Fix ActiveGameAds race conditions with consistent locking

ActiveGameAds was a List<GameAd> accessed from multiple threads with
inconsistent locking. Add a dedicated ActiveGameAdsLock object and
use it at all access sites. SID_STOPADV previously had no lock at all.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wjlafrance

src/Atlasd/Battlenet/Common.cs

@@ -43,6 +43,7 @@ public ShutdownEvent(string adminMessage, bool cancelled, DateTime eventDate, Ti
         public static ConcurrentDictionary<byte[], Clan> ActiveClans;
         public static ConcurrentDictionary<Socket, ClientState> ActiveClientStates;
         public static List<GameAd> ActiveGameAds;
+        public static readonly object ActiveGameAdsLock = new object();
         public static ConcurrentDictionary<string, GameState> ActiveGameStates;
         public static IPAddress DefaultAddress { get; private set; }
         public static int DefaultPort { get; private set; }

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_ENTERCHAT.cs

@@ -102,7 +102,7 @@ public override bool Invoke(MessageContext context)
                             {
                                 var gameAd = gameState.GameAd;
                                 if (gameAd.RemoveClient(gameState)) gameState.GameAd = null;
-                                if (gameAd.Clients.Count == 0) lock (Battlenet.Common.ActiveGameAds) Battlenet.Common.ActiveGameAds.Remove(gameAd);
+                                if (gameAd.Clients.Count == 0) lock (Battlenet.Common.ActiveGameAdsLock) Battlenet.Common.ActiveGameAds.Remove(gameAd);
                             }
 
                             if (gameState.ActiveChannel == null)

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_GETADVLISTEX.cs

@@ -58,7 +58,7 @@ public override bool Invoke(MessageContext context)
 
                         var gameAds = new List<GameAd>();
 
-                        lock (Battlenet.Common.ActiveGameAds)
+                        lock (Battlenet.Common.ActiveGameAdsLock)
                         {
                             IList<GameAd> toDelete = new List<GameAd>();
                             foreach (var gameAd in Battlenet.Common.ActiveGameAds)

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_NOTIFYJOIN.cs

@@ -52,7 +52,7 @@ public override bool Invoke(MessageContext context)
             if (gameState.ActiveChannel != null)
                 gameState.ActiveChannel.RemoveUser(gameState);
 
-            lock (Battlenet.Common.ActiveGameAds)
+            lock (Battlenet.Common.ActiveGameAdsLock)
             {
                 foreach (var gameAd in Battlenet.Common.ActiveGameAds)
                 {

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_STARTADVEX.cs

@@ -69,7 +69,7 @@ public override bool Invoke(MessageContext context)
                         Statuses status = Statuses.Failed;
                         GameAd gameAd = null;
 
-                        lock (Battlenet.Common.ActiveGameAds)
+                        lock (Battlenet.Common.ActiveGameAdsLock)
                         {
                             foreach (GameAd _ad in Battlenet.Common.ActiveGameAds)
                             {

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_STARTADVEX2.cs

@@ -69,7 +69,7 @@ public override bool Invoke(MessageContext context)
                         Statuses status = Statuses.Failed;
                         GameAd gameAd = null;
 
-                        lock (Battlenet.Common.ActiveGameAds)
+                        lock (Battlenet.Common.ActiveGameAdsLock)
                         {
                             foreach (GameAd _ad in Battlenet.Common.ActiveGameAds)
                             {

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_STARTADVEX3.cs

@@ -73,7 +73,7 @@ public override bool Invoke(MessageContext context)
                         Statuses status = Statuses.Error;
                         GameAd gameAd = null;
 
-                        lock (Battlenet.Common.ActiveGameAds)
+                        lock (Battlenet.Common.ActiveGameAdsLock)
                         {
                             foreach (GameAd _ad in Battlenet.Common.ActiveGameAds)
                             {

src/Atlasd/Battlenet/Protocols/Game/Messages/SID_STOPADV.cs

@@ -42,7 +42,7 @@ public override bool Invoke(MessageContext context)
             if (!gameAdOwner)
                 Logging.WriteLine(Logging.LogLevel.Info, Logging.LogType.Client_Game, context.Client.RemoteEndPoint, $"{MessageName(Id)} was received but they are not the owner of the game advertisement");
             else
-                Battlenet.Common.ActiveGameAds.Remove(gs.GameAd);
+                lock (Battlenet.Common.ActiveGameAdsLock) Battlenet.Common.ActiveGameAds.Remove(gs.GameAd);
 
             return true;
         }