sub scan_host {
    while( my( $ip )= $hosts->dequeue() ) {
        warn "Scanning '$ip'";
        ... do real work
        $portstatus->enqueue({
            host => $ip,
            status => 'too lazy',
        });
    };
}

for( 1..$NUM_THREADS ) {
    threads->create( \&scan_host );
};

##</code><code>##

$hosts->end;

while(my $result= $portstatus->dequeue()) {
    print Dumper $result;
};