//-----------------------------------------------
// ballhausen.h: fair solution
//-----------------------------------------------

#ifndef ballhausen_h
#define ballhausen_h

//-----------------------------------------------

#include <cstddef>   // std::size_t
#include <mutex>     // std::mutex
#include <semaphore> // std::counting_semaphore

//-----------------------------------------------

class ballhausen_lock
{
public:
    ballhausen_lock(std::size_t w): writers(w), semaphore(writers) {}

    void reader_lock() { semaphore.acquire(); }

    void reader_unlock() { semaphore.release(); }

    void writer_lock()
    {
        std::unique_lock lock(mutex);
        for (std::size_t i = 0; i < writers; ++i)
            semaphore.acquire();
    }

    void writer_unlock()
    {
        for (std::size_t i = 0; i < writers; ++i)
            semaphore.release();
    }

private:
    std::size_t writers;
    std::mutex mutex;
    std::counting_semaphore<> semaphore;
};

//-----------------------------------------------

#endif // ballhausen_h