full = [name, @@under_path, const_name.to_s, path].compact.join("::")
+        full = [name, @_under_path, const_name.to_s, path].compact.join("::")
         path = Inflector.underscore(full)
       end
 
-      if @@eager_autoload
-        @@autoloads[const_name] = path
+      if @_eager_autoload
+        @_autoloads[const_name] = path
       end
 
       super const_name, path
     end
 
     def autoload_under(path)
-      @@under_path, old_path = path, @@under_path
+      @_under_path, old_path = path, @_under_path
       yield
     ensure
-      @@under_path = old_path
+      @_under_path = old_path
     end
 
     def autoload_at(path)
-      @@at_path, old_path = path, @@at_path
+      @_at_path, old_path = path, @_at_path
       yield
     ensure
-      @@at_path = old_path
+      @_at_path = old_path
     end
 
     def eager_autoload
-      old_eager, @@eager_autoload = @@eager_autoload, true
+      old_eager, @_eager_autoload = @_eager_autoload, true
       yield
     ensure
-      @@eager_autoload = old_eager
+      @_eager_autoload = old_eager
     end
 
-    def self.eager_autoload!
-      @@autoloads.values.each { |file| require file }
+    def eager_load!
+      @_autoloads.values.each { |file| require file }
     end
 
     def autoloads
-      @@autoloads
+      @_autoloads
     end
   end
 end
diff --git a/activesupport/lib/active_support/railtie.rb b/activesupport/lib/active_support/railtie.rb
index 30ac881090..aa8d408da9 100644
--- a/activesupport/lib/active_support/railtie.rb
+++ b/activesupport/lib/active_support/railtie.rb
@@ -5,6 +5,8 @@ module ActiveSupport
   class Railtie < Rails::Railtie
     config.active_support = ActiveSupport::OrderedOptions.new
 
+    config.eager_load_namespaces << ActiveSupport
+
     initializer "active_support.deprecation_behavior" do |app|
       if deprecation = app.config.active_support.deprecation
         ActiveSupport::Deprecation.behavior = deprecation
diff --git a/activesupport/test/autoload.rb b/activesupport/test/autoload_test.rb
index 5d8026a9ca..7d02d835a8 100644
--- a/activesupport/test/autoload.rb
+++ b/activesupport/test/autoload_test.rb
@@ -28,15 +28,6 @@ class TestAutoloadModule < ActiveSupport::TestCase
     assert_nothing_raised { ::Fixtures::Autoload::SomeClass }
   end
 
-  test ":eager constants can be triggered via ActiveSupport::Autoload.eager_autoload!" do
-    module ::Fixtures::Autoload
-      autoload :SomeClass, "fixtures/autoload/some_class"
-    end
-    ActiveSupport::Autoload.eager_autoload!
-    assert $LOADED_FEATURES.include?("fixtures/autoload/some_class.rb")
-    assert_nothing_raised { ::Fixtures::Autoload::SomeClass }
-  end
-
   test "the location of autoloaded constants defaults to :name.underscore" do
     module ::Fixtures::Autoload
       autoload :SomeClass
@@ -51,8 +42,7 @@ class TestAutoloadModule < ActiveSupport::TestCase
       autoload :SomeClass
     end
 
-    ActiveSupport::Autoload.eager_autoload!
-    assert $LOADED_FEATURES.include?("fixtures/autoload/some_class.rb")
+    ::Fixtures::Autoload.eager_load!
     assert_nothing_raised { ::Fixtures::Autoload::SomeClass }
   end
 
diff --git a/guides/source/configuring.textile b/guides/source/configuring.textile
index c29b70ad5b..27eaf1cbc5 100644
--- a/guides/source/configuring.textile
+++ b/guides/source/configuring.textile
@@ -50,8 +50,6 @@ config.after_initialize do
 end
 </ruby>
 
-* +config.allow_concurrency+ should be true to allow concurrent (threadsafe) action processing. False by default. You probably don't want to call this one directly, though, because a series of other adjustments need to be made for threadsafe mode to work properly. Can also be enabled with +threadsafe!+.
-
 * +config.asset_host+ sets the host for the assets. Useful when CDNs are used for hosting assets, or when you want to work around the concurrency constraints builtin in browsers using different domain aliases. Shorter version of +config.action_controller.asset_host+.
 
