Question

I refactored my application a while ago and since then I’ve been having problems with debugging using Visual Studio 2010.

My application works as expected while not debugging (not stepping through the application. An attached debugger does not cause any issues). However, when a breakpoint is triggered and I start to step through the app, Visual Studio and the app both hang after at most 3-4 steps.
To emphasize this point even more: It works well with my customers and regardless of whether I start it from Visual Studio or stand-alone – as long as no break point is triggered.
It does not matter where in the code I place the break point.

IDE: Visual Studio 2010 x64
Platform: .NET 4.0

The refactoring included a lot of cross-thread calls to BeginInvoke – all channeled through the following method:

public static void BeginInvokeIfRequired(this Control control, Action action)
{
    if (control.InvokeRequired)
    {
        control.BeginInvoke(action);
    }
    else
    {
        action.Invoke();
    }
}

There is not a single call to Control.Invoke() in the project.

• Is there something wrong with the above method?

Additionally, I’d appreciate any hints on how you would track down this bug. My current approach is to add output to the console and selectively deactivating parts of the code.

Answer 1

I would suspect that in some cases the code you show poses a problem since InvokeRequired lies in case IsHandleCreated is false – it returns false even if you are not on the GUI thread.

For reference see http://msdn.microsoft.com/en-us/library/system.windows.forms.control.invokerequired.aspx .

The following code throws an exception instead of hanging… the fact that it “works as expected” when no breakpoint is hit might be a result of the debugger freezing all threads on hitting a breakpoint which in turn might lead to a different order of execution etc.

Altogether this means: you might have some “race condition” in your code where BeginInvokeIfRequired is called on a freshly created control before that control has a Handle. This can even be some 3rd-party code you use…

public static void BeginInvokeIfRequired(this Control control, Action action)
{
    if (control.IsHandleCreated)
    {
        if (control.InvokeRequired)
        {
            control.BeginInvoke(action);
        }
        else
        {
            action.Invoke();
        }
    }
    else { 
         // in this case InvokeRequired might lie ! 
         throw new Exception ( "InvokeRequired is possibly wrong in this case" );
         }
}