[sunshowers]

Concurrent maps are generally worse in terms of being able to understand the system than either non-concurrent maps guarded by a lock, or a channel/actor model with single ownership. Data-parallel algorithms should also generally use map-reduce rather than writing into the same map concurrently.

I've written highly concurrent software with bog-standard hash maps plus channels. There are so many advantages to this style, such as events being linearized (and thus being easy to test against, log, etc).