use threads::shared;
use Parallel::Queue;

print concatenate_parallel( ['a' .. 'z'], 4 ) . "\n";

sub concatenate_parallel {
    my $result :shared;
    my @input = map {
        my $string = $_;
        sub {
            $result .= $string;
        };
    } @{ shift @_ };
    my $max_threads = shift @_;

    my $mgr = Parallel::Queue->construct( 'thread' );
    $mgr->runqueue( $max_threads, @input );

    return $result;
}