signal to the executing Perl program after
On some older systems, alarms go off "at the top of the second,"
so, for instance, an
may go off anywhere between 0 to 1 seconds from now,
depending on when in the current second it is. An
may go off anywhere from 1 to 2 seconds from now. And so on.
Each call disables the previous timer, and an argument of
supplied to cancel the previous timer without starting a new one. The
return value is the number of seconds remaining on the previous timer.