1 files changed, 78 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/execution_wrapper.rb b/activesupport/lib/active_support/execution_wrapper.rb
new file mode 100644
index 0000000000..2bd1c01d35
--- /dev/null
+++ b/activesupport/lib/active_support/execution_wrapper.rb
@@ -0,0 +1,78 @@
+require 'active_support/callbacks'
+
+module ActiveSupport
+  class ExecutionWrapper
+    include ActiveSupport::Callbacks
+
+    Null = Object.new # :nodoc:
+    def Null.complete! # :nodoc:
+    end
+
+    define_callbacks :run
+    define_callbacks :complete
+
+    def self.to_run(*args, &block)
+      set_callback(:run, *args, &block)
+    end
+
+    def self.to_complete(*args, &block)
+      set_callback(:complete, *args, &block)
+    end
+
+    # Run this execution.
+    #
+    # Returns an instance, whose +complete!+ method *must* be invoked
+    # after the work has been performed.
+    #
+    # Where possible, prefer +wrap+.
+    def self.run!
+      if active?
+        Null
+      else
+        new.tap(&:run!)
+      end
+    end
+
+    # Perform the work in the supplied block as an execution.
+    def self.wrap
+      return yield if active?
+
+      state = run!
+      begin
+        yield
+      ensure
+        state.complete!
+      end
+    end
+
+    class << self # :nodoc:
+      attr_accessor :active
+    end
+
+    def self.inherited(other) # :nodoc:
+      super
+      other.active = Concurrent::Hash.new
+    end
+
+    self.active = Concurrent::Hash.new
+
+    def self.active? # :nodoc:
+      @active[Thread.current]
+    end
+
+    def run! # :nodoc:
+      self.class.active[Thread.current] = true
+      run_callbacks(:run)
+    end
+
+    # Complete this in-flight execution. This method *must* be called
+    # exactly once on the result of any call to +run!+.
+    #
+    # Where possible, prefer +wrap+.
+    def complete!
+      run_callbacks(:complete)
+    ensure
+      self.class.active.delete Thread.current
+    end
+  end
+end