1 files changed, 13 insertions, 1 deletions
diff --git a/actionpack/lib/action_controller/dispatcher.rb b/actionpack/lib/action_controller/dispatcher.rb
index 106d9605af..90c8400c11 100644
--- a/actionpack/lib/action_controller/dispatcher.rb
+++ b/actionpack/lib/action_controller/dispatcher.rb
@@ -2,6 +2,8 @@ module ActionController
   # Dispatches requests to the appropriate controller and takes care of
   # reloading the app after each request when Dependencies.load? is true.
   class Dispatcher
+    @@guard = Mutex.new
+
     class << self
       def define_dispatcher_callbacks(cache_classes)
         unless cache_classes
@@ -99,7 +101,7 @@ module ActionController
       @output, @request, @response = output, request, response
     end
 
-    def dispatch
+    def dispatch_unlocked
       begin
         run_callbacks :before_dispatch
         handle_request
@@ -110,6 +112,16 @@ module ActionController
       end
     end
 
+    def dispatch
+      if ActionController::Base.allow_concurrency
+        dispatch_unlocked
+      else
+        @@guard.synchronize do
+          dispatch_unlocked
+        end
+      end
+    end
+
     def dispatch_cgi(cgi, session_options)
       if cgi ||= self.class.failsafe_response(@output, '400 Bad Request') { CGI.new }
         @request = CgiRequest.new(cgi, session_options)