C# WinApp System.Threading.Thread อยาก shutdown เครื่องหลังจากที่ทุก thread ทำงานเสร็จต้องเขียนโค๊ดยังไงครับ

using System.Diagnostics;

ProcessStartInfo startinfo = new ProcessStartInfo("shutdown.exe", "-s");
Process.Start(startinfo);

         private void CheckFile(object obj)
        {
            string cri = "";
            int min = (int)((object[])obj)[0];
            int max = (int)((object[])obj)[1];
            int i = min;
            while (true)
            {

                if (this.sONGDataGridView[3, i].Value.ToString().Trim().Replace(" ", "").ToUpper() != cri)
                {
                    cri = this.sONGDataGridView[3, i].Value.ToString().Trim().Replace(" ", "").ToUpper();
                }
                else
                {
                    sngDel++;
                    if (this.sONGDataGridView[2, i].Value.ToString() == "EMK")
                    {
                        MIDI_Dll.MIDI_Dll.MoveFile(PathKARA + "\\SONGS\\MIDI\\EMK\\" + this.sONGDataGridView[0, i].Value.ToString().Substring(0, 1) + "\\" + this.sONGDataGridView[0, i].Value.ToString() + ".emk");
                    }
                    else if (this.sONGDataGridView[2, i].Value.ToString() == "NCN")
                    {
                        MIDI_Dll.MIDI_Dll.MoveFile(PathKARA + "\\SONGS\\MIDI\\NCN\\Lyrics\\" + this.sONGDataGridView[0, i].Value.ToString().Substring(0, 1) + "\\" + this.sONGDataGridView[0, i].Value.ToString() + ".lyr");
                        MIDI_Dll.MIDI_Dll.MoveFile(PathKARA + "\\SONGS\\MIDI\\NCN\\Cursor\\" + this.sONGDataGridView[0, i].Value.ToString().Substring(0, 1) + "\\" + this.sONGDataGridView[0, i].Value.ToString() + ".cur");
                        MIDI_Dll.MIDI_Dll.MoveFile(PathKARA + "\\SONGS\\MIDI\\NCN\\Song\\" + this.sONGDataGridView[0, i].Value.ToString().Substring(0, 1) + "\\" + this.sONGDataGridView[0, i].Value.ToString() + ".mid");
                    }

                }
                try
                {


                    this.progressBar2.Invoke(new Action(() => { this.progressBar2.Value = sngRun; }));
                    if (sngRun > 0)
                    {
                        double t = DateTime.Now.TimeOfDay.TotalSeconds - startCounter;
                        double strt = (double)((this.sONGDataGridView.RowCount - sngRun) * t / sngRun);

                        this.label3.Invoke(new Action(() =>
                        {

                            this.label3.Text = "Cri =" + cri + Environment.NewLine +
                                "Check code " + this.sONGDataGridView[0, i].Value.ToString() + this.sONGDataGridView[2, i].Value.ToString() + Environment.NewLine +
                                "Delete file;" + sngDel + Environment.NewLine +
                                "File: " + sngRun + "/" + (this.sONGDataGridView.RowCount - 1) + Environment.NewLine +
                                "Completion Ratio:" + string.Format("{0:0.0000}", Convert.ToDouble(100 * (double)sngRun / (double)(this.sONGDataGridView.RowCount - 1))) + " %" + Environment.NewLine +
                                "Speed:" + string.Format("{0:0.00}", ((double)sngRun / t)) + "file/s" + Environment.NewLine +
                                "Elapsed time:" + MIDI_Dll.MIDI_Dll.Time(t) + Environment.NewLine +
                                "Remaining time:" + MIDI_Dll.MIDI_Dll.Time(strt);
                        }));
                    }
                    this.progressBar2.Invoke(new Action(() => { this.progressBar2.Value = sngRun; }));
                }
                catch { }
                System.Threading.Thread.Sleep(10);
                sngRun++;

                i++;
                if (i >= max) { return; }
            }
        }

         private void frmCuteMIDI_Load(object sender, EventArgs e)
         {
              for (int i = 0; i < 20; i++)
            {
                new System.Threading.Thread(CheckFile).Start(new object[] {  i * sngPer, (i + 1) * sngPer - 1 });
            }
         }