Using ConcurrentHashMap can block a thread coroutine is running on

it’s true, but probability of blocking is very low. If you for some reason care about blocking, you can use lock-free hash map (e.g. one from JCTools library). If you care about general utilization, it’s ok to use CHM

JCTools looks awesome. Can help us with more data structures

another solution is

kotlinx.collections.immutable

and

kotlinx.coroutines...Mutex

, those two in conjunction should could you pretty straight-forward concurrency.

that's what my second question was, I've implemented a class called

SuspendableMap

that uses the Mutex and wraps the standard map to make it work.

Be careful with it. CHM is extremely performant (since Java 8 ), most likely

SuspendableMap

will be visibly slower. Usually it’s not worth to implement your own primitives instead of [well-tested and polished by years] already implemented ones even if there is a small probability of blocking. It’s worth doing after measuring and understanding that CHM is actually a bottleneck (which is unlikely true for an average application)