#!/usr/bin/perl - w
use strict;

# test case on ActivePerl 5.10 under WinXP

$|++;	       #turns off stdout buffering 
               #good for testing but a big performance
               #penalty

use Fcntl qw (:flock);
$SIG{INT}  =  \&release_lock;
$SIG{QUIT} =  \&release_lock;

my $lock_file = "$0.lck";

#this next open will succeed if you have w permission...
#even if you you don't have the lock yet or lock file
#doesn't exist yet..

open LOCKFILE, ">>$lock_file" || die "Cannot open $lock_file";

my  $got_lock =flock(LOCKFILE, LOCK_EX | LOCK_NB);
if ($got_lock)
{
   print "lock acquired\n";
   foreach (1..10)
   {
     print "Locked..doing something..$_ seconds\n";
     sleep(1);
   }
}
else
{
   print STDERR "could not acquire lock\n";
   exit(1);
}

print "Finished...Normal Exit, releasing lock\n";
close LOCKFILE    || die "Cannot close $lock_file";
unlink $lock_file || die "Internal program error";
exit(0);  #not needed but this is normal close

sub release_lock
{
   print STDERR "Abnormal exit...releasing lock\n";
   close LOCKFILE     || die "Cannot close $lock_file";
   unlink $lock_file  || die "Internal program error";
   exit(2);
}