#!/usr/bin/perl

use strict;
use warnings;

sub helper
{
        # forked process, wastes 10 seconds
        for (1..10) {
                print "helper: start of second $_\n";
                select(undef,undef,undef,1); # poor man's sleep, without messing with alarm
                print "helper: end of second $_\n";
        }
}

sub main
{
        # main process
        print "Helper will die in 5 seconds\n";
        alarm(5); # kill me in five seconds ...
        exec($^X,$0,"dummy argument") # start perl with this script and a parameter
                or die "Could not start helper: $!";
}

if (@ARGV) {
        helper();
} else {
        main();
}


##</code><code>##

>perl alarmtest.pl
Helper will die in 5 seconds
helper: start of second 1
helper: end of second 1
helper: start of second 2
helper: end of second 2
helper: start of second 3
helper: end of second 3
helper: start of second 4
helper: end of second 4
helper: start of second 5
Alarm clock

>

##</code><code>##

sub helper
{
        $SIG{'ALRM'}=sub { print "I am immortal, you fool!\n" };
        # forked process, wastes 10 seconds
        for (1..10) {
                print "helper: start of second $_\n";
                select(undef,undef,undef,1); # poor man's sleep, without messing with alarm
                print "helper: end of second $_\n";
        }
}


##</code><code>##

>perl alarmtest.pl
Helper will die in 5 seconds
helper: start of second 1
helper: end of second 1
helper: start of second 2
helper: end of second 2
helper: start of second 3
helper: end of second 3
helper: start of second 4
helper: end of second 4
helper: start of second 5
I am immortal, you fool!
helper: end of second 5
helper: start of second 6
helper: end of second 6
helper: start of second 7
helper: end of second 7
helper: start of second 8
helper: end of second 8
helper: start of second 9
helper: end of second 9
helper: start of second 10
helper: end of second 10

>