C / C++ / MFC

static T* GetInstance()
{
    if( ! m_pInstance )
    {
        m_pInstance = new T;
    }
    TRACE( "CSingleton::GetInstance() returning %p\n", m_pInstance );
    return m_pInstance;
}

CMyClass * p = NULL;
p = CreateMyClass();
if( p )
{
    TRACE( "CMyClass instance 1 is %p\n", p );
}
p = CreateMyClass();
if( p )
{
    TRACE( "CMyClass instance 2 is %p\n", p );
}

CMyClass::Destroy();

#ifdef DLL_EXPORTS
#define DLL_API __declspec(dllexport)
#else
#define DLL_API __declspec(dllimport)
#endif // DLL_EXPORT

DLL_API CMyClass* CreateClass();
DLL_API void DestroyClass();

Cedric Moonen wrote:

Any idea of what's happening here and how to solve the problem ?

led mike wrote:

My question is based on the assumption that the singleton design does NOT produce this problem when contained in a single executable project correct?

led mike wrote:

Why do you need this design? Why do you need a singleton class to reside in a DLL? DLL's are supposed to be libraries. The requirement for the Singleton should be at the application level rather than at the library level so I am not seeing the benefit in this layout.

Cedric Moonen wrote:

Does that make sense ?

led mike wrote:

You are designing a render engine into a DLL library to be used by different applications?

led mike wrote:

This would simplify the engine design as well as provide a more flexible use model.

led mike wrote:

Then the application is responsible for these assignments. Responsibility == Flexibility.

// logger.h
<class t=""><class t=""><T>template <class T> class singleton{
protected:
	static T* _pinstance;

	singleton(){}
	virtual ~singleton(){}

public:
	static T& getInstance(){
		if( !_pinstance)
			_pinstance = new T();
		return *_pinstance;
	}

	static void release(){
		delete _pinstance;
		_pinstance = NULL;
	}
};

template<class T> T* singleton<T>::_pinstance = NULL;

class LOGLIBSINGLETON_API Logger : public singleton< Logger>
{
public:
	Logger(void);

	bool log( LPTSTR eventSource, DWORD dwEventID, WORD wCategory, LPCTSTR message);

public:
	~Logger(void);
};

</T></class></class>

Logger::getInstance().log( msg, 0, 1, msg);
Logger::release();

DLL_API CEngine* CreateEngine(....)
{
   CEngine* pEngine = CEngine::GetInstance();
   pEngine->....;
   return pEngine;
}

DLL_API void ReleaseEngine()
{
   CEngine::release();
}

// logger.h
LOGLIBSINGLETON_API Logger& GetLogger();

// logger.cpp
LOGLIBSINGLETON_API Logger& GetLogger()
{
	return Logger::getInstance();
}

// application code
Logger& logger = GetLogger();
logger.log( msg, 0, 1, msg);
Logger::release();

led mike wrote:

Well I added that new twist of the exported function but I still cannot reproduce your problem

led mike wrote:

I don't understand why you need an exported function that just returns a pointer to an instance but that's just me.

Cedric Moonen wrote:

What IDE are you using ? I'm working with VC2005 Express.

Cedric Moonen wrote:

If I use several public function to do that it is not clean:

Cedric Moonen wrote:

but I don't know if it can export classes.

Cedric Moonen wrote:

So, being able to use this dll in other language will require only to rewrite the interfaces.

led mike wrote:

That is confusing since the "interfaces" you mention must be exported from your library correct?

