FIX: Failure In InternalCreateSchemaRowset Causes Access Violation

ID: Q217187

The information in this article applies to:

SYMPTOMS

Access violation can occur when using OLE DB Provider Template macro with SCHEMA_ENTRY.


CAUSE

Following is the code in ATLDB.H for CreateSchemaRowset. CreateSchemaRowset is called by the SCHEMA_ENTRY macro.

The rowset class is created and then a pointer to it is sent to InternalCreateSchemaRowset.

NOTE: A failed hr will cause the object to be deleted. 



HRESULT CreateSchemaRowset(IUnknown *pUnkOuter, ULONG cRestrictions,
			   const VARIANT rgRestrictions[], REFIID riid,
			   ULONG cPropertySets, DBPROPSET rgPropertySets[],
			   IUnknown** ppRowset, SchemaRowsetClass*& pSchemaRowset)
{
  HRESULT hrProps, hr = S_OK;
  SessionClass* pT = (SessionClass*) this;
  CComPolyObject<SchemaRowsetClass>* pPolyObj;
  if (FAILED(hr = ComPolyObject<SchemaRowsetClass>::CreateInstance(pUnkOuter, &pPolyObj)))
    return hr;
  
  pSchemaRowset = &(pPolyObj->m_contained);
  hr = InternalCreateSchemaRowset(pUnkOuter, cRestrictions, rgRestrictions,
riid, cPropertySets, rgPropertySets, ppRowset,pPolyObj, pT, pT->GetUnknown());

  // Ref the created COM object and Auto release it on failure
  if (FAILED(hr))
  {
//Here is the problem delete
    delete pPolyObj; // must hand delete as it is not ref'd
    return hr;  
  }
}


Following is the code for InternalCreateSchemaRowset. If a failure occurs when trying to set a property, the function returns with an error but not before the spUnk smart pointer calls release and frees the object. When execution returns from this function, the CreateSchemaRowset function attempts to delete the object (which has already been deleted) and the access violation occurs. 


OUT_OF_LINE HRESULT InternalCreateSchemaRowset(IUnknown *pUnkOuter, ULONG cRestrictions, const VARIANT rgRestrictions[], REFIID riid,						   ULONG cPropertySets, DBPROPSET rgPropertySets[], IUnknown** ppRowset, IUnknown* pUnkThis, CUtlPropsBase* pProps, IUnknown* pUnkSession)
{
  HRESULT hr, hrProps = S_OK;
  if (ppRowset != NULL)
    *ppRowset = NULL;
  if ((pUnkOuter != NULL) && !InlineIsEqualUnknown(riid))
    return DB_E_NOAGGREGATION;

//Smart pointer, spUnk will automatically call Release() when it goes out of scope
  CComPtr<IUnknown> spUnk;
  hr = pUnkThis->QueryInterface(IID_IUnknown, (void**)&spUnk);
	
  if (FAILED(hr))
    return hr;
  hr = pProps->FInit();
  if (FAILED(hr))
    return hr;
  hr = pProps->SetPropertiesArgChk(cPropertySets, rgPropertySets);
  if (FAILED(hr))
    return hr;
  const GUID* ppGuid[1];
  ppGuid[0] = &DBPROPSET_ROWSET;

  // Call SetProperties.  The true in the last parameter indicates
  // the special behavior that takes place on rowset creation (i.e.
  // it succeeds as long as any of the properties were not marked
  // as DBPROPS_REQUIRED.

  hrProps = pProps->SetProperties(0, cPropertySets,rgPropertySets,1,ppGuid, true);
  if (FAILED(hrProps))
    return hrProps;
}


STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

Additional query words: 


Keywords          : kbservicepack kbATL kbDatabase kbOLEDB kbProvider kbVC600bug kbVJ600bug kbVS600sp2 kbVS600SP1 kbVS600sp3fix kbGrpVCDB 
Version           : winnt:6.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: May 19, 1999