use Parallel::ForkManager;
$threads=4;
if($threads==1)
	{
	read_genome();
	read_mapfile();
	read_GTF();
	read_RM();
	}
else
	{
	@eval_code=("read_genome();","read_mapfile();","read_GTF();","read_RM();");
	my$pm=new Parallel::ForkManager($threads);
	foreach$eval_code(@eval_code)
		{
		$pm->start and next;
		eval$eval_code;
		$pm->finish;
		}
	$pm->wait_all_children;
	}

sub read_genome
	{
	# do something
	}
sub read_mapfile;
	{
	# do something
	}
sub read_GTF
	{
	# do something
	}
sub read_RM
	{
	# do something
	}

# use data generated in the subroutines