{
    "api": "YAML JSON TOON Database",
    "version": "1.0.0",
    "format": "json",
    "dataset": {
        "id": 60,
        "slug": "concurrent-data-structures",
        "title": "Concurrent Data Structures",
        "description": "Thread-safe data structures: concurrent hash maps, skip lists, queues, stacks, read-write locks, lock-free algorithms, and compare-and-swap patterns.",
        "category": "Data Structures",
        "category_slug": "data-structures",
        "tags": "concurrency,lock-free,compare-and-swap,concurrent-hash-map,concurrent-queue,read-write-lock,atomic",
        "view_count": 0,
        "created_at": 1778695229,
        "updated_at": 1778695229
    },
    "data": {
        "structures": [
            {"name": "Concurrent Hash Map (Striped/Segmented)", "type": "Lock-based", "description": "Hash map with segmented locking: different buckets can be locked independently, allowing concurrent access to different segments", "implementations": ["Java ConcurrentHashMap (striped, CAS-based)", "C++ tbb::concurrent_unordered_map", ".NET ConcurrentDictionary"], "contention": "Low (only on same segment)", "notes": "Java 8+ uses CAS + synchronized on individual bins; read operations often lock-free"},
            {"name": "Concurrent Skip List", "type": "Lock-free (optimistic)", "description": "Probabilistic balanced search structure; uses CAS for lock-free insertion/deletion with high probability", "implementations": ["Java ConcurrentSkipListMap/Set", "C++ concurrent_skiplist"], "operations": "O(log n) expected for search/insert/delete", "notes": "Better concurrency than balanced trees (no rebalancing); used as concurrent sorted map"},
            {"name": "Lock-Free Queue (Michael-Scott)", "type": "Lock-free", "description": "Linked-list queue using CAS on head and tail pointers; multiple producers/consumers without locks", "implementations": ["Java ConcurrentLinkedQueue", "C++ boost::lockfree::queue"], "operations": "O(1) amortized enqueue/dequeue", "notes": "May have memory reclamation issues (ABA problem); use hazard pointers or epoch-based reclamation in production"},
            {"name": "Concurrent Stack (Treiber Stack)", "type": "Lock-free", "description": "Linked-list stack using CAS on top pointer; simple but can have contention on single atomic variable", "implementations": ["C++ tbb::concurrent_bounded_queue (similar)", "Java ConcurrentLinkedDeque"], "operations": "O(1) push/pop", "notes": "High contention under heavy concurrent use; consider combining techniques or elimination backoff"},
            {"name": "Read-Write Lock", "type": "Lock-based (shared/exclusive)", "description": "Allows multiple concurrent readers OR one exclusive writer; optimizes read-heavy workloads", "implementations": ["Java ReentrantReadWriteLock", "C++ shared_mutex (C++17)", "POSIX pthread_rwlock_t"], "operations": "Read: O(1), Write: O(1) + potential writer starvation", "notes": "Risk of writer starvation under heavy read load; use StampedLock (Java) or upgradeable read locks"},
            {"name": "Compare-And-Swap (CAS)", "type": "Atomic primitive", "description": "Atomically: if (location == expected) location = new_value; return success/failure. Foundation of all lock-free algorithms", "implementations": ["Java Unsafe.compareAndSwap*()", "C++ std::atomic<T>::compare_exchange_weak/strong", "x86 CMPXCHG instruction"], "operations": "O(1) atomic", "notes": "CAS loop pattern: while (!CAS(loc, expected, new)) expected = *loc; ABA problem requires versioned pointers or hazard pointers"},
            {"name": "Hazard Pointers", "type": "Memory reclamation", "description": "Lock-free memory reclamation technique: threads announce which nodes they're accessing; nodes not in any hazard list can be safely freed", "implementations": ["Boost.Lockfree", "Folly (Facebook)", "DPDK"], "operations": "O(1) publish/unpublish", "notes": "Solves ABA and use-after-free in lock-free structures; bounded memory overhead (O(threads × hazard_slots))"},
            {"name": "Epoch-Based Reclamation", "type": "Memory reclamation", "description": "Threads announce their epoch; retired nodes are freed when all threads have moved past the epoch when node was retired", "implementations": ["Seastar", "Folly", "RCU (Read-Copy-Update) in Linux kernel"], "operations": "O(1) enter/exit epoch", "notes": "Lower overhead than hazard pointers for read-heavy workloads; used extensively in kernel RCU"}
        ]
    }
}