@Override
        public boolean hasNext() {
            while (ready.isEmpty()) {
                if (slot == topTier.length) {
                    return false;
                }
                BaseHashTable.unpackSlot(ready, topTier, slot);
                slot++;
            }
            return true;
        }
Iterate over the values that currently exist in the hash table.

You can use this iterator even if you are making changes to the map.
The changes may or may not be visible while you are iterating.
server-common/src/main/java/org/apache/kafka/timeline/SnapshottableHashTable.java