Discuss lock-free data structures and their implementation challenges.

Lock-free data structures allow concurrent access without traditional locks, using atomic operations like CAS (Compare-And-Swap). Challenges include: ABA problem (value changes A->B->A between read and CAS, resolved with version numbers or hazard pointers), memory management (safe reclamation without garbage collection), and proving correctness (linearizability). Examples: Michael-Scott queue, Harris's linked list. Benefits: no deadlocks, better scalability, progress guarantees. Used in high-performance systems like Java's ConcurrentLinkedQueue.