how can single instance app restart itself?

Is there any way for a "single instance" app to restart itself via CreateProcess()?

I have an app that uses a Mutex as it must ensure only one instance of itself is allowed to run. It is an MFC MDI single document app that "reinitializes" then "restarts" itself after its user reconfigures its database path. It does this by closing its main document and reloading it, but, unfortunately, it does not reinitialize all of itself. The app fails to reinitialize Crystal Reports which in turn uses an ODBC DSN to show database reports. Even though the database pointer changes in the text of the DSN file, there seems to be no way to tell Crystal Reports to reload its DSN.

The app works fine if the user exits the app and then restarts it.
I read the FAQ "How can I start a process" though it is unclear to me how to start a process from a process that uses a mutex to ensure only one copy of itself runs. Any ideas?

Perhaps you could start a second process that would shut down the mutex app, start it up again and then close itself?

Quote:

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Originally posted by RNEELY
Is there any way for a "single instance" app to restart itself via CreateProcess()?

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I think this is not really required. If you do this, I think it is going to be only a workaround for the issue.

Quote:

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It does this by closing its main document and reloading it, but, unfortunately, it does not reinitialize all of itself. The app fails to reinitialize Crystal Reports which in turn uses an ODBC DSN to show database reports. Even though the database pointer changes in the text of the DSN file, there seems to be no way to tell Crystal Reports to reload its DSN.

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There may be some bug here. You may want to investigate that first. It is kinda ugly to kill the app and relaunch it just for the heck of it.

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The app works fine if the user exits the app and then restarts it.
I read the FAQ "How can I start a process" though it is unclear to me how to start a process from a process that uses a mutex to ensure only one copy of itself runs. Any ideas?

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I would still encourage you to find the exact problem instead :)

If you are using a mutex, just delete it (CloseHandle() iirc) before you call CreateProcess().

That way the second one won't find the mutex and it will think it is the first instance, and will run. You can then exit the one that called CreateProcess().

Thank you all for your responses. The trick was to wait until after the mutex was released before starting the next instance of the app. Yes, kirants, this is a workaround. I don't have the source code for Crystal Reports.

Code:

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class CMyApp : public CWinApp
{
        public:
        CMyApp();
        void Restart();
        // . . .
        protected:
        HANDLE        m_hMutex;
        bool m_bRestartAppOnExit;
};


CMyApp::CMyApp() :
        m_hMutex(NULL),
        m_bRestartAppOnExit(false)
{
        // ...
}

BOOL CMyApp::InitInstance()
{
        // Single-instance code
        m_hMutex = NULL;
        HANDLE hMutex;
        if (hMutex = ::OpenMutex(MUTEX_ALL_ACCESS, FALSE, m_pszAppName))
        {
                CString sErrorMsg;
                sErrorMsg.Format(_T("Only one %s is allowed to run."), m_pszAppName);
                ::MessageBox(NULL, sErrorMsg, m_pszAppName, MB_OK);
                return FALSE;
        }
        else
        {
                m_hMutex=::CreateMutex(NULL, TRUE, m_pszAppName);
        }
        // ...
        return TRUE;
}

void CMyApp::Restart()
{
        m_bRestartAppOnExit = true;
        PostQuitMessage(ERROR_SUCCESS_RESTART_REQUIRED);
}

int CMyApp::ExitInstance()
{
        if (m_hMutex)
        {
                ::ReleaseMutex(m_hMutex);
                CloseHandle(m_hMutex);
                m_hMutex = NULL;
        }
        if (m_bRestartAppOnExit)
        {
                TCHAR szFileName[MAX_PATH];       
                szFileName[0] = 0;
                DWORD dwSize = MAX_PATH;       
                GetModuleFileName(0, szFileName, dwSize);
                HINSTANCE hInst = ShellExecute(0,                         
                        _T("open"), // Operation to perform
                        szFileName, // Application name
                        _T(""),    // Additional parameters
                        0,          // Default directory
                        SW_SHOW);
        }
        return CWinApp::ExitInstance();
}

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