.net使用Task多线程执行任务 .net限制线程数量

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using System.Text.Json;

namespace WinFormsApp
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 更新消息框
        /// </summary>
        /// <param name="msg"></param>
        public void UpdateMsg(string msg)
        {
            if (txtMsg.InvokeRequired)
            {
                Action<string> action = UpdateMsg;
                Invoke(action, msg);
                return;
            }
            txtMsg.AppendText(msg + "\r\n");
            //滚动到底部
            txtMsg.ScrollToCaret();
        }

        /// <summary>
        /// 启用、禁用 按钮。
        /// </summary>
        /// <param name="enabled"></param>
        private void SetBtnEnable(bool enabled)
        {
            if (btnStart.InvokeRequired)
            {
                Action<bool> action = SetBtnEnable;
                Invoke(action, enabled);
                return;
            }
            btnStart.Enabled = enabled;
        }

        /// <summary>
        /// 开始执行线程
        /// </summary>
        private async void btnStart_Click(object sender, EventArgs e)
        {
            //开启一个子线程，不然等待时会卡主线程。
            await Task.Run(async () => { await TestIt(); });
        }

        public async Task TestIt()
        {
            //搞个集合
            List<int> list = new List<int>();
            for (int i = 0; i < 10; i++)
            {
                list.Add(i);
            }

            //任务集合
            List<Task> tasks = new List<Task>();

            //执行方法体
            Func<int, string> func = (id) =>
            {
                using (var context = new XCGDbContext())
                {
                    var stus = context.Students.Where(x => x.Id == id).FirstOrDefault();
                    if (stus == null)
                    {
                        return "id：" + id + " 无数据";
                    }
                    var str = JsonSerializer.Serialize(stus);
                    return str;
                }
            };

            int maxTaskCount = 3;
            foreach (int i in list)
            {
                int k = i;
                tasks.Add(Task.Run(() =>
                {
                    var res = func(k);
                    UpdateMsg(res);
                }));
                //判断线程数量不能超过最大设定数。
                if (tasks.Count > maxTaskCount)
                {
                    //等待任何一个完成，会卡当前线程。
                    Task.WaitAny(tasks.ToArray());
                    //排除掉已完成的任务
                    tasks = tasks.Where(t => t.Status != TaskStatus.RanToCompletion).ToList();
                }
            }

            TaskFactory taskFac = new TaskFactory();
            //不卡主线程，所有Task完成，才执行下面的操作
            await taskFac.ContinueWhenAll(tasks.ToArray(), arr =>
            {
                //全部完成，执行其他操作...
                UpdateMsg("执行完毕");
            });
        }
    }
}