Bric::App::Cache(3p)

NAME
Bric::App::Cache - Object for managing Application-wide global data.

VERSION
$LastChangedRevision$

DATE
$LastChangedDate: 2006-03-18 01:26:34 +0100 (Sat, 18 Mar 2006) $

SYNOPSIS
  use Bric::App::Cache;
  my $c = Bric::App::Cache->new;
  $c = $c->set($key, $val);
  my $val = $c->get($key);

  my $time = $c->get_lmu_time;
  $c = $c->set_lmu_time;

  my $site_id = $c->get_user_cx($user_id);
  $c = $c->set_user_cx($user_id, $site_id);

DESCRIPTION
This module provides a cache object to cache data that needs to persist across all processes and across all requests, through time and space. The cache is cleared on server restart - for more permenant storage see Bric::Util::DBI.

A Bric::App::Cache object is available from Mason components in the global variable $c.

IMPLEMENTATION
This module is implemented as a two-level cache in order to provide the best possible performance.

The first level is provided by Cache::Mmap. Cache::Mmap is a very fast, shared, file-based cache. However, it is also a fixed-size cache that will drop items from the cache when the cache becomes full or the item to be stored is too large.

When an object cannot be stored in the first-level cache it is passed to the second-level. The second-level cache (also known as a backing store) is provided by Cache::Cache. Cache::Cache is quite a bit slower than Cache::Mmap but has the advantage of being variable-sized. As such it grows dynamically and won't refuse to store an object unless it runs out of disk space.

The "get()" procedure is:

•   Look in first-level cache for item. If found, return it and finish.

•   Look in second-level cache for item. If found, return it and finish.

•   Note in first-level cache that item is not in second-level cache. This will prevent a look in the second-level cache on the next request for this item.

And the "set()" prodedure is:

•   Try to set the item in the first-level cache. If success, finish. If fail, delete old item if it exists.

•   Set the item in the second-level cache. This must succeed or a fatal error will result.

NOTE: Under "QA_MODE" all "set()"s are sent to the secondary-cache to allow the cache to be debugged. Cache::Mmap lacks the ability to list all keys in the cache which is used by the "QA_MODE" code.

INTERFACE

  Constructors

my $c = Bric::App::Cache->new()
    Instantiates a Bric::App::Cache object. No initial values may be passed.

    Throws:

    *   Unable to instantiate cache.

    Side Effects: NONE.

    Notes: NONE.

my $org = Bric::App::Cache->lookup()
    Not implemented - not needed.

    Throws:

    *   Bric::App::Cache::lookup() method not implemented.

    Side Effects: NONE.

    Notes: NONE.

Bric::App::Cache->list()
    Not implemented - not needed.

    Throws:

    *   Bric::App::Cache::list() method not implemented.

    Side Effects: NONE.

    Notes: NONE.

  Destructors

$org->DESTROY
    Dummy method to prevent wasting time trying to AUTOLOAD DESTROY.

    Throws: NONE.

    Side Effects: NONE.

    Notes: NONE.

  Public Class Methods

Bric::App::Cache->list_ids()
    Not implemented - not needed.

    Throws:

    *   Bric::App::Cache::list_ids() method not implemented.

    Side Effects: NONE.

    Notes: NONE.

Bric::App::Cache->clear()
    Clears the cache of all stored data.

    Throws: NONE.

    Side Effects: NONE.

    Notes: NONE.

  Public Instance Methods

my $val = $c->get($key)
    Returns a value for the specified key. Call $c->set($key, $value) to store a value.

    Throws:

    *   Unable to fetch value from the cache.

    Side Effects: NONE.

    Notes: NONE.

$self = $c->set($key, $value);
    Stores $value as referenced by $key. Call $c->get($key) to retrieve $value.

    Throws:

    *   Unable to cache value.

    Side Effects: NONE.

    Notes: NONE.

my $lmu_time = $c->get_lmu_time
    Returns the epoch time when a user object was last modified.

    Throws:

    *   Unable to fetch value from the cache.

    Side Effects: NONE.

    Notes: NONE.

$self = $c->set_lmu_time($lmu_time)
    Sets the epoch time when a user object was last modified.

    Throws:

    *   Unable to cache value.

    Side Effects: NONE.

    Notes: NONE.

my $site_id = $c->get_user_cx($user_id)
    Returns the current site context for the user with the $user_id ID. A value of 0 (zero) means that there is no context, in which case the user can see all the workflows from all the sites to which she has access. If the value is undefined, then the context isn't set.

    Side Effects: If "QA_MODE" is enabled, then $user_id and $site_id will be checked to ensure that they are proper arguments.

$c = $c->set_user_cx($user_id, $site_id)
    Sets the site context for the user with the $user_id ID. Pass in "undef" to indicate an unknown context. Pass in 0 (zero) to indicate that the user has no context, and so can access all of the workflows in all of the sites to which she has access. Otherwise, simply pass in the site ID the user has selected.

    Side Effects: If "QA_MODE" is enabled, then $user_id and $site_id will be checked to ensure that they are proper arguments.

PRIVATE

  Private Class Methods
NONE.

  Private Instance Methods
NONE.

  Private Functions

$val = _read_backing_store($key)
    Reads a value from the backing store. See the IMPLEMENTATION section avove for details.

    Throws:

    *   Unable to fetch value from the backing cache.

    Side Effects: NONE.

    Notes: NONE.

_write_backing_store($key, $val)
    Writes a value to the backing store. See the IMPLEMENTATION section avove for details.

    Throws:

    *   Unable to cache value in the backing cache.

    Side Effects: NONE.

    Notes: NONE.

NOTES
NONE.

AUTHOR
David Wheeler <david@justatheory.com>

Sam Tregar <stregar@about-inc.com>

SEE ALSO
Bric, Bric::App::Session, Apache::Session