wp_start_object_cache()

Description

Compatibility

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Performance profile

How much work a call to wp_start_object_cache() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class

Heavy

Reads or writes the filesystem via file_exists().

Scaling

Constant

No loop in the body: the same number of instructions runs whatever you pass in.

Instructions

22–70

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 88.

Plugin surface

1 hook

Third-party callbacks on 'enable_loading_object_cache_dropin' run inside this call, and their cost is not bounded by anything here.

Called by

0

Nothing in core calls this; the cost is only what you spend yourself.

What it touches

• hookthird-party callbacksapply_filters()called directly
• cacheobject cachewp_cache_switch_to_blog()called directly
• filesystemfilesystem accessfile_exists()called directly

What one call costs · 100 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost wp_start_object_cache() can have, taken from its control-flow graph on PHP 8.5.

Hooks and filters fired · 1

One hook fires while wp_start_object_cache() runs, in this order:

1. 1
   apply_filters( enable_loading_object_cache_dropin )filterline 850 (+17 into the body)

   Filters whether to enable loading of the object-cache.php drop-in.

Uses · 8

• apply_filters()Calls the callback functions that have been added to a filter hook.
• wp_using_ext_object_cache()Toggles `$_wp_using_ext_object_cache` on and off without directly touching global.
• wp_cache_switch_to_blog()Used when switch_to_blog() and restore_current_blog() are called, but only when a persistent object cache drop-in plugin has omitted the wp_cache_switch_to_blog() function that was introduced in 3.5.0.
• get_current_blog_id()Retrieves the current site ID.
• wp_cache_init()Sets up Object Cache Global and assigns it.
• wp_cache_add_global_groups()Adds a group or set of groups to the list of global groups.
• wp_cache_add_non_persistent_groups()Adds a group or set of groups to the list of non-persistent groups.
• WP_Hook::build_preinitialized_hooks()Normalizes filters set up before WordPress has initialized to WP_Hook objects.

Source code

View on Trac ↗View on GitHub ↗

833function wp_start_object_cache() {834	global $wp_filter;835	static $first_init = true;836 837	// Only perform the following checks once.838 839	/**840	 * Filters whether to enable loading of the object-cache.php drop-in.841	 *842	 * This filter runs before it can be used by plugins. It is designed for non-web843	 * runtimes. If false is returned, object-cache.php will never be loaded.844	 *845	 * @since 5.8.0846	 *847	 * @param bool $enable_object_cache Whether to enable loading object-cache.php (if present).848	 *                                  Default true.849	 */850	if ( $first_init && apply_filters( 'enable_loading_object_cache_dropin', true ) ) {851		if ( ! function_exists( 'wp_cache_init' ) ) {852			/*853			 * This is the normal situation. First-run of this function. No854			 * caching backend has been loaded.855			 *856			 * We try to load a custom caching backend, and then, if it857			 * results in a wp_cache_init() function existing, we note858			 * that an external object cache is being used.859			 */860			if ( file_exists( WP_CONTENT_DIR . '/object-cache.php' ) ) {861				require_once WP_CONTENT_DIR . '/object-cache.php';862 863				if ( function_exists( 'wp_cache_init' ) ) {864					wp_using_ext_object_cache( true );865				}866 867				// Re-initialize any hooks added manually by object-cache.php.868				if ( $wp_filter ) {869					$wp_filter = WP_Hook::build_preinitialized_hooks( $wp_filter );870				}871			}872		} elseif ( ! wp_using_ext_object_cache() && file_exists( WP_CONTENT_DIR . '/object-cache.php' ) ) {873			/*874			 * Sometimes advanced-cache.php can load object-cache.php before875			 * this function is run. This breaks the function_exists() check876			 * above and can result in wp_using_ext_object_cache() returning877			 * false when actually an external cache is in use.878			 */879			wp_using_ext_object_cache( true );880		}881	}882 883	if ( ! wp_using_ext_object_cache() ) {884		require_once ABSPATH . WPINC . '/cache.php';885	}886 887	require_once ABSPATH . WPINC . '/cache-compat.php';888 889	/*890	 * If cache supports reset, reset instead of init if already891	 * initialized. Reset signals to the cache that global IDs892	 * have changed and it may need to update keys and cleanup caches.893	 */894	if ( ! $first_init && function_exists( 'wp_cache_switch_to_blog' ) ) {895		wp_cache_switch_to_blog( get_current_blog_id() );896	} elseif ( function_exists( 'wp_cache_init' ) ) {897		wp_cache_init();898	}899 900	if ( function_exists( 'wp_cache_add_global_groups' ) ) {901		wp_cache_add_global_groups(902			array(903				'blog-details',904				'blog-id-cache',905				'blog-lookup',906				'blog_meta',907				'global-posts',908				'image_editor',909				'networks',910				'network-queries',911				'sites',912				'site-details',

Changelog

Introduced in 3.0.0. Unchanged from 6.7.7 through 7.1.0.

1. 6.7.7
2. 6.8.8
3. 6.9.7
4. 7.0.4
5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

Parsed data

Generated from the wordpress-develop 7.0.4 tag, from src/wp-includes/load.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.

Corrections

Something wrong on this page? Report it and it gets fixed in the next regeneration.