 * +config.asset_path+ lets you decorate asset paths. This can be a callable, a string, or be +nil+ which is the default. For example, the normal path for +blog.js+ would be +/javascripts/blog.js+, let that absolute path be +path+. If +config.asset_path+ is a callable, Rails calls it when generating asset paths passing +path+ as argument. If +config.asset_path+ is a string, it is expected to be a +sprintf+ format string with a +%s+ where +path+ will get inserted. In either case, Rails outputs the decorated path. Shorter version of +config.action_controller.asset_path+.
@@ -89,6 +87,10 @@ end
 
 * +config.dependency_loading+ is a flag that allows you to disable constant autoloading setting it to false. It only has effect if +config.cache_classes+ is true, which it is by default in production mode. This flag is set to false by +config.threadsafe!+.
 
+* +config.eager_load+ when true, eager loads all registered `config.eager_load_namespaces`. This includes your application, engines, Rails frameworks and any other registered namespace.
+
+* +config.eager_load_namespaces+ registers namespaces that are eager loaded when +config.eager_load+ is true. All namespaces in the list must respond to the +eager_load!+ method.
+
 * +config.eager_load_paths+ accepts an array of paths from which Rails will eager load on boot if cache classes is enabled. Defaults to every folder in the +app+ directory of the application.
 
 * +config.encoding+ sets up the application-wide encoding. Defaults to UTF-8.
@@ -109,8 +111,6 @@ end
 
 * +config.middleware+ allows you to configure the application's middleware. This is covered in depth in the "Configuring Middleware":#configuring-middleware section below.
 
-* +config.preload_frameworks+ enables or disables preloading all frameworks at startup. Enabled by +config.threadsafe!+. Defaults to +nil+, so is disabled.
-
 * +config.queue+ configures a different queue implementation for the application. Defaults to +Rails::Queueing::Queue+. Note that, if the default queue is changed, the default +queue_consumer+ is not going to be initialized, it is up to the new queue implementation to handle starting and shutting down its own consumer(s).
 
 * +config.queue_consumer+ configures a different consumer implementation for the default queue. Defaults to +Rails::Queueing::ThreadedConsumer+.
@@ -129,10 +129,6 @@ config.session_store :my_custom_store
 
 This custom store must be defined as +ActionDispatch::Session::MyCustomStore+. In addition to symbols, they can also be objects implementing a certain API, like +ActiveRecord::SessionStore+, in which case no special namespace is required.
 
-* +config.threadsafe!+ enables +allow_concurrency+, +cache_classes+, +dependency_loading+ and +preload_frameworks+ to make the application threadsafe.
-
-WARNING: Threadsafe operation is incompatible with the normal workings of development mode Rails. In particular, automatic dependency loading and class reloading are automatically disabled when you call +config.threadsafe!+.
-
 * +config.time_zone+ sets the default time zone for the application and enables time zone awareness for Active Record.
 
 * +config.whiny_nils+ enables or disables warnings when a certain set of methods are invoked on +nil+ and it does not respond to them. Defaults to true in development and test environments.
@@ -203,7 +199,7 @@ Every Rails application comes with a standard set of middleware which it uses in
 
 * +ActionDispatch::SSL+ forces every request to be under HTTPS protocol. Will be available if +config.force_ssl+ is set to +true+. Options passed to this can be configured by using +config.ssl_options+.
 * +ActionDispatch::Static+ is used to serve static assets. Disabled if +config.serve_static_assets+ is +true+.
-* +Rack::Lock+ wraps the app in mutex so it can only be called by a single thread at a time. Only enabled if +config.action_controller.allow_concurrency+ is set to +false+, which it is by default.
+* +Rack::Lock+ wraps the app in mutex so it can only be called by a single thread at a time. Only enabled when +config.cache_classes_+ is +false+.
 * +ActiveSupport::Cache::Strategy::LocalCache+ serves as a basic memory backed cache. This cache is not thread safe and is intended only for serving as a temporary memory cache for a single thread.
 * +Rack::Runtime+ sets an +X-Runtime+ header, containing the time (in seconds) taken to execute the request.
 * +Rails::Rack::Logger+ notifies the logs that the request has began. After request is complete, flushes all the logs.
@@ -656,8 +652,6 @@ Serves as a placeholder so that +:load_environment_config+ can be defined to run
 
 *+load_active_support+* Requires +active_support/dependencies+ which sets up the basis for Active Support. Optionally requires +active_support/all+ if +config.active_support.bare+ is un-truthful, which is the default.
 
