utun2/tools/chatgui/src/audio_event_queue.h

#pragma once
#include <array>
#include <atomic>
#include <cstddef>
#include <cstdint>

/* Ограниченная очередь с несколькими producers. Producer не меняет позицию consumer.
 * Резервирование и публикация разделены sequence каждого слота; callback не ждёт занятый слот.
 * reset допустим только до запуска всех участников. Последние 8 слотов зарезервированы для команд. */
template<class T, size_t Capacity> class AudioEventQueue {
    static_assert(Capacity > 8);
    struct Slot { std::atomic<uint64_t> sequence{0}; T value{}; };
    std::array<Slot, Capacity> m_slots;
    alignas(64) std::atomic<uint64_t> m_write{0};
    alignas(64) std::atomic<uint64_t> m_read{0};
public:
    AudioEventQueue() { reset(); }
    void reset() {
        m_write = 0; m_read = 0;
        for (size_t i = 0; i < Capacity; ++i) m_slots[i].sequence = i;
    }
    bool push(const T& value, bool control = false) {
        uint64_t position = m_write.load(std::memory_order_relaxed);
        for (int attempt = 0; attempt < 8; ++attempt) {
            uint64_t read = m_read.load(std::memory_order_acquire);
            if (read > position) { position = m_write.load(std::memory_order_relaxed); continue; }
            if (position - read >= Capacity - (control ? 0 : 8)) return false;
            auto& slot = m_slots[position % Capacity];
            int64_t difference = (int64_t)(slot.sequence.load(std::memory_order_acquire) - position);
            if (difference < 0) return false;
            if (difference == 0 && m_write.compare_exchange_weak(position, position + 1, std::memory_order_relaxed)) {
                slot.value = value;
                slot.sequence.store(position + 1, std::memory_order_release);
                return true;
            }
            position = m_write.load(std::memory_order_relaxed);
        }
        return false;
    }
    bool pop(T& value) {
        uint64_t position = m_read.load(std::memory_order_relaxed);
        auto& slot = m_slots[position % Capacity];
        if (slot.sequence.load(std::memory_order_acquire) != position + 1) return false;
        value = slot.value;
        slot.sequence.store(position + Capacity, std::memory_order_release);
        m_read.store(position + 1, std::memory_order_release);
        return true;
    }
    size_t size() const {
        uint64_t read = m_read.load(std::memory_order_acquire);
        uint64_t count = m_write.load(std::memory_order_acquire) - read;
        return (size_t)(count > Capacity ? Capacity : count); // Приблизительный снимок, включая ещё не опубликованные слоты.
    }
};