private void WriteXML(string context)
{
    lock
    {
      //你的代码逻辑
    }
}

------解决方案--------------------
C# code
 
 using System; 
 using System.Collections.Generic; 
 using System.ComponentModel; 
 using System.Drawing; 
 using System.Collections; 
 using System.Text; 
 using System.Windows.Forms; 
 using System.Data; 
 using System.Data.SqlClient; 
 using System.Data.OleDb; 
 using System.Configuration; 
 using System.Threading; 
 using MySql.Data.MySqlClient; 
 namespace qxjshuju 
 { 
   public partial class qxjshuju : Form 
   { 
     delegate void SetTextCallback(string text); 
     //private Thread demoThread = null; 
     //private BackgroundWorker backgroundWorker1; 
  
     //用到的变量 
     ArrayList Zm_list; 
     ArrayList Zm_Name; 
     ArrayList starttime; 
     ArrayList endtime; 
     ArrayList windstation; 
     ArrayList windname; 
     ArrayList windstime; 
     ArrayList windetime; 
     public string strtext; 
     public bool sum; 
     public int con; 
     public bool st; 
     System.Timers.Timer t; 
     private MySqlConnection conn; 
     private SqlConnection innerconn; 
     private DataTable data; 
     private MySqlDataAdapter da; 
     private MySqlCommandBuilder cb; 
     public qxjshuju() 
     { 
       InitializeComponent(); 
       sum = true; 
       st = true; 
       con = 0; 
       this.lblxszt.Text = "服务运行中"; 
       if (st) 
       { 
         btnstart.Enabled = false; 
       } 
       t = new System.Timers.Timer(300000);//实例化Timer类，每5分种一次 
       t.Elapsed += new System.Timers.ElapsedEventHandler(ReadData);//到达时间的时候执行事件； 
       t.AutoReset = true;//设置是执行一次（false）还是一直执行(true)；  
       t.Enabled = true;//是否执行System.Timers.Timer.Elapsed事件；  
       ReadData(null, null); 
     } 
  
     #region 线程数据提示语 
     private void ThreadProcUnsafe() 
     { 
       this.txtbox.Text = "This text was set unsafely."; 
     } 
  
     private void ThreadProcSafe() 
     { 
       this.SetText("This text was set safely."); 
     } 
     #endregion 
  
     #region 利用委托方法把内容显示在textbox上 
     private void SetText(string text) 
     { 
       if (this.txtbox.InvokeRequired) 
       { 
         SetTextCallback d = new SetTextCallback(SetText); 
         this.Invoke(d, new object[] { text }); 
       } 
       else 
       { 
         this.txtbox.Text = text; 
       } 
     } 
     #endregion 
  
     #region 函数入口 
     ///  <summary> 
     /// 应用程序的主入口点。 
     ///  </summary>