Improve performance of the rendering stack by freezing formats as a sign that they shouldn't be further modified.

2 files changed, 12 insertions, 6 deletions

diff --git a/actionpack/lib/action_view/render/layouts.rb b/actionpack/lib/action_view/render/layouts.rb
index b4720aa681..c790a70b3e 100644
--- a/actionpack/lib/action_view/render/layouts.rb
+++ b/actionpack/lib/action_view/render/layouts.rb
@@ -51,7 +51,7 @@ module ActionView
         if formats.size == 1
           _find_layout(layout)
         else
-          update_details(:formats => self.formats[0,1]){ _find_layout(layout) }
+          update_details(:formats => self.formats.first){ _find_layout(layout) }
         end
       rescue ActionView::MissingTemplate => e
         update_details(:formats => nil) do
diff --git a/actionpack/lib/action_view/render/rendering.rb b/actionpack/lib/action_view/render/rendering.rb
index b0fed556c3..a8f745afd1 100644
--- a/actionpack/lib/action_view/render/rendering.rb
+++ b/actionpack/lib/action_view/render/rendering.rb
@@ -21,7 +21,7 @@ module ActionView
           _render_partial(options)
         else
           template = _determine_template(options)
-          self.formats = template.formats
+          _freeze_formats(template.formats)
           _render_template(template, options[:layout], options)
         end
       when :update
@@ -58,12 +58,18 @@ module ActionView
         content = template.render(self, locals) { |*name| _layout_for(*name) }
         @_content_for[:layout] = content
 
-        if layout
-          content  = _render_layout(layout, locals)
-        end
-
+        content = _render_layout(layout, locals) if layout
         content
       end
     end
+
+    # Freeze the current formats in the lookup context. By freezing them, you are guaranteeing
+    # that next template lookups are not going to modify the formats. The controller can also
+    # use this, to ensure that formats won't be further modified (as it does in respond_to blocks).
+    def _freeze_formats(formats) #:nodoc:
+      return if self.formats.frozen?
+      self.formats = formats
+      self.formats.freeze
+    end
   end
 end