#!/usr/bin/perl
use strict;
use warnings;
use Storable qw/lock_store lock_retrieve/;
use CGI;
use Thread::Semaphore;

my $q = new CGI;
my $s = new Thread::Semaphore;
$s->up;
my $x = lock_retrieve('k.dat') or die "Can't open k.dat: $!";
$x->{counter}++;
$x = lock_store('k.dat') or die "Can't save k.dat: $!";
$s->down;

print $q->header;
print "<h1>Hi</h1>\n";