spmc.hpp

/*
 * rtchan - Realtime-safe channels via lock-free ringbuffer queues
 * Copyright (c) 2025 Fawn <rubiefawn@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
 
#pragma once
#include "rtchan.hpp"
#include "internal/busy_wait_hint.h"
#include <array>
#include <bit> // std::has_single_bit() to ensure the buffer length is a power of 2
 
namespace rtchan {

template<typename T, size_t N>
requires (0 < N) && (std::has_single_bit(N))
class spmc : public chan<T> {
private:
    static constexpr auto index_wrapped(size_t index) noexcept -> size_t { return index & (N - 1); };
    std::array<T, N> buf = {};
    alignas(std::hardware_destructive_interference_size) std::atomic_size_t read_committed = 0;
    alignas(std::hardware_destructive_interference_size) std::atomic_size_t read_claimed = 0;
    alignas(std::hardware_destructive_interference_size) std::atomic_size_t write_index = 0;
};
 
} // namespace rtchan