Complex Patterns

// Generated singleton pattern (from binding generator)
class Engine : public Object {
    static Engine *singleton;

public:
    static Engine *get_singleton() {
        // Thread-safe lazy initialization without explicit locks
        if (unlikely(singleton == nullptr)) {
            // Get singleton from engine (thread-safe on engine side)
            GDExtensionObjectPtr singleton_obj =
                internal::gdextension_interface_global_get_singleton(
                    Engine::get_class_static()._native_ptr()
                );

            // Create binding (potential race handled by assignment)
            singleton = reinterpret_cast<Engine *>(
                internal::gdextension_interface_object_get_instance_binding(
                    singleton_obj,
                    internal::token,
                    &Engine::_gde_binding_callbacks
                )
            );

            // Register for cleanup
            if (likely(singleton)) {
                ClassDB::_register_engine_singleton(
                    Engine::get_class_static(),
                    singleton
                );
            }
        }
        return singleton;
    }
};

// ClassDB singleton management
class ClassDB {
    // Engine handles synchronization internally
    static std::unordered_map<StringName, ClassInfo> classes;
    static std::vector<StringName> class_register_order;
    static std::unordered_map<StringName, Object *> engine_singletons;

    template <typename T>
    static void register_class(bool p_virtual = false) {
        // Registration happens during initialization (single-threaded)
        // Runtime registration uses engine's internal locks
        T::initialize_class();
        ClassInfo &info = classes[T::get_class_static()];
        info.name = T::get_class_static();
        info.parent_name = T::get_parent_class_static();

        // Engine handles thread safety for runtime registration
        if (p_runtime) {
            internal::gdextension_interface_classdb_register_extension_class(
                internal::library,
                &info.name,
                &info.parent_name,
                &T::_gde_binding_callbacks
            );
        }
    }
};

// include/godot_cpp/templates/[spin_lock.hpp:37](https://github.com/godotengine/godot-cpp/blob/master/include/godot_cpp/templates/spin_lock.hpp#L37)
class SpinLock {
    std::atomic_flag locked = ATOMIC_FLAG_INIT;

public:
    _ALWAYS_INLINE_ void lock() {
        // Busy-wait with test-and-set
        while (locked.test_and_set(std::memory_order_acquire)) {
            // Spin until lock is available
            ;
        }
    }

    _ALWAYS_INLINE_ void unlock() {
        // Release lock with memory barrier
        locked.clear(std::memory_order_release);
    }
};

// include/godot_cpp/templates/safe_refcount.hpp
class SafeRefCount {
    std::atomic<uint32_t> count{0};

public:
    _ALWAYS_INLINE_ bool ref() {
        // Atomic increment with relaxed ordering
        return ++count != 1;
    }

    _ALWAYS_INLINE_ uint32_t refval() const {
        // Atomic read with acquire semantics
        return count.load(std::memory_order_acquire);
    }

    _ALWAYS_INLINE_ bool unref() {
        // Atomic decrement with release-acquire ordering
        return --count == 0;
    }

    _ALWAYS_INLINE_ uint32_t unrefval() {
        // Return value after decrement
        return --count;
    }
};

// include/godot_cpp/templates/[cowdata.hpp:65](https://github.com/godotengine/godot-cpp/blob/master/include/godot_cpp/templates/cowdata.hpp#L65)
template <typename T>
class CowData {
private:
    // Memory layout:
    // [RefCount][Size][Data...]
    static constexpr size_t REF_COUNT_OFFSET = 0;
    static constexpr size_t SIZE_OFFSET = /* aligned after refcount */;
    static constexpr size_t DATA_OFFSET = /* aligned after size */;

    mutable T *_ptr = nullptr;

    _FORCE_INLINE_ SafeNumeric<USize> *_get_refcount() const {
        if (!_ptr) return nullptr;
        return (SafeNumeric<USize> *)((uint8_t *)_ptr - DATA_OFFSET + REF_COUNT_OFFSET);
    }

    USize _copy_on_write() {
        if (!_ptr) return 0;

        SafeNumeric<USize> *refc = _get_refcount();
        USize rc = refc->get();

        if (likely(rc > 1)) {
            // Multiple references - need to copy
            USize current_size = *_get_size();

            // Allocate new buffer
            uint8_t *mem_new = (uint8_t *)Memory::alloc_static(
                DATA_OFFSET + _get_alloc_size(current_size)
            );

            // Initialize new refcount
            SafeNumeric<USize> *refc_new = _get_refcount_ptr(mem_new);
            refc_new->set(1);

            // Copy size
            USize *size_new = _get_size_ptr(mem_new);
            *size_new = current_size;

            // Copy data
            T *_data_new = _get_data_ptr(mem_new);
            for (USize i = 0; i < current_size; i++) {
                memnew_placement(&_data_new[i], T(_ptr[i]));
            }

