java中线程池的关闭问题

Runtime.getRuntime().addShutdownHook(new Thread(() -> {
    try {
        executorService.shutdown();
        while(!executorService.awaitTermination(10,TimeUnit.SECONDS)) {}
    } catch(Exception e) {
    }
}));

/**
 * @param corePoolSize the number of threads to keep in the pool, even
 *           if they are idle, unless {@code allowCoreThreadTimeOut} is set
 *        核心线程数：即使是空闲状态也可以在线程池存活的线程数量，除非           
 *        allowCoreThreadTimeOut 设置为 true。
 * @param keepAliveTime when the number of threads is greater than
 *        the core, this is the maximum time that excess idle threads
 *        will wait for new tasks before terminating.
 *         存活时间：对于超出核心线程数的线程，空闲时间一旦达到存活时间，就会被销毁。
 */
public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory,
                           RejectedExecutionHandler handler) { ... ... }

ThreadPoolExecutor executor = new ThreadPoolExecutor(0, 5,
                30L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(15));
for (int i = 0; i < 20; i++) {
    executor.execute(() -> {
        // 简单地打印当前线程名称
        System.out.println(Thread.currentThread().getName());
    });
}

public class Executors {
    ... ...
    public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                          60L, TimeUnit.SECONDS,
                                          new SynchronousQueue<Runnable>());
    }
    ... ...
}

public void allowCoreThreadTimeOut(boolean value) {
    // 核心线程存活时间必须大于0，一旦开启，keepAliveTime 也必须大于0
    if (value && keepAliveTime <= 0)
        throw new IllegalArgumentException("Core threads must have nonzero keep alive times");
    // 将 allowCoreThreadTimeOut 值设为传入的参数值
    if (value != allowCoreThreadTimeOut) {
        allowCoreThreadTimeOut = value;
        // 开启后，清理所有的超时空闲线程，包括核心线程
        if (value)
            interruptIdleWorkers();
    }
}

ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 5,
                30L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(15));
executor.allowCoreThreadTimeOut(true);
for (int i = 0; i < 20; i++) {
            executor.execute(() -> {
               // 简单地打印当前线程名称
                System.out.println(Thread.currentThread().getName());
            });
}

ThreadPoolExecutor executor2 = new ThreadPoolExecutor(1, 5, 30, TimeUnit.SECONDS,
            new ArrayBlockingQueue<Runnable>(150),
            new ThreadFactory() { 
                public Thread newThread(Runnable r) {
                    Thread thread = new Thread(r, r.hashCode()+"");
                    thread.setDaemon(true);//设置成守护线程
                    return thread;
                }
            }
);
for (int i = 0; i < 20; i++) {
            executor2.execute(() -> {
               // 简单地打印当前线程名称
                System.out.println(Thread.currentThread().getName());
            });
}