IUnknow base vptr meory is getting lost

Mrutyunjaya Mahapatra 1

I have one project where I am creating one COM component. I am trying to get pointer to interface which is derived from IUnknown and After 10/15 mins of getting pointer to interface, Base interface (Iunknown ) Vptr memory locations are getting lost/

class ATL_NO_VTABLE CIndustrial_IT_HistoryHandler :
public CClientHelper,
public CComCoClass<CIndustrial_IT_HistoryHandler, &CLSID_Industrial_IT_HistoryHandler>,
public IIndustrial_IT_HistoryHandler,
public IConnectionPointContainerImpl<CIndustrial_IT_HistoryHandler>,
public CProxy_IIndustrial_IT_HistoryHandlerEvents<CIndustrial_IT_HistoryHandler>
{
.....

}

I am trying to get pointer to IIndustrial_IT_HistoryHandler which is derived from IUnknown . After 10/15 mins Iunknown vptr memory locations, means vptr[0], vptr[1], vptr[2] memory locations are getting lost

Can anybody please suggest How can I track in runtime how is it getting lost ?

RLWA32 42,551 Reputation points

2021-05-23T15:19:44.07+00:00

Its not clear what you are trying to do or what you mean by "Vptr memory locations are getting lost".

Are you calling QueryInterface to obtain the desired interface pointer?
Xiaopo Yang - MSFT 12,151 Reputation points Microsoft Vendor

2021-05-24T05:37:33.837+00:00

And could you please show a minimal, reproducible sample without private information ?
Mrutyunjaya Mahapatra 1 Reputation point

2021-05-24T05:48:51.39+00:00

Component Class
class ATL_NO_VTABLE CIndustrial_IT_HistoryHandler :
public CClientHelper,
public CComCoClass<CIndustrial_IT_HistoryHandler, &CLSID_Industrial_IT_HistoryHandler>,
public IIndustrial_IT_HistoryHandler,
public IConnectionPointContainerImpl<CIndustrial_IT_HistoryHandler>,
public CProxy_IIndustrial_IT_HistoryHandlerEvents<CIndustrial_IT_HistoryHandler>
{
.....

}

IDL File

interface IIndustrial_IT_HistoryHandler : IUnknown
{
}

Creating Instance :

CComPtr<IIndustrial_IT_HistoryHandler> pHistHdlr;
pHistHdlr.CoCreateInstance(CLSID_Industrial_IT_HistoryHandler)

After 10/15 base IUnknown pointers are getting lost..
Xiaopo Yang - MSFT 12,151 Reputation points Microsoft Vendor

2021-05-24T06:10:56.067+00:00

With this snippet, I am afraid I cannot reproduce your problem and understand what do the words After 10/15 mean. Could you please show a minimal, sound sample without private information ?
Mrutyunjaya Mahapatra 1 Reputation point

2021-05-24T10:10:30.897+00:00

Basically Base IUnknown pointers are getting lost after some time. Can you please suggest any idea or tool to track this. where is it getting lost?

Bets regards
Mruytunjaya
RLWA32 42,551 Reputation points

2021-05-24T10:31:34.217+00:00

@Mrutyunjaya Mahapatra

Basically Base IUnknown pointers are getting lost after some time.

Exactly what does this mean? To me, your stated problem remains a mystery.

You should create and share with us a minimum, verifiable sample that reliably reproduces the issue with code that can be tested.

Have you tried using the ATL debugging macros _ATL_DEBUG_INTERFACES and _ATL_DEBUG_QI documented here - debugging-and-error-reporting-macros

2 answers

Mrutyunjaya Mahapatra 1 Reputation point

2021-05-24T11:08:25.89+00:00

This is during initialization...

After 10/15 mins / Crash..
Please sign in to rate this answer.

0 comments No comments
Sign in to comment
RLWA32 42,551 Reputation points

2021-05-24T11:20:53.397+00:00

The posted images indicate that hsHistSvcInterfaces.dll has been unloaded. That would be the source of your "missing" vptr entries. You need to debug some more to find out why this problem has occurred.

Update:
It also seems wrong that before the dll is unloaded the IUnknown vtable entries point to hsHistSvcInterfaces!DllUnregisterServer instead of to QueryInterface, AddRef and Release.
Please sign in to rate this answer.
Mrutyunjaya Mahapatra 1 Reputation point

2021-05-28T16:58:31.567+00:00

Hi, Yes hsHistSvcInterfaces.dll was getting unloaded. I fixed by changing

HRESULT hr = PrxDllCanUnloadNow(); if (FAILED(hr)) return hr;

to:

HRESULT hr = PrxDllCanUnloadNow(); if (hr != S_OK) return hr;

May I know what could be the reason of (FAILED(hr)) which was failing to validate hr value S_FALSE returned by PrxDllCanUnloadNow().

RLWA32 42,551 Reputation points

2021-05-28T17:18:57.157+00:00

HRESULT hr = PrxDllCanUnloadNow(); if (FAILED(hr)) return hr;

The above code is incorrect and has been changed from the code that is generated by the ATL project template when the merge proxy/stub option has been selected. The default code is

// Used to determine whether the DLL can be unloaded by OLE. _Use_decl_annotations_ STDAPI DllCanUnloadNow(void) { #ifdef _MERGE_PROXYSTUB HRESULT hr = PrxDllCanUnloadNow(); if (hr != S_OK) return hr; #endif return _AtlModule.DllCanUnloadNow(); }

Additionally note that DllCanUnloadNow should not return anything other than S_OK or S_FALSE. Both of these are success codes that will not be treated as errors by the FAIL macro. Refer to the docs for this function at DllCanUnloadNow function
Sign in to comment

Share via

IUnknow base vptr meory is getting lost

2 answers