202 lines
7.6 KiB
C++
202 lines
7.6 KiB
C++
#pragma once
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#include <array>
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#include <atomic>
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#include <cstdint>
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namespace renderive {
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static constexpr std::uint8_t triple_buffer_invalid_index = 255;
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/// 三缓冲操作结果。
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enum class Triple_Buffer_Result : std::uint8_t {
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/// 操作成功。
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Success,
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/// 目标物理缓冲正在被占用。
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Busy,
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/// 角色映射在操作期间发生变化。
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State_Changed,
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/// 交换条件拒绝，不代表错误。
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Condition_Failed
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};
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/// 三个逻辑角色到三个物理缓冲的当前映射。
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struct Triple_Buffer_View {
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std::array<std::uint8_t, 3> index{};
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/// 返回指定角色当前对应的物理缓冲索引。
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std::uint8_t operator[](std::uint8_t role) const {
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return index[role];
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}
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};
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/// 一次物理缓冲占用租约。
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struct Triple_Buffer_Lease {
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std::uint8_t index = triple_buffer_invalid_index;
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/// 判断租约是否持有有效物理缓冲。
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explicit operator bool() const {
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return index != triple_buffer_invalid_index;
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}
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};
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struct Triple_Buffer_Mark_Record {
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Triple_Buffer_Result result = Triple_Buffer_Result::Condition_Failed;
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Triple_Buffer_Lease lease{};
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std::uint8_t busy_index = triple_buffer_invalid_index;
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};
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struct Triple_Buffer_Swap_Record {
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Triple_Buffer_Result result = Triple_Buffer_Result::Condition_Failed;
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Triple_Buffer_View old_view{};
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std::uint8_t busy_index = triple_buffer_invalid_index;
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};
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struct alignas(64) Triple_Buffer_Busy {
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std::atomic_bool busy{false};
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};
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class Triple_Role_Buffer_Control {
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public:
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/// 设置性能统计写入目标。
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/// 重置角色映射和全部 busy 标记。
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void reset() {
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slot_state.store(0, std::memory_order_release);
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for (auto& item : buffer_busy) {
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item.busy.store(false, std::memory_order_release);
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item.busy.notify_all();
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}
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slot_state.notify_all();
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}
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Triple_Buffer_View read_view() const {
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return decode_order(slot_state.load(std::memory_order_acquire));
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}
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/// 尝试占用指定角色当前对应的物理缓冲。
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Triple_Buffer_Mark_Record try_mark_use_role(std::uint8_t role) {
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auto order = slot_state.load(std::memory_order_acquire);
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auto view = decode_order(order);
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auto index = view[role];
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if (!try_mark_index(index)) {
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return {Triple_Buffer_Result::Busy, {}, index};
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}
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auto cur_order = slot_state.load(std::memory_order_acquire);
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if (cur_order != order) {
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unmark_index(index);
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return {Triple_Buffer_Result::State_Changed, {}, triple_buffer_invalid_index};
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}
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return {Triple_Buffer_Result::Success, {index}, triple_buffer_invalid_index};
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}
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Triple_Buffer_Lease mark_use_role(std::uint8_t role) {
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for (;;) {
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auto record = try_mark_use_role(role);
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if (record.result == Triple_Buffer_Result::Success) {
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return record.lease;
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}
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}
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}
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/// 释放租约持有的物理缓冲。
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void unmark_use(Triple_Buffer_Lease lease) {
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unmark_index(lease.index);
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}
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/// 尝试交换两个角色的物理缓冲映射。
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template <typename Can_Swap>
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Triple_Buffer_Swap_Record try_swap_role(std::uint8_t left_role, std::uint8_t right_role, Can_Swap can_swap) {
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std::uint8_t busy_index = triple_buffer_invalid_index;
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return try_swap_role_once(left_role, right_role, can_swap, busy_index);
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}
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bool role_busy(std::uint8_t role) const {
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auto view = read_view();
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return buffer_busy[view[role]].busy.load(std::memory_order_acquire);
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}
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private:
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std::atomic<std::uint8_t> slot_state{0};
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std::array<Triple_Buffer_Busy, 3> buffer_busy{};
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static Triple_Buffer_View decode_order(std::uint8_t order) {
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switch (order) {
