Convert NIO objects to TypedData API

[casperisfine]

The replacement API was introduced in Ruby 1.9.2 (2010),
and the old untyped data API was marked a deprecated in the documentation
as of Ruby 2.3.0 (2015)

Ref: https://bugs.ruby-lang.org/issues/19998

Since it was quite trivial I also implemented write barriers and memsize functions.

[ioquatix]

Thanks for your effort, I can merge and release this right away.

By the way, I don't just mean your effort here. I completely agree with the deprecation of non-TypedData interface in CRuby and also believe we need more effort in this regard (deprecating/removing old interfaces).

[ioquatix]

Just for my own edification, what is the nature of RB_OBJ_WRITE and when should it be used?

[casperisfine]

It's a helper to assign a reference and trigger write barriers, it is required to allow Monitor objects to be marked as WB_PROTECTED which is what allow them to reach the old generation.

In short, when an object get to the old generation, it's no longer marked during minor GC. So if you create a reference from an old to a young object, the GC won't see it and mayincorrectly assume the young object is no longer referenced by anyone.

Write barriers are a way to tell the GC: "Hey, this old object created a new reference, you should check it".

In this specific instance, it's actually not really required because it's an object creating a reference to itself, so from a GC point of view, it's a bit useless. Similarly when you assign to an immediate like Qnil, it's not a big deal if you forget it.

But I like to always do it as I think consistency here help avoiding future patches to forget it.

[ioquatix]

Thanks, LGTM.

[casperisfine]

Thanks for the quick merge!