多个任务运行终止以及资源共享例子

场景：
公园的管理人员希望知道每天通过多个大门进入公园的总人数，这样为每个门设置一个计数器，总人数也就是各个计数器的和，代码如下所示：

计数器类

public class Count {
         private int count=0;
 private Random rand=new Random(47);

         public synchronized int increment(){
  int temp=count;
  if(rand.nextBoolean())
   Thread.yield();
  return (count=++temp);
 }

 public synchronized int value(){
  return count;
 }


}

=====================Entrance
public class Entrance implements Runnable{
 private static Count count=new Count();

 private static List<Entrance> entrances=new ArrayList<Entrance>();

 private int sum=0;

 private final int id;

 private static volatile boolean canceled=false;

 public static void cancel(){
  canceled=true;
 }


 public Entrance(int id) {
  // TODO Auto-generated constructor stub
  this.id=id;
  entrances.add(this);
 }



 @Override
 public void run() {
  // TODO Auto-generated method stub
  while(!canceled){
   synchronized(this){
    ++sum;
   }

   System.out.println(this+" Total:"+count.increment());
   try {
    TimeUnit.MILLISECONDS.sleep(500);
   } catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    System.out.println("sleep interrupted...");
   }


  }

  System.out.println("Stopping:"+this);
 }


 public synchronized int getValue(){
  return sum;
 }

 @Override
 public String toString() {
  // TODO Auto-generated method stub
  return "Entrance "+id+":"+getValue();
 }


 public static int getTotalCount(){
  return count.value();
 }

 public static int sumEntrances(){
  int sum=0;
  for(Entrance entrance:entrances){
   sum+=entrance.getValue();

  }
  return sum;
 }
}

===========================公园管理人员查看这几个门的进入人数

public class Garden {

 public static void main(String[] args) throws InterruptedException{
  ExecutorService exec=Executors.newCachedThreadPool();
  for(int i=0;i<5;i++)  //这里面有5个入口
   exec.execute(new Entrance(i));//启动线程计数人数
  try {
   TimeUnit.SECONDS.sleep(4);
  } catch (InterruptedException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  Entrance.cancel();//各个任务共享的变量终止
  exec.shutdown();
  if(!exec.awaitTermination(250,TimeUnit.MILLISECONDS ));
   System.out.println("some tasks was not terminated!");
   System.out.println("total:"+Entrance.getTotalCount());
   System.out.println("sum of entrances :"+Entrance.sumEntrances());

 }
}