-*+preload_frameworks+* Loads all autoload dependencies of Rails automatically if +config.preload_frameworks+ is +true+ or "truthful". By default this configuration option is disabled. In Rails, when internal classes are referenced for the first time they are autoloaded. +:preload_frameworks+ loads all of this at once on initialization.
-
 *+initialize_logger+* Initializes the logger (an +ActiveSupport::BufferedLogger+ object) for the application and makes it accessible at +Rails.logger+, provided that no initializer inserted before this point has defined +Rails.logger+.
 
 *+initialize_cache+* If +Rails.cache+ isn't set yet, initializes the cache by referencing the value in +config.cache_store+ and stores the outcome as +Rails.cache+. If this object responds to the +middleware+ method, its middleware is inserted before +Rack::Runtime+ in the middleware stack.
@@ -752,13 +746,13 @@ The error occurred while evaluating nil.each
 
 *+build_middleware_stack+* Builds the middleware stack for the application, returning an object which has a +call+ method which takes a Rack environment object for the request.
 
-*+eager_load!+* If +config.cache_classes+ is true, runs the +config.before_eager_load+ hooks and then calls +eager_load!+ which will load all the Ruby files from +config.eager_load_paths+.
+*+eager_load!+* If +config.eager_load+ is true, runs the +config.before_eager_load+ hooks and then calls +eager_load!+ which will load all +config.eager_load_namespaces+.
 
 *+finisher_hook+* Provides a hook for after the initialization of process of the application is complete, as well as running all the +config.after_initialize+ blocks for the application, railties and engines.
 
 *+set_routes_reloader+* Configures Action Dispatch to reload the routes file using +ActionDispatch::Callbacks.to_prepare+.
 
-*+disable_dependency_loading+* Disables the automatic dependency loading if the +config.cache_classes+ is set to true and +config.dependency_loading+ is set to false.
+*+disable_dependency_loading+* Disables the automatic dependency loading if the +config.eager_load+ is set to true.
 
 h3. Database pooling
 
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 851f41249a..fea18b5f47 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -5,6 +5,8 @@
     default_url_options[:script_name] to set proper application's mount point by
     yourself. *Piotr Sarnacki*
 
+*   `config.threadsafe!` is deprecated in favor of `config.eager_load` which provides a more fine grained control on what is eager loaded *José Valim*
+
 *   The migration generator will now produce AddXXXToYYY/RemoveXXXFromYYY migrations with references statements, for instance
 
         rails g migration AddReferencesToProducts user:references supplier:references{polymorphic}
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index 3531728421..ae872f2bb0 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -16,7 +16,7 @@ module Rails
   #
   # Besides providing the same configuration as Rails::Engine and Rails::Railtie,
   # the application object has several specific configurations, for example
-  # "allow_concurrency", "cache_classes", "consider_all_requests_local", "filter_parameters",
+  # "cache_classes", "consider_all_requests_local", "filter_parameters",
   # "logger" and so forth.
   #
   # Check Rails::Application::Configuration to see them all.
@@ -216,8 +216,9 @@ module Rails
       railties.each { |r| r.run_tasks_blocks(app) }
       super
       require "rails/tasks"
+      config = self.config
       task :environment do
-        $rails_rake_task = true
+        config.eager_load = false
         require_environment!
       end
     end
@@ -296,7 +297,7 @@ module Rails
           middleware.use ::ActionDispatch::Static, paths["public"].first, config.static_cache_control
         end
 
-        middleware.use ::Rack::Lock unless config.allow_concurrency
+        middleware.use ::Rack::Lock unless config.cache_classes
         middleware.use ::Rack::Runtime
         middleware.use ::Rack::MethodOverride
         middleware.use ::ActionDispatch::RequestId
diff --git a/railties/lib/rails/application/bootstrap.rb b/railties/lib/rails/application/bootstrap.rb
index e567df7162..a1bc95550b 100644
--- a/railties/lib/rails/application/bootstrap.rb
+++ b/railties/lib/rails/application/bootstrap.rb
@@ -13,11 +13,18 @@ module Rails
         require "active_support/all" unless config.active_support.bare
       end
 
