//-----------------------------------------------
// bacon.h: writer-priority
//-----------------------------------------------

#ifndef bacon_h
#define bacon_h

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

#include <semaphore>

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

class bacon_lock
{
public:
    bacon_lock(int)
        : R(0), W(0), WGUARD(1), CGUARD(1), ar(0), rr(0), aw(0), ww(0)
    {
    }

    void reader_lock()
    {
        CGUARD.acquire();
        ar = ar + 1;
        if (aw == 0)
        {
            rr = rr + 1;
            R.release();
        }
        CGUARD.release();
        R.acquire();
    }

    void reader_unlock()
    {
        CGUARD.acquire();
        rr = rr - 1;
        ar = ar - 1;
        if (rr == 0)
            while (ww < aw)
            {
                ww = ww + 1;
                W.release();
            }
        CGUARD.release();
    }

    void writer_lock()
    {
        CGUARD.acquire();
        aw = aw + 1;
        if (rr == 0)
        {
            ww = ww + 1;
            W.release();
        }
        CGUARD.release();
        W.acquire();
        WGUARD.acquire();
    }

    void writer_unlock()
    {
        WGUARD.release();
        CGUARD.acquire();
        ww = ww - 1;
        aw = aw - 1;
        if (aw == 0)
            while (rr < ar)
            {
                rr = rr + 1;
                R.release();
            }
        CGUARD.release();
    }

private:
    std::binary_semaphore R, // lecturas pendientes
        W,                   // escrituras pendientes
        WGUARD,              // escritura exclusiva
        CGUARD;              // exclusión contadores
    int ar,                  // lectores activos
        rr,                  // lectores leyendo
        aw,                  // escritores activos
        ww;                  // escritores escribiendo
};

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

#endif // bacon_h