I came here to correct my code but you have corrected it already :)

Yes, that's the problem. Although I have said in my first post that locking does not help, I have done it wrong.

What I have tried was this:

for(my $i = 0; $i < 100; $i++) {
        $pm->start and next;
        (tied $testvr)->shlock;
        if($testvr >= 5) {
            $testvr = 0;
         }
        $testvr++;
        (tied $testvr)->shunlock;
        (tied $testvr)->shlock;
        print $testvr . "\n";
        tied $testvr)->shunlock;
        $pm->finish;
}
$pm->wait_all_children;
[download]

It does not work correctly. I was locking and unlocking twice. As it was a testing code, I did not care to write locking statement twice, I assumed that it is doing the same thing.

Thanks