root/trunk/wp-includes/cache.php

<?php
/**
 * Object Cache API
 *
 * @link http://codex.wordpress.org/Function_Reference/WP_Cache
 *
 * @package WordPress
 * @subpackage Cache
 */

/**
 * Adds data to the cache, if the cache key doesn't aleady exist.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::add()
 *
 * @param int|string $key The cache ID to use for retrieval later
 * @param mixed $data The data to add to the cache store
 * @param string $flag The group to add the cache to
 * @param int $expire When the cache data should be expired
 * @return unknown
 */
function wp_cache_add($key, $data, $flag = '', $expire = 0) {
    global $wp_object_cache;

    return $wp_object_cache->add($key, $data, $flag, $expire);
}

/**
 * Closes the cache.
 *
 * This function has ceased to do anything since WordPress 2.5. The
 * functionality was removed along with the rest of the persistant cache. This
 * does not mean that plugins can't implement this function when they need to
 * make sure that the cache is cleaned up after WordPress no longer needs it.
 *
 * @since 2.0
 *
 * @return bool Always returns True
 */
function wp_cache_close() {
    return true;
}

/**
 * Removes the cache contents matching ID and flag.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::delete()
 *
 * @param int|string $id What the contents in the cache are called
 * @param string $flag Where the cache contents are grouped
 * @return bool True on successful removal, false on failure
 */
function wp_cache_delete($id, $flag = '') {
    global $wp_object_cache;

    return $wp_object_cache->delete($id, $flag);
}

/**
 * Removes all cache items.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::flush()
 *
 * @return bool Always returns true
 */
function wp_cache_flush() {
    global $wp_object_cache;

    return $wp_object_cache->flush();
}

/**
 * Retrieves the cache contents from the cache by ID and flag.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::get()
 *
 * @param int|string $id What the contents in the cache are called
 * @param string $flag Where the cache contents are grouped
 * @return bool|mixed False on failure to retrieve contents or the cache
 *        contents on success
 */
function wp_cache_get($id, $flag = '') {
    global $wp_object_cache;

    return $wp_object_cache->get($id, $flag);
}

/**
 * Sets up Object Cache Global and assigns it.
 *
 * @since 2.0
 * @global WP_Object_Cache $wp_object_cache WordPress Object Cache
 */
function wp_cache_init() {
    $GLOBALS['wp_object_cache'] =& new WP_Object_Cache();
}

/**
 * Replaces the contents of the cache with new data.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::replace()
 *
 * @param int|string $id What to call the contents in the cache
 * @param mixed $data The contents to store in the cache
 * @param string $flag Where to group the cache contents
 * @param int $expire When to expire the cache contents
 * @return bool False if cache ID and group already exists, true on success
 */
function wp_cache_replace($key, $data, $flag = '', $expire = 0) {
    global $wp_object_cache;

    return $wp_object_cache->replace($key, $data, $flag, $expire);
}

/**
 * Saves the data to the cache.
 *
 * @since 2.0
 * @uses $wp_object_cache Object Cache Class
 * @see WP_Object_Cache::set()
 *
 * @param int|string $id What to call the contents in the cache
 * @param mixed $data The contents to store in the cache
 * @param string $flag Where to group the cache contents
 * @param int $expire When to expire the cache contents
 * @return bool False if cache ID and group already exists, true on success
 */
function wp_cache_set($key, $data, $flag = '', $expire = 0) {
    global $wp_object_cache;

    return $wp_object_cache->set($key, $data, $flag, $expire);
}

/**
 * Adds a group or set of groups to the list of global groups.
 *
 * @since 2.6
 *
 * @param string|array $groups A group or an array of groups to add
 */
function wp_cache_add_global_groups( $groups ) {
    // Default cache doesn't persist so nothing to do here.
    return;
}

/**
 * Adds a group or set of groups to the list of non-persistent groups.
 *
 * @since 2.6
 *
 * @param string|array $groups A group or an array of groups to add
 */
function wp_cache_add_non_persistent_groups( $groups ) {
    // Default cache doesn't persist so nothing to do here.
    return;
}

/**
 * WordPress Object Cache
 *
 * The WordPress Object Cache is used to save on trips to the database. The
 * Object Cache stores all of the cache data to memory and makes the cache
 * contents available by using a key, which is used to name and later retrieve
 * the cache contents.
 *
 * The Object Cache can be replaced by other caching mechanisms by placing files
 * in the wp-content folder which is looked at in wp-settings. If that file
 * exists, then this file will not be included.
 *
 * @package WordPress
 * @subpackage Cache
 * @since 2.0
 */
class WP_Object_Cache {

    /**
     * Holds the cached objects
     *
     * @var array
     * @access private
     * @since 2.0
     */
    var $cache = array ();

    /**
     * Cache objects that do not exist in the cache
     *
     * @var array
     * @access private
     * @since 2.0
     */
    var $non_existant_objects = array ();

    /**
     * The amount of times the cache data was already stored in the cache.
     *
     * @since 2.5
     * @access private
     * @var int
     */
    var $cache_hits = 0;

    /**
     * Amount of times the cache did not have the request in cache
     *
     * @var int
     * @access public
     * @since 2.0
     */
    var $cache_misses = 0;

