WPF shows that some windows in multithreading will be locked in the PenThreadWorker constructor when

Problem description: WPF will initialize pen thread when the window initializing. But I find the window may be locked in PenThreadWorker constructor. The UnsafeNativeMethods.CreateResetEvent will lock the thread.

Actual behavior: I use multithreading to create some windows by this code and maybe the thread be locked in PenThreadWorker constructor. The Demo code

    public partial class App : Application
    {
        /// <inheritdoc />
        protected override void OnStartup(StartupEventArgs e)
        {
            var thread = new Thread(() =>
            {
                var mainWindow = new MainWindow();
                mainWindow.Show();
                Dispatcher.Run();
            });
            thread.SetApartmentState(ApartmentState.STA);
            thread.Start();
            base.OnStartup(e);
        }
    }

The step

1. Run the code
2. Use the VisualStudio to suspend the application Maybe you can find the application only create a Stylus Input thread and show only a main window and the other main window and the thread be locked in PenThreadWorker constructor and the window can not show Why I need multithreading to show the windows? I need the splash window to show the welcome page and then I should show the main window in other thread to do the bussiness code and I should close the splash window when the main window showed. But I found some users could not show the main window and the main window be lock in PenThreadWorker constructor. I use dnspy to suspend the application and find the code run in PenThreadWorker constructor and the UnsafeNativeMethods.CreateResetEvent will lock the thread. PenThreadWorker..ctor() PenThread..ctor() PenThreadPool.GetPenThreadForPenContextHelper(PenContext penContext) PenThreadPool.GetPenThreadForPenContext(PenContext penContext) WispTabletDeviceCollection.UpdateTabletsImpl() WispTabletDeviceCollection.UpdateTablets() WispTabletDeviceCollection..ctor() WispLogic.get_WispTabletDevices() WispLogic.RegisterHwndForInput(InputManager inputManager, PresentationSource inputSource) HwndStylusInputProvider..ctor(HwndSource source) HwndSource.Initialize(HwndSourceParameters parameters) HwndSource..ctor(HwndSourceParameters parameters) PresentationFramework.dll!System.Windows.Window.CreateSourceWindow(bool duringShow) PresentationFramework.dll!System.Windows.Window.CreateSourceWindowDuringShow() PresentationFramework.dll!System.Windows.Window.ShowHelper(object booleanBox) Expected behavior: The UnsafeNativeMethods.CreateResetEvent do not lock the thread

Minimal repro:

Create a empty WPF application and then change the app.xaml.cs code

    public partial class App : Application
    {
        /// <inheritdoc />
        protected override void OnStartup(StartupEventArgs e)
        {
            var thread = new Thread(() =>
            {
                var mainWindow = new MainWindow();
                mainWindow.Show();
                Dispatcher.Run();
            });
            thread.SetApartmentState(ApartmentState.STA);
            thread.Start();
            base.OnStartup(e);
        }
    }

Run the code and maybe you can find one of the main window can not show and it stop in UnsafeNativeMethods.CreateResetEvent and I wait for a hour but it can not run.

本文会经常更新，请阅读原文： https://blog.lindexi.com/post/WPF-shows-that-some-windows-in-multithreading-will-be-locked-in-the-PenThreadWorker-constructor-when-the-application-starts.html ，以避免陈旧错误知识的误导，同时有更好的阅读体验。