Provided by: libcache-perl_2.11-2_all 
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@leishman.org>
Based on work by DeWitt Clinton <dewitt@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 $
perl v5.34.0 2022-06-09 Cache(3pm)