support mutable BitSet

[nevillelyh]

No description provided.

[johnynek]

can we do .forClass here? subclass is pretty dangerous because the type information of which subclass you have is lost. If you want to support subclasses, we need to write the class name, instantiate that, and fill it back up.

[johnynek]

Thanks for doing this. Will merge after you change to avoid subclasses.

[nevillelyh]

Thanks. Have very little experience with Kryo before, ran across this with Spark.
Fixed forSubclass => forClass.

[rxin]

Thanks for submitting this. Can you look into the implementation of toImmutable to see how expensive it is? If it is expensive, I'm not sure if it is a good idea to do this transformation. If it is very cheap, maybe it is ok.

[nevillelyh]

Here's the impl for toImmutable, seems fairly cheap.
def toImmutable = immutable.BitSet.fromArray(elems)

[rxin]

What if we change the signature of BitSetSerializer to take scala.collection.BitSet, so it can be used to serialize both immutable and mutable bitsets and then you get around this new object allocation?

While you are at it, I'm wondering if you can replace the foreach loop in the serializer with a while loop - it will get higher performance ...

[nevillelyh]

Not sure how that works since s.c.BitSet is just an trait while we still need to deserialize to original version of (im)mutable impl.

I can do the for -> while change if you guys think it's worth it :)

[rxin]

I think the write side is entirely reusable, whereas on the read side you'd need need to pick the right mutable vs immutable BitSet to initialize. Basically it is best to avoid creating a whole immutable bitset, and then creating a mutable bitset from that with foreach.

[johnynek]

I actually think you just want this:
https://github.com/twitter/chill/blob/develop/chill-scala/src/main/scala/com/twitter/chill/Traversable.scala#L21

.forTraversableClass[Any, MBitSet[Any]](MBitSet.empty[Any], false)

I don't think you need to write your own serializer here, just register one for mutable sets.

[rxin]

Cool if there is already a built-in serializer for serializing general traversable collections.

[nevillelyh]

Revised. Thanks for pointing this out!

[johnynek]

Thanks for your help!