;Autor:  PureLust

EnableExplicit
 
Global g_hMutexAppRunning
Define EventID

Procedure AppInstanceExists()
  Protected bAppRunning = #False
  g_hMutexAppRunning = CreateMutex_( #Null, #Null, "Global\MyApplication1")
  If (g_hMutexAppRunning <> #Null) And (GetLastError_() = #ERROR_ALREADY_EXISTS)
    CloseHandle_( g_hMutexAppRunning )
    g_hMutexAppRunning = #Null
  EndIf
  If g_hMutexAppRunning
    ProcedureReturn #False
  Else
    ProcedureReturn #True
  EndIf
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  If AppInstanceExists()
    MessageRequester("", "Die Anwendung läuft bereits."+Chr(13)+"Die zweite Instanz wird beendet.",#MB_ICONERROR)
    CloseHandle_(g_hMutexAppRunning)
    End
  Else
    MessageRequester("", "Die Anwendung läuft noch nicht."+Chr(13)+"Das ist die erste Instanz.",#MB_ICONINFORMATION)
  EndIf
  
Repeat
EventID=WaitWindowEvent()
If EventID = #PB_Event_CloseWindow
  CloseHandle_(g_hMutexAppRunning)
EndIf
Until  EventID = #PB_Event_CloseWindow
EndIf