Code RoomDouble-checked locking without volatile
HardPrep Room Coding #4137

Double-checked locking without volatile

Vibe & agenticAlgorithms & data structuresSenior~20 min

You asked an AI to write a thread-safe lazy singleton cache initializer in Java. It produced this double-checked-locking variant and assured you it's the canonical pattern. Review it.

It mostly works. Under what conditions does a thread see a broken object, and what's the fix?

Implement
reader_can_see_broken_object(events: list[str], instance_is_volatile: bool) → bool
Examples
in[["W:ctor_data","W:publish","R:read_ref","R:read_data"],false]outtrue
in[["W:ctor_data","W:publish","R:read_ref","R:read_data"],true]outfalse
What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it (tests, edge cases, reading critically), and how you’d re-prompt or decompose to get it right.

0:00 of about 20 min

Vibe & agentic: describe the solution in plain language (or narrate it) and the coach grades your approach.

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.