Java Thread - 如何使用CountDownLatch协调线程...

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Main {
  static Random rand = new Random();
  static final Lock lock = new ReentrantLock();
  static boolean updating = false;
  static List<Future<Integer>> futureList = new ArrayList<Future<Integer>>();
  static ExecutorService pool = Executors.newFixedThreadPool(Runtime
      .getRuntime().availableProcessors());
  static Callable<Integer> callable = new Callable<Integer>() {
    @Override
    public Integer call() {
      return rand.nextInt();
    }
  };
  static void doUpdate() {
    if (lock.tryLock()) {
      updating = true;
      try {
        for (Future<Integer> future : futureList) {
          System.out.println(future.get());
        }
        futureList.clear();
      } catch (Exception e) {
        e.printStackTrace();
      } finally {
        System.out.println();
        lock.unlock();
        updating = false;
      }
    }
  }
  public static void main(String[] args) throws Exception {
    new Thread(()-> {
        int submitCount = 0;
        while (submitCount < 10) {
          if (!updating) {
            futureList.add(pool.submit(callable));
            submitCount++;
          }
          try {
            Thread.sleep(1000); // arbitrary
          } catch (Exception e) {
            e.printStackTrace();
          }
        }
    }).start();
    // update thread
    new Thread(()->{
        int updateCount = 0;
        while (updateCount < 5) {
          doUpdate();
          updateCount++;
          try {
            Thread.sleep(2000);
          } catch (Exception e) {
            e.printStackTrace();
          }
        }
    }).start();
  }
}