TransactionTracer concurrency for Maui Transactions

src/Sentry.Maui/Internal/MauiEventsBinder.cs

@@ -420,21 +420,19 @@ internal void StartUiTransaction(string name)
         if (CurrentUiTx is not null)
         {
             // Idle timer will clean up any previous UI transaction, but we don't want any more child spans on it
-            _hub.ConfigureScope(scope => scope.ResetTransaction(CurrentUiTx));
+            _hub.ConfigureScope(static (scope, tx) => scope.ResetTransaction(tx), CurrentUiTx);
         }
-        CurrentUiTx = null;
 
         var context = new TransactionContext(name, UserInteractionClickOp)
         {
             NameSource = TransactionNameSource.Component
         };
         CurrentUiTx = _hub is IHubInternal internalHub
             ? internalHub.StartTransaction(context, _options.AutoTransactionIdleTimeout)
-            // never called in practice... all our hubs implement IHubInternal
             : _hub.StartTransaction(context);
 
-        // Only bind to scope if there is no other transaction already there (user-created or SDK-owned navigation).
-        _hub.ConfigureScope(scope => scope.Transaction ??= CurrentUiTx);
+        // Bind to scope only if no other transaction is already there (user-installed or SDK-owned navigation).
+        _hub.ConfigureScope(static (scope, tx) => scope.Transaction ??= tx, CurrentUiTx);
     }
 
     // Application Events
@@ -472,13 +470,13 @@ private void OnWindowOnStopped(object? sender, EventArgs _)
                 if (uiTx.Spans.Count > 0)
                 {
                     // Only finish UI transactions with child spans.
-                    // Childless transactions will be discarded by the idle timeout.
+                    // Childless transactions get discarded by the idle timeout.
                     uiTx.Finish(SpanStatus.Ok);
                 }
                 else
                 {
-                    // No child spans, so just detach from scope and let idle timeout handle it.
-                    _hub.ConfigureScope(scope => scope.ResetTransaction(CurrentUiTx));
+                    // No child spans, so just detach from scope and let idle timeout handle it
+                    _hub.ConfigureScope(static (scope, tx) => scope.ResetTransaction(tx), uiTx);
                 }
             }
             CurrentUiTx = null;

src/Sentry/SpanTracer.cs

@@ -34,11 +34,32 @@ public sealed class SpanTracer : IBaseTracer, ISpan
     /// <inheritdoc />
     public DateTimeOffset StartTimestamp { get; internal set; }
 
+    private DateTimeOffset? _endTimestamp;
+    private bool _isFinished;
+
     /// <inheritdoc />
-    public DateTimeOffset? EndTimestamp { get; internal set; }
+    public DateTimeOffset? EndTimestamp
+    {
+        get => Volatile.Read(ref _isFinished) ? _endTimestamp : null;
+        internal set
+        {
+            // Ordering is load-bearing: the gate-flip is release-ordered against the data write,
+            // so lock-free readers gating on `_isFinished` see a consistent (timestamp, finished) pair.
+            if (value is null)
+            {
+                Volatile.Write(ref _isFinished, false);
+                _endTimestamp = null;
+            }
+            else
+            {
+                _endTimestamp = value;
+                Volatile.Write(ref _isFinished, true);
+            }
+        }
+    }
 
     /// <inheritdoc />
-    public bool IsFinished => EndTimestamp is not null;
+    public bool IsFinished => Volatile.Read(ref _isFinished);
 
     // Not readonly because of deserialization
     internal Dictionary<string, Measurement>? InternalMeasurements { get; private set; }