Re: COM Singleton object and static members lifetime

"Alexander Nickolov" <>
Fri, 12 Jan 2007 17:14:41 -0800
Static C++ members have the same lifetime as global
objects. And global objects are destroyed in random
order as far as you are concerned - you should never
allow one global object to depend on another global
object in its destructor. So what happens in your case
is your static members are destroyed before your singleton
(e.g. global object). Then you try to access them in that
object's destructor and you crash.

Since this is a singleton, why would you want to use
static members in the first place? Make them regular
members and access them through the singleton instance
instead. Note I'm assuming your singleton is a regular
C++ object. If you've attempted a COM singleton, now
is the time to get rid of it - COM singletons cannot be
hosted in DLLs.

Alexander Nickolov
Microsoft MVP [VC], MCSD

<> wrote in message

Hello everybody
Here is a question about COM singleton object and static members

The problem:
I have a COM Singleton object in a DLL that is instantiated in a EXE
application. When I close the EXE app, the DLL is unloaded and a call
to FinalRelease() function is executed for a COM Singleton object
before it is destroyed . The problem is that when the code tries to
access some static members during this time, the application crashes.

The question:
What is the lifetime of the static members in this case? Can we assume
that static members are still valid when the COM singleton object's
FinalRelease() function is called?

More explanation:
We were using a previous version of ATL before and it was working fine.
But the problem appeared I think when we ported the code to VS2005 with
ATL 8.0.

Here is a description of what is happening. You can see the stack below
this description.

1) OmniDir.exe is the EXE application. You can see in the stack that it
is closing, then some calls are made in msvcr80d.dll and other DLLs.

2) After that, my DLL GxResource.dll is unloaded when
DllMainCRTStartup() is called.

3) This eventually calls FinalRelease() on my COM singleton object
CResource before it is destroyed

4) The CDisplayHelper::Terminate() static function is finally called
and this function tries to access static members which in turn crash
the application because these members are invalid at this point.

ATL::CComObjectCached<CResources>::`scalar deleting destructor'()


::~CComObjectCached<ATL::CComClassFactorySingleton<CResources> >()


::`scalar deleting destructor'()



ATL::`dynamic atexit destructor for '_AtlComModule''()
_CRT_INIT(void * hDllHandle=0x07710000, [...])
__DllMainCRTStartup(void * hDllHandle=0x07710000, [...])
_DllMainCRTStartup(void * hDllHandle=0x07710000, [...])


msvcr80d.dll!__crtCorExitProcess(int status=0)
msvcr80d.dll!__crtExitProcess(int status=0)
msvcr80d.dll!doexit(int code=0, int quick=0, int retcaller=0)
msvcr80d.dll!exit(int code=0)

Any idea on what is happening here?

Best regards,

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