สอบถามการ ใช้ backgroundWorker หน่อยครับ winfrom c#

public static void _login(object obj)
        {
            string _pass;

            string s = (string)((object[])obj)[0];

            for (int r = 0; r < symbolKey.Length; r++)
            {
                _pass = s + symbolKey[r];
                WriteToFile(_pass);
                System.Threading.Thread.Sleep(100);
            }
        }
       
        static void login()
        {
            string str = "";
            string[] reg = _KeyReg.Split('_');
            List<int> rmin = new List<int>();
            for (int i = 0; i < 9; i++)
            {
                rmin.Add(int.Parse(reg[i]));
            }

            do

        }

new System.Threading.Thread(login).Start(); 
new System.Threading.Thread(_login).Start(new object[] { str });