-      # Preload all frameworks specified by the Configuration#frameworks.
-      # Used by Passenger to ensure everything's loaded before forking and
-      # to avoid autoload race conditions in JRuby.
-      initializer :preload_frameworks, :group => :all do
-        ActiveSupport::Autoload.eager_autoload! if config.preload_frameworks
+      initializer :set_eager_load, :group => :all do
+        if config.eager_load.nil?
+          warn <<-INFO
+config.eager_load is set to nil. Please update your config/environments/*.rb files accordingly:
+
+  * development - set it to false
+  * test - set it to false (unless you use a tool that preloads your test environment)
+  * production - set it to true
+
+INFO
+          config.eager_load = config.cache_classes
+        end
       end
 
       # Initialize the logger early in the stack in case we need to log some deprecation.
@@ -60,7 +67,6 @@ module Rails
       end
 
       # Sets the dependency loading mechanism.
-      # TODO: Remove files from the $" and always use require.
       initializer :initialize_dependency_mechanism, :group => :all do
         ActiveSupport::Dependencies.mechanism = config.cache_classes ? :require : :load
       end
diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index 2b36cc9d0d..7f05b2e7e1 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -5,11 +5,11 @@ require 'rails/engine/configuration'
 module Rails
   class Application
     class Configuration < ::Rails::Engine::Configuration
-      attr_accessor :allow_concurrency, :asset_host, :asset_path, :assets, :autoflush_log,
+      attr_accessor :asset_host, :asset_path, :assets, :autoflush_log,
                     :cache_classes, :cache_store, :consider_all_requests_local, :console,
-                    :dependency_loading, :exceptions_app, :file_watcher, :filter_parameters,
+                    :eager_load, :exceptions_app, :file_watcher, :filter_parameters,
                     :force_ssl, :helpers_paths, :logger, :log_formatter, :log_tags,
-                    :preload_frameworks, :railties_order, :relative_url_root, :secret_token,
+                    :railties_order, :relative_url_root, :secret_token,
                     :serve_static_assets, :ssl_options, :static_cache_control, :session_options,
                     :time_zone, :reload_classes_only_on_change,
                     :queue, :queue_consumer
@@ -20,11 +20,9 @@ module Rails
       def initialize(*)
         super
         self.encoding = "utf-8"
-        @allow_concurrency             = false
         @consider_all_requests_local   = false
         @filter_parameters             = []
         @helpers_paths                 = []
-        @dependency_loading            = true
         @serve_static_assets           = true
         @static_cache_control          = nil
         @force_ssl                     = false
@@ -45,6 +43,7 @@ module Rails
         @log_formatter                 = ActiveSupport::Logger::SimpleFormatter.new
         @queue                         = Rails::Queueing::Queue
         @queue_consumer                = Rails::Queueing::ThreadedConsumer
+        @eager_load                    = nil
 
         @assets = ActiveSupport::OrderedOptions.new
         @assets.enabled                  = false
@@ -91,15 +90,12 @@ module Rails
         end
       end
 
-      # Enable threaded mode. Allows concurrent requests to controller actions and
-      # multiple database connections. Also disables automatic dependency loading
-      # after boot, and disables reloading code on every request, as these are
-      # fundamentally incompatible with thread safety.
       def threadsafe!
-        @preload_frameworks = true
+        ActiveSupport::Deprecation.warn "config.threadsafe! is deprecated. Rails applications " \
+          "behave by default as thread safe in production as long as config.cache_classes and " \
+          "config.eager_load are set to true"
         @cache_classes = true
-        @dependency_loading = false
-        @allow_concurrency = true
+        @eager_load = true
         self
       end
 
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 60aa40b92f..1952a0fc3a 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -50,9 +50,9 @@ module Rails
       end
 
       initializer :eager_load! do
-        if config.cache_classes && !(defined?($rails_rake_task) && $rails_rake_task)
+        if config.eager_load
           ActiveSupport.run_load_hooks(:before_eager_load, self)
-          eager_load!
+          config.eager_load_namespaces.each(&:eager_load!)
         end
       end
 
