2 files changed, 45 insertions, 5 deletions
diff --git a/activesupport/lib/active_support/notifications.rb b/activesupport/lib/active_support/notifications.rb
index ab2bb5fafe..5c985601f4 100644
--- a/activesupport/lib/active_support/notifications.rb
+++ b/activesupport/lib/active_support/notifications.rb
@@ -1,5 +1,6 @@
 require 'active_support/notifications/instrumenter'
 require 'active_support/notifications/fanout'
+require 'active_support/per_thread_registry'
 
 module ActiveSupport
   # = Notifications
@@ -190,12 +191,10 @@ module ActiveSupport
     # The instrumenters for multiple notifiers are held in a single instance of
     # this class.
     class InstrumentationRegistry # :nodoc:
-      class << self
-        delegate :instrumenter_for, to: :current
+      extend ActiveSupport::PerThreadRegistry
 
-        def current
-          Thread.current[:instrumentation_registry] ||= new
-        end
+      class << self
+        delegate :instrumenter_for, to: :instance
       end
 
       def initialize
diff --git a/activesupport/lib/active_support/per_thread_registry.rb b/activesupport/lib/active_support/per_thread_registry.rb
new file mode 100644
index 0000000000..b89ce2cbeb
--- /dev/null
+++ b/activesupport/lib/active_support/per_thread_registry.rb
@@ -0,0 +1,41 @@
+module ActiveSupport
+  # This module creates a local registry class inside each thread. It provides
+  # basic methods which will store thread locals in a single class. This
+  # prevents the proliferation of too many thread locals and allows you to
+  # explicitly keep track of each of the variables you're using as thread
+  # locals in a class which includes this module.
+  #
+  # For example, instead of using a bunch of different thread locals to keep
+  # track of some variables like so:
+  #
+  #   Thread.current[:active_record_connection_handler] = connection_handler
+  #   Thread.current[:active_record_sql_runtime]        = sql_runtime
+  #
+  # You could use the following class which implements the +PerThreadRegistry+
+  # module:
+  #
+  #   class NewRegistry
+  #     extend ActiveSupport::PerThreadRegistry
+  #
+  #     attr_accessor :connection_handler, :sql_runtime
+  #   end
+  #
+  #   NewRegistry.instance.connection_handler = connection_handler
+  #   NewRegistry.instance.sql_runtime        = sql_runtime
+  #
+  # The new way of keeping track of the thread locals will create a new local
+  # inside of +Thread.current+ with a key which is the name of the extended
+  # class. Now you can easily access per thread variables by just calling the
+  # variable name on the registry.
+  module PerThreadRegistry
+    def instance
+      Thread.current[self.name] ||= new
+    end
+
+    protected
+
+      def method_missing(*args, &block)
+        instance.send(*args, &block)
+      end
+  end
+end