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wp_start_object_cache()

This function’s access is marked private. This means it is not intended for use by plugin or theme developers, only in other core functions. It is listed here for completeness.

Start the WordPress object cache.

Description

If an object-cache.php file exists in the wp-content directory, it uses that drop-in as an external object cache.

Source

File: wp-includes/load.php 

function wp_start_object_cache() {
	global $wp_filter;
	static $first_init = true;

	// Only perform the following checks once.
	if ( $first_init ) {
		if ( ! function_exists( 'wp_cache_init' ) ) {
			/*
			 * This is the normal situation. First-run of this function. No
			 * caching backend has been loaded.
			 *
			 * We try to load a custom caching backend, and then, if it
			 * results in a wp_cache_init() function existing, we note
			 * that an external object cache is being used.
			 */
			if ( file_exists( WP_CONTENT_DIR . '/object-cache.php' ) ) {
				require_once WP_CONTENT_DIR . '/object-cache.php';
				if ( function_exists( 'wp_cache_init' ) ) {
					wp_using_ext_object_cache( true );
				}

				// Re-initialize any hooks added manually by object-cache.php.
				if ( $wp_filter ) {
					$wp_filter = WP_Hook::build_preinitialized_hooks( $wp_filter );
				}
			}
		} elseif ( ! wp_using_ext_object_cache() && file_exists( WP_CONTENT_DIR . '/object-cache.php' ) ) {
			/*
			 * Sometimes advanced-cache.php can load object-cache.php before
			 * this function is run. This breaks the function_exists() check
			 * above and can result in wp_using_ext_object_cache() returning
			 * false when actually an external cache is in use.
			 */
			wp_using_ext_object_cache( true );
		}
	}

	if ( ! wp_using_ext_object_cache() ) {
		require_once ABSPATH . WPINC . '/cache.php';
	}

	require_once ABSPATH . WPINC . '/cache-compat.php';

	/*
	 * If cache supports reset, reset instead of init if already
	 * initialized. Reset signals to the cache that global IDs
	 * have changed and it may need to update keys and cleanup caches.
	 */
	if ( ! $first_init && function_exists( 'wp_cache_switch_to_blog' ) ) {
		wp_cache_switch_to_blog( get_current_blog_id() );
	} elseif ( function_exists( 'wp_cache_init' ) ) {
		wp_cache_init();
	}

	if ( function_exists( 'wp_cache_add_global_groups' ) ) {
		wp_cache_add_global_groups( array( 'users', 'userlogins', 'usermeta', 'user_meta', 'useremail', 'userslugs', 'site-transient', 'site-options', 'blog-lookup', 'blog-details', 'site-details', 'rss', 'global-posts', 'blog-id-cache', 'networks', 'sites', 'blog_meta' ) );
		wp_cache_add_non_persistent_groups( array( 'counts', 'plugins' ) );
	}

	$first_init = false;
}

Uses

Uses Description
wp-includes/class-wp-hook.php: WP_Hook::build_preinitialized_hooks()

Normalizes filters set up before WordPress has initialized to WP_Hook objects.
wp-includes/cache.php: wp_cache_switch_to_blog()

Switches the internal blog ID.
wp-includes/cache.php: wp_cache_init()

Sets up Object Cache Global and assigns it.
wp-includes/cache.php: wp_cache_add_global_groups()

Adds a group or set of groups to the list of global groups.
wp-includes/cache.php: wp_cache_add_non_persistent_groups()

Adds a group or set of groups to the list of non-persistent groups.
wp-includes/load.php: get_current_blog_id()

Retrieve the current site ID.
wp-includes/load.php: wp_using_ext_object_cache()

Toggle $_wp_using_ext_object_cache on and off without directly touching global.

Changelog

Version Description
3.0.0 Introduced.

© 2003–2019 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/functions/wp_start_object_cache