Read/write mutex

Designed and implemented by Chris M. Thomasson. Complete implementation can be found on GitHub.

mutex.h:

class rw_fast_mutex
{
public:
	rw_fast_mutex()
	: m_wrstate(1), m_count(INT_MAX), m_rdwake(0),
	m_rdwset(0), m_wrwset(0), m_wrmtx(0) {}

	void read_lock()
	{
		if (m_count.fetch_add(-1, std::memory_order_acquire) < 1)
			m_rdwset.wait();
	}

	void read_unlock()
	{
		if (m_count.fetch_add(1, std::memory_order_release) < 0)
			if (m_rdwake.fetch_add(-1, std::memory_order_acq_rel) == 1)
				m_wrwset.post();
	}

	void write_lock()
	{
		if (m_wrstate.fetch_sub(1, std::memory_order_acquire) < 1)
			m_wrmtx.wait();
		int count = m_count.fetch_add(-INT_MAX, std::memory_order_acquire);
		if (count < INT_MAX)
		{
			int rdwake = m_rdwake.fetch_add(INT_MAX - count, std::memory_order_acquire);
			if (rdwake + INT_MAX - count)
				m_wrwset.wait();
		}
	}

	void write_unlock()
	{
		int count = m_count.fetch_add(INT_MAX, std::memory_order_release);
		if (count < 0)
			m_rdwset.post(-count);
		if (m_wrstate.fetch_add(1, std::memory_order_release) < 0)
			m_wrmtx.post();
	}

private:
	std::atomic m_wrstate;
	std::atomic m_count;
	std::atomic m_rdwake;

	semaphore m_rdwset;
	semaphore m_wrwset;
	semaphore m_wrmtx;
};