WordPress at a glance
function is not described

cache_users() WP 3.0.0

Retrieve info for user lists to prevent multiple queries by get_userdata()

  • Global. wpdb. $wpdb WordPress database abstraction object.

This is a pluggable function, and it can be replaced by a plugin. It means that this function is defined (works) only after all plugins are loaded (included), but before this moment this function has not defined. Therefore, you cannot call this and all functions depended on this function directly from a plugin code. It must be called on plugins_loaded hook or later, for example on init hook.

Function replacement (override) — in a plugin you can create a function with the same name, then it replace this function.

No Hooks.

Return

Nothing (null).

Usage

cache_users( $user_ids );
$user_ids(array) (required)
User ID numbers list

Code of cache users: wp-includes/pluggable.php VER 5.1.1

<?php
function cache_users( $user_ids ) {
	global $wpdb;

	$clean = _get_non_cached_ids( $user_ids, 'users' );

	if ( empty( $clean ) ) {
		return;
	}

	$list = implode( ',', $clean );

	$users = $wpdb->get_results( "SELECT * FROM $wpdb->users WHERE ID IN ($list)" );

	$ids = array();
	foreach ( $users as $user ) {
		update_user_caches( $user );
		$ids[] = $user->ID;
	}
	update_meta_cache( 'user', $ids );
}