Remove allow_concurrency as a flag

The flag was mainly used to add a Rack::Lock middleware to
the stack, but the only scenario the lock is desired is in
development.

If you are deploying on a not-threaded server, the Rack::Lock
does not provide any benefit since you don't have concurrent
accesses. On the other hand, if you are on a threaded server,
you don't want the lock, since it defeats the purpose of using
a threaded server.

If there is someone out there, running on a thread server
and does want a lock, it can be added to your environment
as easy as: `use Rack::Lock`

4 files changed, 7 insertions, 8 deletions

diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index 9f624437e5..32039c26f3 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.
@@ -304,7 +304,7 @@ 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/configuration.rb b/railties/lib/rails/application/configuration.rb
index 7dffe91bb9..77d89f0cb9 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -5,7 +5,7 @@ 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,
                     :eager_load, :exceptions_app, :file_watcher, :filter_parameters,
                     :force_ssl, :helpers_paths, :logger, :log_formatter, :log_tags,
@@ -20,7 +20,6 @@ module Rails
       def initialize(*)
         super
         self.encoding = "utf-8"
-        @allow_concurrency             = false
         @consider_all_requests_local   = false
         @filter_parameters             = []
         @helpers_paths                 = []
@@ -99,7 +98,6 @@ module Rails
         @preload_frameworks = true
         @cache_classes = true
         @eager_load = true
-        @allow_concurrency = true
         self
       end
 
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index c813defe93..eb808f5473 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -145,7 +145,8 @@ module ApplicationTests
       RUBY
 
       require "#{app_path}/config/application"
-      assert AppTemplate::Application.config.allow_concurrency
+      assert AppTemplate::Application.config.cache_classes
+      assert AppTemplate::Application.config.eager_load
     end
 
     test "initialize a threadsafe app" do
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