各位帮我看看这段代码

 看下这段代码，  我开一个线程  处理完 10000条 要 13 秒  开 10 个线程 处理完 10000条要 21 秒 ,请问我要怎么改这段代码呢？     //启动按钮
        private void button1_Click(object sender, EventArgs e)
        {
            #region  读取
            using (System.IO.StreamReader sr = new System.IO.StreamReader(this.txtRecePer.Text.Trim()))
            {
                while (!sr.EndOfStream)
                {                
                    al.Add(sr.ReadLine());                   
                }
            }
            #endregion
            this.lblShow.Text = "总数:" + al.Count.ToString();
            int threadnum = Int32.Parse(txtThreads.Text.Trim());
            #region 线程分配
             th = new System.Threading.Thread[threadnum];
           
                //线程分配
                for (int j = 0; j < threadnum; j++)
                {
                    th[j] = new System.Threading.Thread(new System.Threading.ThreadStart(SetValues));
                    th[j].Name = "线程" + j.ToString();
                    th[j].IsBackground = true;
                    th[j].Start();
                } 
            #endregion
        }
        private void SetValues()
        {
            
            while(al.Count>0)
            {
                System.Threading.Monitor.Enter(al);
                if (al.Count > 0)
                {
                    string a = al[0].ToString();
                    if (this.rtbIng.InvokeRequired)
                    {
                        setControlValue scv = new setControlValue(InValues);
                        this.Invoke(scv, new object[] { System.Threading.Thread.CurrentThread.Name, a });
                    }
                    else
                    {
                        this.rtbIng.AppendText("[" + System.DateTime.Now + "]" + System.Threading.Thread.CurrentThread.Name + "--" + a + "\r\n");
                    }
                    al.RemoveAt(0);
                }
                else
                {
                    break;
                }
                System.Threading.Monitor.Exit(al);
            } 
        }
        public  void InValues(string name, string info)
        {
            this.rtbIng.AppendText("["+System.DateTime.Now+"]"+ name + "--" + info + "\r\n");
        }
        //停止
        private void btnStop_Click(object sender, EventArgs e)
        {
            for (int i=0; i < th.Length; i++)
            {
                th[i].Abort();
            }
        }