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

#ifndef stallings_m_h
#define stallings_m_h

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

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

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

class stallings_m_lock
{
public:
    stallings_m_lock(std::size_t): readers(0) {}

    void reader_lock()
    {
        std::unique_lock lock(reader_mutex);
        if (++readers == 1)
            writer_mutex.lock();
    }

    void reader_unlock()
    {
        std::unique_lock lock(reader_mutex);
        if (--readers == 0)
            writer_mutex.unlock();
    }

    void writer_lock() { writer_mutex.lock(); }

    void writer_unlock() { writer_mutex.unlock(); }

private:
    std::mutex reader_mutex, writer_mutex;
    std::size_t readers;
};

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

#endif // stallings_m_h