Code
private void FrmMain_Load(object sender, EventArgs e)
{
   private Thread sendPrintThread = new Thread(new ThreadStart(SendPrintControl))
   sendPrintThread.Name = "SendPrint";
   sendPrintThread.IsBackground = true;
   sendPrintThread.Start();
}

  private void SendPrintControl()
        {
            bool flag = true;
            while (flag)
            {
                int count = this.GetFileCount();
                if (count < 2)
                {
                    flag = SendPrint();
                    RefreshPaperStatus();
                }
            }
            if (sendPrintThread != null && sendPrintThread.ThreadState == ThreadState.Background)
            {
                sendPrintThread.Suspend();
            }
    
            if (toolStrip.InvokeRequired)
            {
                SetTextCallback d = new SetTextCallback(SetText);
                this.Invoke(d, new object[] { "打印开始" });
                SetControlEnable EnableControl = new SetControlEnable(SetToolFunction);
                this.Invoke(EnableControl, new object[] { false, true });
            }  
        }