pushTimeRing在并发场景会出现任务丢失

[yiyuankafei]

Please answer some questions before submitting your issue. Thanks!

Which version of XXL-JOB do you using?

2.4.0

    private volatile static Map<Integer, List<Integer>> ringData = new ConcurrentHashMap<>();

并发情况下，会出现两个线程同时走到ringItemData == null，导致其中一个线程add的jobId被另一个线程的空List覆盖掉

    private void pushTimeRing(int ringSecond, int jobId){
        // push async ring
        List<Integer> ringItemData = ringData.get(ringSecond);
        if (ringItemData == null) {
            ringItemData = new ArrayList<Integer>();
            ringData.put(ringSecond, ringItemData);
        }
        ringItemData.add(jobId);

        logger.debug(">>>>>>>>>>> xxl-job, schedule push time-ring : " + ringSecond + " = " + Arrays.asList(ringItemData) );
    }

虽然目前看只有一个守护线程会调用pushTimeRing，感觉在将来扩展的时候会成为一个隐患