fix(galaxy.browser): volatile _disposed, RootAsync gate, O(1) child hint

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browser/GalaxyBrowseSession.cs

@@ -20,7 +20,9 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
     private readonly GalaxyRepositoryClient _client;
     private readonly ConcurrentDictionary<string, GalaxyObject> _byTagName = new(StringComparer.Ordinal);
     private readonly ConcurrentDictionary<int, GalaxyObject> _byGobjectId = new();
-    private bool _disposed;
+    private volatile bool _disposed;
+    private readonly SemaphoreSlim _rootGate = new(1, 1);
+    private HashSet<int> _hasChildrenSet = new();
 
     /// <summary>Opaque token identifying this session in the AdminUI registry.</summary>
     public Guid Token { get; } = Guid.NewGuid();
@@ -48,25 +50,37 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
     public async Task<IReadOnlyList<BrowseNode>> RootAsync(CancellationToken cancellationToken)
     {
         ObjectDisposedException.ThrowIf(_disposed, this);
-        var all = await _client.DiscoverHierarchyAsync(
+        await _rootGate.WaitAsync(cancellationToken).ConfigureAwait(false);
-            new DiscoverHierarchyOptions { IncludeAttributes = false }, cancellationToken)
+        try
-            .ConfigureAwait(false);
-
-        // Populate caches so later ExpandAsync calls can resolve children in-memory.
-        foreach (var obj in all)
         {
-            _byTagName[obj.TagName] = obj;
+            var all = await _client.DiscoverHierarchyAsync(
-            _byGobjectId[obj.GobjectId] = obj;
+                new DiscoverHierarchyOptions { IncludeAttributes = false }, cancellationToken)
+                .ConfigureAwait(false);
+
+            // Populate caches so later ExpandAsync calls can resolve children in-memory.
+            foreach (var obj in all)
+            {
+                _byTagName[obj.TagName] = obj;
+                _byGobjectId[obj.GobjectId] = obj;
+            }
+
+            // Precompute the set of GobjectIds that appear as a parent — used by
+            // Project to compute HasChildrenHint in O(1) instead of O(n²).
+            _hasChildrenSet = new HashSet<int>(_byGobjectId.Values.Select(o => o.ParentGobjectId));
+
+            // Roots are objects whose parent isn't part of the returned set (typically
+            // ParentGobjectId == 0 for WinPlatforms / top-level Areas).
+            var roots = all
+                .Where(o => o.ParentGobjectId == 0 || !_byGobjectId.ContainsKey(o.ParentGobjectId))
+                .ToList();
+
+            LastUsedUtc = DateTime.UtcNow;
+            return Project(roots);
+        }
+        finally
+        {
+            _rootGate.Release();
         }
-
-        // Roots are objects whose parent isn't part of the returned set (typically
-        // ParentGobjectId == 0 for WinPlatforms / top-level Areas).
-        var roots = all
-            .Where(o => o.ParentGobjectId == 0 || !_byGobjectId.ContainsKey(o.ParentGobjectId))
-            .ToList();
-
-        LastUsedUtc = DateTime.UtcNow;
-        return Project(roots);
     }
 
     /// <summary>
@@ -146,7 +160,7 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
             _byGobjectId[obj.GobjectId] = obj;
 
             var displayName = !string.IsNullOrEmpty(obj.ContainedName) ? obj.ContainedName : obj.TagName;
-            var hasChildrenHint = _byGobjectId.Values.Any(o => o.ParentGobjectId == obj.GobjectId);
+            var hasChildrenHint = _hasChildrenSet.Contains(obj.GobjectId);
             result.Add(new BrowseNode(
                 NodeId: obj.TagName,
                 DisplayName: displayName,
@@ -179,6 +193,7 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
     {
         if (_disposed) return;
         _disposed = true;
+        _rootGate.Dispose();
         try
         {
             await _session.DisposeAsync().ConfigureAwait(false);