At the risk of belaboring the points, here's v0.02:

sub getNewCounter
# ---------------------------------------------------------------
# Reads and incremements the counter value.  Implementation based 
# on wisdom gained from perlmonks.org and the Perl Cookbook.
# ---------------------------------------------------------------
{
   my( $datafile ) = @_;
   my( $lockfile );

   # Determine the name of the lock file
   $_ = $datafile;
   s/\.dat/\.lck/;
   $lockfile = $_;

   # The idea here is to wait up to ten seconds to gain access to 
   # the lock file.  If that fails, well, try again later.

   my( $retries ) = 10;

   open( LOCK, "$lockfile" )  or die "Cannot open lock file for readin
+g. $!";
   while ( $retries )
   {
      if ( flock( LOCK, LOCK_EX | LOCK_NB ) )  # if Fcntl isn't availa
+ble (it should be), try 2 | 4.
      {  
         last;
      } 
      else
      {
         $retries--;
         sleep( 1 ) ;
      }
   }

   # How did we get out of that loop?  If we failed to flock, then fle
+e
   unless ( $retries ) 
      { die "Cannot lock counter for reading. $!"; }

   # Okay, we're assuming here...   
   open( FILE, "+< $datafile" ) or die "Can't open data file for readi
+ng. $!";

   my( $countval ) = <FILE>;
   
   seek( FILE, 0, 0 )           or die "Can't reset data file for writ
+ing. $!";
   truncate( FILE, 0 )          or die "Can't clear data file for writ
+ing. $!";

   print FILE ++$countval;

   close( FILE )                or die "Cannot close counter after wri
+ting. $!";
   close( LOCK )                or die "Cannot close lock file. $!";
   return( $countval );

}
[download]

Yes, it assumes that the sentinel file already exists.

Better? (I ask because I may not be able to get the SecuroTroopers to install File::CounterFile.)

--f

P.S. Thanks to jptxs for picking up on the other question. Also, tilly's newest sub looks interesting and that will go into 0.03, should anything else?

Update: Thanks, tilly for your extreme patience in this. Point by Point:

1. .dat is fine for this script, but good advice for future ones.
2. Added LOCK_NB, per advice; see above.
3. I was under the impression that one second was the finest granularity available for sleep()?
4. You mean, like the 0.01 did?
5. *blush*
6. /me hies himself to a Monastery library...

Update #2: Quickly fixed the || typo and the magic numbers before running off to write v0.03.

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