Databases
StackOverflow2013
Postsdbo
POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
    primarykey
    data
    text
    <p>We're calling methods on an ActiveX component from within a WPF and STA application. This calling is late-bound performed via:</p> <pre><code>res = ocx.GetType().InvokeMember(methodName, flags, null, ocx, args); </code></pre> <p>...where ocx is the ActiveX object retrieved with the System.Windows.Forms.AxHost.GetOcx() method.</p> <p>This call is performed from within a WPF event handler, say 'mouse clicked'.</p> <p>Now the problem. If we double-click the 'mouse clicked' event will trigger, running InvokeMember(). However, <em>during</em> this call, we see that the 'mouse clicked' event is re-entered. So in the same thread, we see the event handler twice on the call stack. This is very unexpected, and we're trying to prevent that. How can we prevent this from happening?</p> <p>The only reason we can think of <em>why</em> it happens is:</p> <ul> <li>The COM object is created in another STA, so we're performing a cross-STA call which needs to be marshalled</li> <li>cross-thread STA calls uses a Windows Message to send an RPC request to the COM component</li> <li>cross-thread STA calls use the Windows Message pump to receive RPC answer</li> <li>During the waiting another type of event comes in (like 'mouse clicked'), and this gets handled before the RPC answer gets handled.</li> <li>This RPC answer gets handled</li> </ul> <p>Things we tried to fix the problem:</p> <ul> <li>use lock() in all event handlers. This does not work since lock() will lock a thread, and in this case it is the same thread which re-enters the event handler.</li> <li>use custom locking like 'bool locked = false; if (!locked) { locked = true; InvokeMethod(); ...; locked = false; }'. This works partially: it throws away the events instead of queuing them for later, and need an extensive change to <em>all</em> our event handlers, which is not nice to do.</li> <li>use Dispatcher.DisableProcessing to stop (other) messages from being processed. This does not help: it throws an exception because of messages being processed anyways.</li> <li>create a second dispatcher in a new thread, and run ocx.InvokeMehod() via Dispatcher.Invoke() to have it handled by another thread. This gives 'An event was unable to invoke any of the subscribers (Exception from HRESULT: 0x80040201)' (Yes, we're also subscribed to COM events of the ActiveX object).</li> <li>use Dispatcher.PushFrame() to stop event handling from happening. This also fails.</li> </ul> <p>A wild idea which might work, but don't know how to implement this would be creating a new message pump as the WPF message pump which can be configured to temporarily handle only RPC calls. This is along the lines of <a href="http://jmorrill.hjtcentral.com/Home/tabid/428/EntryId/430/WPF-MediaKit-Updates.aspx">http://jmorrill.hjtcentral.com/Home/tabid/428/EntryId/430/WPF-MediaKit-Updates.aspx</a> , but still somewhat different from this situation.</p> <p>So the question boils down to how can we make ActiveX call synchronously like we expected it already to be instead of async?</p> <p><strong>Update</strong></p> <p>To make it more clear that the mechanism involved is not only about mouse-events, but the more generic problem of 'a new event is handled while the old is being executed', I'll give another example with a stack trace:</p> <p>Context: we've got a WPF Grid on which we get a mouseclick (Grid_MouseDown), we've got an ActiveX object on which we perform the method 'CloseShelf'. Opening the shelf will take time, so we are subscribed to the event 'EventShelfClosed', which in the event handler of EventShelfClosed will call 'ListShelf' to know which shelfs are left.</p> <p>This is how the managed stack trace looks like (Hans asked for an unmanaged stacktrace, but I don't know how to get one):</p> <pre><code>MyAxWrapper.dll!MyAxWrapper.MyAxWrapper.InvokeMember(string methodName, System.Reflection.BindingFlags flags, object[] args, int refArgIdx) Line 53 C# MyAxWrapper.dll!MyAxWrapper.LoggingMyAxWrapper.InvokeMember(string methodName, System.Reflection.BindingFlags flags, object[] args, int refArgIdx) Line 151 + 0x14 bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxWrapper.InvokeMethod(string methodName, object[] args) Line 92 + 0x18 bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxAppWrapper.ListShelfs(string CanvasPageId) Line 300 + 0x42 bytes C# PACS.dll!PACS.MyAxDatabase.GetShelfIdsOn(string canvasPageId) Line 223 + 0xf bytes C# MyAxCanvas.dll!MyAxCanvas.MyAxCanvasPlugin.UpdateTimeLineSelection(string canvasPageId) Line 123 + 0x10 bytes C# MyAxCanvas.dll!MyAxCanvas.MyAxCanvasPlugin.EventShelfClosed(string canvasPageId, string shelfId) Line 180 + 0xb bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxAppWrapper.FireEvent(string eventName, object[] args) Line 21 + 0x73 bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxEventForwarder.EventShelfClosed(string CanvasPageID, string ShelfID) Line 177 + 0x58 bytes C# [Native to Managed Transition] [Native to Managed Transition] MyAxWrapper.dll!MyAxWrapper.MyAxWrapper.InvokeMember(string methodName, System.Reflection.BindingFlags flags, object[] args, int refArgIdx) Line 75 + 0x2b bytes C# MyAxWrapper.dll!MyAxWrapper.LoggingMyAxWrapper.InvokeMember(string methodName, System.Reflection.BindingFlags flags, object[] args, int refArgIdx) Line 151 + 0x14 bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxWrapper.InvokeMethod(string methodName, object[] args) Line 92 + 0x18 bytes C# MyAxWrapper.dll!MyAxWrapper.MyAxAppWrapper.CloseShelf(string a) Line 218 + 0x42 bytes C# MyAxCanvas.dll!MyAxCanvas.MyAxCanvasPlugin.EventCanvasPageCreated.AnonymousMethod__0(DataModel.Item exam) Line 110 + 0x1d bytes C# ItemPresenter.dll!ItemPresenter.ItemPresenter.OnItemClicked(DataModel.Item study) Line 36 + 0x14 bytes C# ItemPresenter.dll!ItemPresenter.ItemPresenter.ItemPresenterPerYearControls_Click(object sender, System.Windows.RoutedEventArgs e) Line 215 + 0x1e bytes C# PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) + 0x78 bytes PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x1ae bytes PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args) + 0x79 bytes PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs e) + 0x17 bytes ItemPresenter.dll!ItemPresenter.ItemPresenterControl.Grid_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e) Line 47 + 0x29 bytes C# PresentationCore.dll!System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(System.Delegate genericHandler, object genericTarget) + 0x31 bytes PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target) + 0x29 bytes PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) + 0x3e bytes PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x1ae bytes PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args) + 0x79 bytes PresentationCore.dll!System.Windows.UIElement.RaiseTrustedEvent(System.Windows.RoutedEventArgs args) + 0x41 bytes PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs args, bool trusted) + 0x2c bytes PresentationCore.dll!System.Windows.Input.InputManager.ProcessStagingArea() + 0x1ff bytes PresentationCore.dll!System.Windows.Input.InputManager.ProcessInput(System.Windows.Input.InputEventArgs input) + 0x45 bytes PresentationCore.dll!System.Windows.Input.InputProviderSite.ReportInput(System.Windows.Input.InputReport inputReport) + 0x62 bytes PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.ReportInput(System.IntPtr hwnd, System.Windows.Input.InputMode mode, int timestamp, System.Windows.Input.RawMouseActions actions, int x, int y, int wheel) + 0x263 bytes PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.FilterMessage(System.IntPtr hwnd, MS.Internal.Interop.WindowMessage msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x46d bytes PresentationCore.dll!System.Windows.Interop.HwndSource.InputFilterMessage(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x75 bytes WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0xbe bytes WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) + 0x7d bytes WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs) + 0x53 bytes WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source, System.Delegate method, object args, int numArgs, System.Delegate catchHandler) + 0x42 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.InvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs) + 0xb4 bytes WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x104 bytes [Native to Managed Transition] [Managed to Native Transition] WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame) + 0xc1 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame) + 0x49 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.Run() + 0x4c bytes PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore) + 0x17 bytes PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) + 0x6f bytes PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window) + 0x26 bytes PresentationFramework.dll!System.Windows.Application.Run() + 0x1b bytes MyAxCanvasStandalone.exe!MyAxCanvasStandalone.App.Main(string[] args) Line 37 + 0xa bytes C# [Native to Managed Transition] [Managed to Native Transition] mscorlib.dll!System.AppDomain.ExecuteAssembly(string assemblyFile, System.Security.Policy.Evidence assemblySecurity, string[] args) + 0x6d bytes Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() + 0x2a bytes mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x63 bytes mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool ignoreSyncCtx) + 0xb0 bytes mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x2c bytes mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x44 bytes [Native to Managed Transition] </code></pre> <p>What happens is the the method 'CloseShelf' will close the shelf, but in this case 'CloseShelf' is so fast that the event 'EventShelfClosed' is emitted and handled <em>during</em> the call to CloseShelf. Now CloseShelf will call ListShelfs, but ListShelfs will fail and return null because the ActiveX component is locked by the 'CloseShelf' call which is still active.</p> <p>Why is this a problem? Becasue the programmer does not expect a method call to be async. This hit us after creating a large program, which now means auditting all calls for unexpected behaviour.</p> <p>What would we like to see in this case? We would like to see that 'CloseShelf' returns without handling other events during the call. The method should be synchronous, and any pending events handled during the main (non-recursive) message loop.</p> <p>Having a 'lock' kind of boolean won't help here, since we would be missing events here, which locks up the application.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USRutger Nijlunsing
    1. USRutger Nijlunsing
    plurals
    1. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. USRutger Nijlunsing
      1. VTBountyStart
    2. VO
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO"use lock() in all event handlers. This does not work since lock() will lock a thread, and in this case it is the same thread which re-enters the event handler." How can this be possible?
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. USspender
    2. COspender: This is possible because InvokeMethod() on an ActiveX component constructed in a different thread is an async call as I found out the hard way. During the async call, it will processes different messages, and may re-enter the same event handler because of that.
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. USRutger Nijlunsing
    3. COThe COM modal loop can certainly cause re-entrancy trouble similar to this. But it shouldn't be used here since you've got an STA thread. A re-entrant mouse click is also extraordinary strange. Document your question better with at least a stack trace, captured with unmanaged debugging and the Microsoft symbol server enabled.
      singulars
      1. POHow to prevent re-entrancy of WPF event handler during ActiveX method call?
      1. USHans Passant
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload