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fix(index): address thread safety issues in lock-free stats implementation
- Add mutex protection for queue_ access in WindowResultQueue - Initialize result_queues_ keys in constructor to avoid concurrent map modification - Use at() instead of operator[] for thread-safe map access - Add n_ios > 0 check to prevent division by zero in IO time calculation Addresses review comments on PR #1721 Signed-off-by: LHT129 <tianlan.lht@antgroup.com> Co-authored-by: Kimi-K2.5 <assistant@example.com>
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‎TASK.md‎

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/home/tianlan.lht/code/workspace/agent-hive/tasks/2026-03-13-替换-hnsw-stats-mutex-为无锁计数器.md

‎plan.md‎

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# 实施计划: 替换 HNSW 搜索路径中的排他 stats_mutex_ 为无锁方案
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## 1. 目标概述
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- **任务目标**: 将 `WindowResultQueue` 改为无锁实现，消除高并发场景下的 `stats_mutex_` 竞争
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- **预期成果**: 搜索路径无需获取锁即可记录统计数据，提升多线程吞吐量
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- **完成标准**: 构建通过、测试通过、lint 通过
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## 2. 当前状态分析
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- **已存在的实现**: `WindowResultQueue` 是简单的环形缓冲区，非线程安全，通过 `stats_mutex_` 保护
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- **需要修改的部分**:
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- `src/utils/window_result_queue.h` - 添加原子类型
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- `src/utils/window_result_queue.cpp` - 无锁 Push 实现
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- `src/index/hnsw.cpp` - 移除 stats_mutex_ 保护
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- `src/index/diskann.cpp` - 移除 stats_mutex_ 保护
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- **依赖项**: 无新依赖，使用标准库 `std::atomic`
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## 3. 技术方案
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- **核心思路**: 将 `count_` 改为原子类型，使用 `fetch_add` 实现无锁写入
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- **关键设计**:
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- 写入端：`fetch_add` 原子获取写入位置，零等待
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- 读取端：`relaxed` 内存序读取快照，可接受微小数据竞争
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- **接口定义**: 保持现有 API 不变（`Push`、`GetAvgResult`）
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### 无锁 Push 实现原理
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```cpp
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void WindowResultQueue::Push(float value) {
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uint64_t window_size = queue_.size();
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uint64_t pos = count_.fetch_add(1, std::memory_order_relaxed);
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queue_[pos % window_size] = value; // 可能有数据竞争，但任务说明可接受
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}
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```
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### GetAvgResult 实现原理
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```cpp
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float WindowResultQueue::GetAvgResult() const {
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uint64_t statistic_num = std::min<uint64_t>(
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count_.load(std::memory_order_relaxed), queue_.size());
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if (statistic_num == 0) {
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return 0.0F;
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}
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float result = 0;
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for (uint64_t i = 0; i < statistic_num; i++) {
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result += queue_[i]; // 可能有数据竞争，可接受
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}
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return result / static_cast<float>(statistic_num);
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}
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```
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## 4. 实施步骤
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| 序号 | 步骤 | 涉及文件 | 详细说明 |
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|------|------|----------|----------|
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| 1 | 修改头文件 | src/utils/window_result_queue.h | 添加 `#include <atomic>`，将 `count_` 声明为 `std::atomic<uint64_t>` |
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| 2 | 修改实现 | src/utils/window_result_queue.cpp | Push 使用 `fetch_add`，GetAvgResult 使用 `load(relaxed)` |
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| 3 | 移除 hnsw.cpp 中的锁 | src/index/hnsw.cpp | 移除 331、463、750 行的 `std::lock_guard` |
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| 4 | 移除 diskann.cpp 中的锁 | src/index/diskann.cpp | 移除 519、653、1088 行的 `std::lock_guard` |
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| 5 | 验证构建 | - | 执行 `make release` |
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| 6 | 验证测试 | - | 执行 `make test` |
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| 7 | 验证代码风格 | - | 执行 `make lint` 和 `make fmt` |
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## 5. 测试计划
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- **单元测试**: 现有测试应继续通过（API 不变）
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- **集成测试**: 搜索功能正常，统计数据正确
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- **性能测试**: 可选，验证高并发场景下吞吐量提升
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## 6. 风险与应对
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| 风险 | 影响 | 应对措施 |
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|------|------|----------|
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| 数据竞争导致统计偏差 | 低 | 任务说明可接受微小偏差 |
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| 内存序选择不当 | 中 | 参考项目中 `spsc_queue.h` 的实现 |
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| 现有测试失败 | 低 | 保持 API 不变，行为兼容 |
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## 7. 验收标准
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- [ ] `make release` 构建成功
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- [ ] `make test` 测试通过
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- [ ] `make lint` 代码风格检查通过
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- [ ] hnsw.cpp 中移除了 stats_mutex_ 保护
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- [ ] diskann.cpp 中移除了 stats_mutex_ 保护
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## 8. 相关资源
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- **参考代码**: `src/utils/spsc_queue.h` — 项目中已有的无锁队列实现
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- **原始任务**: `agent-hive/tasks/2026-03-13-替换-hnsw-stats-mutex-为无锁计数器.md`

