foreach ( $meta_ids as $meta_id ) {
    /**
     * Fires immediately before updating metadata of a specific type.
     *
     * The dynamic portion of the hook, `$meta_type`, refers to the meta
     * object type (comment, post, or user).
     *
     * @since 2.9.0
     *
     * @param int    $meta_id    ID of the metadata entry to update.
     * @param int    $object_id  Object ID.
     * @param string $meta_key   Meta key.
     * @param mixed  $meta_value Meta value.
     */
    do_action( "update_{$meta_type}_meta", $meta_id, $object_id, $meta_key, $_meta_value );
}

if ( 'post' == $meta_type ) {
    foreach ( $meta_ids as $meta_id ) {
        /**
         * Fires immediately before updating a post's metadata.
         *
         * @since 2.9.0
         *
         * @param int    $meta_id    ID of metadata entry to update.
         * @param int    $object_id  Object ID.
         * @param string $meta_key   Meta key.
         * @param mixed  $meta_value Meta value.
         */
        do_action( 'update_postmeta', $meta_id, $object_id, $meta_key, $meta_value );
    }
}

$_meta_value = $meta_value;
$meta_value = maybe_serialize( $meta_value );