st time plugins were run before checking plugin versions.
 *
 * This might have been backported to WordPress 2.6.1 for performance reasons.
 * This is used for the wp-admin to check only so often instead of every page
 * load.
 *
 * @since 2.7.0
 * @access private
 */
function _maybe_update_plugins() {
	$current = get_site_transient( 'update_plugins' );

	if ( isset( $current->last_checked )
		&& 12 * HOUR_IN_SECONDS > ( time() - $current->last_checked )
	) {
		return;
	}

	wp_update_plugins();
}

/**
 * Checks themes versions only after a duration of time.
 *
 * This is for performance reasons to make sure that on the theme version
 * checker is not run on every page load.
 *
 * @since 2.7.0
 * @access private
 */
function _maybe_update_themes() {
	$current = get_site_transient( 'update_themes' );

	if ( isset( $current->last_checked )
		&& 12 * HOUR_IN_SECONDS > ( time() - $current->last_checked )
	) {
		return;
	}

	wp_update_themes();
}

/**
 * Schedules core, theme, and plugin update checks.
 *
 * @since 3.1.0
 */
function wp_schedule_update_checks() {
	if ( ! wp_next_scheduled( 'wp_version_check' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_version_check' );
	}

	if ( ! wp_next_scheduled( 'wp_update_plugins' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_update_plugins' );
	}

	if ( ! wp_next_scheduled( 'wp_update_themes' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_update_themes' );
	}
}

/**
 * Clears existing update caches for plugins, themes, and core.
 *
 * @since 4.1.0
 */
function wp_clean_update_cache() {
	if ( function_exists( 'wp_clean_plugins_cache' ) ) {
		wp_clean_plugins_cache();
	} else {
		delete_site_transient( 'update_plugins' );
	}

	wp_clean_themes_cache();

	delete_site_transient( 'update_core' );
}

/**
 * Schedules the removal of all contents in the temporary backup directory.
 *
 * @since 6.3.0
 */
function wp_delete_all_temp_backups() {
	/*
	 * Check if there is a lock, or if currently performing an Ajax request,
	 * in which case there is a chance an update is running.
	 * Reschedule for an hour from now and exit early.
	 */
	if ( get_option( 'core_updater.lock' ) || get_option( 'auto_updater.lock' ) || wp_doing_ajax() ) {
		wp_schedule_single_event( time() + HOUR_IN_SECONDS, 'wp_delete_temp_updater_backups' );
		return;
	}

	// This action runs on shutdown to make sure there are no plugin updates currently running.
	add_action( 'shutdown', '_wp_delete_all_temp_backups' );
}

/**
 * Deletes all contents in the temporary backup directory.
 *
 * @since 6.3.0
 *
 * @access private
 *
 * @global WP_Filesystem_Base $wp_filesystem WordPress filesystem subclass.
 */
function _wp_delete_all_temp_backups() {
	global $wp_filesystem;

	if ( ! function_exists( 'WP_Filesystem' ) ) {
		require_once ABSPATH . 'wp-admin/includes/file.php';
	}

	ob_start();
	$credentials = request_filesystem_credentials( '' );
	ob_end_clean();

	if ( false === $credentials || ! WP_Filesystem( $credentials ) ) {
		wp_trigger_error( __FUNCTION__, __( 'Could not access filesystem.' ) );
		return;
	}

	if ( ! $wp_filesystem->wp_content_dir() ) {
		wp_trigger_error(
			__FUNCTION__,
			/* translators: %s: Directory name. */
			sprintf( __( 'Unable to locate WordPress content directory (%s).' ), 'wp-content' )
		);
		return;
	}

	$temp_backup_dir = $wp_filesystem->wp_content_dir() . 'upgrade-temp-backup/';
	$dirlist         = $wp_filesystem->dirlist( $temp_backup_dir );
	$dirlist         = $dirlist ? $dirlist : array();

	foreach ( array_keys( $dirlist ) as $dir ) {
		if ( '.' === $dir || '..' === $dir ) {
			continue;
		}

		$wp_filesystem->delete( $temp_backup_dir . $dir, true );
	}
}

if ( ( ! is_main_site() && ! is_network_admin() ) || wp_doing_ajax() ) {
	return;
}

add_action( 'admin_init', '_maybe_update_core' );
add_action( 'wp_version_check', 'wp_version_check' );

add_action( 'load-plugins.php', 'wp_update_plugins' );
add_action( 'load-update.php', 'wp_update_plugins' );
add_action( 'load-update-core.php', 'wp_update_plugins' );
add_action( 'admin_init', '_maybe_update_plugins' );
add_action( 'wp_update_plugins', 'wp_update_plugins' );

add_action( 'load-themes.php', 'wp_update_themes' );
add_action( 'load-update.php', 'wp_update_themes' );
add_action( 'load-update-core.php', 'wp_update_themes' );
add_action( 'admin_init', '_maybe_update_themes' );
add_action( 'wp_update_themes', 'wp_update_themes' );

add_action( 'update_option_WPLANG', 'wp_clean_update_cache', 10, 0 );

add_action( 'wp_maybe_auto_update', 'wp_maybe_auto_update' );

add_action( 'init', 'wp_schedule_update_checks' );

add_action( 'wp_delete_temp_updater_backups', 'wp_delete_all_temp_backups' );
<br />
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<br />
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