Re: Application crash on calling a COM method

From:
Scot T Brennecke <ScotB@Spamhater.MVPs.org>
Newsgroups:
microsoft.public.vc.atl
Date:
Wed, 05 Aug 2009 00:42:40 -0500
Message-ID:
<eSaHN#YFKHA.6020@TK2MSFTNGP05.phx.gbl>
Since Brian has given you very good answers so far, I will only add that you can still attach something like DebugDiag or the ADPlus
script to your release execution and capture crash dumps with those. Have you built all your binaries with matching symbol files
(PDBs)?

Gopal wrote:

Thanks for your reply Scot. Here are additional details.

This is how the function inside my win32 dll looks like:
*********************************************************
void MyClass::FuncInsideWin32DLL(const char * p1, const char * p2,
    const char * p3, const char * p4, const char * p5)
{
    _bstr_t result;

       result = pIntf->Func(_bstr_t(p1),
        _bstr_t(p2),
                _bstr_t(p3),
                _bstr_t(p4),
                _bstr_t(p5));

}
******************************************************
And here is how the interface is defined inside the tlh file

*******************************************************
IMyInterface : IDispatch
{
    //
    // Wrapper methods for error-handling
    //

    _bstr_t Func (
        _bstr_t CmdName,
        _bstr_t Param1,
        _bstr_t Param2,
        _bstr_t Param3,
        _bstr_t Param4 );

    //
    // Raw methods provided by interface
    //

      virtual HRESULT __stdcall raw_Func (
        /*[in]*/ BSTR CmdName,
        /*[in]*/ BSTR Param1,
        /*[in]*/ BSTR Param2,
        /*[in]*/ BSTR Param3,
        /*[in]*/ BSTR Param4,
        /*[out,retval]*/ BSTR * __MIDL_0011 ) = 0;
};
*******************************************************

The crash usually occurs in the destruction of MyClass where I call
pIntf->Release() and CoUnintialize(). The Constructor of my MyClass calls
CoCreateInstance().

For environment constraint, I can only test with release binaries and hence
I am unable to get to the cause of this. I have COM exception handlers but
none of them are getting hit. My application freezes and dies.

Let me know if you need more information.

regards,
~GOpal

"Scot T Brennecke" wrote:

Gopal wrote:

At the outset, apologies for not providing the exact code. I cannot share the
code snippets here.

I have an MFC application which uses a normal win32 helper DLL. This DLL
inturn #imports a COM server (out of process EXE) which has a an interface
derived from IDispatch. Now all I do in the win32 dll is
- CoCreateInstance
- Addref
- Intf->function()
- Release

The above code worked perfectly fine when I was compiling it in VC6. The
moment I moved the MFC app and the win32 to VS2005, my application crashes
randomly after the function is called. This may happen at the first instance,
or sometime it takes 10-15 tries to get it to crash.

I suspect some kind of memory corruption because of marshalling, but haven't
quite been able to catch the culprit.

Any pointers would be of immense help.

regards,
~GOpal


So, tell us what is involved in the function call; are you passing any objects in either direction? Where does your app crash;
i.e., what code is executing when the crash occurs? Is it an access violation? Are you able to make it happen with a debugger (VS,
WinDbg, ADPlus, DebugDiag, etc.) attached?

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