C# 本进程执行完毕后再执行下一线程

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ExecutionCourseSystem
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }
        CountdownEvent latch = new CountdownEvent(1);
        private void refreshData(CountdownEvent latch)
        {
            latch.Signal();
        }

        delegate void UpdateText(Control control ,string text);
        UpdateText color = delegate (Control control,string text)
        {
            control.Text = text;
        };


        private void button1_Click(object sender, EventArgs e)
        {
            Thread th = new Thread(ProcessMain);
            th.IsBackground = true;
            th.Start();
        }

        /// <summary>
        /// 主线程函数
        /// </summary>
        void ProcessMain()
        {
            Process1();
            Process2();
            Process3();
        }

        /// <summary>
        /// 动作1
        /// </summary>
        void Process1()
        { 
            latch = new CountdownEvent(1);
            Thread thread = new Thread(() => {
                bool flag = true;
                int i = 0;
                while (flag)
                {
                    if (i > 99)
                    {
                        flag = false;
                    }
                    i++;
                    Thread.Sleep(50);
                }
                refreshData(latch);
            });
            thread.Start();
            latch.Wait();
            this.Invoke(color, new object[] {textBox1, "1" }); 

        }

        /// <summary>
        /// 动作2
        /// </summary>
        void Process2()
        {
            latch = new CountdownEvent(1);
            Thread thread = new Thread(() => {
                bool flag = true;
                int i = 0;
                while (flag)
                {
                    if (i > 99)
                    {
                        flag = false;
                    }
                    i++;
                    Thread.Sleep(50);
                }
                refreshData(latch);
            });
            thread.Start();
            latch.Wait();
            this.Invoke(color, new object[] { textBox1, "2" });
        }

        /// <summary>
        /// 动作3
        /// </summary>
        void Process3()
        {
            latch = new CountdownEvent(1);
            Thread thread = new Thread(() => {
                bool flag = true;
                int i = 0;
                while (flag)
                {
                    if (i > 99)
                    {
                        flag = false;
                    }
                    i++;
                    Thread.Sleep(50);
                }
                refreshData(latch);
            });
            thread.Start();
            latch.Wait();
            this.Invoke(color, new object[] { textBox1, "3" });
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ExecutionCourseSystem
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        CountdownEvent latch = new CountdownEvent(5);
        private void Form3_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        { 
            Thread thread = new Thread(() => refreshData());
            thread.Start();
            thread = new Thread(() => refreshData());
            thread.Start();
            thread = new Thread(() => refreshData());
            thread.Start();
            thread = new Thread(() => refreshData());
            thread.Start();
            thread = new Thread(() => refreshData()); 
            thread.Start();
            latch.Wait();
            MessageBox.Show("线程全部执行完毕"); 
        }
        private void refreshData()
        {
            latch.Signal();
        }
    }
}