//---------------------------------------------------------
// switch.h: mutex based switch
//---------------------------------------------------------

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

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

class mutex_switch
{
public:
    void lock(std::mutex &key)
    {
        std::unique_lock lock(mutex);
        if (++counter == 1)
            key.lock();
    }

    void unlock(std::mutex &key)
    {
        std::unique_lock lock(mutex);
        if (--counter == 0)
            key.unlock();
    }

protected:
    std::mutex mutex;
    size_t counter = 0;
};

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

class switch_lock
{
public:
    switch_lock(std::size_t) {}
    void reader_lock() { sw.lock(mutex); }
    void reader_unlock() { sw.unlock(mutex); }
    void writer_lock() { mutex.lock(); }
    void writer_unlock() { mutex.unlock(); }

private:
    std::mutex mutex; // writers mutex
    mutex_switch sw;  // protects readers from writers
};

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