<br />
<br />
LRESULT CALLBACK DlgProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)<br />
{<br />
  <br />
  switch(uMsg) <br />
  {<br />
  <br />
  case WM_INITDIALOG:<br />
    <br />
		return TRUE;<br />
<br />
  case WM_COMMAND:<br />
   switch(LOWORD(wParam)) <br />
    {<br />
		<br />
      case IDCANCEL:<br />
			  <br />
		    DestroyWindow(MainDlgBox);<br />
		    PostQuitMessage(0);<br />
<br />
		    return	TRUE;<br />
<br />
		  case IDC_SETIPADDR:	// Adds fucntionality to the close button.<br />
<br />
		    SendDlgItemMessage(MainDlgBox, IDC_IPADDRESS, IPM_GETADDRESS, 0, (LPARAM)(LPDWORD)NewAddr);<br />
<br />
        wsprintf(strAddr,"%d",NewAddr);<br />
<br />
		    SendCommand(&DataSocket, SET_IP_ADDRESS, sizeof(CommandStruct), messageFromHost);<br />
		  <br />
		    strAddr[cSetIP.length] = '\r';<br />
<br />
		    SendCommand(&DataSocket, strAddr, strlen(strAddr), messageFromHost); <br />
<br />
			  MessageBox(NULL,"IP Address has been changed sucessfully","Address Changed",MB_OK);<br />
		    <br />
		    return TRUE;<br />
<br />
<br />
      case IDC_SETIPMASK:<br />
<br />
        SendDlgItemMessage(MainDlgBox, IDC_IPMASK, IPM_GETADDRESS, 0, (LPARAM)(LPDWORD)NewMask);<br />
<br />
        wsprintf(strAddr,"%d",ConnectAddr);<br />
<br />
		    SendCommand(&DataSocket, SET_IP_MASK, sizeof(CommandStruct), messageFromHost);<br />
		  <br />
		    strAddr[cSetMask.length] = '\r';<br />
<br />
		    SendCommand(&DataSocket, strAddr, strlen(strAddr), messageFromHost); <br />
<br />
			  MessageBox(NULL,"IP Mask has been changed sucessfully","Address Changed",MB_OK);<br />
<br />
        return TRUE;<br />
<br />
		    <br />
		  case IDC_CONNECTBTN:<br />
			  <br />
		    WSAStartup(MAKEWORD(2, 0), &wsaData);<br />
		    <br />
		    SendDlgItemMessage(MainDlgBox, IDC_CONNECT, IPM_GETADDRESS,0,<br />
          (LPARAM)(LPDWORD)ConnectAddr); <br />
			  <br />
        wsprintf(strAddr,"%d",ConnectAddr);<br />
		    <br />
		    if(ConnectToSocket(MainDlgBox, &DataSocket, strAddr, DATA_PORT, WINSOCK_DATA_MESSAGE,FD_CONNECT|FD_CLOSE|FD_READ))<br />
          MessageBox(NULL,"Connection attempt with AuraNET Headbox was sucessfull!","Connected with AuraNET",NULL);<br />
      <br />
        else<br />
        { <br />
          if(MessageBox(NULL,"Connection attempt with AuraNET Headbox was unsucessfull!","Not Connected with AuraNET",MB_RETRYCANCEL) == IDRETRY)<br />
            PostMessage(MainDlgBox,WM_COMMAND,(WPARAM)IDC_CONNECTBTN,0);<br />
         <br />
          else<br />
            return TRUE;<br />
        }<br />
      <br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_DISCONNECTBTN),TRUE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_SETIPADDR),TRUE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_SETIPMASK),TRUE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_GETSTATUS),TRUE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_CONNECTBTN),FALSE);<br />
		    <br />
		  <br />
		    return TRUE;<br />
<br />
		  case IDC_DISCONNECTBTN:	// This button provides the majority of<br />
								  // functionality for the parsing program.<br />
		    <br />
			  if(!DisconnectFromSocket(&DataSocket))<br />
          if(MessageBox(NULL,"Attempt to disconnect was unsucessful.  Press Retry to attempt to disconnect again, or Cancel to stay connected","Disconnection Failure",MB_RETRYCANCEL) == IDRETRY)<br />
            PostMessage(MainDlgBox,WM_COMMAND,(WPARAM)IDC_DISCONNECTBTN,0);<br />
          else<br />
            return TRUE;<br />
      <br />
      <br />
        WSACleanup();<br />
<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_DISCONNECTBTN),FALSE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_SETIPADDR),FALSE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_SETIPMASK),FALSE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_GETSTATUS),FALSE);<br />
        EnableWindow(GetDlgItem(MainDlgBox,IDC_CONNECTBTN),TRUE);<br />
<br />
			  <br />
			  return TRUE;			//  Didn't process a message.<br />
<br />
<br />
      case IDC_PAIR:<br />
<br />
        SendCommand(&DataSocket, SETUP_PAIR, sizeof(CommandStruct), messageFromHost);<br />
<br />
        return  TRUE;<br />
<br />
    <br />
   }<br />
<br />
  return TRUE;<br />
  <br />
  case WINSOCK_DATA_MESSAGE:<br />
     <br />
	  WinsockHeadboxDataMessageLoop(MainDlgBox, wParam , lParam);<br />
    <br />
    return TRUE;<br />
 }<br />
 return FALSE; <br />
<br />
}<br />
<br />

while (GetMessage(&msg, NULL, NULL, NULL)) 
{ 
    if (!IsWindow(hwndGoto) || !IsDialogMessage(hwndGoto, &msg)) 
    { 
        TranslateMessage(&msg); 
        DispatchMessage(&msg); 
    } 
}