Identify and handle race conditions

Race Conditions in KV Store & Hit Counter - System Design Interview Guide Problem Statement Concurrency in an In-Memory Key-Value Store and Hit Counter Context and Assumptions Assume you are implementing an in-memory key-value store and a hit counter within a single process, shared by multiple threads: KeyValueStore supports: get(k), put(k, v), delete(k), and optionally compareAndSet(k, expected, new). HitCounter supports: increment([key]), getCount([key]) — either a single global counter or per-key counters. Data structure backing the store is a hash map with buckets and possible resizing. High read-to-write ratio is common, but hot keys and heavy write bursts can occur. Tasks Identify the race conditions that can occur under concurrent access. Propose thread-safety mechanisms (coarse-/fine-grained locks, read/write locks, atomic operations, lock-free designs) and explain their correctness. Discuss performance trade-offs of the chosen mechanisms. Outline how to test and validate concurrency behavior. Interview Script (45-minute format) | Time | Phase | What to Cover | |------|-------|---------------| | 0-5 min | Context | Identify the race conditions | | 5-20 min | Thread-Safety | Mechanisms and correctness | | 20-35 min | Performance | Trade-offs of different approaches | | 35-45 min | Testing | Validation strategies | Problem Context What to SAY: "Before proposing solutions, I need to systematically identify where race conditions can occur. A race condition happens when th