public class A
{
private int ticket;
        public int Ticket
        {
            get
            {
                lock (ticket.ToString())
                    return ticket;
            }
            set
            {
                lock (ticket.ToString())
                    ticket = value;
            }
        }
}

　　A a=new A();
   private void Test()
        {
            while (a.Ticket> 0)
            {

                MessageBox.Show(a.Ticket.ToString());
                    a.Ticket--;
                
            }
        }
        private void button3_Click(object sender, EventArgs e)
        {
            

            new Thread(new ThreadStart(Test)).Start();
            new Thread(new ThreadStart(Test)).Start();
        }