/**
     * Sets the policy governing whether core threads may time out and
     * terminate if no tasks arrive within the keep-alive time, being
     * replaced if needed when new tasks arrive. When false, core
     * threads are never terminated due to lack of incoming
     * tasks. When true, the same keep-alive policy applying to
     * non-core threads applies also to core threads. To avoid
     * continual thread replacement, the keep-alive time must be
     * greater than zero when setting <tt>true</tt>. This method
     * should in general be called before the pool is actively used.
     * @param value <tt>true</tt> if should time out, else <tt>false</tt>
     * @throws IllegalArgumentException if value is <tt>true</tt>
     * and the current keep-alive time is not greater than zero.
     *
     * @since 1.6
     */
    public void allowCoreThreadTimeOut(boolean value) {
        if (value && keepAliveTime <= 0)
            throw new IllegalArgumentException("Core threads must have nonzero keep alive times");

        allowCoreThreadTimeOut = value;
    }

/**
     * Gets the next task for a worker thread to run.  The general
     * approach is similar to execute() in that worker threads trying
     * to get a task to run do so on the basis of prevailing state
     * accessed outside of locks.  This may cause them to choose the
     * "wrong" action, such as trying to exit because no tasks
     * appear to be available, or entering a take when the pool is in
     * the process of being shut down.  These potential problems are
     * countered by (1) rechecking pool state (in workerCanExit)
     * before giving up, and (2) interrupting other workers upon
     * shutdown, so they can recheck state. All other user-based state
     * changes (to allowCoreThreadTimeOut etc) are OK even when
     * performed asynchronously wrt getTask.
     *
     * @return the task
     */
    Runnable getTask() {
        for (;;) {
            try {
                int state = runState;
                if (state > SHUTDOWN)
                    return null;
                Runnable r;
                if (state == SHUTDOWN)  // Help drain queue
                    r = workQueue.poll();
                else if (poolSize > corePoolSize || allowCoreThreadTimeOut)
                    r = workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS);
                else
                    r = workQueue.take();
                if (r != null)
                    return r;
                if (workerCanExit()) {
                    if (runState >= SHUTDOWN) // Wake up others
                        interruptIdleWorkers();
                    return null;
                }
                // Else retry
            } catch (InterruptedException ie) {
                // On interruption, re-check runState
            }
        }
    }

class MyThreadFactory implements ThreadFactory {
        static final AtomicInteger poolNumber = new AtomicInteger(1);
        final ThreadGroup group;
        final AtomicInteger threadNumber = new AtomicInteger(1);
        final String namePrefix;

        MyThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" + poolNumber.getAndIncrement() + "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r, namePrefix + threadNumber.getAndIncrement(), 0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
        
        // 我所增加的方法，为了获取线程组
        public ThreadGroup getThreadGroup() {
            return this.group;
        }
    }

MyThreadFactory myThreadFactory = new MyThreadFactory();
ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 5, 5, TimeUnit.SECONDS,
                                new LinkedBlockingQueue<Runnable>(), myThreadFactory); 
// executor.allowCoreThreadTimeOut(true);
for (int i = 0; i <= 20; i++) {
  executor.submit(new MyRunnable());
}
System.out.println(myThreadFactory.getThreadGroup().activeCount());     // 6 
Thread.sleep(20000);
System.out.println("After destroy, active thread count:" + myThreadFactory.getThreadGroup().activeCount());             // 6/1
executor.shutdown();

    private volatile ThreadPoolExecutor searchExecutors; 
    
    private final Object lock = new Object();
    
    /**
     * 初始化线程池，开始不进行初始化，免得浪费系统资源
     */
    private void initExecutor() {
        if (searchExecutors != null) {
            return;
        }
        
        synchronized (lock) {
            if (searchExecutors == null) {
                 // 设置一个固定大小为10，核心线程如果超过10分钟空闲也可销毁的线程池
                ThreadPoolExecutor tempExecutor = new ThreadPoolExecutor(10, 10, 10, TimeUnit.MINUTES, new LinkedBlockingQueue<Runnable>(), Executors.defaultThreadFactory());
                tempExecutor.allowCoreThreadTimeOut(true);
                this.searchExecutors = tempExecutor;
            }
        }
    }

    @PreDestroy
    public void destroy() {
        if (searchExecutors != null) {
            searchExecutors.shutdown();
        }
    }