WP_Object_Cache()

Core class that implements an object cache.


Description Description

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.


Source Source

File: wp-includes/cache.php

class WP_Object_Cache {

	/**
	 * Holds the cached objects.
	 *
	 * @since 2.0.0
	 * @access private
	 * @var array
	 */
	private $cache = array();

	/**
	 * The amount of times the cache data was already stored in the cache.
	 *
	 * @since 2.5.0
	 * @access public
	 * @var int
	 */
	public $cache_hits = 0;

	/**
	 * Amount of times the cache did not have the request in cache.
	 *
	 * @since 2.0.0
	 * @access public
	 * @var int
	 */
	public $cache_misses = 0;

	/**
	 * List of global cache groups.
	 *
	 * @since 3.0.0
	 * @access protected
	 * @var array
	 */
	protected $global_groups = array();

	/**
	 * The blog prefix to prepend to keys in non-global groups.
	 *
	 * @since 3.5.0
	 * @access private
	 * @var int
	 */
	private $blog_prefix;

	/**
	 * Holds the value of is_multisite().
	 *
	 * @since 3.5.0
	 * @access private
	 * @var bool
	 */
	private $multisite;

	/**
	 * Makes private properties readable for backward compatibility.
	 *
	 * @since 4.0.0
	 * @access public
	 *
	 * @param string $name Property to get.
	 * @return mixed Property.
	 */
	public function __get( $name ) {
		return $this->$name;
	}

	/**
	 * Makes private properties settable for backward compatibility.
	 *
	 * @since 4.0.0
	 * @access public
	 *
	 * @param string $name  Property to set.
	 * @param mixed  $value Property value.
	 * @return mixed Newly-set property.
	 */
	public function __set( $name, $value ) {
		return $this->$name = $value;
	}

	/**
	 * Makes private properties checkable for backward compatibility.
	 *
	 * @since 4.0.0
	 * @access public
	 *
	 * @param string $name Property to check if set.
	 * @return bool Whether the property is set.
	 */
	public function __isset( $name ) {
		return isset( $this->$name );
	}

	/**
	 * Makes private properties un-settable for backward compatibility.
	 *
	 * @since 4.0.0
	 * @access public
	 *
	 * @param string $name Property to unset.
	 */
	public function __unset( $name ) {
		unset( $this->$name );
	}

	/**
	 * Adds data to the cache if it doesn't already exist.
	 *
	 * @since 2.0.0
	 * @access public
	 *
	 * @uses WP_Object_Cache::_exists() Checks to see if the cache already has data.
	 * @uses WP_Object_Cache::set()     Sets the data after the checking the cache
	 *		                            contents existence.
	 *
	 * @param int|string $key    What to call the contents in the cache.
	 * @param mixed      $data   The contents to store in the cache.
	 * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
	 * @param int        $expire Optional. When to expire the cache contents. Default 0 (no expiration).
	 * @return bool False if cache key and group already exist, true on success
	 */
	public function add( $key, $data, $group = 'default', $expire = 0 ) {
		if ( wp_suspend_cache_addition() )
			return false;

		if ( empty( $group ) )
			$group = 'default';

		$id = $key;
		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$id = $this->blog_prefix . $key;

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

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

	/**
	 * Sets the list of global cache groups.
	 *
	 * @since 3.0.0
	 * @access public
	 *
	 * @param array $groups List of groups that are global.
	 */
	public function add_global_groups( $groups ) {
		$groups = (array) $groups;

		$groups = array_fill_keys( $groups, true );
		$this->global_groups = array_merge( $this->global_groups, $groups );
	}

	/**
	 * Decrements numeric cache item's value.
	 *
	 * @since 3.3.0
	 * @access public
	 *
	 * @param int|string $key    The cache key to decrement.
	 * @param int        $offset Optional. The amount by which to decrement the item's value. Default 1.
	 * @param string     $group  Optional. The group the key is in. Default 'default'.
	 * @return false|int False on failure, the item's new value on success.
	 */
	public function decr( $key, $offset = 1, $group = 'default' ) {
		if ( empty( $group ) )
			$group = 'default';

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$key = $this->blog_prefix . $key;

		if ( ! $this->_exists( $key, $group ) )
			return false;

		if ( ! is_numeric( $this->cache[ $group ][ $key ] ) )
			$this->cache[ $group ][ $key ] = 0;

		$offset = (int) $offset;

