# Standard library header <semaphore> (C++20)

From cppreference.com
< cpp‎ | header

This header is part of the thread support library.

### Classes

counting_semaphore (C++20) | semaphore that models a non-negative resource count (class template)
binary_semaphore (C++20) | semaphore that has only two states (typedef)

### Synopsis

    namespace std {
      template<ptrdiff_t LeastMaxValue = /* implementation-defined */>
        class counting_semaphore;

      using binary_semaphore = counting_semaphore<1>;
    }

#### Class template std::counting_semaphore

    namespace std {
      template<ptrdiff_t LeastMaxValue = /* implementation-defined */>
      class counting_semaphore {
      public:
        static constexpr ptrdiff_t max() noexcept;

        constexpr explicit counting_semaphore(ptrdiff_t desired);
        ~counting_semaphore();

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

        void release(ptrdiff_t update = 1);
        void acquire();
        bool try_acquire() noexcept;
        template<class Rep, class Period>
          bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time);
        template<class Clock, class Duration>
          bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time);

      private:
        ptrdiff_t counter;          // exposition only
      };
    }

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/header/semaphore&oldid=163980"