Creates and executes a periodic action that becomes enabled first after the given
initial delay, and subsequently with the given period; that is executions will
commence after initialDelay then initialDelay+period, then initialDelay + 2 * period,
and so on.
Creates and executes a periodic action that becomes enabled first after
the given initial delay, and subsequently with the given delay between
the termination of one execution and the commencement of the next.