WordPress at a glance
filter is not described

pre_wp_update_comment_count_now filter-hook . WP 4.5.0

Filters a post's comment count before it is updated in the database.

Usage

add_filter( 'pre_wp_update_comment_count_now', 'filter_function_name_245', 10, 3 );
function filter_function_name_245( $new, $old, $post_id ){
	// filter...

	return $new;
}
$new(int)
The new comment count.
Default: null
$old(int)
The old comment count.
$post_id(int)
Post ID.

Where the hook is called

wp_update_comment_count_now()
wp-includes/comment.php 2372
$new = apply_filters( 'pre_wp_update_comment_count_now', null, $old, $post_id );

Where the hook is used (in WP core)

Does not used.