Only one instance of an application

Procedure DupStart
#DEFINE SW_NORMAL    1
#DEFINE SW_MAXIMIZE  3
#DEFINE SW_MINIMIZE  6

DECLARE Long FindWindow in user32 String, String
DECLARE Long BringWindowToTop in user32 Long
DECLARE Long ShowWindow in user32 Long, Long

Local lnHWND,lcTitle
lcTitle = _screen.Caption
_screen.Caption = Sys(3)
lnHWND = FindWindow(null,m.lcTitle)
_Screen.Caption = m.lcTitle

IF m.lnHWND >0
  BringWindowToTop(m.lnHWND)
  ShowWindow(m.lnHWND,SW_MAXIMIZE)
  qUIT
ENDIF
ENDPROC

SET LIBRARY TO SYS(2004)+'foxtools.fll' ADDITIVE
   * FindWindow() takes two parameters and returns the handle of the
   * window, HWND, if it was found.
   GetWind = RegFn('FindWindow', 'CC', 'I')
   *Set the first parameter of the call to getwind to 0, null.
   wclass=0
   winname='My Application'
   apphand=CallFn(GetWind,wclass ,winname)
   *If the call was successful, stop processing.
   IF apphand<>0
      WAIT WINDOW ;
        'You cannot start another instance of the window 'My Application'!'
      QUIT
   ENDIF
   MODIFY WINDOW screen TITLE 'My Application'
   WAIT WINDOW ;
     'The first instance of the window 'My Application' is running.'

#Define AtomStrLength   512
Local lcAtomName
lcAtomName = "mon application"
Declare Integer GlobalAddAtom In win32api String
Declare Integer GlobalDeleteAtom In win32api Integer
Declare Integer GlobalGetAtomName In kernel32;
     INTEGER  nAtom,;
     STRING @ lpBuffer,;
     INTEGER  nSize
findAtom(lcAtomName)
Function findAtom(tcAtom)
Create Cursor cs (atom N(12), strlen N(5), Name C(100))
Index On Allt(Name) Tag Name
For nAtom = 49152 To 65535
     lpBuffer = Repli(Chr(0), AtomStrLength)
     lnResult = GlobalGetAtomName (nAtom, @lpBuffer, AtomStrLength)

     If lnResult > 0
          Insert Into cs Values (nAtom, lnResult, Left(lpBuffer, lnResult))
     Endif
Endfor
Select cs
If Seek(tcAtom)
     Messagebox("Application is already running")
     Quit
Else
     = GlobalAddAtom(tcAtom)
Endif