End if Previous Instance

[Rudy Steury]

VB6 has a very convenient way to end a new instance of an application if the application has an instance running.

The VB code would be : If App.PrevInstance Then End

I know this could be done with API calls but I am not sure what is the best way to accomplish it in the console and windows powerbasic programs. I think one method would be to detect the window of the running programs or an other way apparantly uses "mutex" API's - which I haven't really investigated enough to understand.

Right now I need to "end" a couple of console powerbasic programs if they are launched when the programs are already running. If more than one instance of either of these programs runs it will completely corrupt a data base.

Can anyone point me to the code I need? Or to an explanation of what I need to do to solve the multiple instances problem.

Thanks

Rudy Steury

[Roger Garstang]

Local hWnd As Dword

hWnd= FindWindow(App_ClassName, ByVal %Null)
If hWnd Then 
      If IsWindowVisible(hWnd)= 0 Then ShowWindow hWnd, %SW_SHOW
      SetForegroundWindow hWnd 
      'End Current Duplicate Instance
Else
      'Continue with this instance
End If

[Michael Mattias]

There have got to be literally dozens of "previnstance" code snippets here.

I'd use one which uses a mutex, not one of those which use "FindWindow" but that's probably just a 'panache points' thing....

MCM

[Gösta H. Lovgren-2]

Rudy,

Here's a Mutex example:

Function PBMain
 
     Mutex_Name$ = "Progam_To_Check_if_Running"
       ' GHL Added Mutex code from PB Forum by ???
            'Check to see if program already running
               Local hmutex&, smutex$ 'just used for testing program existence
            smutex$ = Mutex_Name$   'Program name 
            hmutex& = CreateMutex(ByVal %Null, 0, ByVal StrPtr(smutex$))'check if running
            If hmutex& <> %Null Then 'Program probably already running
               If GetLastError() = %error_already_exists Then 'Constant defined in WinAPI
                  MsgBox $CrLf & " is already running",, _
                         SmuTex$
                 Exit Function
              End If 
            End If
'Rest of code ...
End Function

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[Dave Biggs]

Here's another version based on some code once posted by Semen which will bring the already running program to the fore..

'Function PBMain
'Mutex check
Dim WinName As Asciiz * %MAX_PATH
Dim hMutex As Dword, hForWnd As Dword, hWin As Dword
 
WinName = $AppTitle

hMutex = CreateMutex(ByVal %NULL, 0, WinName)
  If hMutex = %NULL Then Exit Function
  If GetLastError = %ERROR_ALREADY_EXISTS Then    'already running!
    hWin = FindWindow (ByVal %Null, WinName)      'find handle of target window
    hForWnd = GetForegroundWindow                 'handle of current foreground window
      'Set own window to the top in Z-order with %HWND_TOP
      SetWindowpos hWin, %HWND_TOP, 0, 0, 0, 0, %SWP_NOMOVE Or %SWP_NOSIZE Or %SWP_SHOWWINDOW
      'Disable current foreground window.
      EnableWindow hForWnd, 0 
      'Redirect focus to next window in Z-order / move to foreground and activate
      SetForegroundWindow hWin                    
      'Re-enable previous foreground window
      EnableWindow hForWnd, 1
    Exit Function
  End If