		$this->cache[ $group ][ $key ] -= $offset;

		if ( $this->cache[ $group ][ $key ] < 0 )
			$this->cache[ $group ][ $key ] = 0;

		return $this->cache[ $group ][ $key ];
	}

	/**
	 * Removes the contents of the cache key in the group.
	 *
	 * If the cache key does not exist in the group, then nothing will happen.
	 *
	 * @since 2.0.0
	 * @access public
	 *
	 * @param int|string $key        What the contents in the cache are called.
	 * @param string     $group      Optional. Where the cache contents are grouped. Default 'default'.
	 * @param bool       $deprecated Optional. Unused. Default false.
	 * @return bool False if the contents weren't deleted and true on success.
	 */
	public function delete( $key, $group = 'default', $deprecated = false ) {
		if ( empty( $group ) )
			$group = 'default';

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$key = $this->blog_prefix . $key;

		if ( ! $this->_exists( $key, $group ) )
			return false;

		unset( $this->cache[$group][$key] );
		return true;
	}

	/**
	 * Clears the object cache of all data.
	 *
	 * @since 2.0.0
	 * @access public
	 *
	 * @return true Always returns true.
	 */
	public 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
	 * key in the cache group. If the cache is hit (success) then the contents
	 * are returned.
	 *
	 * On failure, the number of cache misses will be incremented.
	 *
	 * @since 2.0.0
	 * @access public
	 *
	 * @param int|string $key    What the contents in the cache are called.
	 * @param string     $group  Optional. Where the cache contents are grouped. Default 'default'.
	 * @param string     $force  Optional. Unused. Whether to force a refetch rather than relying on the local
	 *                           cache. Default false.
	 * @param bool       $found  Optional. Whether the key was found in the cache. Disambiguates a return of
	 *                           false, a storable value. Passed by reference. Default null.
	 * @return false|mixed False on failure to retrieve contents or the cache contents on success.
	 */
	public function get( $key, $group = 'default', $force = false, &$found = null ) {
		if ( empty( $group ) )
			$group = 'default';

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$key = $this->blog_prefix . $key;

		if ( $this->_exists( $key, $group ) ) {
			$found = true;
			$this->cache_hits += 1;
			if ( is_object($this->cache[$group][$key]) )
				return clone $this->cache[$group][$key];
			else
				return $this->cache[$group][$key];
		}

		$found = false;
		$this->cache_misses += 1;
		return false;
	}

	/**
	 * Increments numeric cache item's value.
	 *
	 * @since 3.3.0
	 * @access public
	 *
	 * @param int|string $key    The cache key to increment
	 * @param int        $offset Optional. The amount by which to increment the item's value. Default 1.
	 * @param string     $group  Optional. The group the key is in. Default 'default'.
	 * @return false|int False on failure, the item's new value on success.
	 */
	public function incr( $key, $offset = 1, $group = 'default' ) {
		if ( empty( $group ) )
			$group = 'default';

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$key = $this->blog_prefix . $key;

		if ( ! $this->_exists( $key, $group ) )
			return false;

		if ( ! is_numeric( $this->cache[ $group ][ $key ] ) )
			$this->cache[ $group ][ $key ] = 0;

		$offset = (int) $offset;

		$this->cache[ $group ][ $key ] += $offset;

		if ( $this->cache[ $group ][ $key ] < 0 )
			$this->cache[ $group ][ $key ] = 0;

		return $this->cache[ $group ][ $key ];
	}

	/**
	 * Replaces the contents in the cache, if contents already exist.
	 *
	 * @since 2.0.0
	 * @access public
	 *
	 * @see WP_Object_Cache::set()
	 *
	 * @param int|string $key    What to call the contents in the cache.
	 * @param mixed      $data   The contents to store in the cache.
	 * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
	 * @param int        $expire Optional. When to expire the cache contents. Default 0 (no expiration).
	 * @return bool False if not exists, true if contents were replaced.
	 */
	public function replace( $key, $data, $group = 'default', $expire = 0 ) {
		if ( empty( $group ) )
			$group = 'default';

		$id = $key;
		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$id = $this->blog_prefix . $key;

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

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

	/**
	 * Resets cache keys.
	 *
	 * @since 3.0.0
	 * @access public
	 *
	 * @deprecated 3.5.0 Use switch_to_blog()
	 * @see switch_to_blog()
	 */
	public function reset() {
		_deprecated_function( __FUNCTION__, '3.5.0', 'switch_to_blog()' );

		// Clear out non-global caches since the blog ID has changed.
		foreach ( array_keys( $this->cache ) as $group ) {
			if ( ! isset( $this->global_groups[ $group ] ) )
				unset( $this->cache[ $group ] );
		}
	}