‎src/index/diskann.cpp‎

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@@ -281,6 +281,14 @@ DiskANN::DiskANN(DiskannParameters& diskann_params, const IndexCommonParam& inde
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this->feature_list_ = std::make_shared<IndexFeatureList>();
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this->init_feature_list();
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result_queues_.try_emplace(STATSTIC_KNN_IO);
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result_queues_.try_emplace(STATSTIC_KNN_TIME);
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result_queues_.try_emplace(STATSTIC_KNN_IO_TIME);
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result_queues_.try_emplace(STATSTIC_RANGE_IO);
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result_queues_.try_emplace(STATSTIC_RANGE_HOP);
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result_queues_.try_emplace(STATSTIC_RANGE_TIME);
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result_queues_.try_emplace(STATSTIC_RANGE_CACHE_HIT);
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result_queues_.try_emplace(STATSTIC_RANGE_IO_TIME);
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}
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tl::expected<std::vector<int64_t>, Error>
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query_stats + i);
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}
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}
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result_queues_[STATSTIC_KNN_IO].Push(static_cast<float>(query_stats[i].n_ios));
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result_queues_[STATSTIC_KNN_TIME].Push(static_cast<float>(time_cost));
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result_queues_[STATSTIC_KNN_IO_TIME].Push(
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(query_stats[i].io_us / static_cast<float>(query_stats[i].n_ios)) /
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MACRO_TO_MILLI);
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result_queues_.at(STATSTIC_KNN_IO).Push(static_cast<float>(query_stats[i].n_ios));
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result_queues_.at(STATSTIC_KNN_TIME).Push(static_cast<float>(time_cost));
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if (query_stats[i].n_ios > 0) {
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result_queues_.at(STATSTIC_KNN_IO_TIME).Push(
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(query_stats[i].io_us / static_cast<float>(query_stats[i].n_ios)) /
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MACRO_TO_MILLI);
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} else {
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result_queues_.at(STATSTIC_KNN_IO_TIME).Push(0.0F);
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}
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} catch (const std::runtime_error& e) {
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delete[] distances;
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params.use_async_io,
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&query_stats);
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}
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result_queues_[STATSTIC_RANGE_IO].Push(static_cast<float>(query_stats.n_ios));
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result_queues_[STATSTIC_RANGE_HOP].Push(static_cast<float>(query_stats.n_hops));
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result_queues_[STATSTIC_RANGE_TIME].Push(static_cast<float>(time_cost));
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result_queues_[STATSTIC_RANGE_CACHE_HIT].Push(
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result_queues_.at(STATSTIC_RANGE_IO).Push(static_cast<float>(query_stats.n_ios));
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result_queues_.at(STATSTIC_RANGE_HOP).Push(static_cast<float>(query_stats.n_hops));
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result_queues_.at(STATSTIC_RANGE_TIME).Push(static_cast<float>(time_cost));
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result_queues_.at(STATSTIC_RANGE_CACHE_HIT).Push(
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static_cast<float>(query_stats.n_cache_hits));
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result_queues_[STATSTIC_RANGE_IO_TIME].Push(
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(query_stats.io_us / static_cast<float>(query_stats.n_ios)) / MACRO_TO_MILLI);
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if (query_stats.n_ios > 0) {
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result_queues_.at(STATSTIC_RANGE_IO_TIME).Push(
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(query_stats.io_us / static_cast<float>(query_stats.n_ios)) / MACRO_TO_MILLI);
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} else {
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result_queues_.at(STATSTIC_RANGE_IO_TIME).Push(0.0F);
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}
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} catch (const std::runtime_error& e) {
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LOG_ERROR_AND_RETURNS(
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ErrorType::INTERNAL_ERROR, "failed to perform range search on diskann: ", e.what());

‎src/index/hnsw.cpp‎

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@@ -100,6 +100,7 @@ HNSW::HNSW(HnswParameters hnsw_params, const IndexCommonParam& index_common_para
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}
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this->init_feature_list();
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result_queues_.try_emplace(STATSTIC_KNN_TIME);
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}
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tl::expected<std::vector<int64_t>, Error>
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e.what());
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}
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result_queues_[STATSTIC_KNN_TIME].Push(static_cast<float>(time_cost));
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result_queues_.at(STATSTIC_KNN_TIME).Push(static_cast<float>(time_cost));
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// return result
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if (results.empty()) {
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e.what());
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}
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result_queues_[STATSTIC_KNN_TIME].Push(static_cast<float>(time_cost));
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result_queues_.at(STATSTIC_KNN_TIME).Push(static_cast<float>(time_cost));
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// return result
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auto target_size = static_cast<int64_t>(results.size());

‎src/utils/window_result_queue.cpp‎

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WindowResultQueue::Push(float value) {
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uint64_t window_size = queue_.size();
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uint64_t pos = count_.fetch_add(1, std::memory_order_relaxed);
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std::lock_guard<std::mutex> lock(queue_mutex_);
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queue_[pos % window_size] = value;
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}
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if (statistic_num == 0) {
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return 0.0F;
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}
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std::lock_guard<std::mutex> lock(queue_mutex_);
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float result = 0;
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for (uint64_t i = 0; i < statistic_num; i++) {
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result += queue_[i];

‎src/utils/window_result_queue.h‎

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#pragma once
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#include <atomic>
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#include <mutex>
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#include <string>
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#include <vector>
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private:
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std::atomic<uint64_t> count_{0};
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std::vector<float> queue_;
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mutable std::mutex queue_mutex_;
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};
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} // namespace vsag

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