NAME¶
File::CounterFile - Persistent counter class
SYNOPSIS¶
use File::CounterFile;
$c = File::CounterFile->new("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 can attempt to access a counter simultaneously 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 if 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, it 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 decremented. 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 are 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 can use the "++" operator for incrementing and
the "--" operator for decrementing the counter, and you can
interpolate counters directly into strings.
COPYRIGHT¶
Copyright (c) 1995-1998,2002,2003 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 <gisle@aas.no>