(PECL ev >= 0.2.0)
EvPeriodic::at — Returns the absolute time that this watcher is supposed to trigger next
When the watcher is active, returns the absolute time that this watcher is supposed to trigger next. This is not the same as the offset argument to EvPeriodic::set() or EvPeriodic::__construct() , but indeed works even in interval mode.
此函数没有参数。
Returns the absolute time this watcher is supposed to trigger next in seconds.