Memory leak in CcomObject - c++

Question

I am working on a memory leak and identified there is a leak in ummanaged code. Using UMDH, we found that the below code is having the leak:
+ 36608 ( 67704 - 31096) 651 allocs BackTraceAF008B48
+ 352 ( 651 - 299) BackTraceAF008B48 allocations
ntdll!RtlpCallInterceptRoutine+3F
ntdll!RtlpAllocateHeapInternal+9E0
MSVCR100!malloc+5B (f:\dd\vctools\crt_bld\self_64_amd64\crt\src\malloc.c, 89)
mfc100!operator new+3E
!ATL::CComObject<CCoreTimeoutObject>::CreateInstance+66 (c:\program files (x86)\microsoft visual studio 10.0\vc\atlmfc\include\atlcom.h, 2907)
!CMyClass::GetTimeoutObject+48 (cmyclass.cpp, 1813)
<no module>!???+0 : 7FFD68AC259D
STDMETHODIMP CMyClass::GetTimeoutObject(/* [out] */ IMyInterface **ppTimeoutObj)
{
ATLASSERT(ppTimeoutObj && !(*ppTimeoutObj));
CComObject<CCoreTimeoutObject> *pTimeoutObj = NULL;
HRESULT hr = CComObject<CCoreTimeoutObject>::CreateInstance(&pTimeoutObj);
if (SUCCEEDED(hr))
{
*ppTimeoutObj = static_cast<IMyInterface *>(pTimeoutObj);
(*ppTimeoutObj)->AddRef();
}
return hr;
}
EDIT: Adding the place where it is called.
This method is called from 2 places. One from managed code, and the other one from unmanaged code.
Managed code:
MYLib.IFlow mySvc = (MyLib.IFlow)MyServices.MySvcCOM;
mySvc.GetTimeoutObject(out _hardwareDoneRecieved);
But there is no code to make the _hardwareDoneReceived to be null. So I hope this is the leak here?
Unmanaged code:
STDMETHODIMP CSourceBase::get_CoreTimeoutObject( /* [retval][out] */ IUnknown **ppTimeoutObj)
{
return GetLocalSvc()->GetTimeoutObject(ppTimeoutObj);
}
I hope there is no leak in the calling part of unmanaged code!!

Answer 1

In the managed code, mySvc and _hardwareDoneRecieved should release their interfaces automatically when they go out of scope. There should be no leak there.
However, in the unmanaged code, I do see some problems.
You did not show the implementation of GetLocalSvc(), so that is a potential leak, depending on what it actually returns. For instance, if it returns an AddRef'ed interface, then get_CoreTimeoutObject() (and any other caller) will need to Release() it.
But more importantly, CMyClass::GetTimeoutObject() takes a IMyInterface** but CSourceBase::get_CoreTimeoutObject() is giving GetTimeoutObject() an IUnknown** instead, so you have a type mismatch that shouldn't even compile.
Either get_CoreTimeoutObject() should output a IMyInterface**:
STDMETHODIMP CSourceBase::get_CoreTimeoutObject( /* [retval][out] */ IMyInterface **ppTimeoutObj)
{
return GetLocalSvc()->GetTimeoutObject(ppTimeoutObj);
// or, if needed:
//
// CComPtr<IFlow> svc;
// svc.Attach(GetLocalSvc());
// return svc->GetTimeoutObject(ppTimeoutObj);
}
Or, it should call GetTimeoutObject() with a local IMyInterface* and then call QueryInterface() on it to get its IUnknown* (and then Release() the local).
STDMETHODIMP CSourceBase::get_CoreTimeoutObject( /* [retval][out] */ IUnknown **ppTimeoutObj)
{
CComPtr<IMyInterface> intf;
HRESULT hr = GetLocalSvc()->GetTimeoutObject(&intf);
if (SUCCEEDED(hr)) {
hr = intf->QueryInterface(IID_IUnknown, reinterpret_cast<void**>(ppTimeoutObj));
}
return hr;
// or, if needed:
//
// CComPtr<IFlow> svc;
// svc.Attach(GetLocalSvc());
// CComPtr<IMyInterface> intf;
// HRESULT hr = svc->GetTimeoutObject(&intf);
// if (SUCCEEDED(hr)) {
// hr = intf->QueryInterface(IID_IUnknown, reinterpret_cast<void**>(ppTimeoutObj));
// }
// return hr;
}
Also, you also did not show the code that is calling get_CoreTimeoutObject(), so we can't determine if that caller is leaking or not.