Code reviewHardcr-g224

Subject False sharingLevel Senior–Staff~40 minCommon in Code quality & review interviewsIndustries Software development

Question

Review this C++ per-thread counter array used in a hot parallel loop.

It's correct but a senior reviewer flagged it. What's the concurrency-related problem?

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix — specific and kind.

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Talk through your review

Code to reviewcpp

1struct Counters {2    std::atomic<long> hits[8];   // one slot per worker thread3};4 5void worker(Counters& c, int tid, const std::vector<int>& work) {6    for (int v : work) {7        if (heavy_predicate(v))8            c.hits[tid].fetch_add(1, std::memory_order_relaxed);  // (1)9    }10}

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