如果線程池中線程任務已經執行完畢了，當前線程的狀態是怎樣的？

1.代碼樣例

int corePoolSize = 2;
    int maximumPoolSize = 4;
    long keepAliveTime = 20;
    TimeUnit unit = TimeUnit.SECONDS;
    ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize,
        keepAliveTime, unit, new ArrayBlockingQueue<>(10), new NameTreadFactory(),
        new ThreadPoolExecutor.CallerRunsPolicy());
//    executor.allowCoreThreadTimeOut(true);
 // 如果設置此值，線程執行完畢，會等keepAliveTime時長，如果還沒有任務執行，線程池中線程就關閉了
    executor.prestartAllCoreThreads(); // 預啓動所有核心線程
    try {
      Thread.sleep(10 * 1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    System.out.println("開始任務-------------------");
    for (int i = 0; i < 20; i++) {
      Task task = new Task(i);
      executor.execute(task);
    }
    System.out.println("結束任務--------------------------");

    try {
      Thread.sleep(300 * 1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    executor.shutdown();

public class NameTreadFactory implements ThreadFactory {

    private final AtomicInteger mThreadNum = new AtomicInteger(1);

    @Override
    public Thread newThread(Runnable r) {
        Thread t = new Thread(r, "my-thread-" + mThreadNum.getAndIncrement());
        System.out.println(t.getName() + " has been created");
        return t;
    }
}

2.如使用默認的線程池，任務執行完畢，線程池中會保持核心線程池的個數（2個）處於等待狀態 waiting。