複数のタスクの実行終了およびリソース共有の例

シーン:
公園の管理者は毎日複数のゲートを通って公園に入る総人数を知りたいと思っています.このようにドアごとにカウンタを設置します.総人数は各カウンタの和で、コードは以下の通りです.
カウンタクラス

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 entrances=new ArrayList();

	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;
	}
}

===========================================================================

public class Garden {

	public static void main(String[] args) throws InterruptedException{
		ExecutorService exec=Executors.newCachedThreadPool();
		for(int i=0;i<5;i++)  // 5 
			exec.execute(new Entrance(i));// 
		try {
			TimeUnit.SECONDS.sleep(4);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		Entrance.cancel();// 
		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());

	}
}