Event::add

说明

Marks event pending. Non-pending event will never occur, and the event callback will never be called. In conjuction with Event::del() an event could be re-scheduled by user at any time.

If Event::add() is called on an already pending event, libevent will leave it pending and re-schedule it with the given timeout(if specified). If in this case timeout is not specified, Event::add() has no effect.