lock(expression) statement_block 

using System;
using System.Threading;
namespace ThreadSimple
{
 internal class Account 
 {
  int balance;
  Random r = new Random();
  internal Account(int initial) 
  {
   balance = initial;
  } 
  internal int Withdraw(int amount) 
  {
   if (balance < 0)
   {
    //如果balance小于0則拋出異常
    throw new Exception("Negative Balance");
   }
   //下面的代碼保證在當(dāng)前線程修改balance的值完成之前
   //不會(huì)有其他線程也執(zhí)行這段代碼來修改balance的值
   //因此，balance的值是不可能小于0 的
   lock (this)
   {
    Console.WriteLine("Current Thread:"+Thread.CurrentThread.Name);
    //如果沒有l(wèi)ock關(guān)鍵字的保護(hù)，那么可能在執(zhí)行完if的條件判斷之后
    //另外一個(gè)線程卻執(zhí)行了balance=balance-amount修改了balance的值
    //而這個(gè)修改對(duì)這個(gè)線程是不可見的，所以可能導(dǎo)致這時(shí)if的條件已經(jīng)不成立了
    //但是，這個(gè)線程卻繼續(xù)執(zhí)行balance=balance-amount，所以導(dǎo)致balance可能小于0
    if (balance >= amount) 
    {
     Thread.Sleep(5);
     balance = balance - amount;
     return amount;
    } 
    else 
    {
     return 0; // transaction rejected
     }
   }
  }
  internal void DoTransactions() 
  {
   for (int i = 0; i < 100; i++) 
   Withdraw(r.Next(-50, 100));
  }
 } 

 internal class Test 
 {
  static internal Thread[] threads = new Thread[10];
  public static void Main() 
  {
   Account acc = new Account (0);
   for (int i = 0; i < 10; i++) 
   {
    Thread t = new Thread(new ThreadStart(acc.DoTransactions));
    threads[i] = t;
   }
   for (int i = 0; i < 10; i++) 
    threads[i].Name=i.ToString();
   for (int i = 0; i < 10; i++) 
    threads[i].Start();
   Console.ReadLine();
  }
 }
}

......
Queue oQueue=new Queue();
......
Monitor.Enter(oQueue);
......//現(xiàn)在oQueue對(duì)象只能被當(dāng)前線程操縱了
Monitor.Exit(oQueue);//釋放鎖

using System;
using System.Threading;

public class Cell
{
  int cellContents; // Cell對(duì)象里邊的內(nèi)容
  bool readerFlag = false; // 狀態(tài)標(biāo)志，為true時(shí)可以讀取，為false則正在寫入
  public int ReadFromCell( )
  {
   lock(this) // Lock關(guān)鍵字保證了什么，請(qǐng)大家看前面對(duì)lock的介紹
   {
    if (!readerFlag)//如果現(xiàn)在不可讀取
    { 
     try
     {
      //等待WriteToCell方法中調(diào)用Monitor.Pulse()方法
      Monitor.Wait(this);
     }
     catch (SynchronizationLockException e)
     {
      Console.WriteLine(e);
     }
     catch (ThreadInterruptedException e)
     {
      Console.WriteLine(e);
     }
    }
    Console.WriteLine("Consume: {0}",cellContents);
    readerFlag = false;
    //重置readerFlag標(biāo)志，表示消費(fèi)行為已經(jīng)完成
    Monitor.Pulse(this); 
    //通知WriteToCell()方法（該方法在另外一個(gè)線程中執(zhí)行，等待中）
   }
   return cellContents;
  }
  public void WriteToCell(int n)
  {
   lock(this)
   {
    if (readerFlag)
    {
     try
     {
      Monitor.Wait(this);
     }
     catch (SynchronizationLockException e)
     {
      //當(dāng)同步方法（指Monitor類除Enter之外的方法）在非同步的代碼區(qū)被調(diào)用
      Console.WriteLine(e);
     }
     catch (ThreadInterruptedException e)
     {
       //當(dāng)線程在等待狀態(tài)的時(shí)候中止 
      Console.WriteLine(e);
     }
    }
    cellContents = n;
    Console.WriteLine("Produce: {0}",cellContents);
    readerFlag = true; 
    Monitor.Pulse(this); 
    //通知另外一個(gè)線程中正在等待的ReadFromCell()方法
   }
  }
}

public class CellProd
{
 Cell cell; // 被操作的Cell對(duì)象
 int quantity = 1; // 生產(chǎn)者生產(chǎn)次數(shù)，初始化為1 
 public CellProd(Cell box, int request)
 {
  //構(gòu)造函數(shù)
  cell = box; 
  quantity = request; 
 }
 public void ThreadRun( )
 {
  for(int looper=1; looper<=quantity; looper++)
  cell.WriteToCell(looper); //生產(chǎn)者向操作對(duì)象寫入信息
 }
}
public class CellCons
{
 Cell cell; 
 int quantity = 1; 

 public CellCons(Cell box, int request)
 {
  //構(gòu)造函數(shù)
  cell = box; 
  quantity = request; 
 }
 public void ThreadRun( )
 {
  int valReturned;
  for(int looper=1; looper<=quantity; looper++)
  valReturned=cell.ReadFromCell( );//消費(fèi)者從操作對(duì)象中讀取信息
 }
}

public class MonitorSample
{
 public static void Main(String[] args)
 {
  int result = 0; 
 //一個(gè)標(biāo)志位，如果是0表示程序沒有出錯(cuò)，如果是1表明有錯(cuò)誤發(fā)生
  Cell cell = new Cell( ); 
  //下面使用cell初始化CellProd和CellCons兩個(gè)類，生產(chǎn)和消費(fèi)次數(shù)均為20次
  CellProd prod = new CellProd(cell, 20); 
  CellCons cons = new CellCons(cell, 20); 

  Thread producer = new Thread(new ThreadStart(prod.ThreadRun));
  Thread consumer = new Thread(new ThreadStart(cons.ThreadRun));
  //生產(chǎn)者線程和消費(fèi)者線程都已經(jīng)被創(chuàng)建，但是沒有開始執(zhí)行 
  try
  {
 producer.Start( );
 consumer.Start( ); 

 producer.Join( ); 
 consumer.Join( );
 Console.ReadLine();
  }
  catch (ThreadStateException e)
  {
 //當(dāng)線程因?yàn)樗帬顟B(tài)的原因而不能執(zhí)行被請(qǐng)求的操作
 Console.WriteLine(e); 
 result = 1; 
  }
  catch (ThreadInterruptedException e)
  {
 //當(dāng)線程在等待狀態(tài)的時(shí)候中止
 Console.WriteLine(e); 
 result = 1; 
  }
  //盡管Main()函數(shù)沒有返回值，但下面這條語句可以向父進(jìn)程返回執(zhí)行結(jié)果
  Environment.ExitCode = result;
 }
}