1 files changed, 47 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/dependencies/interlock.rb b/activesupport/lib/active_support/dependencies/interlock.rb
new file mode 100644
index 0000000000..fbeb904684
--- /dev/null
+++ b/activesupport/lib/active_support/dependencies/interlock.rb
@@ -0,0 +1,47 @@
+require 'active_support/concurrency/share_lock'
+
+module ActiveSupport #:nodoc:
+  module Dependencies #:nodoc:
+    class Interlock
+      def initialize # :nodoc:
+        @lock = ActiveSupport::Concurrency::ShareLock.new
+      end
+
+      def loading
+        @lock.exclusive(purpose: :load, compatible: [:load]) do
+          yield
+        end
+      end
+
+      def unloading
+        @lock.exclusive(purpose: :unload, compatible: [:load, :unload]) do
+          yield
+        end
+      end
+
+      # Attempt to obtain an "unloading" (exclusive) lock. If possible,
+      # execute the supplied block while holding the lock. If there is
+      # concurrent activity, return immediately (without executing the
+      # block) instead of waiting.
+      def attempt_unloading
+        @lock.exclusive(purpose: :unload, compatible: [:load, :unload], no_wait: true) do
+          yield
+        end
+      end
+
+      def start_running
+        @lock.start_sharing
+      end
+
+      def done_running
+        @lock.stop_sharing
+      end
+
+      def running
+        @lock.sharing do
+          yield
+        end
+      end
+    end
+  end
+end