Jabaco Source

Option Explicit

' a tcp/ip server socket is used as 
' limited resource to check on a running
' application instance
Private sso As java#net#ServerSocket

' change to suitable port number as desired
Const appSpecificPort = 12589

Public Function isAppAlreadyStarted() As Boolean
   
   On Error Goto ErrHandler
   
   sso = New ServerSocket(appSpecificPort, 1)
   
   ' no error! We are the first
   isAppAlreadyStarted = False
   
   Exit Function
   
ErrHandler:
   ' socket already in use! There is somebody active already
   isAppAlreadyStarted = True
End Function

Public Sub Form_Load()
   If isAppAlreadyStarted() Then
      MsgBox "App is already running!"
   Else
      MsgBox "App not running yet!"
   End If   
End Sub