Forcing Only One Instance of an Application to Run at a Time in Visual C++

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how could i use this in SDI
Posted by Legacy on 03/03/2003 12:00am

Originally posted by: Winch Fang
?_?
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Code Update using CreateMutex

Posted by Legacy on 01/17/2003 12:00am

Originally posted by: Simon Soosai

This document is the easist way to check for multiple instances and bring the first instance on to the focus.

//Step 1 ***********************************

//Top of the App .cpp file

#pragma comment(linker, "/SECTION:.shr,RWS")

#pragma data_seg(".shr")

HWND g_hWnd = NULL;

#pragma data_seg()

//Step 2 ***********************************

//On the App::InitInstance() add the code below:

//For single instance checking

HANDLE hMutexOneInstance = ::CreateMutex( NULL, TRUE, _T("AFX_Ideas_H__5B5F33E8_2175_4C23_BB38_A334CADD6B88")); 

bool AlreadyRunning = (GetLastError() == ERROR_ALREADY_EXISTS); 

if (hMutexOneInstance != NULL) ::ReleaseMutex(hMutexOneInstance); 

if (AlreadyRunning)

{

   if (g_hWnd) /* pop up */

   { 

      ::SetForegroundWindow(g_hWnd);

      if (IsIconic(g_hWnd)) ::ShowWindow(g_hWnd, SW_RESTORE);

   }

   return FALSE; // terminates the creation

}

//Step 3 ***********************************

//After Creating the Main Frame, get the handle and store it on the shared variable below.

g_hWnd = m_pMainWnd->m_hWnd;

Is it thread safe & high security?
Posted by Legacy on 01/15/2003 12:00am

Originally posted by: Minh Tuan
The code is nice but I think there are 2 problems:
1. Should we use the InterlockedExchange function to get/set the window handle? Because this function is thread & process safe.
2. I think it's not suitable for Window Services because other untrusted applications can modify our shared variable. For example, they may terminate or forbit our application to start.
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Easiest != Safest
Posted by Legacy on 01/15/2003 12:00am

Originally posted by: Blake Miller
"This document is the easist way to check for multiple instances and bring the first instance on to the focus"
He makes no claims that it is the safest or most reliable...

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Good article,thanks.
Posted by Legacy on 01/14/2003 12:00am

Originally posted by: Artem
And by the way, thank you very much for discovering to
me - what is the 'beast' - "pragma <....>".
Good luck,man!
Reply
Not thread safe, use mutex instead
Posted by Legacy on 01/14/2003 12:00am

Originally posted by: Brian Friesen
If you need to solve the problem of a single instance application, please use one of the mutex based solutions. It's the only way to guarantee it is thread-safe.

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Forcing Only One Instance of an Application to Run at a Time in Visual C++

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Comments

how could i use this in SDI

Code Update using CreateMutex

Is it thread safe & high security?

Easiest != Safest

Good article,thanks.

Not thread safe, use mutex instead

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