I'm not sure what you are tring to do, but your second example has
my @results :shared = 1;
which adds an unneccesary element to the array. It should be:
my @results :shared;

This seems to work right for me. Remember, it's up to the system as to which thread gets run first, unless you prioritize them. So run the code below multiple times, and see how the system sometimes gets the order right, but will sometimes lets a different thread order. Also you should lock @results

#!/usr/bin/perl -w
use strict;
use threads;
use threads::shared;
use Thread::Semaphore;

my $sem = Thread::Semaphore->new(15); # max 15 threads

my @results:shared;

for my $i (0..5) {
    $sem->down;
    my $t = threads->create(\&mySubName, $i);
}


<>;
print join(" ",@results);
<>;


sub mySubName {
    threads->detach();
    my $foo = shift(@_);
    print "$foo\n";
    lock @results;
    push (@results,$foo);
    $sem->up;
}
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