NAME

       Vend::CounterFile - Persistent counter class

SYNOPSIS

        use Vend::CounterFile;
        $c = new Vend::CounterFile "COUNTER", "aa00";

        $id = $c->inc;
        open(F, ">F$id");

DESCRIPTION

       (This module is modified from Gisle Aas File::CounterFile to use
        Interchange's locking protocols -- lack of fcntl locking was causing
        counter problems.)

       This module implements a persistent counter class.  Each counter is represented by a
       separate file in the file system.  File locking is applied, so multiple processes might
       try to access the same counters at the same time without risk of counter destruction.

       You give the file name as the first parameter to the object constructor ("new").  The file
       is created if it does not exist.

       If the file name does not start with "/" or ".", then it is interpreted as a file relative
       to $Vend::CounterFile::DEFAULT_DIR.  The default value for this variable is initialized
       from the environment variable "TMPDIR", or /usr/tmp is no environment variable is defined.
       You may want to assign a different value to this variable before creating counters.

       If you pass a second parameter to the constructor, that sets the initial value for a new
       counter.  This parameter only takes effect when the file is created (i.e. it does not
       exist before the call).

       When you call the "inc()" method, you increment the counter value by one. When you call
       "dec()" the counter value is decrementd.  In both cases the new value is returned.  The
       "dec()" method only works for numerical counters (digits only).

       You can peek at the value of the counter (without incrementing it) by using the "value()"
       method.

       The counter can be locked and unlocked with the "lock()" and "unlock()" methods.
       Incrementing and value retrieval is faster when the counter is locked, because we do not
       have to update the counter file all the time.  You can query whether the counter is locked
       with the "locked()" method.

       There is also an operator overloading interface to the Vend::CounterFile object.  This
       means that you might use the "++" operator for incrementing the counter, "--" operator for
       decrementing and you can interpolate counters diretly into strings.

BUGS

       (This problem alleviated by this modified module)

       It uses flock(2) to lock the counter file.  This does not work on all systems.  Perhaps we
       should use the File::Lock module?

COPYRIGHT

       Copyright (c) 1995-1998 Gisle Aas. All rights reserved.  Modifications made by and
       copyright (C) 2002 Red Hat, Inc.  and (c) 2002-2007 Interchange Development Group

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

AUTHOR

       Gisle Aas <aas@sn.no>