@@ -91,7 +91,7 @@ module Rails
 
       # Disable dependency loading during request cycle
       initializer :disable_dependency_loading do
-        if config.cache_classes && !config.dependency_loading
+        if config.eager_load
           ActiveSupport::Dependencies.unhook!
         end
       end
diff --git a/railties/lib/rails/commands/server.rb b/railties/lib/rails/commands/server.rb
index 9ef64da3ef..a684129353 100644
--- a/railties/lib/rails/commands/server.rb
+++ b/railties/lib/rails/commands/server.rb
@@ -87,6 +87,15 @@ module Rails
       middlewares = []
       middlewares << [Rails::Rack::Debugger]  if options[:debugger]
       middlewares << [::Rack::ContentLength]
+
+      # FIXME: add Rack::Lock in the case people are using webrick.
+      # This is to remain backwards compatible for those who are
+      # running webrick in production. We should consider removing this
+      # in development.
+      if server.name == 'Rack::Handler::WEBrick'
+        middlewares << [::Rack::Lock]
+      end
+
       Hash.new(middlewares)
     end
 
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 40f35ae5a6..3a5caf9f62 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -339,11 +339,16 @@ module Rails
 
     class << self
       attr_accessor :called_from, :isolated
+
       alias :isolated? :isolated
       alias :engine_name :railtie_name
 
+      delegate :eager_load!, to: :instance
+
       def inherited(base)
         unless base.abstract_railtie?
+          Rails::Railtie::Configuration.eager_load_namespaces << base
+
           base.called_from = begin
             # Remove the line number from backtraces making sure we don't leave anything behind
             call_stack = caller.map { |p| p.sub(/:\d+.*/, '') }
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
index 2016eb8b05..122e7e2b34 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
@@ -6,6 +6,9 @@
   # since you don't have to restart the web server when you make code changes.
   config.cache_classes = false
 
+  # Do not eager load code on boot.
+  config.eager_load = false
+
   # Show full error reports and disable caching.
   config.consider_all_requests_local       = true
   config.action_controller.perform_caching = false
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
index 80413be0d3..a627636089 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
@@ -4,6 +4,12 @@
   # Code is not reloaded between requests.
   config.cache_classes = true
 
+  # Eager load code on boot. This eager loads most of Rails and
+  # your application in memory, allowing both thread web servers
+  # and those relying on copy on write to perform better.
+  # Rake tasks automatically ignore this option for performance.
+  config.eager_load = true
+
   # Full error reports are disabled and caching is turned on.
   config.consider_all_requests_local       = false
   config.action_controller.perform_caching = true
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt
index 878deb49d7..8ab27eb6e1 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt
@@ -7,6 +7,11 @@
   # and recreated between test runs. Don't rely on the data there!
   config.cache_classes = true
 
+  # Do not eager load code on boot. This avoids loading your whole application
+  # just for the purpose of running a single test. If you are using a tool that
+  # preloads Rails for running tests, you may have to set it to true.
+  config.eager_load = false
+
   # Configure static asset server for tests with Cache-Control for performance.
   config.serve_static_assets = true
   config.static_cache_control = "public, max-age=3600"
diff --git a/railties/lib/rails/railtie.rb b/railties/lib/rails/railtie.rb
index 1cb99463cc..fba685c769 100644
--- a/railties/lib/rails/railtie.rb
+++ b/railties/lib/rails/railtie.rb
@@ -178,9 +178,6 @@ module Rails
       @config ||= Railtie::Configuration.new
     end
 
-    def eager_load!
-    end
-
     def railtie_namespace
       @railtie_namespace ||= self.class.parents.detect { |n| n.respond_to?(:railtie_namespace) }
     end
diff --git a/railties/lib/rails/railtie/configuration.rb b/railties/lib/rails/railtie/configuration.rb
index 1c6b3769a5..9dc8843887 100644
--- a/railties/lib/rails/railtie/configuration.rb
+++ b/railties/lib/rails/railtie/configuration.rb
@@ -7,6 +7,16 @@ module Rails
         @@options ||= {}
       end
 
+      # Expose the eager_load_namespaces at "module" level for convenience.
+      def self.eager_load_namespaces #:nodoc:
+        @@eager_load_namespaces ||= []
+      end
+
+      # All namespaces that are eager loaded
+      def eager_load_namespaces
+        @@eager_load_namespaces ||= []
+      end
+
       # Add files that should be watched for change.
       def watchable_files
         @@watchable_files ||= []
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index c813defe93..ebdbbaee8b 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -139,22 +139,19 @@ module ApplicationTests
       assert_instance_of Pathname, Rails.root
     end
 
