Added back ActionController::Base.allow_concurrency flag and moved lock down to controller processing.

actionpack/CHANGELOG

@@ -1,5 +1,7 @@
 *Edge*
 
+* Added back ActionController::Base.allow_concurrency flag [Josh Peek]
+
 * AbstractRequest.relative_url_root is no longer automatically configured by a HTTP header. It can now be set in your configuration environment with config.action_controller.relative_url_root [Josh Peek]
 
 * Update Prototype to 1.6.0.2 #599 [Patrick Joyce]

actionpack/lib/action_controller/base.rb

@@ -283,6 +283,14 @@ class Base
     @@debug_routes = true
     cattr_accessor :debug_routes
 
+    # Indicates whether to allow concurrent action processing. Your
+    # controller actions and any other code they call must also behave well
+    # when called from concurrent threads. Turned off by default.
+    @@allow_concurrency = false
+    cattr_accessor :allow_concurrency
+
+    @@guard = Monitor.new
+
     # Modern REST web services often need to submit complex data to the web application.
     # The <tt>@@param_parsers</tt> hash lets you register handlers which will process the HTTP body and add parameters to the
     # <tt>params</tt> hash. These handlers are invoked for POST and PUT requests.
@@ -537,7 +545,12 @@ def process(request, response, method = :perform_action, *arguments) #:nodoc:
         forget_variables_added_to_assigns
 
         log_processing
-        send(method, *arguments)
+
+        if @@allow_concurrency
+          send(method, *arguments)
+        else
+          @@guard.synchronize { send(method, *arguments) }
+        end
 
         assign_default_content_type_and_charset
         response.prepare! unless component_request?

actionpack/lib/action_controller/dispatcher.rb

@@ -2,8 +2,6 @@ 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
@@ -101,15 +99,13 @@ def initialize(output = $stdout, request = nil, response = nil)
     end
 
     def dispatch
-      @@guard.synchronize do
-        begin
-          run_callbacks :before_dispatch
-          handle_request
-        rescue Exception => exception
-          failsafe_rescue exception
-        ensure
-          run_callbacks :after_dispatch, :enumerator => :reverse_each
-        end
+      begin
+        run_callbacks :before_dispatch
+        handle_request
+      rescue Exception => exception
+        failsafe_rescue exception
+      ensure
+        run_callbacks :after_dispatch, :enumerator => :reverse_each
       end
     end