Java 并发编程之线程挂起、恢复与终止

public class DeprecatedSuspendResume extends Object implements Runnable{ 
  //volatile关键字，表示该变量可能在被一个线程使用的同时，被另一个线程修改 
 private volatile int firstVal; 
 private volatile int secondVal; 
 //判断二者是否相等 
 public boolean areValuesEqual(){ 
  return ( firstVal == secondVal); 
 } 
 public void run() { 
  try{ 
   firstVal = 0; 
   secondVal = 0; 
   workMethod(); 
  }catch(InterruptedException x){ 
   System.out.println("interrupted while in workMethod()"); 
  } 
 } 
 private void workMethod() throws InterruptedException { 
  int val = 1; 
  while (true){ 
   stepOne(val); 
   stepTwo(val); 
   val++; 
   Thread.sleep(200); //再次循环钱休眠200毫秒 
  } 
 } 
 //赋值后，休眠300毫秒，从而使线程有机会在stepOne操作和stepTwo操作之间被挂起 
 private void stepOne(int newVal) throws InterruptedException{ 
  firstVal = newVal; 
  Thread.sleep(300); //模拟长时间运行的情况 
 } 
 private void stepTwo(int newVal){ 
  secondVal = newVal; 
 } 
 public static void main(String[] args){ 
  DeprecatedSuspendResume dsr = new DeprecatedSuspendResume(); 
  Thread t = new Thread(dsr); 
  t.start(); 
  //休眠1秒，让其他线程有机会获得执行 
  try { 
   Thread.sleep(1000);} 
  catch(InterruptedException x){} 
  for (int i = 0; i < 10; i++){ 
   //挂起线程 
   t.suspend(); 
   System.out.println("dsr.areValuesEqual()=" + dsr.areValuesEqual()); 
   //恢复线程 
   t.resume(); 
   try{ 
    //线程随机休眠0~2秒 
    Thread.sleep((long)(Math.random()*2000.0)); 
   }catch(InterruptedException x){ 
    //略 
   } 
  } 
  System.exit(0); //中断应用程序 
 } 
} 

public class AlternateSuspendResume extends Object implements Runnable { 
 private volatile int firstVal; 
 private volatile int secondVal; 
 //增加标志位，用来实现线程的挂起和恢复 
 private volatile boolean suspended; 
 public boolean areValuesEqual() { 
  return ( firstVal == secondVal ); 
 } 
 public void run() { 
  try { 
   suspended = false; 
   firstVal = 0; 
   secondVal = 0; 
   workMethod(); 
  } catch ( InterruptedException x ) { 
   System.out.println("interrupted while in workMethod()"); 
  } 
 } 
 private void workMethod() throws InterruptedException { 
  int val = 1; 
  while ( true ) { 
   //仅当贤臣挂起时，才运行这行代码 
   waitWhileSuspended(); 
   stepOne(val); 
   stepTwo(val); 
   val++; 
   //仅当线程挂起时，才运行这行代码 
   waitWhileSuspended(); 
   Thread.sleep(200); 
  } 
 } 
 private void stepOne(int newVal) 
     throws InterruptedException { 
  firstVal = newVal; 
  Thread.sleep(300); 
 } 
 private void stepTwo(int newVal) { 
  secondVal = newVal; 
 } 
 public void suspendRequest() { 
  suspended = true; 
 } 
 public void resumeRequest() { 
  suspended = false; 
 } 
 private void waitWhileSuspended() 
    throws InterruptedException { 
  //这是一个“繁忙等待”技术的示例。 
  //它是非等待条件改变的最佳途径，因为它会不断请求处理器周期地执行检查， 
  //更佳的技术是：使用Java的内置“通知-等待”机制 
  while ( suspended ) { 
   Thread.sleep(200); 
  } 
 } 
 public static void main(String[] args) { 
  AlternateSuspendResume asr = 
    new AlternateSuspendResume(); 
  Thread t = new Thread(asr); 
  t.start(); 
  //休眠1秒，让其他线程有机会获得执行 
  try { Thread.sleep(1000); } 
  catch ( InterruptedException x ) { } 
  for ( int i = 0; i < 10; i++ ) { 
   asr.suspendRequest(); 
   //让线程有机会注意到挂起请求 
   //注意：这里休眠时间一定要大于 
   //stepOne操作对firstVal赋值后的休眠时间，即300ms， 
   //目的是为了防止在执行asr.areValuesEqual（）进行比较时, 
   //恰逢stepOne操作执行完，而stepTwo操作还没执行 
   try { Thread.sleep(350); } 
   catch ( InterruptedException x ) { } 
   System.out.println("dsr.areValuesEqual()=" + 
     asr.areValuesEqual()); 
   asr.resumeRequest(); 
   try { 
    //线程随机休眠0~2秒 
    Thread.sleep( 
      ( long ) (Math.random() * 2000.0) ); 
   } catch ( InterruptedException x ) { 
    //略 
   } 
  } 
  System.exit(0); //退出应用程序 
 } 
}