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Is Lock-Free Faster?
Someone proposes rewriting a contended queue as a lock-free structure for performance. How do you respond?
The scenario
A team wants to replace a
std::mutex-guarded work queue with a hand-written lock-free MPMC queue. The profile shows 4% of wall time in queue operations and 61% in a downstream JSON serializer.What it tests
- Whether the candidate knows lock-free is a progress guarantee, not a speed claim
- Whether they can name the specific costs: CAS retries, ABA, memory reclamation
- Whether they ask for a measurement and a reason before agreeing
Answer it out loud first. Recognising a good answer is not the same skill as producing one.