my @waiting = @chromosomes;
my %threads;
my $max_threads = 10;

while ( scalar(@waiting) || scalar( keys(%threads) ) ) {

        if ( scalar( keys(%threads) ) < $max_threads ) {
                my $chr = pop(@waiting);
                $threads{$chr} = threads->new(\&threading_function, $chr);
                }

        else {

                foreach my $chr ( keys(%threads) ) {

                        if ( $threads{$chr}->is_joinable() ) {
                                $threads{$chr}->join();
                                delete $threads{$chr};
                                }

                        }

                }

        }