	/**
	 * Sets the data contents into the cache.
	 *
	 * The cache contents is grouped by the $group parameter followed by the
	 * $key. 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 2.0.0
	 * @access public
	 *
	 * @param int|string $key    What to call the contents in the cache.
	 * @param mixed      $data   The contents to store in the cache.
	 * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
	 * @param int        $expire Not Used.
	 * @return true Always returns true.
	 */
	public function set( $key, $data, $group = 'default', $expire = 0 ) {
		if ( empty( $group ) )
			$group = 'default';

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) )
			$key = $this->blog_prefix . $key;

		if ( is_object( $data ) )
			$data = clone $data;

		$this->cache[$group][$key] = $data;
		return true;
	}

	/**
	 * Echoes the stats of the caching.
	 *
	 * Gives the cache hits, and cache misses. Also prints every cached group,
	 * key and the data.
	 *
	 * @since 2.0.0
	 * @access public
	 */
	public function stats() {
		echo "<p>";
		echo "<strong>Cache Hits:</strong> {$this->cache_hits}<br />";
		echo "<strong>Cache Misses:</strong> {$this->cache_misses}<br />";
		echo "</p>";
		echo '<ul>';
		foreach ($this->cache as $group => $cache) {
			echo "<li><strong>Group:</strong> $group - ( " . number_format( strlen( serialize( $cache ) ) / KB_IN_BYTES, 2 ) . 'k )</li>';
		}
		echo '</ul>';
	}

	/**
	 * Switches the internal blog ID.
	 *
	 * This changes the blog ID used to create keys in blog specific groups.
	 *
	 * @since 3.5.0
	 * @access public
	 *
	 * @param int $blog_id Blog ID.
	 */
	public function switch_to_blog( $blog_id ) {
		$blog_id = (int) $blog_id;
		$this->blog_prefix = $this->multisite ? $blog_id . ':' : '';
	}

	/**
	 * Serves as a utility function to determine whether a key exists in the cache.
	 *
	 * @since 3.4.0
	 * @access protected
	 *
	 * @param int|string $key   Cache key to check for existence.
	 * @param string     $group Cache group for the key existence check.
	 * @return bool Whether the key exists in the cache for the given group.
	 */
	protected function _exists( $key, $group ) {
		return isset( $this->cache[ $group ] ) && ( isset( $this->cache[ $group ][ $key ] ) || array_key_exists( $key, $this->cache[ $group ] ) );
	}

	/**
	 * Sets up object properties; PHP 5 style constructor.
	 *
	 * @since 2.0.8
	 */
	public function __construct() {
		$this->multisite = is_multisite();
		$this->blog_prefix =  $this->multisite ? get_current_blog_id() . ':' : '';


		/**
		 * @todo This should be moved to the PHP4 style constructor, PHP5
		 * already calls __destruct()
		 */
		register_shutdown_function( array( $this, '__destruct' ) );
	}

	/**
	 * Saves the object cache before object is completely destroyed.
	 *
	 * Called upon object destruction, which should be when PHP ends.
	 *
	 * @since 2.0.8
	 *
	 * @return true Always returns true.
	 */
	public function __destruct() {
		return true;
	}
}

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Changelog Changelog

Changelog
Version Description
2.0.0 Introduced.

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Methods Methods

  • __construct — Sets up object properties; PHP 5 style constructor.
  • __destruct — Saves the object cache before object is completely destroyed.
  • __get — Makes private properties readable for backward compatibility.
  • __isset — Makes private properties checkable for backward compatibility.
  • __set — Makes private properties settable for backward compatibility.
  • __unset — Makes private properties un-settable for backward compatibility.
  • _exists — Serves as a utility function to determine whether a key exists in the cache.
  • add — Adds data to the cache if it doesn't already exist.
  • add_global_groups — Sets the list of global cache groups.
  • decr — Decrements numeric cache item's value.
  • delete — Removes the contents of the cache key in the group.
  • flush — Clears the object cache of all data.
  • get — Retrieves the cache contents, if it exists.
  • incr — Increments numeric cache item's value.
  • replace — Replaces the contents in the cache, if contents already exist.
  • reset — Resets cache keys. — deprecated
  • set — Sets the data contents into the cache.
  • stats — Echoes the stats of the caching.
  • switch_to_blog — Switches the internal blog ID.

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User Contributed Notes User Contributed Notes

  1. Skip to note content
    Contributed by Priyanka Behera

    The object cache is used for caching the results of expensive SQL queries. So they’re not performed multiple times within a page load. In the below example, imagine the $query variable is an expensive SQL query.

    $result = wp_cache_get( 'my_result' );
    if ( false === $result ) {
    	$result = $wpdb->get_results( $query );
    	wp_cache_set( 'my_result', $result );
    } 
    // Do something with $result;
    

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