            // Decrement old refcount
            if (refc->decrement() == 0) {
                // We were the last one, free old buffer
                _free_data();
            }

            // Switch to new buffer
            _ptr = _data_new;
        }

        return rc;
    }

public:
    _FORCE_INLINE_ T *ptrw() {
        // Get writable pointer (triggers COW if needed)
        _copy_on_write();
        return _ptr;
    }

    _FORCE_INLINE_ const T *ptr() const {
        // Read-only access doesn't trigger COW
        return _ptr;
    }
};

// Example: Vector COW behavior
Vector<int> a;
a.push_back(1);
a.push_back(2);

Vector<int> b = a;  // Shallow copy, shares data
// Both a and b point to same data, refcount = 2

const int *read_ptr = b.ptr();  // Read doesn't trigger COW
int value = read_ptr[0];  // OK, reading shared data

int *write_ptr = b.ptrw();  // Write triggers COW
write_ptr[0] = 5;  // b now has its own copy, a unchanged

// include/godot_cpp/core/memory.hpp
class Memory {
    // Static allocation functions use engine's memory pools
    static void *alloc_static(size_t p_bytes, bool p_pad_align = false) {
        return internal::gdextension_interface_mem_alloc(p_bytes);
    }

    static void *realloc_static(void *p_memory, size_t p_bytes, bool p_pad_align = false) {
        return internal::gdextension_interface_mem_realloc(p_memory, p_bytes);
    }

    static void free_static(void *p_ptr, bool p_pad_align = false) {
        internal::gdextension_interface_mem_free(p_ptr);
    }
};

// Placement new operators for memory pool allocation
template <typename T>
T *memnew() {
    // Allocate from pool
    void *mem = Memory::alloc_static(sizeof(T));
    // Construct in-place
    return memnew_placement(mem, T);
}

template <typename T>
void memdelete(T *p_class) {
    // Destruct
    if (p_class) {
        p_class->~T();
        // Return to pool
        Memory::free_static(p_class);
    }
}

// Memory alignment for different platforms
#ifdef _MSC_VER
    #define GD_ALIGNMENT(x) __declspec(align(x))
#else
    #define GD_ALIGNMENT(x) __attribute__((aligned(x)))
#endif

// SIMD-aligned structures
struct GD_ALIGNMENT(16) AlignedData {
    float values[4];  // 16-byte aligned for SSE
};

// Pool allocation with alignment
void *alloc_aligned(size_t size, size_t alignment) {
    size_t padded = size + alignment - 1;
    void *mem = Memory::alloc_static(padded + sizeof(void*));

    // Store original pointer for free
    void **result = (void**)((uintptr_t(mem) + sizeof(void*) + alignment - 1) & ~(alignment - 1));
    result[-1] = mem;

    return result;
}

// Example: Custom physics server
class CustomPhysicsServer : public PhysicsServer3D {
    static CustomPhysicsServer *singleton;

    // Thread pool for parallel processing
    WorkerThreadPool::TaskID current_task = WorkerThreadPool::INVALID_TASK_ID;

public:
    static void register_server() {
        // Register with engine during initialization
        ClassDB::register_class<CustomPhysicsServer>();

        // Create instance
        singleton = memnew(CustomPhysicsServer);

        // Register as physics singleton
        PhysicsServer3D::singleton = singleton;
        Engine::get_singleton()->register_singleton(
            "PhysicsServer3D",
            singleton
        );
    }

    // Parallel processing pattern
    void step(real_t p_delta) override {
        // Submit parallel work
        current_task = WorkerThreadPool::get_singleton()->add_native_group_task(
            &CustomPhysicsServer::_thread_step,
            this,
            island_count,
            -1,  // Use all available threads
            true,  // High priority
            "PhysicsStep"
        );

        // Wait for completion
        WorkerThreadPool::get_singleton()->wait_for_task_completion(current_task);
    }

private:
    static void _thread_step(void *p_userdata, uint32_t p_index) {
        CustomPhysicsServer *server = (CustomPhysicsServer *)p_userdata;
        server->process_island(p_index);
    }
};

// include/godot_cpp/core/[mutex_lock.hpp:37](https://github.com/godotengine/godot-cpp/blob/master/include/godot_cpp/core/mutex_lock.hpp#L37)
class MutexLock {
    const Mutex &mutex;

public:
    _ALWAYS_INLINE_ explicit MutexLock(const Mutex &p_mutex) :
            mutex(p_mutex) {
        // Lock on construction
        const_cast<Mutex *>(&mutex)->lock();
    }

    _ALWAYS_INLINE_ ~MutexLock() {
        // Unlock on destruction (exception-safe)
        const_cast<Mutex *>(&mutex)->unlock();
    }
};

