Prevent race conditions in chat storage with semaphores

app/MindWork AI Studio/Tools/WorkspaceBehaviour.cs

@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using System.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
@@ -13,6 +14,19 @@ public static class WorkspaceBehaviour
 {
     private static string TB(string fallbackEN) => I18N.I.T(fallbackEN, typeof(WorkspaceBehaviour).Namespace, nameof(WorkspaceBehaviour));
 
+    /// <summary>
+    /// Semaphores for synchronizing chat storage operations per chat.
+    /// This prevents race conditions when multiple threads try to write
+    /// the same chat file simultaneously.
+    /// </summary>
+    private static readonly ConcurrentDictionary<string, SemaphoreSlim> CHAT_STORAGE_SEMAPHORES = new();
+
+    private static SemaphoreSlim GetChatSemaphore(Guid workspaceId, Guid chatId)
+    {
+        var key = $"{workspaceId}_{chatId}";
+        return CHAT_STORAGE_SEMAPHORES.GetOrAdd(key, _ => new SemaphoreSlim(1, 1));
+    }
+
     public static readonly JsonSerializerOptions JSON_OPTIONS = new()
     {
         WriteIndented = true,
@@ -36,6 +50,12 @@ public static class WorkspaceBehaviour
     }
 
     public static async Task StoreChat(ChatThread chat)
+    {
+        // Acquire the semaphore for this specific chat to prevent concurrent writes to the same file:
+        var semaphore = GetChatSemaphore(chat.WorkspaceId, chat.ChatId);
+        await semaphore.WaitAsync();
+        
+        try
         {
             string chatDirectory;
             if (chat.WorkspaceId == Guid.Empty)
@@ -54,8 +74,19 @@ public static class WorkspaceBehaviour
             var chatPath = Path.Join(chatDirectory, "thread.json");
             await File.WriteAllTextAsync(chatPath, JsonSerializer.Serialize(chat, JSON_OPTIONS), Encoding.UTF8);
         }
+        finally
+        {
+            semaphore.Release();
+        }
+    }
 
     public static async Task<ChatThread?> LoadChat(LoadChat loadChat)
+    {
+        // Acquire the semaphore for this specific chat to prevent concurrent read/writes to the same file:
+        var semaphore = GetChatSemaphore(loadChat.WorkspaceId, loadChat.ChatId);
+        await semaphore.WaitAsync();
+        
+        try
         {
             var chatPath = loadChat.WorkspaceId == Guid.Empty
                 ? Path.Join(SettingsManager.DataDirectory, "tempChats", loadChat.ChatId.ToString())
@@ -64,8 +95,6 @@ public static class WorkspaceBehaviour
             if(!Directory.Exists(chatPath))
                 return null;
             
-        try
-        {
             var chatData = await File.ReadAllTextAsync(Path.Join(chatPath, "thread.json"), Encoding.UTF8);
             var chat = JsonSerializer.Deserialize<ChatThread>(chatData, JSON_OPTIONS);
             return chat;
@@ -74,6 +103,10 @@ public static class WorkspaceBehaviour
         {
             return null;
         }
+        finally
+        {
+            semaphore.Release();
+        }
     }
     
     public static async Task<string> LoadWorkspaceName(Guid workspaceId)
@@ -144,8 +177,19 @@ public static class WorkspaceBehaviour
         else
             chatDirectory = Path.Join(SettingsManager.DataDirectory, "workspaces", chat.WorkspaceId.ToString(), chat.ChatId.ToString());
 
+        // Acquire the semaphore to prevent deleting while another thread is writing:
+        var semaphore = GetChatSemaphore(workspaceId, chatId);
+        await semaphore.WaitAsync();
+        
+        try
+        {
             Directory.Delete(chatDirectory, true);
         }
+        finally
+        {
+            semaphore.Release();
+        }
+    }
 
     private static async Task EnsureWorkspace(Guid workspaceId, string workspaceName)
     {

app/MindWork AI Studio/wwwroot/changelog/v26.1.2.md

@@ -8,3 +8,4 @@
 - Fixed a bug with local transcription providers by handling errors correctly when the local provider is unavailable.
 - Fixed a bug with local transcription providers by correctly handling empty model IDs.
 - Fixed a bug affecting the transcription preview: previously, when you stopped music or other media, recorded or dictated text, and then tried to resume playback, the media wouldn’t resume as expected. This behavior is now fixed.
+- Fixed a rare bug that occurred when multiple threads tried to manage the same chat thread.