It works as long as you know which locks you need in advance. You'll get much better concurrency than with the one-lock model when there's a low probability tha

It works as long as you know which locks you need in advance. You'll get much better concurrency than with the one-lock model when there's a low probability that two processes need any of the same locks (e.g. locking a whole table vs. locking individual records). It fails you if you have a monadic rather than applicative requirement on the computation; that is, if intermediate computations can require you to take more locks that you couldn't have predicted needing in advance. In that case, you're going to need a transactional-memory system that can abort and retry computations, and that is powerful but hard to get right.