使用ThreadPool来实现线程的复用

protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            //1.同步读取数据
            //GetCustomers();

            //2.异步读取数据
             BackgroundWorker worker = new BackgroundWorker();
            //picLoading.Visible = true;
             IsBusy = true;
            worker.DoWork += (obj, arg) =>
            {
                arg.Result = GetCustomers();
            };
            worker.RunWorkerCompleted += (obj, arg) =>
            {
                BindingSource bs = new BindingSource(arg.Result, null);
                lstCustomers.DataSource = bs;
                lstCustomers.DisplayMember = "CompanyName";
                lstCustomers.ValueMember = "CustomerID";

                IsBusy = false;
                //picLoading.Visible = false;
             };
            worker.RunWorkerAsync();

        }

        private bool IsBusy
        {
            set
            {
                picLoading.Visible = value;
            }
        }

private List<CustomerInfo> GetCustomers()
        {
            List<CustomerInfo> result = new List<CustomerInfo>();

            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                Thread.Sleep(5000);
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "SELECT CustomerID,CompanyName FROM Customers";
                    conn.Open();
                    SqlDataReader reader = cmd.ExecuteReader();
                    while (reader.Read())
                    {
                        result.Add(
                            new CustomerInfo()
                            {
                                CustomerID = reader.GetString(0),
                                CompanyName = reader.GetString(1)
                            });
                    }
                    reader.Close();
                    conn.Close();

                }
            }
            return result;
        }

        public class CustomerInfo
        {
            public string CustomerID { get; set; }
            public string CompanyName { get; set; }
        }

        private void lstCustomers_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (lstCustomers.SelectedIndex != -1)
            {
                var customerId = ((CustomerInfo)lstCustomers.SelectedItem).CustomerID;
                //picLoading.Visible = true;
                IsBusy = true;
                //3.使用ThreadPool(线程池）来实现线程的复用
                ThreadPool.QueueUserWorkItem((obj) =>
                {
                    var orders = GetOrderByCustomerID(customerId);
                    this.BeginInvoke(new Action(() =>
                    {
                        dgvOrders.DataSource = orders.Tables[0];
                        //picLoading.Visible = false;
                        IsBusy = false;
                    }));
                });
            }
        }