hashmap陷入get方法陷入死循环

让HashMap陷入死循环

public class HashMapDead {
    private static Logger logger = Logger.getLogger("hashMapDead");
    private static long    Cycle  = 100000;

    public static void main(String[] args) throws InterruptedException {
        Map map = new HashMap();
        CountDownLatch latch = new CountDownLatch(1);

        int i = 0;
        for (; i < 3; i++) {
            new Thread(new Write(map,i*Cycle,latch)).start();
        }

        new Thread(new Read(map,(i)*Cycle,latch)).start();
        latch.countDown();
        System.out.println(" main end");

    }



    private static class Write implements Runnable {
        private Map map;
        private long                startIdx;
        private CountDownLatch      latch;

        public Write(Map map, long start, CountDownLatch latch) {
            this.map = map;
            this.startIdx = start;
            this.latch = latch;
        }

        /** 
         * @see java.lang.Runnable#run()
         */

        @Override
        public void run() {
            try {
                latch.await();
            } catch (InterruptedException e) {
                logger.warning(e.toString());
            }
            System.out.println(Thread.currentThread().getName() + "recover");

            long end = startIdx + Cycle;
            for (; startIdx < end; startIdx++) {
                String tmp = String.valueOf(startIdx);
                map.put(tmp, tmp);
            }
            System.out.println(Thread.currentThread().getName() + "over");
        }
    }



    private static class Read implements Runnable {
        private Map map;
        private long                size;
        private CountDownLatch      latch;

        public Read(Map map, long end, CountDownLatch latch) {  
            this.map = map;
            this.size = end;
            this.latch = latch;
        }

        /** 
         * @see java.lang.Runnable#run()
         */
        @Override
        public void run() {
            try {
                latch.await();
            } catch (InterruptedException e) {
                logger.warning(e.toString());
            }
            System.out.println(Thread.currentThread().getName() + "recover");
            while (true) {
                Random random = new Random();
                long l = random.nextLong() % size - 1;
                String result = map.get(String.valueOf(l));
                System.out.println(System.currentTimeMillis() + ": " + result);
            }
        }
    }
}

原因

hashMap在并发访问时，resize时候读取。详细分析见下一篇