cross-thread interaction c#

Question

can someone help me how to set Thread.join() method within my class or if there is a neat way how to deal with SynchronizationContext class and thread.join method. basically, im trying to update a datagridview (dgv) cell and progress bar (pb) every 2 seconds from a different thread (not UI thread). the functionality works fine when one thread does the job; however, i would like to set 2 threads so that the first thread (Thread 1) will update the controls (in my case, it will update the datagridview and display 10 rows and the progress bar will be update to 50%). as soon as thread 1 has done its job, Thread 2 should start and update the controls (in my case, it will update the datagridview and display 10 more rows and the progress bar will be update to 100%). Please see code below.

using System;
using System.Diagnostics;
using System.Threading;
using System.Windows.Forms;

namespace DelegatesAndCallback
{
public partial class Form1 : Form
{
    private Thread newThread1;
    private Thread newThread2;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {

        int id = Thread.CurrentThread.ManagedThreadId;
        Trace.WriteLine("Button thread "+id);

        SynchronizationContext uiContext = SynchronizationContext.Current;

        // thread #1
        startThread1(uiContext);

        // thread #2
        startThread2(uiContext);
    }

    public void startThread1(SynchronizationContext sc)
    {
        // thread #1
        newThread1 = new Thread(Process1) { Name = "Thread 1" };
        newThread1.Start(sc);
        //newThread1.Join();
    }

    public void startThread2(SynchronizationContext sc)
    {
        // thread #2
        newThread2 = new Thread(Process2) { Name = "Thread 2" };
        newThread2.Start(sc);
        //newThread2.Join();
    }

    public  void updateProgressBarValue(object state)
    {
        double val = Convert.ToDouble(state)/19.0;
        pb.Value = (int)(100*val);
    }

    public  void updateDataGridViewValue(object state)
    {
        dgv.Rows.Add((int) state, (int) state);
    }

    public void Process1(object state)
    {
        SynchronizationContext uiContext = state as SynchronizationContext;

        for (int i = 0; i < 10; i++)
        {
            uiContext.Send(updateDataGridViewValue, i);
            uiContext.Send(updateProgressBarValue, i);
            Thread.Sleep(2000);
        }
    }

    public void Process2(object state)
    {
        SynchronizationContext uiContext = state as SynchronizationContext;

        for (int i = 10; i < 20; i++)
        {
            if (uiContext != null) uiContext.Send(updateProgressBarValue, i);
            if (uiContext != null) uiContext.Send(updateDataGridViewValue, i);
            Thread.Sleep(2000);
        }
    }
}
}