多线程执行时数据库插入重复记录

Question

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int i = 0;
        ThreadStart thread = null;
        Thread thread1 = null;
        DataTable dt = null;
        private void button1_Click(object sender, EventArgs e)
        {
            string sql = "select top 1000 id,content from articleinfo";
            dt = DBHelper.GetDataSet(sql);
            startThread();
        }
        public void startThread()
        {
            thread = new ThreadStart(addnum);
           
            Thread[] th = new Thread[5];
            for (int j = 0; j < th.Length; j++)
            {
                th[j] = new Thread(thread);
                th[j].IsBackground = true;
                th[j].Start();            }
            thread1 = new Thread(new ThreadStart(DshowNum));
            thread1.IsBackground = true;
            thread1.Start();
         }
        public void addnum()
        {
            foreach (DataRow dr in dt.Rows)
            {
                string id = dr["id"].ToString();
                string content = dr["content"].ToString();
                lock (this)
                {
                    InsertData(id,content);  //  每个线程都会执行一次
                    i++;
                }
            }
                          
        }        public void InsertData(string id,string content)
        {
            try
            {
                string sql = "insert into articleInfo2(id,content)values('" + id + "','" + content + "')";
                DBHelper.ExecuteNonQuery(sql);
            }
            catch (Exception ex)
            { }
        }
        public void DshowNum()
        {
            MethodInvoker mi = new MethodInvoker(showNum);
            while (true)
            {
                Invoke(mi);
            }
        }        public void showNum()
        {
            this.label1.Text = "这是第" + i + "个数";
        }
    }
}大侠帮我看一下，在注释的那个方法处，每个线程都会执行一次，怎样才能让其中一个线程访问，别的线程处理下一条数据

Answer 1

用Monitor, Mutex, Event, 和Semaphore，以同步线程，别的就不多说了。

Answer 2

先在主方法里定义好数目：
int count = dt.Rows.Cout;
int i = 0;
然后addnum每次取出一个currentIndex并行处理 public void addnum()
        {       
            while (true)
            {
                int currentIndex = -1;
                if (i < count)
                {
                    lock (this)
                    {
                        if (i < count)
                        {
                            currentIndex = i;
                            i = i + 1;
                        }
                        else
                        {
                            break;
                        }
                    }
                    if (currentIndex != -1)
                    {
                        string id =dt.Rows[currentIndex]["id"].ToString();
                        string content = dt.Rows[currentIndex]["content"].ToString();
                        InsertData(id, content); 
                    }                }
                else
                {
                    break;
                }
            }
        }