using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;
namespace bar4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private delegate int myde(int a);

        private void button1_Click(object sender, EventArgs e)
        {
            myde my = new myde(mymethod);
           textBox1.Text= my(1000).ToString();
        }
        private int mymethod(int s)
        {
            Thread.Sleep(10000);
            return s * s;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            myde my = new myde(mymethod);
            IAsyncResult async=my.BeginInvoke(5,null,null);
            int result = my.EndInvoke(async);
            textBox1.Text = result.ToString();
            //this.Invoke(my, new Object[] { 1000 });
            
        }
    }
}

Thread _threadShow = new Thread();
if(_threadShow != null && _threadShow.ThreadState == ThreadState.Running)
{
 return;
}
_threadShow = new Thread(new ThreadStart(mymethod));
_threadShow.Start();