Question

I’m trying to implement single instance application using mutex.
the application can run only one instance from a given directory.
i tried to implement it in Applicationsevents class but it’s not working.

I replicated it with a test harness with a single form.
my ApplicationEvents.vb code:

   Private Sub SingleInstanceCheck(ByVal sender As Object, ByVal e As Microsoft.VisualBasic.ApplicationServices.StartupEventArgs) Handles Me.Startup

        Dim strLoc As String = Assembly.GetExecutingAssembly().Location
        Dim fileInfo As IO.FileSystemInfo = New IO.FileInfo(strLoc)
        Dim sExeName As String = fileInfo.Name

        strLoc = strLoc.Replace("\", "//")

        Using mutex As New Threading.Mutex(False, "Global\" + strLoc)
            If Not mutex.WaitOne(0, False) Then
                File.WriteAllText("c:\log.txt", "instance already running")
                Environment.Exit(1)
            End If

            GC.Collect()


        End Using

    End Sub

it runs multiple instances.

Things I am not able change:
1.project setting has “Enable Application framework” ticked
2. ApplicationEvents.vb handles UnhandleException which means i cant have a module as startup.

please helpppp!!!

Answer 1

If you use:

Dim newInstance as boolean
myMutex = New Threading.Mutex(True, "Global\" + strLoc, newInstance)

You can check the ‘newInstance’ value, if it created a new one, then there was no previous instance, otherwise if it didn’t create a new one then another instance of your app did, so you can exit…

Also you need to keep the mutex around for the life of your application: your mutex will only stay around for the scope of your using statement, then it is released. You have to store it somewhere.