lib::File::CounUseriContributed Perl Doclib::File::CounterFile(3)NAMEFile::CounterFile - Persistent counter class
SYNOPSIS
use File::CounterFile;
$c = new File::CounterFile "COUNTER", "aa00";
$id = $c->inc;
open(F, ">F$id");
DESCRIPTION
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
$File::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
File::CounterFile object. This means that you might use
the ++ operator for incrementing the counter, -- operator
for decrementing and you can interpolate counters diretly
24/Aug/1997 perl 5.005, patch 03 1
lib::File::CounUseriContributed Perl Doclib::File::CounterFile(3)
into strings.
BUGS
It uses flock(2) to lock the counter file. This does not
work on all systems. Perhaps we should use the File::Lock
module?
INSTALLATION
Copy this file to the File subdirectory of your Perl 5
library directory (often /usr/local/lib/perl5).
COPYRIGHT
Copyright (c) 1995-1996 Gisle Aas. All rights reserved.
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>
24/Aug/1997 perl 5.005, patch 03 2
