public class Promise {

  private static ExecutorService executorService = Executors.newScheduledThreadPool(16);

  private Promise() {
    throw new AssertionError();
  }

  /**
   * 實現并發同時地對某個action并發執行并返回執行結果
   * 實現思路：
   * 并發創建所有執行的線程，并通過鎖(start)阻塞等待著
   * 在創建所有執行的線程后(ready)開始計時，并解鎖然所有的線程啟動
   * 通過另外一個鎖（done）記錄執行完的線程
   * 主線程只需關心3點
   * - 所有線程是否準備好
   * - 準備好的話開始計時并解鎖開始執行
   * - 等待執行完畢
   *
   * @param callableList 要并發執行的列表
   * @return list 執行結果，list.item為null的話表示執行異常
   * @throws InterruptedException 異常
   */
  public static <T> List<T> all(final List<Callable<T>> callableList) throws InterruptedException {
    final List<T> result = new ArrayList<>();
    int length = callableList.size();
    final CountDownLatch ready = new CountDownLatch(length);
    final CountDownLatch start = new CountDownLatch(1);
    final CountDownLatch done = new CountDownLatch(length);
    for (final Callable<T> callable : callableList) {
      executorService.execute(new Runnable() {
        @Override
        public void run() {
          ready.countDown();
          try {
            start.await();
            T t = callable.call();
            result.add(t);
          } catch (Exception e) {
            // interrupt when exception
            Thread.currentThread().interrupt();
            // set null mean exception
            result.add(null);
            e.printStackTrace();
          } finally {
            done.countDown();
          }
        }
      });
    }
    ready.await();
    long startnano = System.nanoTime();
    start.countDown();
    done.await();
    long cause = System.nanoTime() - startnano;
    System.out.println(String.format("Promise all done,cause time millSecond: %s", cause / 1000000));
    return result;
  }
}

public void promiseAllTest() throws Exception{

  List<Callable<String>> callables = new ArrayList<>();

  for (int i = 0; i < 10; i++) {
    int finalI = i;
    callables.add(new Callable<String>() {
      @Override
      public String call() throws Exception {
        int millis = new Random().nextInt(10000);
        Thread.sleep(millis);
        System.out.println(String.format("thread%s sleep %s millis" ,finalI,millis));
        return "Thread" + finalI;
      }
    });
  }

  List<String> result = Promise.all(callables);

  System.out.println(result);
  System.out.println("done...");

}