Re: Calling unmanaged code from managed MFC worker thread

"Klaus" <Klaus@nowhere.invalid>
Thu, 2 Aug 2007 11:14:19 +0200
Thanks for your help!

Here is the code:
myHeader.h, shared in both projects, MFC 6.0 App and VC 2005 DLL:
class CMyBase
 CMyBase() {};
 virtual ~CMyBase() {};
 virtual bool MyExample() = 0;

In MFC App this class will be derived:
class CMyBaseDerived : public CMyBase
 virtual ~CMyBaseDerived();
 virtual bool MyExample();

In VC2005, I have a pointer to the instance of CMyBaseDerived:
CMyBase *PMyBase;
This pointer will be initialized by calling a function in the DLL from the
void MyInit(CMyBase *p)
    PMyBase = p;

When I use this pointer in the DLL from the MFC worker thread an
AccessViolationException will be thrown:

Using this pointer within the main thread no problem occurs.

Best regards,

"" <> wrote in message

On Aug 1, 12:34 pm, "Klaus" <Kl...@nowhere.invalid> wrote:


I have an existing VC 6 MFC application which communicates asynchronly
a VC 2005 managed code dll.
I use an unmanaged base class with virtual functions to access methods in
the MFC application.
Furthermore, I use a pointer to an unmanaged function to jump back into
managed dll.

The managed part is basically a remoting enhancement which asynchronly
initiates a call from the remoting thread to the MFC application. The
information is collected within the main thread of the MFC application.
managed code dll is invoked via a function pointer. From the managed code
additional calls to the unmanaged MFC application will be done via a
to an object in the MFC. When this code is executed within the main
of the MFC application everything works fine.

However, if I switch to a MFC worker thread, calls via the base class
pointer results in System.AccessViolationException!

Scenario, which works:
1. Remoting thread imvoked
2. Managed DLL -> MFC App asynchron, no result
3. Switch thread to App main thread
4. MFC App -> Managed DLL
5. Managed DLL -> MFC App (synchron)

Scenario, which does not work:
1. Remoting thread imvoked
2. Managed DLL -> MFC App (asynchron, no result)
3. Switch thread to MFC worker thread!!!
4. MFC App -> Managed DLL
5. Managed DLL -> MFC App (synchron): System.AccessViolationException !!

How can I access pointer to unmanaged classes from managed code within a
worker thread?

Best regards,

Hi, Klaus,

I assume you are already using delegates, and marshaling of delegate
method pointers to access unmanaged functions from managed code,

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