namespace std {
    class shared_mutex;
    class shared_timed_mutex;
 
    template <class Mutex> class shared_lock;
 
    template <class Mutex>
    void swap(shared_lock<Mutex>& x, shared_lock<Mutex>& y) noexcept;
}

class shared_mutex {
 public:
    typedef /*implementation-defined*/ native_handle_type;
 
    shared_mutex();
    ~shared_mutex();
    shared_mutex(const shared_mutex&) = delete;
    shared_mutex& operator=(const shared_mutex&) = delete;
 
    // Exclusive ownership
    void lock(); // blocking
    bool try_lock();
    void unlock();
 
    // Shared ownership
    void lock_shared(); // blocking
    bool try_lock_shared();
    void unlock_shared();
 
    // Getters
    native_handle_type native_handle();
};

class shared_timed_mutex {
 public:
    shared_timed_mutex();
    ~shared_timed_mutex();
    shared_timed_mutex(const shared_timed_mutex&) = delete;
    shared_timed_mutex& operator=(const shared_timed_mutex&) = delete;
 
    // Exclusive ownership
    void lock(); // blocking
    bool try_lock();
    template <class Rep, class Period>
    bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
    bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
    void unlock();
 
    // Shared ownership
    void lock_shared(); // blocking
    bool try_lock_shared();
    template <class Rep, class Period>
    bool try_lock_shared_for(const chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
    bool try_lock_shared_until(const chrono::time_point<Clock, Duration>& abs_time);
    void unlock_shared();
};

template <class Mutex>
class shared_lock {
 public:
    typedef Mutex mutex_type;
 
    shared_lock() noexcept;
    explicit shared_lock(mutex_type& m); // blocking
    shared_lock(mutex_type& m, defer_lock_t) noexcept;
    shared_lock(mutex_type& m, try_to_lock_t);
    shared_lock(mutex_type& m, adopt_lock_t);
    template <class Clock, class Duration>
    shared_lock(mutex_type& m,
    const chrono::time_point<Clock, Duration>& abs_time);
    template <class Rep, class Period>
    shared_lock(mutex_type& m,
    const chrono::duration<Rep, Period>& rel_time);
    ~shared_lock();
    shared_lock(shared_lock const&) = delete;
    shared_lock& operator=(shared_lock const&) = delete;
    shared_lock(shared_lock&& u) noexcept;
    shared_lock& operator=(shared_lock&& u) noexcept;
 
    void lock(); // blocking
    bool try_lock();
    template <class Rep, class Period>
    bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
    bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
    void unlock();
 
    // Setters
    void swap(shared_lock& u) noexcept;
    mutex_type* release() noexcept;
 
    // Getters
    bool owns_lock() const noexcept;
    explicit operator bool () const noexcept;
    mutex_type* mutex() const noexcept;
 
 private:
    mutex_type* pm; // exposition only
    bool owns; // exposition only
};