B4J Question jServer hungs during background work

Sub PingCamera (host As String, timeoutMs As Int) As Boolean
    Private inetaddress As JavaObject
    inetaddress.InitializeStatic("java.net.InetAddress")
    Dim b As Boolean = inetaddress.RunMethodJO("getByName",Array As String(host)).RunMethod("isReachable",Array As Object(timeoutMs))
    Return b
End Sub

Sub tim_tick
    If Grabbing = False Then
        Return
    End If
    Dim H As String = Get_Host(RTSP_URL)
    If PingCamera(h, 500) = False Then
        LastGrabbingError = H & " is not reachable"
        Log(LastGrabbingError)
        Return
    Else
        Log("!")
        Get_Frame
    End If
End Sub

'parse the host to use for Ping
Sub Get_Host(u As String) As String
    Dim m As Matcher = Regex.Matcher("(.*:)//([A-Za-z0-9\-\.]+)(:[0-9]+)?(.*)", u)
    Do While m.Find
        For g = 1 To m.GroupCount
            If g = 2 Then    'host name
                Return m.Group(g)
            End If
        Next
    Loop
    Return ""
End Sub