// Convenience macros for thread-safe classes
#define _THREAD_SAFE_CLASS_ mutable Mutex _thread_safe_;
#define _THREAD_SAFE_METHOD_ MutexLock _thread_safe_method_(_thread_safe_);
#define _THREAD_SAFE_LOCK_ _thread_safe_.lock();
#define _THREAD_SAFE_UNLOCK_ _thread_safe_.unlock();

class ThreadSafeContainer {
    _THREAD_SAFE_CLASS_  // Adds mutable Mutex _thread_safe_

    Vector<int> data;

public:
    void add(int value) {
        _THREAD_SAFE_METHOD_  // Locks for entire method scope
        data.push_back(value);
    }

    int get(int index) const {
        _THREAD_SAFE_METHOD_  // Works with const methods
        return data[index];
    }

    void complex_operation() {
        _THREAD_SAFE_LOCK_  // Manual lock

        // Do first part
        data.push_back(1);

        _THREAD_SAFE_UNLOCK_  // Unlock for expensive operation

        int result = expensive_calculation();

        _THREAD_SAFE_LOCK_  // Re-lock
        data.push_back(result);
        _THREAD_SAFE_UNLOCK_
    }
};

// include/godot_cpp/core/defs.hpp
#ifdef __GNUC__
    #define likely(x) __builtin_expect(!!(x), 1)
    #define unlikely(x) __builtin_expect(!!(x), 0)
#else
    #define likely(x) (x)
    #define unlikely(x) (x)
#endif

// Usage in performance-critical code
void process_data(T *data, size_t count) {
    if (unlikely(data == nullptr)) {
        // Error path (rare)
        ERR_FAIL_MSG("Null data");
    }

    if (likely(count > 0)) {
        // Common case - optimized for prediction
        for (size_t i = 0; i < count; i++) {
            process_item(data[i]);
        }
    }
}

// Platform-specific force inline
#ifdef _MSC_VER
    #define _FORCE_INLINE_ __forceinline
#elif defined(__GNUC__)
    #define _FORCE_INLINE_ __attribute__((always_inline)) inline
#else
    #define _FORCE_INLINE_ inline
#endif

// Applied to hot path functions
_FORCE_INLINE_ int fast_mul(int a, int b) {
    return a * b;  // Always inlined
}

// Template methods automatically considered for inlining
template <typename T>
_FORCE_INLINE_ T *_call_native_mb_ret_obj(
    GDExtensionMethodBindPtr p_method_bind,
    void *p_instance) {

    GDExtensionObjectPtr ret_obj;
    p_method_bind(p_instance, nullptr, &ret_obj, 0);
    return reinterpret_cast<T *>(
        internal::get_object_instance_binding(ret_obj)
    );
}

// Array-of-Structures (AoS) - poor cache utilization
struct Particle_AoS {
    Vector3 position;
    Vector3 velocity;
    Color color;
    float lifetime;
};
Vector<Particle_AoS> particles_aos;

// Structure-of-Arrays (SoA) - better cache utilization
struct ParticleSystem_SoA {
    PackedVector3Array positions;
    PackedVector3Array velocities;
    PackedColorArray colors;
    PackedFloat32Array lifetimes;

    void update(float delta) {
        // Process positions together (cache-friendly)
        float *pos_ptr = positions.ptrw();
        float *vel_ptr = velocities.ptr();

        for (int i = 0; i < positions.size(); i++) {
            // Contiguous memory access
            pos_ptr[i * 3 + 0] += vel_ptr[i * 3 + 0] * delta;
            pos_ptr[i * 3 + 1] += vel_ptr[i * 3 + 1] * delta;
            pos_ptr[i * 3 + 2] += vel_ptr[i * 3 + 2] * delta;
        }
    }
};

// Compile-time type selection
template <typename T>
struct OptimalInt {
    using type = std::conditional_t<
        sizeof(T) <= 4,
        int32_t,
        int64_t
    >;
};

// Compile-time string hashing
constexpr uint32_t hash_djb2(const char *str) {
    uint32_t hash = 5381;
    while (*str) {
        hash = ((hash << 5) + hash) + *str++;
    }
    return hash;
}

// Usage: Zero runtime cost
constexpr uint32_t method_hash = hash_djb2("get_position");

// SFINAE for optimal overload selection
template <typename T>
typename std::enable_if<std::is_pod<T>::value, void>::type
fast_copy(T *dst, const T *src, size_t count) {
    // POD types: use memcpy
    memcpy(dst, src, count * sizeof(T));
}

template <typename T>
typename std::enable_if<!std::is_pod<T>::value, void>::type
fast_copy(T *dst, const T *src, size_t count) {
    // Non-POD: use copy constructors
    for (size_t i = 0; i < count; i++) {
        new(&dst[i]) T(src[i]);
    }
}