Rely on the load interlock for non-caching reloads, too

2 files changed, 11 insertions, 17 deletions

diff --git a/railties/lib/rails/application/default_middleware_stack.rb b/railties/lib/rails/application/default_middleware_stack.rb
index 14ea073039..88eade5c5a 100644
--- a/railties/lib/rails/application/default_middleware_stack.rb
+++ b/railties/lib/rails/application/default_middleware_stack.rb
@@ -32,26 +32,18 @@ module Rails
 
             middleware.use ::Rack::Lock
 
-          elsif config.allow_concurrency
-            # Do nothing, even if we know this is dangerous
+          elsif config.allow_concurrency == :unsafe
+            # Do nothing, even if we know this is dangerous. This is the
+            # historical behaviour for true.
 
           else
-            # Default concurrency setting
+            # Default concurrency setting: enabled, but safe
 
-            if config.cache_classes && config.eager_load
-              # No lock required
-
-            elsif config.cache_classes
-              # The load interlock is required, but not a full request
-              # lock
+            unless config.cache_classes && config.eager_load
+              # Without cache_classes + eager_load, the load interlock
+              # is required for proper operation
 
               middleware.use ::ActionDispatch::LoadInterlock
-
-            else
-              # If we're reloading on each request, they all need to be
-              # run in isolation
-
-              middleware.use ::Rack::Lock
             end
           end
 
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 0599e988d9..f8f92792a7 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -86,8 +86,10 @@ module Rails
       # added in the hook are taken into account.
       initializer :set_clear_dependencies_hook, group: :all do
         callback = lambda do
-          ActiveSupport::DescendantsTracker.clear
-          ActiveSupport::Dependencies.clear
+          ActiveSupport::Dependencies.interlock.attempt_loading do
+            ActiveSupport::DescendantsTracker.clear
+            ActiveSupport::Dependencies.clear
+          end
         end
 
         if config.reload_classes_only_on_change