Merge pull request #17102 from matthewd/load-interlock

Concurrent load interlock (rm Rack::Lock)

2 files changed, 25 insertions, 11 deletions

diff --git a/railties/lib/rails/application/default_middleware_stack.rb b/railties/lib/rails/application/default_middleware_stack.rb
index 6f9ccec137..88eade5c5a 100644
--- a/railties/lib/rails/application/default_middleware_stack.rb
+++ b/railties/lib/rails/application/default_middleware_stack.rb
@@ -26,7 +26,27 @@ module Rails
             middleware.use ::Rack::Cache, rack_cache
           end
 
-          middleware.use ::Rack::Lock unless allow_concurrency?
+          if config.allow_concurrency == false
+            # User has explicitly opted out of concurrent request
+            # handling: presumably their code is not threadsafe
+
+            middleware.use ::Rack::Lock
+
+          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: enabled, but safe
+
+            unless config.cache_classes && config.eager_load
+              # Without cache_classes + eager_load, the load interlock
+              # is required for proper operation
+
+              middleware.use ::ActionDispatch::LoadInterlock
+            end
+          end
+
           middleware.use ::Rack::Runtime
           middleware.use ::Rack::MethodOverride unless config.api_only
           middleware.use ::ActionDispatch::RequestId
@@ -65,14 +85,6 @@ module Rails
           config.reload_classes_only_on_change != true || app.reloaders.map(&:updated?).any?
         end
 
-        def allow_concurrency?
-          if config.allow_concurrency.nil?
-            config.cache_classes && config.eager_load
-          else
-            config.allow_concurrency
-          end
-        end
-
         def load_rack_cache
           rack_cache = config.action_dispatch.rack_cache
           return unless rack_cache
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