Re: strange crush when using template singleton class

From:

"aao" <aao@work.com>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 19 Mar 2007 11:43:05 -0500

Message-ID:

<u0VLCWkaHHA.1240@TK2MSFTNGP04.phx.gbl>

May I suggest to check 2 very basic items, before you go looking for oo
patterns

1. Could it be that you just do not call AddRef when you create
CComPtr<SomeClass1> m_pObj1 or CComPtr<SomeClass2> m_pObj2;. I know it is
creasy since you use CComPtr, but can you show how you create those?
2. the sequence Init;Do would not be executed in some other static block of
code, would it? Again I know it is bit strange but did you check that
sequence is executed only once. Since it is not protected I can defiantly
see double invoke like "Init;Init;Do;Do" would produce the error you see.

"andrew" <user@earth> wrote in message
news:uYD$KVJaHHA.3996@TK2MSFTNGP03.phx.gbl...

Hi,

I have a strange situation.
I created a simple singlethreaded singleton template class:

template<class T>
class CSingleton
{
public:
static T* Instance()
{
static T obj;
return &obj;
}

protected:
CSingleton() {}

private:
operator=(const CSingleton&);
CSingleton(const CSingleton&);
};

in order to the singleton:

class CMyClass : public class CSingleton<CMyClass>
{
   friend class CSingleton<CMyClass>;

protected:
         CMyClass() { }

          CComPtr<SomeClass1> m_pObj1;
          CComPtr<SomeClass2> m_pObj2;

          int m_var;
public:
      void Init(SomeClass1* pParam) { m_pObj1 = pParam; m_var = 0; }
       void Do() { }
};

CMyClass::Instance()->Init(pParam);
CMyClass::Instance()->Do();

the code works find in debug(doh) but in release it crushes with an access
violation on address 0x0000000 in Do() method when trying to access
m_pObj1 because m_pObj1.p is NULL !

how in the earth m_pObj1 gets NULL ??

i tried to debug in release and step into dissambly code when
CMyClass::Instance() is called

from the little assembly coding i know it seemed to me like this:
CMyClass::Instance()
{
     TESTing some registers
      if not equal then jmp to address1

     set m_pObj1 to NULL
     set m_pObj2 to NULL

address1:
     return;
}

in release it seems that 'if' test results in setting the m_pObj1 and
m_pObj2 to NULL
in debug the test result in just returning (no setting).

the test look like the code verifies if the CMyClass object was created.
in release it seems that when Do() is called the test fails. :|

i was thinking that i am not looking at the right part of code and the
mistake is in other place (some bufferoverun or something) but I did not
find any.
the code is not working at its very beginning and there is no other code
which might interfere (and if it was any bufferoverrun i suppose it should
had happen in debug also).

the strange thing I see is that if I dont use the template singleton (i
put Instance() method inside CMyClass and i remove inheritance from
template class) there is no crushing.
it is not crushnig also if i put the initialization code (m_var = 0; )
inside the ctor:
CMyClasss:CMyClass() { m_var = 0; }
( keeping the inheritance from the template singleton class).

I tried to use BoundsChecker but I did not get anything. I don't get
anything before the app crushes. ( memory tracking is enabled)

Do you have any idea why the crush occurs ?
Or, can you give me some hints \ ideas how to debug this ?

thank you.