From 998786c45da0eca9854fbe5fedbaca68f2eeda55 Mon Sep 17 00:00:00 2001
From: zh Wang <zihao.wang@zilliz.com>
Date: Thu, 1 Dec 2022 18:01:12 +0800
Subject: [PATCH] Fix thread safety in hnsw (#575)

Signed-off-by: zh Wang <zihao.wang@zilliz.com>

Signed-off-by: zh Wang <zihao.wang@zilliz.com>
---
 thirdparty/hnswlib/hnswlib/visited_list_pool.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/thirdparty/hnswlib/hnswlib/visited_list_pool.h b/thirdparty/hnswlib/hnswlib/visited_list_pool.h
index a0bcdccd1..2f0169059 100644
--- a/thirdparty/hnswlib/hnswlib/visited_list_pool.h
+++ b/thirdparty/hnswlib/hnswlib/visited_list_pool.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <algorithm>
+#include <mutex>
 #include <thread>
 #include <unordered_map>
 #include <vector>
@@ -16,6 +17,7 @@ namespace hnswlib {
 class VisitedListPool {
     int numelements;
     std::unordered_map<std::thread::id, std::vector<bool>> map;
+    std::mutex mtx;
 
  public:
     VisitedListPool(int numelements1) {
@@ -24,7 +26,9 @@ class VisitedListPool {
 
     std::vector<bool>&
     getFreeVisitedList() {
+        std::unique_lock lk(mtx);
         auto& res = map[std::this_thread::get_id()];
+        lk.unlock();
         if (res.size() != numelements) {
             res.assign(numelements, false);
         } else {