From 83e066c1e237c16212b3758f8de6cb525e6a8308 Mon Sep 17 00:00:00 2001
From: Takashi Hashida <hashida@clear-code.com>
Date: Mon, 23 Mar 2026 09:30:47 -0700
Subject: [PATCH] Fix: protect static cache in RaceDataManager with a lock to
 prevent race conditions

CachedHoldingInformation is a static field accessed from both the UI thread
and background Task.Run threads without synchronization, creating a data race.
Add a dedicated static lock object (_cacheLock) and mark the field volatile
so that reads and writes to the cache are properly serialized across threads.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 Domain/RaceDataManager.cs | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/Domain/RaceDataManager.cs b/Domain/RaceDataManager.cs
index 2725b2f..2f7e753 100644
--- a/Domain/RaceDataManager.cs
+++ b/Domain/RaceDataManager.cs
@@ -12,23 +12,32 @@ namespace HorseRacingAutoPurchaser.Domain
 {
     public class RaceDataManager
     {
-        private static HoldingInformation CachedHoldingInformation { get; set; }
+        private static volatile HoldingInformation CachedHoldingInformation;
+        private static readonly object _cacheLock = new object();
 
-        public static void ResetCache()
-        {
-            CachedHoldingInformation = null;
+        public static void ResetCache()
+        {
+            lock (_cacheLock)
+            {
+                CachedHoldingInformation = null;
+            }
         }
 
         public static IEnumerable<RaceData> GetRaceDataOfDay(DateTime date, bool useHoldingInformationCache = false)
         {
             var holdingInformationRepository = new HoldingInformationRepository();
             HoldingInformation currentHoldingInformation;
-            if (useHoldingInformationCache && CachedHoldingInformation != null) {
-                currentHoldingInformation = CachedHoldingInformation;
-            }
-            else { 
-                currentHoldingInformation = holdingInformationRepository.ReadAll();
-                CachedHoldingInformation = currentHoldingInformation;
+            lock (_cacheLock)
+            {
+                if (useHoldingInformationCache && CachedHoldingInformation != null)
+                {
+                    currentHoldingInformation = CachedHoldingInformation;
+                }
+                else
+                {
+                    currentHoldingInformation = holdingInformationRepository.ReadAll();
+                    CachedHoldingInformation = currentHoldingInformation;
+                }
             }
 
             var holdingData = new List<HoldingDatum>();
@@ -58,8 +67,8 @@ public static IEnumerable<RaceData> GetRaceDataOfDay(DateTime date, bool useHold
         public static IEnumerable<RaceData> GetAndStoreRaceDataOfDay(DateTime date, Scraper scraper)
         {
             var holdingInformationRepository = new HoldingInformationRepository();
-            var currentHoldingInformation = holdingInformationRepository.ReadAll() ?? new HoldingInformation(new List<HoldingDatum>());
-
+            var currentHoldingInformation = holdingInformationRepository.ReadAll() ?? new HoldingInformation(new List<HoldingDatum>());
+
 
             if (!currentHoldingInformation.HoldingData.Any(_ => _.HeldDate.Date == date.Date))
             {