From d6606e2cf80e76161b71aeecca2bce69b01e29c4 Mon Sep 17 00:00:00 2001
From: Arun Sharma <arun@sharma-home.net>
Date: Thu, 27 Aug 2026 20:51:37 -0700
Subject: [PATCH] fts: serialize concurrent mutations of QFTSEdgeCompute scores
 map

QFTSEdgeCompute copies share the same scores map by reference (one copy
per worker thread in a scheduled parallel frontier task), but edgeCompute
mutated the map with no synchronization. Concurrent emplace/at() can
rehash the map while other threads mutate it, corrupting the heap.

Guard all mutations with a shared mutex, mirroring the existing
MatchTermsVertexCompute::resDfsMutex pattern.

Related to LadybugDB/ladybug#840.
---
 fts/src/function/query_fts_index.cpp | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fts/src/function/query_fts_index.cpp b/fts/src/function/query_fts_index.cpp
index aaf3435d..1c007e7e 100644
--- a/fts/src/function/query_fts_index.cpp
+++ b/fts/src/function/query_fts_index.cpp
@@ -1,5 +1,6 @@
 #include "function/query_fts_index.h"
 
+#include <mutex>
 #include <queue>
 
 #include "binder/binder.h"
@@ -131,10 +132,18 @@ struct ScoreInfo {
 struct QFTSEdgeCompute final : EdgeCompute {
     node_id_map_t<ScoreInfo>& scores;
     const std::unordered_map<offset_t, uint64_t>& dfs;
+    // The scores map is shared by reference between copies of this edge compute (one per
+    // worker thread in a parallel frontier task), so all mutations must be serialized.
+    std::shared_ptr<std::mutex> scoresMutex;
 
     QFTSEdgeCompute(node_id_map_t<ScoreInfo>& scores,
         const std::unordered_map<offset_t, uint64_t>& dfs)
-        : scores{scores}, dfs{dfs} {}
+        : scores{scores}, dfs{dfs}, scoresMutex{std::make_shared<std::mutex>()} {}
+
+    QFTSEdgeCompute(node_id_map_t<ScoreInfo>& scores,
+        const std::unordered_map<offset_t, uint64_t>& dfs,
+        std::shared_ptr<std::mutex> scoresMutex)
+        : scores{scores}, dfs{dfs}, scoresMutex{std::move(scoresMutex)} {}
 
     std::vector<nodeID_t> edgeCompute(nodeID_t boundNodeID, graph::NbrScanState::Chunk& resultChunk,
         bool) override {
@@ -143,6 +152,7 @@ struct QFTSEdgeCompute final : EdgeCompute {
         std::vector<nodeID_t> activeNodes;
         resultChunk.forEach([&](auto neighbors, auto propertyVectors, auto i) {
             auto docNodeID = neighbors[i];
+            std::lock_guard guard{*scoresMutex};
             if (!scores.contains(docNodeID)) {
                 scores.emplace(docNodeID, ScoreInfo{});
             }
@@ -154,7 +164,7 @@ struct QFTSEdgeCompute final : EdgeCompute {
     }
 
     std::unique_ptr<EdgeCompute> copy() override {
-        return std::make_unique<QFTSEdgeCompute>(scores, dfs);
+        return std::make_unique<QFTSEdgeCompute>(scores, dfs, scoresMutex);
     }
 };