man File::CounterFile () - Persistent counter class

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 (CWnew). 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 CW$File::CounterFile::DEFAULT_DIR. The default value for this variable is initialized from the environment variable CWTMPDIR, 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 CWinc() method, you increment the counter value by one. When you call CWdec(), the counter value is decremented. In both cases the new value is returned. The CWdec() method only works for numerical counters (digits only).

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

The counter can be locked and unlocked with the CWlock() and CWunlock() 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 CWlocked() method.

There is also an operator overloading interface to the File::CounterFile object. This means that you can use the CW++ operator for incrementing and the CW-- 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>