Explain lock-free programming and compare-and-swap operations.

Lock-free algorithms ensure at least one thread makes progress, avoiding blocking. Core primitive: CAS (Compare-And-Swap) - atomically update if current value matches expected. Java: AtomicInteger.compareAndSet(), VarHandle. C++: std::atomic, compare_exchange. Pattern: read current, compute new, CAS; retry on failure. ABA problem: value changes A->B->A; solution: version counters, hazard pointers. Benefits: no deadlocks, better scalability, interrupt-safe. Challenges: complexity, subtle bugs, memory ordering (acquire/release semantics). Use cases: concurrent queues, counters, reference counting. Consider: is lock contention actually the bottleneck?