1 files changed, 36 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/descendants_tracker.rb b/activesupport/lib/active_support/descendants_tracker.rb
new file mode 100644
index 0000000000..a9379bf95b
--- /dev/null
+++ b/activesupport/lib/active_support/descendants_tracker.rb
@@ -0,0 +1,36 @@
+require 'active_support/dependencies'
+
+module ActiveSupport
+  # This module provides an internal implementation to track descendants
+  # which is faster than iterating through ObjectSpace.
+  module DescendantsTracker
+    mattr_accessor :descendants
+    @@descendants = Hash.new { |h, k| h[k] = [] }
+
+    def self.clear
+      @@descendants.each do |klass, descendants|
+        if ActiveSupport::Dependencies.autoloaded?(klass)
+          @@descendants.delete(klass)
+        else
+          descendants.reject! { |v| ActiveSupport::Dependencies.autoloaded?(v) }
+        end
+      end
+    end
+
+    def inherited(base)
+      self.direct_descendants << base
+      super
+    end
+
+    def direct_descendants
+      @@descendants[self]
+    end
+
+    def descendants
+      @@descendants[self].inject([]) do |descendants, klass|
+        descendants << klass
+        descendants.concat klass.descendants
+      end
+    end
+  end
+end
+\ No newline at end of file