When are Scala objects garbage collected?

Question

This question is about Scala objects, which are defined something like this:

object Pipeline {
   val dispatcher = new Dispatcher
}

I know that, in some circumstances, they are referred to as 'companion' objects, although I don't yet understand the distinction. Anyway, I want to know when they get garbage collected. So, in the above example, I'd like to know when the memory occupied by dispatcher is reclaimed, if ever.

Answer 1

When compiled to jave bytecode companion objects are lazyily initialized static members. For most java implementations this means that they would be eligible for collection when the classloader loading the object is eligible for collection. It's really quite implementation dependent stuff though.

Answer 2

The object Pipeline is always "reachable", and so is dispatcher (similar to a static field in Java), so my guess would be that it isn't garbage collected. If you want to control the life cycle of dispatcher, you could do something like

object Pipeline {
    var dispatcher = Some(new Dispatcher)
    def close() { dispatcher = None }
}