jankotek/mapdb

@jankotek QUES on the hashmap or treemap with nested data structure. With the following code block:

        HTreeMap<String, List<String>> map = (HTreeMap<String, List<String>>) DBMaker.fileDB("map").make().hashMap("map").createOrOpen();
        for (int i = 0; i< 10; i++) {
            final int finalI = i;
            for (int j = 0; j< 10; j++) {
                final int finalJ = j;
                map.compute(String.valueOf(finalI), (key, value) -> {
                    if (value == null) {
                        value = new ArrayList<>();
                    }
                    value.add(String.format("%d_%d", finalI, finalJ));
                    return value;
                });
            }
        }

It falls into deadloop. Instead, I need to copy the value and then return the modified new copy to make it work.

HTreeMap<String, List<String>> map = (HTreeMap<String, List<String>>) DBMaker.fileDB("map").make().hashMap("map").createOrOpen();
        for (int i = 0; i< 10; i++) {
            final int finalI = i;
            for (int j = 0; j< 10; j++) {
                final int finalJ = j;
                map.compute(String.valueOf(finalI), (key, value) -> {
                    final List<String> newValue;
                    if (value == null) {
                        newValue = new ArrayList<>();
                    } else {
                        newValue = new ArrayList<>(value);
                    }
                    newValue.add(String.format("%d_%d", finalI, finalJ));
                    return newValue;
                });
            }
        }

Is it a bug or it is expected? I think this is not an issue with in-memory counterpart (e.g. concurrentHashMap)