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Merged
brianrob merged 1 commit into from
May 28, 2026
Merged

Stabilize XamlMessageBox UI-thread dispatch test #2430

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112 changes: 23 additions & 89 deletions src/PerfView.Tests/Dialogs/XamlMessageBoxTests.cs
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Original file line number Diff line number Diff line change
@@ -1,15 +1,10 @@
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Media;
using System.Windows.Threading;
using PerfView.Dialogs;
using Xunit;

#pragma warning disable VSTHRD001 // Use JoinableTaskFactory — we're explicitly testing WPF Dispatcher threading
#pragma warning disable VSTHRD110 // Observe awaitable — fire-and-forget Task.Run is intentional in these tests

namespace PerfViewTests.Dialogs
{
/// <summary>
Expand All @@ -25,97 +20,34 @@ public class XamlMessageBoxTests
/// Also verifies that calling from the UI thread directly still works (no-op dispatch).
/// This is the core regression test for issue #2300.
/// </summary>
[Fact]
public void Show_AutoDispatchesToUIThreadFromBackgroundThread()
#pragma warning disable VSTHRD200 // Keep the original regression test name stable.
[WpfFact]
public async Task Show_AutoDispatchesToUIThreadFromBackgroundThread()
#pragma warning restore VSTHRD200
{
Exception exception = null;
MessageBoxResult uiResult = MessageBoxResult.None;
MessageBoxResult bgResult = MessageBoxResult.None;

var staThread = new Thread(() =>
{
try
{
var app = Application.Current ?? new Application();
app.ShutdownMode = ShutdownMode.OnExplicitShutdown;
RegisterMinimalThemeResources(app);

// Catch unhandled dispatcher exceptions so they don't silently hang.
app.DispatcherUnhandledException += (s, args) =>
{
exception = args.Exception;
args.Handled = true;
Dispatcher.CurrentDispatcher.InvokeShutdown();
};
Application app = Application.Current ?? new Application();
app.ShutdownMode = ShutdownMode.OnExplicitShutdown;

@mconnew mconnew May 28, 2026

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If you have multiple WPF based tests, it might be worth using an IFixture to set these things up. But if it's the only test, not worth bothering with.

RegisterMinimalThemeResources(app);

// Auto-close any XamlMessageBox dialogs as soon as they load.
RegisterAutoCloseHandler();
// Auto-close any XamlMessageBox dialogs as soon as they load.
RegisterAutoCloseHandler();

// Safety timeout: force shutdown if the test hangs.
var safetyTimer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(8) };
safetyTimer.Tick += (s, e) =>
{
safetyTimer.Stop();
if (exception == null)
{
exception = new TimeoutException("Safety timer fired — dialog was not auto-closed");
}
Dispatcher.CurrentDispatcher.InvokeShutdown();
};
safetyTimer.Start();
// Part 1: Call directly from the UI thread (dispatch is a no-op).
MessageBoxResult uiResult = XamlMessageBox.Show("Test message", "XamlMBTest_UI", MessageBoxButton.OK);

// Use Dispatcher.CurrentDispatcher (the STA thread's dispatcher being
// pumped by Dispatcher.Run) rather than app.Dispatcher, because if
// Application.Current was reused from a prior test, app.Dispatcher may
// belong to a different thread.
var currentDispatcher = Dispatcher.CurrentDispatcher;
currentDispatcher.BeginInvoke((Action)(() =>
{
try
{
// Part 1: Call directly from the UI thread (dispatch is a no-op).
uiResult = XamlMessageBox.Show("Test message", "XamlMBTest_UI", MessageBoxButton.OK);
// Part 2: Call from a background thread — before the fix for issue #2300,
// this would throw InvalidOperationException ("The calling thread must be STA")
// because XamlMessageBox creates a WPF Window requiring the UI thread.
Task<MessageBoxResult> backgroundShowTask = Task.Run(() =>
XamlMessageBox.Show("Test message", "XamlMBTest_BG", MessageBoxButton.YesNo));

// Part 2: Call from a background thread — before the fix for issue #2300,
// this would throw InvalidOperationException ("The calling thread must be STA")
// because XamlMessageBox creates a WPF Window requiring the UI thread.
Task.Run(() =>
{
try
{
bgResult = XamlMessageBox.Show("Test message", "XamlMBTest_BG", MessageBoxButton.YesNo);
}
catch (Exception ex)
{
exception = ex;
}
finally
{
currentDispatcher.BeginInvoke(
(Action)(() => currentDispatcher.InvokeShutdown()));
}
});
}
catch (Exception ex)
{
exception = ex;
Dispatcher.CurrentDispatcher.InvokeShutdown();
}
}));

Dispatcher.Run();
}
catch (Exception ex)
{
exception = ex;
}
});
Task completedTask = await Task.WhenAny(backgroundShowTask, Task.Delay(TimeSpan.FromSeconds(10)));
Assert.True(
ReferenceEquals(backgroundShowTask, completedTask),
"Timed out waiting for XamlMessageBox.Show to dispatch to the WPF test thread.");

staThread.SetApartmentState(ApartmentState.STA);
staThread.Start();
Assert.True(staThread.Join(TimeSpan.FromSeconds(10)), "Test timed out — dialog may not have been auto-closed");
MessageBoxResult bgResult = await backgroundShowTask;

Assert.Null(exception);
// Both dialogs were auto-closed without clicking a button, so Result is None.
Assert.Equal(MessageBoxResult.None, uiResult);
Assert.Equal(MessageBoxResult.None, bgResult);
Expand Down Expand Up @@ -144,7 +76,9 @@ private static void RegisterAutoCloseHandler()
Window w = sender as Window;
if (w != null && w.Title != null && w.Title.StartsWith("XamlMBTest_"))
{
#pragma warning disable VSTHRD001, VSTHRD110 // Loaded is already on the WPF thread; defer Close until loading completes.
w.Dispatcher.BeginInvoke((Action)(() => w.Close()));
#pragma warning restore VSTHRD001, VSTHRD110
}
}));
}
Expand Down