Benjamin Franz > Tie-FileLRUCache-1.05 > Tie::FileLRUCache

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Module Version: 1.05   Source  

NAME ^

Tie::FileLRUCache - A lightweight but robust filesystem based persistent LRU cache

CHANGES ^

 1.05 2005.09.14   - Changes to pod tests to make them more CPANTS friendly.
                     No functional changes.

 1.04 2005.09.13   - Removed use of 'warnings' to fix compatibility with Perl 5.005.
                     Fixed minor typographical errors in documentation.

 1.03 2005.09.10   - Changed build test to handle difference in treatment of hashes
                     in scalar contect between 5.6.x and 5.8.x versions of Perl that
                     caused a test failure under Perl 5.6.x.

 1.02 2005.09.08   - Added build tests. Major code cleanup. Improved platform portability.
                     Added and documented 'cache_dir', 'keep_last' and 'number_of_entries'
                     methods. Added Module::Build support.

 1.01 1999.12.09   - Added 'detainting' to cache management code.

SYNOPSIS ^

OBJECT INTERFACE

 use Tie::FileLRUCache;
 my $cache = Tie::FileLRUCache->new({ -cache_dir => $directory, -keep_last => 100 });

 # Inserting value into LRU cache using '-key'
 $cache->update({ -key => $key, -value => $value });


 # Inserting value into LRU cache using '-cache_key'
 my $cache_key = $cache->make_cache_key({ -key => $key });
 $cache->update({ -cache_key => $cache_key, -value => $value });


 # Checking LRU cache
 my ($in_cache,$value) = $cache->check({ -key => $key });
 if ($in_cache) {
     return $value;
 }
 # Not in cache - do something else


 # Checking LRU cache with speed up hack for objects, hashes, arrays etc used as keys
 my $cache_key = $cache->make_cache_key({ -key => $something });
 my ($in_cache,$value) = $cache->check({ -cache_key => $cache_key });
 if ($in_cache) {
     return $value;
 }
 # Not in cache - do something else


 # Deleting a key and its value from the cache
 $cache->delete({ -key => $key });


 # Clearing LRU cache
 $cache->clear;

TIED INTERFACE

 use Tie::FileLRUCache;

 [$X =] tie %hash,  'Tie::FileLRUCache', $cache_dir, $keep_last_n;

 # Adding a key/value to the cache
 $hash{$key} = $value;

 # Checking the cache
 if (not exists $hash{$key}) {;
     # No match
       .
       .
       .

 } else {
     my $value = $hash{$key};
       .
       .
       .

 }

 # Removing a value from the cache;
 delete $hash{$key};

 # Clearing the cache
 %hash = ();

Note: Iteration over the cache (each, keys, values) is _NOT_ supported.

DESCRIPTION ^

Provides a lightweight persistent filesystem based LRU cache.

It uses the 'last accessed' timestamp generated by the file system to determine the 'oldest' cache entry and discards the oldest cache entries when needed to stay under the -keep_last limit.

If you store thing very fast (such that many entries receive the same time stamp), it is essentially a coin toss which entry within a single timestamped second gets purged from the cache to make room for new ones.

It is not designed to handle huge numbers of cached items. It is probably unwise to set the 'keep_last' higher than around 100.

OBJECT METHODS ^

new({[ -cache_dir => $cache_directory] [, -keep_last => $keep_last_n ] });

Creates and optionally initializes a Tie::FileLRUCache object:

Example:

  my $cache = Tie::FileLRUCache->new({
                       -cache_dir => '/tmp/testing',
                       -keep_last => 100,
                     });

The default cache size is 100 entries unless specified.

check({ -key => $key });

Reads the cache for the key.

Returns two values: $cache_hit (true if a hit was found, false if not) $value (the cached value, undef if no hit)

Examples:

   my ($cache_hit,$value) = $cache->check({ -key => $key });

   my ($cache_hit,$value) = $cache->check({ -cache_key => $cache_key });

The '-key' form is used when you just want to use a raw key. It can use blessed objects, hash refs, scalars, or array refs as keys. The more complex structures take a speed penalty for computing a canonical form. You can minimize this penalty by using the '-cache_key' form instead.

The '-cache_key' form is used for performance reasons when using keys such as complex blessed objects or hashes as a key. The -cache_key is obtained with a call to 'make_cache_key'. It is legal to mix -cache_key and -key based calls - they are cross-compatible.

make_cache_key({ -key => $key });

Generates a cache key by canonicalizing a passed key as a network ordered canonical Storable string.

Example:

 my $cache_key = $cache->make_cache_key({ -key => $key });
clear;

Completely clears the cache of all cache entries.

update({ [-key => $key,] [-cache_key => $cache_key, ], -value => $value [, -keep_last => $keep_last_n ] });

Updates the Least Recently Used (LRU) cache for the specified key with the passed value. '-keep_last' is optional after the first access to a dataset. It will use the most recent 'keep_last' used if not specified.

It is legal to use ordinary scalars, hash references, or array references as keys as well as objects as -keys or -values. Basically, anything that Storable can reproducibly serialize can be used.

Examples:

 $cache->update({ -key => $key, -value => $value });

 $cache->update({ -key => $key, -value => $value, -keep_last => 100});

 my $cache_key = $cache->make_cache_key({ -key => $key });
 $cache->update({ -cache_key => $cache_key, -value => $value });

 my $cache_key = $cache->make_cache_key({ -key => $key });
 $cache->update({ -cache_key => $cache_key, -value => $value, -keep_last => 50 });

 -cache_key is assumed to be a simple scalar value for use as a key.

 -key can be pretty much anything Storable can successfully and reproducibly serialize.

One or the other must be passed.

delete({ -key => $key });

Forces the deletion of a specific key from the cache.

Example:

 $cache->delete({ -key => $key });
cache_dir([$cache_directory_path]);

Get/Set accessor for the cache directory path.

Ex.

  my $cache_directory = $cache->cache_dir;

  $cache->cache_dir($cache_directory);
keep_last([$keep_last_n]);

Get/Set accessor for the keep last N setting.

Ex.

  my $n_last = $cache->keep_last;

  $cache->keep_last(20);
number_of_entries;

Returns the current number of entries in the cache.

COPYRIGHT ^

Copyright 1999, Benjamin Franz (<URL:http://www.nihongo.org/snowhare/>) and FreeRun Technologies, Inc. (<URL:http://www.freeruntech.com/>). All Rights Reserved.

VERSION ^

 1.05 released 2005.09.14

LICENSE ^

This software may be copied or redistributed under the same terms as Perl itelf.

This means that you can, at your option, redistribute it and/or modify it under either the terms the GNU Public License (GPL) version 1 or later, or under the Perl Artistic License.

See http://dev.perl.org/licenses/

DISCLAIMER ^

THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

Use of this software in any way or in any form, source or binary, is not allowed in any country which prohibits disclaimers of any implied warranties of merchantability or fitness for a particular purpose or any disclaimers of a similar nature.

IN NO EVENT SHALL I BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION (INCLUDING, BUT NOT LIMITED TO, LOST PROFITS) EVEN IF I HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE

AUTHOR ^

Benjamin Franz

TODO ^

Nothing.

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