NAME

Tie::Cache::LRU::Virtual - Virtual base class for Tie::Cache::LRU::*

SYNOPSIS

package My::Tie::Cache::LRU;

use base qw(Tie::Cache::LRU::Virtual);

...override and define key methods...

DESCRIPTION

This is a pure virtual base class defining the public methods of Tie::Cache::LRU. It is intended that you will subclass off of it and fill in the missing/incomplete methods.

You must implement the entire hash interface.

TIEHASH
CLEAR
FETCH
STORE
EXISTS
DELETE
FIRSTKEY
NEXTKEY

And the object interface

curr_size
max_size

As well as DESTROY if necessary.

I'm usually not taken to such heights of OO formality, but in this case a virtual class seemed in order.

USAGE

The cache is extremely simple, is just holds a simple scalar. If you want to cache an object, just place it into the cache:

$cache{$obj->id} = $obj;

This doesn't make a copy of the object, it just holds a reference to it. (Note: This means that your object's destructor will not be called until it has fallen out of the cache (and all other references to it have disappeared, of course)!)

If you want to cache an array, place a reference to it in the cache:

$cache{$some_id} = \@array;

Or, if you're worried about the consequences of tossing around references and want to cache a copy instead, you can do something like this:

$cache{$some_id} = [@array];

Tied Interface

tie

tie %cache, 'Tie::Cache::LRU';
tie %cache, 'Tie::Cache::LRU', $cache_size;

This ties a cache to %cache which will hold a maximum of $cache_size keys. If $cache_size is not given it uses a default value, Tie::Cache::LRU::DEFAULT_MAX_SIZE.

If the size is set to 0, the cache is effectively turned off. This is useful for "removing" the cache from a program without having to make deep alterations to the program itself, or for checking performance differences with and without a cache.

All of the expected hash operations (exists, delete, slices, etc...) work on the %cache.

Object Interface

There's a few things you just can't do through the tied interface. To do them, you need to get at the underlying object, which you do with tied().

$cache_obj = tied %cache;

And then you can call a few methods on that object:

max_size

$cache_obj->max_size($size);
$size = $cache_obj->max_size;

An accessor to alter the maximum size of the cache on the fly.

If max_size() is reset, and it is lower than the current size, the cache is immediately truncated.

The size must be an integer greater than or equal to 0.

curr_size

$size = $cache_obj->curr_size;

Returns the current number of items in the cache.

AUTHOR

Michael G Schwern <schwern@pobox.com>

SEE ALSO

Tie::Cache::LRU, Tie::Cache::LRU::LinkedList, Tie::Cache::LRU::Array, Tie::Cache