#!/usr/bin/perl -w
#testlock.pl
use strict;
use Parallel::ForkManager;
use Fcntl qw(:flock SEEK_END);
my @timenow = localtime;
open (my $out, ">", "output_" . $timenow[1] . "_" . $timenow[0] . ".txt") || die "Could not open output: $!\n";
my $stdout = select ($out);
$| = 1;
select ($stdout);
my @files = (1 ..100);
my $fork = new Parallel::ForkManager(8);
foreach my $file (@files){
    $fork->start and next;
    my $checksum = "md5sum $file";
    flock($out, LOCK_EX) or die "Cannot lock filehandle - $!\n";
    seek($out, 0, SEEK_END) or die "Cannot seek - $!\n";
    print $out "Analysis for file $file\n\tchecksum $checksum\n";
    flock($out, LOCK_UN) or die "Cannot unlock filehandle - $!\n";
    $fork->finish;
}
$fork->wait_all_children;
close $out;