client/dotnet: make LazyBrowseNode.ExpandAsync thread-safe

2026-05-28 14:28:36 -04:00
parent b4bc2df015
commit eacfeff9fb
2 changed files with 70 additions and 21 deletions
@@ -13,6 +13,7 @@ public sealed class LazyBrowseNode
    private readonly GalaxyRepositoryClient _client;
    private readonly BrowseChildrenOptions _options;
    private readonly List<LazyBrowseNode> _children = [];
+    private readonly SemaphoreSlim _expandLock = new(1, 1);
    private bool _isExpanded;

    internal LazyBrowseNode(
@@ -43,6 +44,10 @@ public sealed class LazyBrowseNode
    ///     Fetches direct children from the gateway and populates <see cref="Children"/>.
    ///     Idempotent: subsequent calls are no-ops.
    /// </summary>
+    /// <remarks>
+    ///     Thread-safe: concurrent callers see exactly one fetch; subsequent callers
+    ///     (after the first completes) return immediately.
+    /// </remarks>
    /// <param name="cancellationToken">Token to observe for cancellation.</param>
    public async Task ExpandAsync(CancellationToken cancellationToken = default)
    {
@@ -51,33 +56,46 @@ public sealed class LazyBrowseNode
            return;
        }

-        string pageToken = string.Empty;
-        HashSet<string> seenPageTokens = new(StringComparer.Ordinal);
-        do
+        await _expandLock.WaitAsync(cancellationToken).ConfigureAwait(false);
+        try
        {
-            BrowseChildrenRequest request = GalaxyRepositoryClient.BuildBrowseChildrenRequest(_options);
-            request.ParentGobjectId = Object.GobjectId;
-            request.PageToken = pageToken;
-
-            BrowseChildrenReply reply = await _client
-                .BrowseChildrenRawAsync(request, cancellationToken)
-                .ConfigureAwait(false);
-
-            for (int i = 0; i < reply.Children.Count; i++)
+            if (_isExpanded)
            {
-                bool hint = i < reply.ChildHasChildren.Count && reply.ChildHasChildren[i];
-                _children.Add(new LazyBrowseNode(_client, reply.Children[i], hint, _options));
+                return;
            }

-            pageToken = reply.NextPageToken;
-            if (!string.IsNullOrWhiteSpace(pageToken) && !seenPageTokens.Add(pageToken))
+            string pageToken = string.Empty;
+            HashSet<string> seenPageTokens = new(StringComparer.Ordinal);
+            do
            {
-                throw new MxGatewayException(
-                    $"Galaxy BrowseChildren returned a repeated page token '{pageToken}'.");
+                BrowseChildrenRequest request = GalaxyRepositoryClient.BuildBrowseChildrenRequest(_options);
+                request.ParentGobjectId = Object.GobjectId;
+                request.PageToken = pageToken;
+
+                BrowseChildrenReply reply = await _client
+                    .BrowseChildrenRawAsync(request, cancellationToken)
+                    .ConfigureAwait(false);
+
+                for (int i = 0; i < reply.Children.Count; i++)
+                {
+                    bool hint = i < reply.ChildHasChildren.Count && reply.ChildHasChildren[i];
+                    _children.Add(new LazyBrowseNode(_client, reply.Children[i], hint, _options));
+                }
+
+                pageToken = reply.NextPageToken;
+                if (!string.IsNullOrWhiteSpace(pageToken) && !seenPageTokens.Add(pageToken))
+                {
+                    throw new MxGatewayException(
+                        $"Galaxy BrowseChildren returned a repeated page token '{pageToken}'.");
+                }
            }
+            while (!string.IsNullOrWhiteSpace(pageToken));
+
+            _isExpanded = true;
+        }
+        finally
+        {
+            _expandLock.Release();
        }
-        while (!string.IsNullOrWhiteSpace(pageToken));
-
-        _isExpanded = true;
    }
 }