Dealing with concurrency when accessing BO

Hi,

I'm currently facing the following problem. I have kind of a "singleton" BO which manages number ranges for BOs. The generation of new IDs happens in the "before save" action of the respective BO. Now assuming two BOs are saved at the same time (by different users) they both can get the same ID. Does anybody know how I can aquire somthing like a lock while saving until the save transaction is completed?

- Daniel