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case 0:
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return {{0, 1, 2}};
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case 1:
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return {{0, 2, 1}};
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case 2:
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return {{1, 0, 2}};
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case 3:
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return {{1, 2, 0}};
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case 4:
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return {{2, 0, 1}};
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case 5:
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return {{2, 1, 0}};
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}
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return {{0, 1, 2}};
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}
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static std::uint8_t encode_order(const Triple_Buffer_View& view) {
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if (view.index[0] == 0) {
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return view.index[1] == 1 ? 0 : 1;
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}
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if (view.index[0] == 1) {
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return view.index[1] == 0 ? 2 : 3;
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}
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return view.index[1] == 0 ? 4 : 5;
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}
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static std::uint8_t swap_order(std::uint8_t order, std::uint8_t left_role, std::uint8_t right_role) {
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auto view = decode_order(order);
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auto temp = view.index[left_role];
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view.index[left_role] = view.index[right_role];
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view.index[right_role] = temp;
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return encode_order(view);
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}
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bool try_mark_index(std::uint8_t index) {
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bool expected = false;
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return buffer_busy[index].busy.compare_exchange_strong(expected, true, std::memory_order_acq_rel, std::memory_order_acquire);
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}
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void unmark_index(std::uint8_t index) {
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buffer_busy[index].busy.store(false, std::memory_order_release);
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buffer_busy[index].busy.notify_all();
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}
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bool try_mark_two_indices(std::uint8_t left_index, std::uint8_t right_index, std::uint8_t& busy_index) {
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if (left_index == right_index) {
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if (!try_mark_index(left_index)) {
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busy_index = left_index;
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return false;
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}
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return true;
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}
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auto first = left_index < right_index ? left_index : right_index;
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auto second = left_index < right_index ? right_index : left_index;
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if (!try_mark_index(first)) {
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busy_index = first;
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return false;
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}
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if (!try_mark_index(second)) {
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unmark_index(first);
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busy_index = second;
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return false;
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}
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return true;
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}
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void unmark_two_indices(std::uint8_t left_index, std::uint8_t right_index) {
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if (left_index == right_index) {
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unmark_index(left_index);
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return;
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}
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unmark_index(left_index);
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unmark_index(right_index);
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}
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template <typename Can_Swap>
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Triple_Buffer_Swap_Record try_swap_role_once(std::uint8_t left_role, std::uint8_t right_role, Can_Swap can_swap, std::uint8_t& busy_index) {
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auto old_order = slot_state.load(std::memory_order_acquire);
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auto old_view = decode_order(old_order);
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auto left_index = old_view[left_role];
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auto right_index = old_view[right_role];
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if (!try_mark_two_indices(left_index, right_index, busy_index)) {
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return {Triple_Buffer_Result::Busy, old_view, busy_index};
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}
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auto cur_order = slot_state.load(std::memory_order_acquire);
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if (cur_order != old_order) {
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unmark_two_indices(left_index, right_index);
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return {Triple_Buffer_Result::State_Changed, old_view, triple_buffer_invalid_index};
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}
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if (!can_swap(old_view)) {
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unmark_two_indices(left_index, right_index);
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return {Triple_Buffer_Result::Condition_Failed, old_view, triple_buffer_invalid_index};
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}
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auto new_order = swap_order(old_order, left_role, right_role);
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auto expected = old_order;
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if (!slot_state.compare_exchange_strong(expected, new_order, std::memory_order_acq_rel, std::memory_order_acquire)) {
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unmark_two_indices(left_index, right_index);
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return {Triple_Buffer_Result::State_Changed, old_view, triple_buffer_invalid_index};
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}
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unmark_two_indices(left_index, right_index);
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slot_state.notify_all();
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return {Triple_Buffer_Result::Success, old_view, triple_buffer_invalid_index};
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}
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};
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} // namespace renderive
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