Programming Forums - Createmutex Help???

Well, conventionally you use a mutex like this, though if you have two programs running in parallel you'd need to check for the mutex's existence periodically using a timer or a loop WITH A SLEEP STATEMENT IN IT (the number of BSOD's...). In fact you'd be better off using a hooked atom, checking the task list or actually actively notifying the program's counterpart through DDE, a window message or whatever.

Const ERROR_ALREADY_EXISTS = 183&

Private Declare Function CreateMutex Lib "kernel32" Alias "CreateMutexA" (lpMutexAttributes As Any, ByVal bInitialOwner As Long, ByVal lpName As String) As Long

Private Declare Function ReleaseMutex Lib "kernel32" (ByVal hMutex As Long) As Long

Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Sub Form_Load()

    Dim hMutex As Long

    'Try to create a new Mutex

    hMutex = CreateMutex(ByVal 0&, 1, App.Title)

    'Did the mutex already exist?

    If (Err.LastDllError = ERROR_ALREADY_EXISTS) Then

        'Clean up

        ReleaseMutex hMutex

        CloseHandle hMutex

        'More than one instance detected

        MsgBox "More than one instance"

        End

    Else

        'form load code

    End If

End Sub