//---------------------------------------------------------
// spinlock.h: spinlock based switch
//---------------------------------------------------------

#include <atomic> // std::atomic_flag
#include <mutex>  // std::mutex

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

class spinlock_switch
{
public:
    void lock(std::mutex &key)
    {
        while (spinlock.test() || spinlock.test_and_set())
            ;
        if (++counter == 1)
            key.lock();
        spinlock.clear();
    }

    void unlock(std::mutex &key)
    {
        while (spinlock.test() || spinlock.test_and_set())
            ;
        if (--counter == 0)
            key.unlock();
        spinlock.clear();
    }

protected:
    std::atomic_flag spinlock;
    size_t counter = 0;
};

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

class spinlock_lock
{
public:
    spinlock_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
    spinlock_switch sw; // protects readers from writers
};

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