phpman > man > Cache(3pm)

NAME
    Cache - the Cache interface

DESCRIPTION
    The Cache modules are designed to assist a developer in persisting data for a specified period
    of time. Often these modules are used in web applications to store data locally to save repeated
    and redundant expensive calls to remote machines or databases.

    The Cache interface is implemented by derived classes that store cached data in different
    manners (such as files on a filesystem, or in memory).

USAGE
    To use the Cache system, a cache implementation must be chosen to suit your needs. The most
    common is Cache::File, which is suitable for sharing data between multiple invocations and even
    between concurrent processes.

    Using a cache is simple. Here is some very simple sample code for instantiating and using a file
    system based cache.

      use Cache::File;

      my $cache = Cache::File->new( cache_root => '/tmp/cacheroot' );
      my $customer = $cache->get( $name );

      unless ($customer) {
          $customer = get_customer_from_db( $name );
          $cache->set( $name, $customer, '10 minutes' );
      }

      return $customer;

    Of course, far more powerful methods are available for accessing cached data. Also see the TIE
    INTERFACE below.

METHODS
    my $cache_entry = $c->entry( $key )
        Return a 'Cache::Entry' object for the given key. This object can then be used to manipulate
        the cache entry in various ways. The key can be any scalar string that will uniquely
        identify an entry in the cache.

    $c->purge()
        Remove all expired data from the cache.

    $c->clear()
        Remove all entries from the cache - regardless of their expiry time.

    my $num = $c->count()
        Returns the number of entries in the cache.

    my $size = $c->size()
        Returns the size (in bytes) of the cache.

PROPERTIES
    When a cache is constructed these properties can be supplied as options to the new() method.

    default_expires
        The current default expiry time for new entries into the cache. This property can also be
        reset at any time.

         my $time = $c->default_expires();
         $c->set_default_expires( $expiry );

    removal_strategy
        The removal strategy object for the cache. This is used to remove object from the cache in
        order to maintain the cache size limit.

        When setting the removal strategy in new(), the name of a strategy package or a blessed
        strategy object reference should be provided (in the former case an object is constructed by
        calling the new() method of the named package).

        The strategies 'Cache::RemovalStrategy::LRU' and 'Cache::RemovalStrategy::FIFO' are
        available by default.

         my $strategy = $c->removal_strategy();

    size_limit
        The size limit for the cache.

         my $limit = $c->size_limit();

    load_callback
        The load callback for the cache. This may be set to a function that will get called anytime
        a 'get' is issued for data that does not exist in the cache.

         my $limit = $c->load_callback();
         $c->set_load_callback($callback_func);

    validate_callback
        The validate callback for the cache. This may be set to a function that will get called
        anytime a 'get' is issued for data that does not exist in the cache.

         my $limit = $c->validate_callback();
         $c->set_validate_callback($callback_func);

SHORTCUT METHODS
    These methods all have counterparts in the Cache::Entry package, but are provided here as
    shortcuts. They all default to just wrappers that do '$c->entry($key)->method_name()'. For
    documentation, please refer to Cache::Entry.

    my $bool = $c->exists( $key )
    $c->set( $key, $data, [ $expiry ] )
    my $data = $c->get( $key )
    my $data = $c->size( $key )
    $c->remove( $key )
    $c->expiry( $key )
    $c->set_expiry( $key, $time )
    $c->handle( $key, [$mode, [$expiry] ] )
    $c->validity( $key )
    $c->set_validity( $key, $data )
    $c->freeze( $key, $data, [ $expiry ] )
    $c->thaw( $key )

TIE INTERFACE
      tie %hash, 'Cache::File', { cache_root => $tempdir };

      $hash{'key'} = 'some data';
      $data = $hash{'key'};

    The Cache classes can be used via the tie interface, as shown in the synopsis. This allows the
    cache to be accessed via a hash. All the standard methods for accessing the hash are supported ,
    with the exception of the 'keys' or 'each' call.

    The tie interface is especially useful with the load_callback to automatically populate the
    hash.

REMOVAL STRATEGY METHODS
    These methods are only for use internally (by concrete Cache implementations).

    These methods define the interface by which the removal strategy object can manipulate the cache
    (the Cache is the 'context' of the strategy). By default, methods need to be provided to remove
    the oldest or stalest objects in the cache - thus allowing support for the default FIFO and LRU
    removal strategies. All derived Cache implementations should support these methods and may also
    introduce additional methods (and additional removal strategies to match).

    my $size = $c->remove_oldest()
        Removes the oldest entry in the cache and returns its size.

    my $size = $c->remove_stalest()
        Removes the 'stalest' (least used) object in the cache and returns its size.

    $c->check_size( $size )
        This method isn't actually part of the strategy interface, nor does it need to be defined by
        Cache implementations. Instead it should be called by implementations whenever the size of
        the cache increases. It will take care of checking the size limit and invoking the removal
        strategy if required. The size argument should be the new size of the cache.

UTILITY METHODS
    These methods are only for use internally (by concrete Cache implementations).

    my $time = Cache::Canonicalize_Expiration_Time($timespec)
        Converts a timespec as described for Cache::Entry::set_expiry() into a unix time.

SEE ALSO
    Cache::Entry, Cache::File, Cache::RemovalStrategy

DIFFERENCES FROM CACHE::CACHE
    The Cache modules are a total redesign and reimplementation of Cache::Cache and thus not
    directly compatible. It would be, however, quite possible to write a wrapper module that
    provides an identical interface to Cache::Cache.

    The semantics of use are very similar to Cache::Cache, with the following exceptions:

    The get/set methods DO NOT serialize complex data types. Use freeze/thaw instead (but read the
    notes in Cache::Entry).
    The get_object / set_object methods are not available, but have been superseded by the more
    flexible entry method and Cache::Entry class.
    There is no concept of 'namespace' in the basic cache interface, although implementations (eg.
    Cache::Memory) may choose to provide them. For instance, File::Cache does not provide this - but
    different namespaces can be created by varying cache_root.
    In the current Cache implementations purging is done automatically - there is no need to
    explicitly enable auto purge on get/set. The purging algorithm is no longer implemented in the
    base Cache class, but is left up to the implementations and may thus be implemented in the most
    efficient way for the storage medium.
    Cache::SharedMemory is not yet available.
    Cache::File no longer supports separate masks for entries and directories. It is not a very
    secure configuration and presents numerous issues for cache consistency and is hence deprecated.
    There is still some work to be done to ensure cache consistency between accesses by different
    users.

AUTHOR
     Chris Leishman <chris AT leishman.org>
     Based on work by DeWitt Clinton <dewitt AT unto.net>

COPYRIGHT
     Copyright (C) 2003-2006 Chris Leishman.  All Rights Reserved.

    This module is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either expressed
    or implied. This program is free software; you can redistribute or modify it under the same
    terms as Perl itself.

    $Id: Cache.pm,v 1.7 2006/01/31 15:23:58 caleishm Exp $