-    test "marking the application as threadsafe sets the correct config variables" do
+    test "initialize an eager loaded, cache classes app" do
       add_to_config <<-RUBY
-        config.threadsafe!
+        config.eager_load = true
+        config.cache_classes = true
       RUBY
 
       require "#{app_path}/config/application"
-      assert AppTemplate::Application.config.allow_concurrency
+      assert AppTemplate::Application.initialize!
     end
 
-    test "initialize a threadsafe app" do
-      add_to_config <<-RUBY
-        config.threadsafe!
-      RUBY
-
+    test "application is always added to eager_load namespaces" do
       require "#{app_path}/config/application"
-      assert AppTemplate::Application.initialize!
+      assert AppTemplate::Application, AppTemplate::Application.config.eager_load_namespaces
     end
 
     test "asset_path defaults to nil for application" do
@@ -162,10 +159,11 @@ module ApplicationTests
       assert_equal nil, AppTemplate::Application.config.asset_path
     end
 
-    test "the application can be marked as threadsafe when there are no frameworks" do
+    test "the application can be eager loaded even when there are no frameworks" do
       FileUtils.rm_rf("#{app_path}/config/environments")
       add_to_config <<-RUBY
-        config.threadsafe!
+        config.eager_load = true
+        config.cache_classes = true
       RUBY
 
       use_frameworks []
@@ -175,22 +173,6 @@ module ApplicationTests
       end
     end
 
-    test "frameworks are not preloaded by default" do
-      require "#{app_path}/config/environment"
-
-      assert ActionController.autoload?(:Caching)
-    end
-
-    test "frameworks are preloaded with config.preload_frameworks is set" do
-      add_to_config <<-RUBY
-        config.preload_frameworks = true
-      RUBY
-
-      require "#{app_path}/config/environment"
-
-      assert !ActionView.autoload?(:AssetPaths)
-    end
-
     test "filter_parameters should be able to set via config.filter_parameters" do
       add_to_config <<-RUBY
         config.filter_parameters += [ :foo, 'bar', lambda { |key, value|
diff --git a/railties/test/application/middleware_test.rb b/railties/test/application/middleware_test.rb
index 9c9ed0cd6b..34b460d0a7 100644
--- a/railties/test/application/middleware_test.rb
+++ b/railties/test/application/middleware_test.rb
@@ -87,8 +87,8 @@ module ApplicationTests
       assert !middleware.include?("ActiveRecord::QueryCache")
     end
 
-    test "removes lock if allow concurrency is set" do
-      add_to_config "config.allow_concurrency = true"
+    test "removes lock if cache classes is set" do
+      add_to_config "config.cache_classes = true"
       boot!
       assert !middleware.include?("Rack::Lock")
     end
diff --git a/railties/test/application/rake_test.rb b/railties/test/application/rake_test.rb
index a450f90dbf..b05fe3aed5 100644
--- a/railties/test/application/rake_test.rb
+++ b/railties/test/application/rake_test.rb
@@ -55,6 +55,29 @@ module ApplicationTests
       assert_match "Doing something...", output
     end
 
+    def test_does_not_explode_when_accessing_a_model_with_eager_load
+      add_to_config <<-RUBY
+        config.eager_load = true
+
+        rake_tasks do
+          task :do_nothing => :environment do
+            Hello.new.world
+          end
+        end
+      RUBY
+
+      app_file "app/models/hello.rb", <<-RUBY
+      class Hello
+        def world
+          puts "Hello world"
+        end
+      end
+      RUBY
+
+      output = Dir.chdir(app_path){ `rake do_nothing` }
+      assert_match "Hello world", output
+    end
+
     def test_code_statistics_sanity
       assert_match "Code LOC: 5     Test LOC: 0     Code to Test Ratio: 1:0.0",
         Dir.chdir(app_path){ `rake stats` }
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 8f04692aef..d89cfba56d 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -12,7 +12,6 @@ require 'bundler/setup'
 require 'minitest/autorun'
 require 'active_support/test_case'
 
-# TODO: Remove setting this magic constant
 RAILS_FRAMEWORK_ROOT = File.expand_path("#{File.dirname(__FILE__)}/../../..")
 
 # These files do not require any others and are needed
@@ -118,6 +117,7 @@ module TestHelpers
       end
 
       add_to_config <<-RUBY
+        config.eager_load = false
         config.secret_token = "3b7cd727ee24e8444053437c36cc66c4"
         config.session_store :cookie_store, :key => "_myapp_session"
         config.active_support.deprecation = :log