count the number of executed applications

AppInst.cpp

/******************************************************************************
Module:  AppInst.cpp
Notices: Copyright (c) 2008 Jeffrey Richter & Christophe Nasarre
******************************************************************************/


#include "..\CommonFiles\CmnHdr.h"     /* See Appendix A. */
#include <windowsx.h>
#include <tchar.h>
#include "Resource.h"


///////////////////////////////////////////////////////////////////////////////


// The system-wide window message, unique to the application
UINT g_uMsgAppInstCountUpdate = WM_APP+123;


///////////////////////////////////////////////////////////////////////////////


// Tell the compiler to put this initialized variable in its own Shared 
// section so it is shared by all instances of this application.
#pragma data_seg("Shared")
volatile LONG g_lApplicationInstances = 0;
#pragma data_seg()

// Tell the linker to make the Shared section readable, writable, and shared.
#pragma comment(linker, "/Section:Shared,RWS")


///////////////////////////////////////////////////////////////////////////////


BOOL Dlg_OnInitDialog(HWND hWnd, HWND hWndFocus, LPARAM lParam) {

   chSETDLGICONS(hWnd, IDI_APPINST);

   // Force the static control to be initialized correctly.
   PostMessage(HWND_BROADCAST, g_uMsgAppInstCountUpdate, 0, 0);
   return(TRUE);
}


///////////////////////////////////////////////////////////////////////////////


void Dlg_OnCommand(HWND hWnd, int id, HWND hWndCtl, UINT codeNotify) {

   switch (id) {
      case IDCANCEL:
         EndDialog(hWnd, id);
         break;
   }
}


///////////////////////////////////////////////////////////////////////////////


INT_PTR WINAPI Dlg_Proc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {

   if (uMsg == g_uMsgAppInstCountUpdate) {
      SetDlgItemInt(hWnd, IDC_COUNT, g_lApplicationInstances, FALSE);
   }

   switch (uMsg) {
      chHANDLE_DLGMSG(hWnd, WM_INITDIALOG, Dlg_OnInitDialog);
      chHANDLE_DLGMSG(hWnd, WM_COMMAND,    Dlg_OnCommand);
   }
   return(FALSE);
}


///////////////////////////////////////////////////////////////////////////////


int WINAPI _tWinMain(HINSTANCE hInstExe, HINSTANCE, PTSTR, int) {

   // Get the numeric value of the systemwide window message used to notify 
   // all top-level windows when the module's usage count has changed.
   g_uMsgAppInstCountUpdate =
      RegisterWindowMessage(TEXT("MsgAppInstCountUpdate"));

   // There is another instance of this application running
   InterlockedExchangeAdd(&g_lApplicationInstances, 1);

   DialogBox(hInstExe, MAKEINTRESOURCE(IDD_APPINST), NULL, Dlg_Proc);

   // This instance of the application is terminating
   InterlockedExchangeAdd(&g_lApplicationInstances, -1);

   // Have all other instances update their display
   PostMessage(HWND_BROADCAST, g_uMsgAppInstCountUpdate, 0, 0);

   return(0);
}


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