wp_find_hierarchy_loop() │ WP 3.1.0

Finds hierarchy loops using a callback function that maps object IDs to parent IDs.

Internal function — this function is designed to be used by the kernel itself. It is not recommended to use this function in your code.

No Hooks.

Returns

Array. IDs of all members of loop.

Usage

wp_find_hierarchy_loop( $callback, $start, $start_parent, $callback_args );
$callback(callable) (required)
Function that accepts ( ID, $callback_args ) and outputs parent_ID.
$start(int) (required)
The ID to start the loop check at.
$start_parent(int) (required)
The parent_ID of $start to use instead of calling $callback( $start ). Use null to always use $callback.
$callback_args(array)
Additional arguments to send to $callback.
Default: empty array

Changelog

Since 3.1.0 Introduced.

wp_find_hierarchy_loop() code WP 7.0.2

wp-includes/functions.php 
function wp_find_hierarchy_loop( $callback, $start, $start_parent, $callback_args = array() ) {
	$override = is_null( $start_parent ) ? array() : array( $start => $start_parent );

	$arbitrary_loop_member = wp_find_hierarchy_loop_tortoise_hare( $callback, $start, $override, $callback_args );
	if ( ! $arbitrary_loop_member ) {
		return array();
	}

	return wp_find_hierarchy_loop_tortoise_hare( $callback, $arbitrary_loop_member, $override, $callback_args, true );
}