Periodic watcher operation modes

EvPeriodic watcher works in different modes depending on the offset , interval and reschedule_cb parameters.

  1. Absolute timer . In this mode interval = 0 , reschedule_cb = NULL. This time simply fires at the wallclock time offset and doesn't repeat. It will not adjust when a time jump occurs, that is, if it is to be run at January 1st 2014 then it will run when the system time reaches or surpasses this time.

  2. Repeating interval timer . In this mode interval > 0 , reschedule_cb = NULL; the watcher will always be scheduled to timeout at the next offset + N * interval time(for some integer N ) and then repeat, regardless of any time jumps.

    This can be used to create timers that do not drift with respect to system