    /**
     * Adds data to the cache if it doesn't already exist.
     *
     * @uses WP_Object_Cache::get Checks to see if the cache already has data.
     * @uses WP_Object_Cache::set Sets the data after the checking the cache
     *        contents existance.
     *
     * @since 2.0
     *
     * @param int|string $id What to call the contents in the cache
     * @param mixed $data The contents to store in the cache
     * @param string $group Where to group the cache contents
     * @param int $expire When to expire the cache contents
     * @return bool False if cache ID and group already exists, true on success
     */
    function add($id, $data, $group = 'default', $expire = '') {
        if (empty ($group))
            $group = 'default';

        if (false !== $this->get($id, $group, false))
            return false;

        return $this->set($id, $data, $group, $expire);
    }

    /**
     * Remove the contents of the cache ID in the group
     *
     * If the cache ID does not exist in the group and $force parameter is set
     * to false, then nothing will happen. The $force parameter is set to false
     * by default.
     *
     * On success the group and the id will be added to the 
     * $non_existant_objects property in the class.
     *
     * @since 2.0
     *
     * @param int|string $id What the contents in the cache are called
     * @param string $group Where the cache contents are grouped
     * @param bool $force Optional. Whether to force the unsetting of the cache
     *        ID in the group
     * @return bool False if the contents weren't deleted and true on success
     */
    function delete($id, $group = 'default', $force = false) {
        if (empty ($group))
            $group = 'default';

        if (!$force && false === $this->get($id, $group, false))
            return false;

        unset ($this->cache[$group][$id]);
        $this->non_existant_objects[$group][$id] = true;
        return true;
    }

    /**
     * Clears the object cache of all data
     *
     * @since 2.0
     *
     * @return bool Always returns true
     */
    function flush() {
        $this->cache = array ();

        return true;
    }

    /**
     * Retrieves the cache contents, if it exists
     *
     * The contents will be first attempted to be retrieved by searching by the
     * ID in the cache group. If the cache is hit (success) then the contents
     * are returned.
     *
     * On failure, the $non_existant_objects property is checked and if the
     * cache group and ID exist in there the cache misses will not be
     * incremented. If not in the nonexistant objects property, then the cache
     * misses will be incremented and the cache group and ID will be added to
     * the nonexistant objects.
     *
     * @since 2.0
     *
     * @param int|string $id What the contents in the cache are called
     * @param string $group Where the cache contents are grouped
     * @return bool|mixed False on failure to retrieve contents or the cache
     *        contents on success
     */
    function get($id, $group = 'default') {
        if (empty ($group))
            $group = 'default';

        if (isset ($this->cache[$group][$id])) {
            $this->cache_hits += 1;
            return $this->cache[$group][$id];
        }

        if ( isset ($this->non_existant_objects[$group][$id]) )
            return false;

        $this->non_existant_objects[$group][$id] = true;
        $this->cache_misses += 1;
        return false;
    }

    /**
     * Replace the contents in the cache, if contents already exist
     *
     * @since 2.0
     * @see WP_Object_Cache::set()
     *
     * @param int|string $id What to call the contents in the cache
     * @param mixed $data The contents to store in the cache
     * @param string $group Where to group the cache contents
     * @param int $expire When to expire the cache contents
     * @return bool False if not exists, true if contents were replaced
     */
    function replace($id, $data, $group = 'default', $expire = '') {
        if (empty ($group))
            $group = 'default';

        if (false === $this->get($id, $group, false))
            return false;

        return $this->set($id, $data, $group, $expire);
    }

    /**
     * Sets the data contents into the cache
     *
     * The cache contents is grouped by the $group parameter followed by the
     * $id. This allows for duplicate ids in unique groups. Therefore, naming of
     * the group should be used with care and should follow normal function
     * naming guidelines outside of core WordPress usage.
     *
     * The $expire parameter is not used, because the cache will automatically
     * expire for each time a page is accessed and PHP finishes. The method is
     * more for cache plugins which use files.
     *
     * @since 2.0
     *
     * @param int|string $id What to call the contents in the cache
     * @param mixed $data The contents to store in the cache
     * @param string $group Where to group the cache contents
     * @param int $expire Not Used
     * @return bool Always returns true
     */
    function set($id, $data, $group = 'default', $expire = '') {
        if (empty ($group))
            $group = 'default';

        if (NULL === $data)
            $data = '';

        $this->cache[$group][$id] = $data;

        if(isset($this->non_existant_objects[$group][$id]))
            unset ($this->non_existant_objects[$group][$id]);

        return true;
    }

    /**
     * Echos the stats of the caching.
     *
     * Gives the cache hits, and cache misses. Also prints every cached group,
     * key and the data.
     *
     * @since 2.0
     */
    function stats() {
        echo "<p>";
        echo "<strong>Cache Hits:</strong> {$this->cache_hits}<br />";
        echo "<strong>Cache Misses:</strong> {$this->cache_misses}<br />";
        echo "</p>";

        foreach ($this->cache as $group => $cache) {
            echo "<p>";
            echo "<strong>Group:</strong> $group<br />";
            echo "<strong>Cache:</strong>";
            echo "<pre>";
            print_r($cache);
            echo "</pre>";
        }
    }

    /**
     * PHP4 constructor; Calls PHP 5 style constructor
     *
     * @since 2.0
     *
     * @return WP_Object_Cache
     */
    function WP_Object_Cache() {
        return $this->__construct();
    }

    /**
     * Sets up object properties; PHP 5 style constructor
     *
     * @since 2.0.8
     * @return null|WP_Object_Cache If cache is disabled, returns null.
     */
    function __construct() {
        /**
         * @todo This should be moved to the PHP4 style constructor, PHP5
         * already calls __destruct()
         */
        register_shutdown_function(array(&$this, "__destruct"));
    }

    /**
     * Will save the object cache before object is completely destroyed.
     *
     * Called upon object destruction, which should be when PHP ends.
     *
     * @since  2.0.8
     *
     * @return bool True value. Won't be used by PHP
     */
    function __destruct() {
        return true;
    }
}
?>