final void test() throws Exception {
      Future[] futures = new Future[nthreads];
      for (int i = 0; i < nthreads; ++i) futures[i] = pool.submit(this);

      barrier.await();
      Thread.sleep(TIMEOUT);
      boolean tooLate = false;
      for (int i = 1; i < nthreads; ++i) {
        if (!futures[i].cancel(true)) tooLate = true;
        // Unbunch some of the cancels
        if ((i & 3) == 0) Thread.sleep(1 + rng.next() % 10);
      }

      Object f0 = futures[0].get();
      if (!tooLate) {
        for (int i = 1; i < nthreads; ++i) {
          if (!futures[i].isDone() || !futures[i].isCancelled())
            throw new Error("Only one thread should complete");
        }
      } else System.out.print("(cancelled too late) ");

      long endTime = System.nanoTime();
      long time = endTime - timer.startTime;
      if (print) {
        double secs = (double) (time) / 1000000000.0;
        System.out.println("\t " + secs + "s run time");
      }
    }
  static final class FutureLoop implements Callable {
    private int v = rng.next();
    private final ReentrantLock lock = new ReentrantLock();
    private final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
    private final CyclicBarrier barrier;
    private final int nthreads;

    FutureLoop(int nthreads) {
      this.nthreads = nthreads;
      barrier = new CyclicBarrier(nthreads + 1, timer);
    }

    final void test() throws Exception {
      Future[] futures = new Future[nthreads];
      for (int i = 0; i < nthreads; ++i) futures[i] = pool.submit(this);

      barrier.await();
      Thread.sleep(TIMEOUT);
      boolean tooLate = false;
      for (int i = 1; i < nthreads; ++i) {
        if (!futures[i].cancel(true)) tooLate = true;
        // Unbunch some of the cancels
        if ((i & 3) == 0) Thread.sleep(1 + rng.next() % 10);
      }

      Object f0 = futures[0].get();
      if (!tooLate) {
        for (int i = 1; i < nthreads; ++i) {
          if (!futures[i].isDone() || !futures[i].isCancelled())
            throw new Error("Only one thread should complete");
        }
      } else System.out.print("(cancelled too late) ");

      long endTime = System.nanoTime();
      long time = endTime - timer.startTime;
      if (print) {
        double secs = (double) (time) / 1000000000.0;
        System.out.println("\t " + secs + "s run time");
      }
    }

    public final Object call() throws Exception {
      barrier.await();
      int sum = v;
      int x = 0;
      int n = ITERS;
      while (n-- > 0) {
        lock.lockInterruptibly();
        try {
          v = x = LoopHelpers.compute1(v);
        } finally {
          lock.unlock();
        }
        sum += LoopHelpers.compute2(LoopHelpers.compute2(x));
      }
      return new Integer(sum);
    }
  }