So it was hard because hash table could resize between calls? For HTreeMap I used expanding Hash Tree. There are 4 dir levels, each with 128 entries. If dir be

So it was hard because hash table could resize between calls? For HTreeMap I used expanding Hash Tree. There are 4 dir levels, each with 128 entries. If dir becomes full (or has too many collisions), it splits into another 128 dirs. Iterations is done by increasing counter. If dir at level 2 is not found, it is increased by 128^2. Writing iterators took single day.