perl's threads are not like other language's threads; they operate much like processes in that they don't share variables. Here's a thread example:

use strict;
use warnings;
use 5.010;

use threads;
use threads::shared;

my $val :shared = 10;
my $other_val = 'hello';

sub do_stuff {
    my $thr_id = shift;
    sleep int(rand 3);

    $other_val .= ' world';

    {
        lock $val;  #other threads cannot access $val until after
                    #this block exits

        say "thread$thr_id sees:";
        say "\t\$val = $val";
        say "\t\$other_val = $other_val";
        
        $val += 2;
    }
}

for (1 .. 10) {
    threads->new(\&do_stuff, $_);
}

for my $thr ( threads->list() ) {
    $thr->join();
}

--output:--
thread4 sees:
        $val = 10
        $other_val = hello world
thread6 sees:
        $val = 12
        $other_val = hello world
thread1 sees:
        $val = 14
        $other_val = hello world
thread3 sees:
        $val = 16
        $other_val = hello world
thread5 sees:
        $val = 18
        $other_val = hello world
thread8 sees:
        $val = 20
        $other_val = hello world
thread10 sees:
        $val = 22
        $other_val = hello world
thread2 sees:
        $val = 24
        $other_val = hello world
thread7 sees:
        $val = 26
        $other_val = hello world
thread9 sees:
        $val = 28
        $other_val = hello world
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See perthrtut for more info. Or see perlipc for other ideas.