From a8e5cfe70470967d5c6e907fa1e3a0dd43789edc Mon Sep 17 00:00:00 2001
From: lotva <dlotva@gmail.com>
Date: Thu, 4 Jun 2026 19:36:47 +0300
Subject: [PATCH 1/2] fix: prevent pivot race condition

---
 .../nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp  | 3 ++-
 tasks/nalitov_d_dijkstras_algorithm/stl/src/ops_stl.cpp    | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp b/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
index f2c4a1ad3a..48b395eb9f 100644
--- a/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
+++ b/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
@@ -61,7 +61,8 @@ class NalitovDDijkstrasAlgorithmSTL : public BaseTask {
   int worker_slots_{};
   std::vector<std::thread> pool_;
   std::vector<ShardResult> shard_results_;
-  NodeId pivot_{};
+
+  std::atomic<NodeId> pivot_{};
 
   std::atomic<WorkMode> mode_{WorkMode::kParked};
   std::atomic<bool> shutdown_{false};
diff --git a/tasks/nalitov_d_dijkstras_algorithm/stl/src/ops_stl.cpp b/tasks/nalitov_d_dijkstras_algorithm/stl/src/ops_stl.cpp
index 0269a79706..3a634331a4 100644
--- a/tasks/nalitov_d_dijkstras_algorithm/stl/src/ops_stl.cpp
+++ b/tasks/nalitov_d_dijkstras_algorithm/stl/src/ops_stl.cpp
@@ -124,7 +124,7 @@ void NalitovDDijkstrasAlgorithmSTL::PartitionScanBest(int slot) {
 }
 
 void NalitovDDijkstrasAlgorithmSTL::PartitionPushDist(int slot) {
-  const auto hub = static_cast<std::size_t>(pivot_);
+  const auto hub = static_cast<std::size_t>(pivot_.load(std::memory_order_acquire));
   const auto &bundle = graph_[hub];
   const std::size_t m = bundle.size();
   if (m == 0) {
@@ -218,6 +218,7 @@ bool NalitovDDijkstrasAlgorithmSTL::PreProcessingImpl() {
 
   shutdown_.store(false, std::memory_order_relaxed);
   mode_.store(WorkMode::kParked, std::memory_order_relaxed);
+  pivot_.store(-1, std::memory_order_relaxed);
 
   const int total_parties = worker_slots_ + 1;
   bar_start_ = std::make_unique<std::barrier<>>(total_parties);
@@ -252,8 +253,10 @@ bool NalitovDDijkstrasAlgorithmSTL::RunImpl() {
     if (!ReduceShardResults(shard_results_, worker_slots_, &pick_c, &pick_v)) {
       break;
     }
+
     visited_[static_cast<std::size_t>(pick_v)] = 1;
-    pivot_ = pick_v;
+    pivot_.store(pick_v, std::memory_order_release);
+    std::atomic_thread_fence(std::memory_order_release);
 
     mode_.store(WorkMode::kPushDist, std::memory_order_release);
     bar_start_->arrive_and_wait();

From c4a6166dc87c54a759b7d6d28f65787d70b131e8 Mon Sep 17 00:00:00 2001
From: lotva <dlotva@gmail.com>
Date: Thu, 4 Jun 2026 21:24:22 +0300
Subject: [PATCH 2/2] style: fix warnings

---
 tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp b/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
index 48b395eb9f..cc1c80ba95 100644
--- a/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
+++ b/tasks/nalitov_d_dijkstras_algorithm/stl/include/ops_stl.hpp
@@ -62,7 +62,7 @@ class NalitovDDijkstrasAlgorithmSTL : public BaseTask {
   std::vector<std::thread> pool_;
   std::vector<ShardResult> shard_results_;
 
-  std::atomic<NodeId> pivot_{};
+  std::atomic<NodeId> pivot_;
 
   std::atomic<WorkMode> mode_{WorkMode::kParked};
   std::atomic<bool> shutdown_{false};