class ActiveSupport::ExecutionWrapper

def self.run!

Where possible, prefer +wrap+.

after the work has been performed.
Returns an instance, whose +complete!+ method *must* be invoked

Run this execution. 
def self.run!
  if active?
    Null
  else
    new.tap do |instance|
      success = nil
      begin
        instance.run!
        success = true
      ensure
        instance.complete! unless success
      end
    end
  end
end