Source

File: wp-includes/comment.php

function wp_update_comment_count( $post_id, $do_deferred = false ) {
	static $_deferred = array();

	if ( empty( $post_id ) && ! $do_deferred ) {
		return false;
	}

	if ( $do_deferred ) {
		$_deferred = array_unique( $_deferred );
		foreach ( $_deferred as $i => $_post_id ) {
			wp_update_comment_count_now( $_post_id );
			unset( $_deferred[ $i ] );
			/** @todo Move this outside of the foreach and reset $_deferred to an array instead */
		}
	}

	if ( wp_defer_comment_counting() ) {
		$_deferred[] = $post_id;
		return true;
	} elseif ( $post_id ) {
		return wp_update_comment_count_now( $post_id );
	}

}