WordPress at a glance
function is not described

shutdown_action_hook() WP 1.2.0

Runs just before PHP shuts down execution.

Hooks from the function
Return

Null. Nothing.

Usage

shutdown_action_hook();

Changelog

Since 1.2.0 Introduced.

Code of shutdown action hook: wp-includes/load.php WP 5.2.2

<?php
function shutdown_action_hook() {
	/**
	 * Fires just before PHP shuts down execution.
	 *
	 * @since 1.2.0
	 */
	do_action( 'shutdown' );

	wp_cache_close();
}