salmanoff/include/user/spMcRingBuffer.h

#ifndef _SP_MC_RING_BUFFER_H
#define _SP_MC_RING_BUFFER_H

#include <vector>
#include <cstddef>
#include <stdexcept>
#include <algorithm>
#include <user/sequenceLock.h>

namespace smo {

/**
 * @brief Single-producer, multi-consumer ring buffer w/per-slot sequence locks
 *
 * A ring buffer that maintains data alignment constraints while providing
 * lock-free read access through per-slot sequence locks. The locks are kept
 * separate from the data to preserve alignment requirements for the input
 * engine.
 */
class SpMcRingBuffer
{
public:
	class InputEngineConstraints
	{
	public:
		InputEngineConstraints(
			size_t slotStartAlignmentNBytes_,
			size_t slotPadToNBytes_)
		: slotStartAlignmentNBytes(slotStartAlignmentNBytes_),
		  slotPadToNBytes(slotPadToNBytes_)
		{}

		~InputEngineConstraints() = default;

		// Input-engine layout/constraints
		size_t slotStartAlignmentNBytes;  // power-of-2 alignment (e.g., 4096)
		size_t slotPadToNBytes;       // minimum size per slot
	};

public:
	/**	EXPLANATION:
	 * Constructor initializes the ring buffer with the given constraints and
	 * number of slots. Calculates stride and allocates data buffer and sequence
	 * locks array.
	 */
	explicit SpMcRingBuffer(
		const InputEngineConstraints& constraints_,
		size_t nSlots_)
	: nSlots(nSlots_), strideNBytes(0), bufferNBytes(0),
	  constraints(constraints_)
	{
		if (nSlots == 0)
		{
			throw std::invalid_argument(std::string(__func__)
				+ ": SpMcRingBuffer: nSlots must be > 0");
		}

		computeStrideAndBufferSize();
		// Allocate data buffer: bufferNBytes (aligned up to alignment)
		data.resize(bufferNBytes);
		// Initialize sequence locks array: one lock per slot
		sequenceLocks.resize(nSlots);
	}

	~SpMcRingBuffer() = default;

	// Non-copyable, movable
	SpMcRingBuffer(const SpMcRingBuffer&) = delete;
	SpMcRingBuffer& operator=(const SpMcRingBuffer&) = delete;
	SpMcRingBuffer(SpMcRingBuffer&&) = default;
	SpMcRingBuffer& operator=(SpMcRingBuffer&&) = default;

public:
	/**
	 * @brief Get a reference to data at the specified slot
	 *
	 * @tparam T The type of data stored in the slot
	 * @param slotIndex The index of the slot (0-based)
	 * @return Reference to T at the slot
	 * @throws std::out_of_range if slotIndex >= nSlots
	 */
	template<typename T>
	T& getDataAtSlot(size_t slotIndex)
	{
		if (slotIndex >= nSlots)
		{
			throw std::out_of_range(std::string(__func__)
				+ ": SpMcRingBuffer: slotIndex must be < nSlots");
		}

		size_t offset = slotIndex * strideNBytes;
		return *reinterpret_cast<T*>(data.data() + offset);
	}

	SequenceLock& getSequenceLockAtSlot(size_t slotIndex)
	{
		if (slotIndex >= nSlots)
		{
			throw std::out_of_range(std::string(__func__)
				+ ": SpMcRingBuffer: slotIndex must be < nSlots");
		}
		return sequenceLocks[slotIndex];
	}

private:
	void computeStrideAndBufferSize()
	{
		// Stride is the maximum of alignment and padding
		strideNBytes = std::max(
			constraints.slotStartAlignmentNBytes,
			constraints.slotPadToNBytes);

		// Buffer size is nSlots * strideNBytes, aligned up to alignment
		size_t rawSize = nSlots * strideNBytes;
		bufferNBytes = ((rawSize + constraints.slotStartAlignmentNBytes - 1)
		                / constraints.slotStartAlignmentNBytes)
		               * constraints.slotStartAlignmentNBytes;
	}

	// Buffer data
	std::vector<uint8_t> data;

	// Sequence locks array: one lock per slot
	std::vector<SequenceLock> sequenceLocks;

public:
	// Layout/invariants
	size_t nSlots;
	size_t strideNBytes;
	size_t bufferNBytes;
	InputEngineConstraints constraints;
};

} // namespace smo

#endif // _SP_MC_RING_BUFFER_H