How do I fix a "Too many posts to a semaphore" error in a vb app?

Question

I am writing a vb application on a new Windows 11 Surface.  When the application opens the serial port, I receive a "Too many posts made to a semaphore" error.  I have followed all steps I have found on the subjects (disabled anti-virus, disabled all startup apps, running as administrator).  Any help would be greatly appreciated.    

 Private Sub Button_Click(sender As Object, e As RoutedEventArgs)

        Dim myport As SerialPort

        myport = New SerialPort()

        myport.PortName = "COM4"   'Assign the port name to the MyCOMPort object

        myport.BaudRate = 9600      'Assign the Baudrate to the MyCOMPort object

        myport.Parity = Parity.None   'Parity bits = none  

        myport.DataBits = 8             'No of Data bits = 8

        myport.StopBits = StopBits.One  'No of Stop bits = 1

        myport.Open()

        myport.Write("A")           ' Write an ascii "A"

        myport.Close()

        Frame1.Content = "Change"

    End Sub

Answer 1

Hi @09849128 ,

Please check if adding the following lines to your Package.appxmanifest helps if your project is UWP.

<DeviceCapability Name="serialcommunication">
      <Device Id="any">
          <Function Type="name:serialPort" />
      </Device>
</DeviceCapability>

Or consider moving serial port operations to a separate thread. You can use the class BackgroundWorker to achieve this.

Private WithEvents backgroundWorker As New BackgroundWorker
Private myport As SerialPort

Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
    backgroundWorker.RunWorkerAsync()
    Frame1.Content = "Opening serial port..."
End Sub

Private Sub backgroundWorker_DoWork(sender As Object, e As DoWorkEventArgs) Handles backgroundWorker.DoWork
    myport = New SerialPort()

    myport.PortName = "COM4"
    myport.BaudRate = 9600
    myport.Parity = Parity.None
    myport.DataBits = 8
    myport.StopBits = StopBits.One

    Try
        myport.Open()
        myport.Write("A")
    Catch ex As Exception
        ' Handle any exceptions here
    Finally
        If myport.IsOpen Then
            myport.Close()
        End If
    End Try
End Sub

Private Sub backgroundWorker_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles backgroundWorker.RunWorkerCompleted
    Frame1.Content = "Change"
End Sub

Best Regards.

Jiachen Li

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