Code reviewHardcr-g227

Subject Race conditionsLevel Senior–Staff~40 minCommon in Concurrency interviewsIndustries Software development

Question

Review this C++ lock-free Treiber stack pop.

A reviewer says this lock-free stack has a classic bug. Which one, and how does it manifest?

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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Code to reviewcpp

1template <class T>2struct Node { T val; Node* next; };3 4std::atomic<Node<int>*> head;5 6int pop() {7    Node<int>* old = head.load(std::memory_order_acquire);8    while (old &&9           !head.compare_exchange_weak(old, old->next,   // (1)10                                       std::memory_order_acq_rel)) {11    }12    int v = old->val;13    delete old;                                            // (2) free immediately14    return v;15}

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