Indices not closing CloseableIterators

[yrashk]

See the discussion at 0e343eb#commitcomment-18041324

It looks like the workaround of self-closing CloseableIterators doesn't always work so it is best to ensure we're closing those. As a first step, we can do a quick fix that checks if the iterator is closeable in all applicable situations and closes it if necessary.

In the longer term, we can improve the internal API.

Thoughts?

[npgall]

Just a heads up that I have started work on a better internal API for this.

Basically, I'm replacing the Collection, with a new abstraction called ObjectSet. ObjectSet is like an Iterable, and it can wrap an ObjectStore or a Collection. But it keeps track of the iterators which have been opened and it implements Closeable where close() will close the open iterators.

It will be a fairly simple fix. However I'm working on another feature for my employer at the moment, so I hope to complete this issue in the next week or so.

[yrashk]

How hard will it be to migrate other index implementations to this ObjectSet thing, relatively straightforward?

[npgall]

Yes it will be very straightforward - fairly trivial. It will probably take 30 seconds of coding to migrate the index.

[npgall]

I've committed the change to introduce ObjectSet.

I'm still not sure that there was a resource leak, because closeRequestScopeResourcesIfNecessary() was always called anyway. But anyway, this change does make it easier for indexes to close iterators and release connections sooner than before. Let me know if you have any issues!

[yrashk]

Thank you so much! This change looks good to me — I will upgrade my indices once new cqengine is released.