With Perl, there is always more than one way to do things! There is always a YMMV aspect!

In the spirit of trying to be helpful, I wrote some simple code that I tested on my Windows machine. Attached below. I think the poster has a couple of solid ideas to work from and can decide what is best for what is likely a complex situation, of which we've only been given a part. It could also be that sometimes method A is best and sometimes method B is best. Sometimes method C is just fine even though it fails 1 of 100,000 times. The below is just an idea of how to implement one of many suggestions. 

#!/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);
}

[download]

In reply to Re^4: Abort if instance already running? by Marshall
in thread Abort if instance already running? by pileofrogs

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.