Your question is Concurrent Hash Map Internals. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Explain how a thread-safe collection works internally, using a concurrent hash map as the example. How does it allow parallel reads and writes, what locking or atomic primitives does it use, and what trade-offs does that design make?