Java 并發(fā)編程之線程掛起、恢復(fù)與終止

public class DeprecatedSuspendResume extends Object implements Runnable{ 
  //volatile關(guān)鍵字，表示該變量可能在被一個(gè)線程使用的同時(shí)，被另一個(gè)線程修改 
 private volatile int firstVal; 
 private volatile int secondVal; 
 //判斷二者是否相等 
 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); //再次循環(huán)錢休眠200毫秒 
  } 
 } 
 //賦值后，休眠300毫秒，從而使線程有機(jī)會(huì)在stepOne操作和stepTwo操作之間被掛起 
 private void stepOne(int newVal) throws InterruptedException{ 
  firstVal = newVal; 
  Thread.sleep(300); //模擬長(zhǎng)時(shí)間運(yùn)行的情況 
 } 
 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，讓其他線程有機(jī)會(huì)獲得執(zhí)行 
  try { 
   Thread.sleep(1000);} 
  catch(InterruptedException x){} 
  for (int i = 0; i < 10; i++){ 
   //掛起線程 
   t.suspend(); 
   System.out.println("dsr.areValuesEqual()=" + dsr.areValuesEqual()); 
   //恢復(fù)線程 
   t.resume(); 
   try{ 
    //線程隨機(jī)休眠0~2秒 
    Thread.sleep((long)(Math.random()*2000.0)); 
   }catch(InterruptedException x){ 
    //略 
   } 
  } 
  System.exit(0); //中斷應(yīng)用程序 
 } 
} 

public class AlternateSuspendResume extends Object implements Runnable { 
 private volatile int firstVal; 
 private volatile int secondVal; 
 //增加標(biāo)志位，用來實(shí)現(xiàn)線程的掛起和恢復(fù) 
 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 ) { 
   //僅當(dāng)賢臣掛起時(shí)，才運(yùn)行這行代碼 
   waitWhileSuspended(); 
   stepOne(val); 
   stepTwo(val); 
   val++; 
   //僅當(dāng)線程掛起時(shí)，才運(yùn)行這行代碼 
   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 { 
  //這是一個(gè)“繁忙等待”技術(shù)的示例。 
  //它是非等待條件改變的最佳途徑，因?yàn)樗鼤?huì)不斷請(qǐng)求處理器周期地執(zhí)行檢查， 
  //更佳的技術(shù)是：使用Java的內(nèi)置“通知-等待”機(jī)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，讓其他線程有機(jī)會(huì)獲得執(zhí)行 
  try { Thread.sleep(1000); } 
  catch ( InterruptedException x ) { } 
  for ( int i = 0; i < 10; i++ ) { 
   asr.suspendRequest(); 
   //讓線程有機(jī)會(huì)注意到掛起請(qǐng)求 
   //注意：這里休眠時(shí)間一定要大于 
   //stepOne操作對(duì)firstVal賦值后的休眠時(shí)間，即300ms， 
   //目的是為了防止在執(zhí)行asr.areValuesEqual（）進(jìn)行比較時(shí), 
   //恰逢stepOne操作執(zhí)行完，而stepTwo操作還沒執(zhí)行 
   try { Thread.sleep(350); } 
   catch ( InterruptedException x ) { } 
   System.out.println("dsr.areValuesEqual()=" + 
     asr.areValuesEqual()); 
   asr.resumeRequest(); 
   try { 
    //線程隨機(jī)休眠0~2秒 
    Thread.sleep( 
      ( long ) (Math.random() * 2000.0) ); 
   } catch ( InterruptedException x ) { 
    //略 
   } 
  } 
  System.exit(0); //退出應(yīng)用程序 
 } 
}