1 files changed, 27 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/concurrent_hash.rb b/activesupport/lib/active_support/concurrent_hash.rb
new file mode 100644
index 0000000000..40224765a7
--- /dev/null
+++ b/activesupport/lib/active_support/concurrent_hash.rb
@@ -0,0 +1,27 @@
+module ActiveSupport
+  class ConcurrentHash
+    def initialize(hash = {})
+      @backup_cache = hash.dup
+      @frozen_cache = hash.dup.freeze
+      @mutex = Mutex.new
+    end
+
+    def []=(k,v)
+      @mutex.synchronize { @backup_cache[k] = v }
+      @frozen_cache = @backup_cache.dup.freeze
+      v
+    end
+
+    def [](k)
+      if @frozen_cache.key?(k)
+        @frozen_cache[k]
+      else
+        @mutex.synchronize { @backup_cache[k] }
+      end
+    end
+
+    def empty?
+      @backup_cache.empty?
+    end
+  end
+end