class ActiveSupport::Notifications::Instrumenter

def instrument(name, payload={})

in the passed-in block.
and publish it. Notice that events get sent even if an error occurs
Instrument the given block by measuring the time taken to execute it 
def instrument(name, payload={})
  start name, payload
  begin
    yield payload
  rescue Exception => e
    payload[:exception] = [e.class.name, e.message]
    raise e
  ensure
    finish name, payload
  end
end