m2dev-client-src/src/EterLib/SPSCQueue.h

#ifndef __INC_ETERLIB_SPSCQUEUE_H__
#define __INC_ETERLIB_SPSCQUEUE_H__

#include <atomic>
#include <vector>
#include <cassert>

// Lock-free queue for single producer/consumer pairs
template<typename T>
class SPSCQueue
{
public:
	explicit SPSCQueue(size_t capacity)
		: m_capacity(capacity + 1) // +1 to distinguish full from empty
		, m_buffer(m_capacity)
		, m_head(0)
		, m_tail(0)
	{
		assert(capacity > 0);
	}

	~SPSCQueue()
	{
	}

	// Push item (returns false if full)
	bool Push(const T& item)
	{
		const size_t head = m_head.load(std::memory_order_relaxed);
		const size_t next_head = (head + 1) % m_capacity;

		if (next_head == m_tail.load(std::memory_order_acquire))
			return false; // Queue is full

		m_buffer[head] = item;
		m_head.store(next_head, std::memory_order_release);
		return true;
	}

	// Pop item (returns false if empty)
	bool Pop(T& item)
	{
		const size_t tail = m_tail.load(std::memory_order_relaxed);

		if (tail == m_head.load(std::memory_order_acquire))
			return false; // Queue is empty

		item = m_buffer[tail];
		m_tail.store((tail + 1) % m_capacity, std::memory_order_release);
		return true;
	}

	// Check if empty
	bool IsEmpty() const
	{
		return m_tail.load(std::memory_order_acquire) == m_head.load(std::memory_order_acquire);
	}

	// Get queue size
	size_t Size() const
	{
		const size_t head = m_head.load(std::memory_order_acquire);
		const size_t tail = m_tail.load(std::memory_order_acquire);

		if (head >= tail)
			return head - tail;
		else
			return m_capacity - tail + head;
	}

private:
	const size_t m_capacity;
	std::vector<T> m_buffer;

	alignas(64) std::atomic<size_t> m_head;
	alignas(64) std::atomic<size_t> m_tail;
};

#endif // __INC_ETERLIB_SPSCQUEUE_H__