#!/usr/bin/perl -w

use strict;

use IPC::SysV qw(IPC_PRIVATE S_IRWXU IPC_CREAT SEM_UNDO ftok);
use IPC::Semaphore;

srand;

my $sem =
  new IPC::Semaphore( ftok( $0, 0 ), 1, S_IRWXU | IPC_CREAT );

my $semval = $sem->getval(0);
$semval = 0 unless ( defined($semval) );

exit(0) if ( $semval >= 10 );
$sem->op( 0, 1, SEM_UNDO );

#
# Do work... or in this case, 
# print the value of $semval and sleep for a while
#
print $semval + 1, "\n";
sleep( int( rand(20) + 1 ) );

#
# Decrement the semaphore value
#
$semval = $sem->getval(0);
if ($semval) {
    $sem->op( 0, -1, SEM_UNDO );
}
else {
    $sem->remove;
}
__END__
#
# Sample test execution (in bash):
#
# index=500
# while [ $index -gt 0 ] 
# do 
#     perl test.pl & 
#     let "index=index-1" 
# done
#