read data on UDP port using thread in race condition

 public partial class FormUDP : Form
    {
        UdpClient listener = new UdpClient(9871);
        IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, 0);

        bool ProcessStatus; //process
        Thread _UDPthread; //Thread

     private void btn_rcve_Click(object sender, EventArgs e)
       {
           ThreadStart _process = new ThreadStart(receivemessages);
           _UDPthread = new Thread(_process);
           ProcessStatus = true;
           _UDPthread.Start();

       }


private void receivemessages()
       {
           MessageBox.Show("start");
           while (ProcessStatus)
           {
               try
               {
                   if (listener.Available > 0)
                   {
                       byte[] buffer = listener.Receive(ref groupEP);
                       ///**Start convert **//
                       TBCastMessageHeader bcastHeader = new TBCastMessageHeader();
                       IntPtr bcastHeaderPtr;
                       bcastHeaderPtr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(TBCastMessageHeader)));
                       Marshal.Copy(buffer, 0, bcastHeaderPtr, buffer.Length);
                       bcastHeader = (TBCastMessageHeader)(Marshal.PtrToStructure(bcastHeaderPtr, typeof(TBCastMessageHeader)));  


                  try
                      {
                          switch (bcastHeader.MessageCode)
                          {
                           case 10:
                                     // convert byte to structure and insert into sql database
                                   break;
                          }
                        }
                      catch (Exception ex)
                        { }
                        finally { Marshal.FreeHGlobal(bcastHeaderPtr); C.Collect();}
               if (ProcessStatus)
                {
                    Thread.Sleep(new TimeSpan(0, 0, 0, 0, 5)); // 5 miliseconds
                }
 
        }

// Structure defined
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 0x1)]
    public struct TBCastMessageHeader
    {
        public ushort MessageCode;
        public uint TimeStamp;
        public ushort MessageLength;
        public sbyte NumberOfDecimals;
        public ushort Reserved;
    }


 }