Impossible to serialize nested generic class of the same type e.g. HashMap<Long, HashMap<Long, HashMap<Long, String>>>

[unoexperto]

How can I understand and fix cause of "Parent scope can be set just once" exception?

I have following object that I'm trying to serialize

TTHashTable<Long, TTHashTable<Long, TTHashTable<Long, TTBusObj>>>

where TTHashTable is

public class TTHashTable<K, V> extends TTBusObj {
    private Hashtable<K, V> ht;
}

exception is thrown (according to debugger) when we're trying to pass first inner Hashtable into FieldSerializer.write.

I'm using Kryo 2.23.

Thanks!

[romix]

Hi, this is most likely a problem with the way how Kryo handles very complex generic type declarations. There are some problems there.

Could you provide a self-contained test-case for your problem? Then I could look into it.

[romix]

Sorry. It was not meant to be closed. I clicked the wrong button ;-)

[unoexperto]

Here we go
https://github.com/cppexpert/kryo_bug

I use SBT to create IDEA configs so you can run "sbt gen-idea" locally so that IDEA configs reference dependencies correctly

[romix]

Thanks. I'll look into it

[romix]

OK. I could reproduce a problem.

It seems like it occurs if classes are designed in such a way that the same class with generic parameters is used recursively in an object graph. In your case, it is TTHashTable<Long, TTHashTable<Long, TTHashTable<Long, TTBusObj>>> and the like. Here TTHashTable is used recursively, as you can see and each use has different values of generic parameters.

I'll see now how this can be fixed. But it may turn out that it is actually pretty complex to fix properly.

[unoexperto]

I see. What the chances you could fix it in foreseeable future?

[romix]

I'll give it a try this week. But if I don't manage to fix it quickly, I'll schedule it for a later, e.g. after next release time.

[romix]

Please use latest trunk (i.e. a snapshot build) and give it a try. Seems to work for me on your test-case. Close the issue, if everything is OK now.

[unoexperto]

It works. Thanks a lot.

[unoexperto]

romix, could you update SBT repo with new build ?

[romix]

The latest SNAPSHOT build (i.e. the latest trunk build) should be available from Sonatype (see GitHub homepage for more info).

As for the release build, I cannot do it, because we haven't released the latest version yet. But we are planning to do it pretty soon.