Why AccessViolationException cannot be caught by .NET4.0

Question

It is really interesting that the following C# code will crash on .NET4.0 but work fine on .NET2.0.

C# code

class Program
{
    static void Main(string[] args)
    {
        try
        {
            ExceptionTest();
            Console.WriteLine("Done!");
        }
        catch (Exception e)
        {
            Console.WriteLine("Error !!!");
            Console.WriteLine(e.Message);
        }
    }

    [DllImport("badapp")]
    private static extern int ExceptionTest();
}

C++ code

extern "C" __declspec(dllexport) int ExceptionTest()
{
    IUnknown* pUnk = NULL;
    pUnk->AddRef();
    return 0;
}

If compiling the above C# code against .NET2.0, everything works fine. Only compiling it against .NET4.0 will make it crash at runtime.

I'm suspecting that system exception catch mechanism has been changed since .NET4.0. Any ideas?

Answer 1

Yes, it changed in .NET 4. You cannot catch exceptions that indicate a corrupted state. This is because there's pretty much no guarantee that you can do anything at all when a corrupted state exception is thrown. There is practically no reason to want a process with corrupted state to continue executing.

For compatibility with older code, you can change this behaviour by adding the legacyCorruptedStateExceptionsPolicy element to app.config.

You can also do it on a case-by-case basis by marking methods where you want to catch these exceptions with the HandleProcessCorruptedStateExceptions attribute.