line1 data data data
line2 data data dataline3 data data data
line4 data data data

line5 data data data
line6 dataline7 data data data data

line8 data data data data

##</code><code>##

use strict;
use warnings; 
use GRID::Cluster;

my $script = "script.plx";

my @processes = (...);
my @machines = (...);
my %max_num_processes = (...);

my $cluster = GRID::Cluster->new(
  	host_names => \@machines, max_num_np => \%max_num_processes,
);

$cluster->qx(@processes);

##</code><code>##

use strict;
use warnings;
use Fcntl qw(:flock);
my @letters = qw(a b c d);

foreach my $letter (@letters) {

	my $output_file = "output_" . $letter . ".txt";

	# This didn't solve my problem
	# I also tried +< instead of >>, but nothing happened at all
	# when I did that
# 	open my $filehandle, ">>$output_file";
# 	flock($filehandle, LOCK_EX);

	# So instead I tried the version in the comments on the 
	# tutorial page although I don't really understand it :-(
	open my $semaphore, ">$output_file.lock";
	flock($semaphore, LOCK_EX);
	open my $filehandle, ">>$output_file";

	print $filehandle "line$number data data data\t";

	close $filehandle;
	close $semaphore;
}