# Standard library header <shared_mutex>

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< cpp‎ | header

This header is part of the thread support library.

### Classes
shared_mutex (C++17) | provides shared mutual exclusion facility (class)
shared_timed_mutex (C++14) | provides shared mutual exclusion facility and implements locking with a timeout (class)
shared_lock (C++14) | implements movable shared mutex ownership wrapper (class template)
### Functions
std::swap(std::shared_lock) | specialization of std::swap for `shared_lock` (function template)

### Synopsis

    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 std::shared_mutex

    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 std::shared_timed_mutex

    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();
    };

#### Class std::shared_lock

    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
    };

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