[drupal-support] How to use MySQL last_insert_id function with locking?

Hi, I am developing my own module which uses tables that have auto-increment fields. As far as I can tell, drupal uses a single connection for my default configuration. I don't think i think use last_insert_id without locking because the MySQL DB connection is shared accross requests. so what should I lock in order to get the correct result from last_insert_id? Please give me an example. Thanks. Kai