> or per-key concurrency, but no inter-key atomicity (either use nested atoms or use ConcurrentHashMap). I guess it depends upon what you mean by "per key", bu

> or per-key concurrency, but no inter-key atomicity (either use nested atoms or use ConcurrentHashMap). I guess it depends upon what you mean by "per key", but if your map is a ref, and the values are refs, you can get per-value concurrency with inter-value atomicity. You couldn't concurrently add new keys though, since that's changing the map's ref.