Both `no_finalizer` and `no_reference_types` should have the same value

[k-sareen]

Currently no_finalizer is false and no_reference_types is true. This leads to a really odd configuration. Finalization and reference processing are interlinked, so it makes no sense to be able to finalize without dealing with weak references, at least in the context of OpenJDK. Further, if we are comparing against G1 or any stock Hotspot collector, this configuration is just not possible there so comparisons need to be very careful of this inconsistency.

[qinsoon]

no_reference_types and the MMTK core's ref processor will be removed eventually. The binding should use VMRefClosure instead. So in the context of no_reference_types, we really mean Java-style reference types, like SoftRef, WeakRef etc, objects that include weak refs.

Back to your question, finalizers also have weak refs to objects. Finalizers and reference types both include weak references, but they are not the same thing. Java's implementation makes finalizer as a special reference type. But this is not necessarily true for all the languages. For example, Go has finalizers, but does not have weak reference types at all.

[k-sareen]

Yes. But in the meantime, we should make the options consistent. We've been saying we will remove the reference processor for a while, but we haven't done it yet. I'm just saying we should make it semantically correct in the short-term.

I'm aware that finalizers and weak references are different. We don't currently have a Go binding or a binding that treats finalizers different from weak references, so I'm not sure why we can't change this option temporarily while the reference processor still exists in the core.

[wks]

After mmtk/mmtk-openjdk#309 is merged, reference processing should run correctly on OpenJDK. I think it is time for us to enable reference processing by default.

[qinsoon]

I'm not sure why we can't change this option temporarily while the reference processor still exists in the core.

ReferenceProcessor and FinalizableProcessor are two different implementations in MMTk core. I don't think we want to use one option to control both, or enforce them to be the same value.

If Java assumes they are the same or related, this should be handled in the binding side.

[k-sareen]

Sure. Regardless of if they are different or not, I don't see why we can't just set no_reference_types to false in the core right now.

[qinsoon]

Yeah. We can set the default value to false.