class Concurrent::ScheduledTask

def cancel
  if compare_and_set_state(:cancelled, :pending, :unscheduled)
    complete(false, nil, CancelledOperationError.new)
    # To avoid deadlocks this call must occur outside of #synchronize
    # Changing the state above should prevent redundant calls
    @parent.send(:remove_task, self)
  else
    false
  end
end