同時:CountDownLatchの使用

CountDownLatch:他のスレッドで実行されている操作のセットを完了する前に、1つ以上のスレッドを待機させる同期支援クラス.CyclicBarrierとよく似ています.しかし、CountDownLatchのカウンタは一度しか使用できませんが、CyclicBarrierはリサイクルできます.主な方法public CountDownLatch(int count);public void countDown(); public void await()throws InterruptedExceptionの例(「Think In Java」から、少し変更):latchに注意.await()の位置

class TaskPortion implements Runnable{
	private static int counter = 0;
	private final int id = counter++;
	private static Random rand = new Random(47);
	private final CountDownLatch latch;
	
	TaskPortion(CountDownLatch latch){
		this.latch = latch;
	}
	@Override
	public void run() {
		try {
			doWork();
			latch.countDown();
//			latch.await(); ，  CountDownLatch  
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	public void doWork() throws InterruptedException{
		TimeUnit.MILLISECONDS.sleep(rand.nextInt(2000));
		System.out.println(this + "completed!");
	}
	public String toString(){
		return String.format("%1$-3d", id);
	}
}

public class CountDownLatchDemo {
	static final int SIZE = 13;
	public static void main(String[] args) throws InterruptedException{
		ExecutorService exec = Executors.newCachedThreadPool();
		CountDownLatch latch = new CountDownLatch(SIZE);
		for(int i = 0; i < SIZE; i++){
			exec.execute(new TaskPortion(latch));
		}
		latch.await();// 
		System.out.println("Launched all tasks");
		exec.shutdown();
	}
}

出力:
11 completed!
7  completed!
9  completed!
10 completed!
5  completed!
8  completed!
12 completed!
1  completed!
2  completed!
6  completed!
4  completed!
0  completed!
3  completed!
Launched all tasks