java Future 不能及时结束

Question

如下程序运行结束后，还在主线程卡一阵才退出？

public static class Task implements Callable<String> {
        @Override
        public String call() throws Exception {
            String tid = String.valueOf(Thread.currentThread().getId());
            System.out.printf("Thread#%s : in call\n", tid);
            return tid;
        }
    }

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        List<Future<String>> results = new ArrayList<Future<String>>();
        ExecutorService es = Executors.newCachedThreadPool();
        for(int i=0; i<100;i++)
            results.add(es.submit(new Task()));

        for(Future<String> res : results)
            System.out.println(res.get());
    }

Thread#12 : in call
Thread#109 : in call
Thread#110 : in call
Thread#105 : in call
Thread#104 : in call
Thread#88 : in call
Thread#106 : in call
Thread#107 : in call
Thread#103 : in call
Thread#101 : in call
Thread#102 : in call
Thread#99 : in call
Thread#97 : in call
Thread#96 : in call
Thread#98 : in call
Thread#94 : in call
Thread#111 : in call
Thread#95 : in call
Thread#89 : in call
Thread#108 : in call
Thread#91 : in call
Thread#100 : in call
Thread#92 : in call
Thread#93 : in call
Thread#90 : in call
Thread#87 : in call
Thread#86 : in call
Thread#85 : in call
Thread#84 : in call
Thread#83 : in call
Thread#82 : in call
Thread#81 : in call
Thread#80 : in call
Thread#79 : in call
Thread#78 : in call
Thread#77 : in call
Thread#76 : in call
Thread#75 : in call
Thread#74 : in call
Thread#73 : in call
Thread#72 : in call
Thread#71 : in call
Thread#70 : in call
Thread#69 : in call
Thread#68 : in call
Thread#67 : in call
Thread#66 : in call
Thread#65 : in call
Thread#64 : in call
Thread#63 : in call
Thread#62 : in call
Thread#61 : in call
Thread#60 : in call
Thread#59 : in call
Thread#58 : in call
Thread#57 : in call
Thread#56 : in call
Thread#55 : in call
Thread#54 : in call
Thread#53 : in call
Thread#52 : in call
Thread#49 : in call
Thread#48 : in call
Thread#51 : in call
Thread#50 : in call
Thread#47 : in call
Thread#46 : in call
Thread#45 : in call
Thread#44 : in call
Thread#43 : in call
Thread#42 : in call
Thread#41 : in call
Thread#40 : in call
Thread#39 : in call
Thread#38 : in call
Thread#37 : in call
Thread#36 : in call
Thread#35 : in call
Thread#34 : in call
Thread#33 : in call
Thread#32 : in call
Thread#31 : in call
Thread#30 : in call
Thread#29 : in call
Thread#28 : in call
Thread#27 : in call
Thread#26 : in call
Thread#25 : in call
Thread#24 : in call
Thread#23 : in call
Thread#22 : in call
Thread#21 : in call
Thread#20 : in call
Thread#19 : in call
Thread#18 : in call
Thread#17 : in call
Thread#16 : in call
Thread#15 : in call
Thread#14 : in call
Thread#13 : in call
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实际上Future.get都拿到结果了

Answer 1

因为CachedThreadPool在的默认线程是有空闲时间，好像是60s吧 只有在60s内继续没有任务过来才会退出

Answer 2

加上es.shutdown()试试

Answer 3

要shutdown，按照Javadoc里的方法shutdown:

https://docs.oracle.com/javas...

Answer 4

ExecutorService 没有关闭，调用shutdown 方法，和 Future 没有关系