//-----------------------------------------------
// stallings.h: reader-priority
//-----------------------------------------------

#ifndef stallings_h
#define stallings_h

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

#include <cstddef>   // std::size_t
#include <semaphore> // std::*_semaphore

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

class stallings_lock
{
public:
    stallings_lock(std::size_t): reader_sem(1), writer_sem(1), readers(0) {}

    void reader_lock()
    {
        reader_sem.acquire();
        if (++readers == 1)
            writer_sem.acquire();
        reader_sem.release();
    }

    void reader_unlock()
    {
        reader_sem.acquire();
        if (--readers == 0)
            writer_sem.release();
        reader_sem.release();
    }

    void writer_lock() { writer_sem.acquire(); }

    void writer_unlock() { writer_sem.release(); }

private:
    std::binary_semaphore reader_sem, writer_sem;
    std::size_t readers;
};

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

#endif // stallings_h