2019-6-14-WPF-shows-that-some-windows-in-multithreading-will-be-locked-in-the-PenThreadWorker-constr...

title	author	date	CreateTime	categories
WPF shows that some windows in multithreading will be locked in the PenThreadWorker constructor when the application starts	lindexi	2019-06-14 08:50:36 +0800	2019-06-11 19:28:43 +0800	WPF

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

Run the code
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.

巴特西

2019-6-14-WPF-shows-that-some-windows-in-multithreading-will-be-locked-in-the-PenThreadWorker-constr...

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