Java: How to atomically replace all values in a Map?

Question

I have a stateful bean in an multi-threaded enviroment, which keeps its state in a map. Now I need a way to replace all values of that map in one atomic action.

Answer 1

The simplest, least fuss method is to switch the map instead of replacing map contents. Whether using volatile or AtomicReference (I don't see why you'd need AtomicReferenceFieldUpdater particularly), shouldn't make too much of a difference.

This makes sure that your map is always in proper state, and allows you to provide snapshots too. It doesn't protect you from other concurrency issues though, so if something like lost updates are a problem you'll need further code (although AtomicReference would give you CAS methods for handling those).

The question is actually rather simple if you only consider the complete atomic replacement of the map. It would be informative to know what other operations affect the map and how. I'd also like to hear why ConcurrentSkipListMap was chosen over ConcurrentHashMap.