# Standard library header <mutex> (C++11)

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This header is part of the thread support library.

### Classes

mutex (C++11) | provides basic mutual exclusion facility (class)
timed_mutex (C++11) | provides mutual exclusion facility which implements locking with a timeout (class)
recursive_mutex (C++11) | provides mutual exclusion facility which can be locked recursively by the same thread (class)
recursive_timed_mutex (C++11) | provides mutual exclusion facility which can be locked recursively by the same thread and implements locking with a timeout (class)
lock_guard (C++11) | implements a strictly scope-based mutex ownership wrapper (class template)
unique_lock (C++11) | implements movable mutex ownership wrapper (class template)
scoped_lock (C++17) | deadlock-avoiding RAII wrapper for multiple mutexes (class template)
once_flag (C++11) | helper object to ensure that `call_once` invokes the function only once (class)

### Functions

try_lock (C++11) | attempts to obtain ownership of mutexes via repeated calls to `try_lock` (function template)
lock (C++11) | locks specified mutexes, blocks if any are unavailable (function template)
call_once (C++11) | invokes a function only once even if called from multiple threads (function template)
std::swap(std::unique_lock) (C++11) | specializes the std::swap algorithm (function template)

### Tags

defer_locktry_to_lockadopt_lockdefer_lock_ttry_to_lock_tadopt_lock_t (C++11) | tags used to specify locking strategy (tag)

### Synopsis

    namespace std {
      class mutex;
      class recursive_mutex;
      class timed_mutex;
      class recursive_timed_mutex;

      struct defer_lock_t { explicit defer_lock_t() = default; };
      struct try_to_lock_t { explicit try_to_lock_t() = default; };
      struct adopt_lock_t { explicit adopt_lock_t() = default; };

      inline constexpr defer_lock_t  defer_lock { };
      inline constexpr try_to_lock_t try_to_lock { };
      inline constexpr adopt_lock_t  adopt_lock { };

      template<class Mutex> class lock_guard;
      template<class... MutexTypes> class scoped_lock;
      template<class Mutex> class unique_lock;

      template<class Mutex>
        void swap(unique_lock<Mutex>& x, unique_lock<Mutex>& y) noexcept;

      template<class L1, class L2, class... L3> int try_lock(L1&, L2&, L3&...);
      template<class L1, class L2, class... L3> void lock(L1&, L2&, L3&...);

      struct once_flag;

      template<class Callable, class... Args>
        void call_once(once_flag& flag, Callable&& func, Args&&... args);
    }

#### Class std::mutex

    namespace std {
      class mutex {
      public:
        constexpr mutex() noexcept;
        ~mutex();

        mutex(const mutex&) = delete;
        mutex& operator=(const mutex&) = delete;

        void lock();
        bool try_lock();
        void unlock();

        using native_handle_type = /* implementation-defined */;
        native_handle_type native_handle();
      };
    }

#### Class std::recursive_mutex

    namespace std {
      class recursive_mutex {
      public:
        recursive_mutex();
        ~recursive_mutex();

        recursive_mutex(const recursive_mutex&) = delete;
        recursive_mutex& operator=(const recursive_mutex&) = delete;

        void lock();
        bool try_lock() noexcept;
        void unlock();

        using native_handle_type = /* implementation-defined */;
        native_handle_type native_handle();
      };
    }

#### Class std::timed_mutex

    namespace std {
      class timed_mutex {
      public:
        timed_mutex();
        ~timed_mutex();

        timed_mutex(const timed_mutex&) = delete;
        timed_mutex& operator=(const timed_mutex&) = delete;

        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();

        using native_handle_type = /* implementation-defined */;
        native_handle_type native_handle();
      };
    }

#### Class std::recursive_timed_mutex

    namespace std {
      class recursive_timed_mutex {
      public:
        recursive_timed_mutex();
        ~recursive_timed_mutex();

        recursive_timed_mutex(const recursive_timed_mutex&) = delete;
        recursive_timed_mutex& operator=(const recursive_timed_mutex&) = delete;

        void lock();    // blocking
        bool try_lock() noexcept;
        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();

        using native_handle_type = /* implementation-defined */;
        native_handle_type native_handle();
      };
    }

#### Class template std::lock_guard

    namespace std {
      template<class Mutex>
      class lock_guard {
      public:
        using mutex_type = Mutex;

        explicit lock_guard(mutex_type& m);
        lock_guard(mutex_type& m, adopt_lock_t);
        ~lock_guard();

        lock_guard(const lock_guard&) = delete;
        lock_guard& operator=(const lock_guard&) = delete;

      private:
        mutex_type& pm;             // exposition only
      };
    }

#### Class template std::scoped_lock

    namespace std {
      template<class... MutexTypes>
      class scoped_lock {
      public:
        using mutex_type = Mutex;   // If MutexTypes... consists of the single type Mutex

        explicit scoped_lock(MutexTypes&... m);
        explicit scoped_lock(adopt_lock_t, MutexTypes&... m);
        ~scoped_lock();

        scoped_lock(const scoped_lock&) = delete;
        scoped_lock& operator=(const scoped_lock&) = delete;

      private:
        tuple<MutexTypes&...> pm;   // exposition only
      };
    }

#### Class template std::unique_lock

    namespace std {
      template<class Mutex>
      class unique_lock {
      public:
        using mutex_type = Mutex;

        // construct/copy/destroy
        unique_lock() noexcept;
        explicit unique_lock(mutex_type& m);
        unique_lock(mutex_type& m, defer_lock_t) noexcept;
        unique_lock(mutex_type& m, try_to_lock_t);
        unique_lock(mutex_type& m, adopt_lock_t);
        template<class Clock, class Duration>
          unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time);
        template<class Rep, class Period>
          unique_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time);
        ~unique_lock();

        unique_lock(const unique_lock&) = delete;
        unique_lock& operator=(const unique_lock&) = delete;

        unique_lock(unique_lock&& u) noexcept;
        unique_lock& operator=(unique_lock&& u);

        // locking
        void lock();
        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();

        // modifiers
        void swap(unique_lock& u) noexcept;
        mutex_type* release() noexcept;

        // observers
        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
      };

      template<class Mutex>
        void swap(unique_lock<Mutex>& x, unique_lock<Mutex>& y) noexcept;
    }

#### Class std::once_flag

    namespace std {
      struct once_flag {
        constexpr once_flag() noexcept;

        once_flag(const once_flag&) = delete;
        once_flag& operator=(const once_flag&) = delete;
      };
    }

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