#!/usr/bin/perl
use strict;
use warnings;

use threads;
use Thread::Queue;

sub check_num {
    my ($upstream, $cur_prime) = @_;
    my $kid;
    my $downstream = Thread::Queue->new();

    while (my $num = $upstream->dequeue()) {
        next unless ($num % $cur_prime);

        if ($kid) {
            $downstream->enqueue($num);
        } else {
            print("Found prime: $num\n");
            $kid = threads->create(\&check_num, $downstream, $num);
        }
    }

    if ($kid) {
        $downstream->enqueue(undef);
        $kid->join();
    }
}

my $stream = Thread::Queue->new(shift()..shift(), undef);
check_num($stream, 2);