Pretty standard stuff if you've done any concurrent programming.
Start by clarifying the shared resource and access pattern, then present a minimal lock-based solution (e.g., a mutex-protected counter or queue) and walk through the code line by line. For each lock, explicitly state what data it protects, why atomicity/visibility is needed, and discuss trade-offs like contention, granularity, and deadlock avoidance.
Pro tip: Mention that locks protect invariants, not just variables—and that you'd consider lock-free alternatives or read-write locks if contention becomes a bottleneck, showing you understand both correctness and performance.
Ask or state assumptions about what is shared (e.g., counter, list, cache) and whether reads/writes are mixed. This determines the locking strategy and granularity.
Present concise code using a mutex (or read-write lock) around critical sections. Keep it simple and correct first, then optimize if needed.
For each lock acquisition, explain what data it protects and why the operation must be atomic (e.g., check-then-act, compound updates).
Describe the race conditions or data corruption that would occur without the lock, referencing atomicity, visibility, and ordering.
Mention lock granularity, contention, deadlock risks, and when to use read-write locks, atomics, or lock-free structures.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the current solution's concurrency bottlenecks and correctness requirements, then compare the four approaches (read/write locks, per-key locking, CAS, copy-on-write) in terms of contention, complexity, and memory overhead. Pick one approach that best fits the workload characteristics (e.g., read-heavy vs write-heavy) and justify it with concrete trade-offs and a correctness argument.
Pro tip: Always tie your choice to measurable metrics like throughput, latency, and contention rate—interviewers value data-driven decisions over theoretical preferences. Also, mention that you would validate correctness with stress tests and race detectors before and after the change.
Ask about the current solution's concurrency model, workload patterns (read/write ratio, key distribution), and correctness guarantees (linearizability, serializability). Identify the specific bottleneck (e.g., global lock contention).
Briefly explain each: read/write locks allow concurrent reads but serialize writes; per-key locking reduces contention by partitioning locks; CAS enables lock-free updates for simple atomic operations; copy-on-write avoids locking for reads by creating new versions on write.
Choose the approach that best matches the workload. For example, per-key locking for a sharded key-value store with high write concurrency, or copy-on-write for a read-mostly configuration map. Justify with expected contention reduction, complexity, and memory trade-offs.
Explain how the chosen approach maintains correctness: e.g., per-key locking requires consistent lock ordering to avoid deadlocks; CAS needs retry loops and ABA handling; copy-on-write must ensure atomic reference swaps.
Describe how you would test the solution: stress tests, race detectors, and performance benchmarks. Mention that you would monitor contention metrics and iterate if needed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.