RFR: 8203028: Simplify reference processing in light of JDK-8175797

[Kim Barrett]

> On May 23, 2018, at 12:09 AM, mandy chung <mandy.chung at oracle.com> wrote:
> 
> Hi Kim,
> 
> Thanks for doing this work and rewriting the comments.  It's great to see this simplification.  It looks good in general.  I have a couple of personal preferences if you are okay to update them.

Thanks for looking at this.

> I like to keep the existing indentation of the description of different states (line 50-75) that makes them easy to read.

Done

> "normal reference"  - I suggest to change it to "soft, weak, or phantom reference".   FinalReference is also a Reference object and it's an implementation class that supports finalization.   Making it explicit would avoid confusion.

I’ve eliminated the use of “normal”.

> 86 * FinalReference (which exists to support finalization, which was
> 87 * deprecated in JDK 9) differs from normal references
> 
> I suggest to drop "which was deprecated in JDK 9" since @Deprecated is in the javadoc and no implication to the implementation.

Done.

> Thanks for adding the comment of the possible transitions.   I was tempted to make an ascii flow chart.   State change due to the API makes it harder to draw.   This is my first snap but it's not yet in a satisfying state.   I think this is clearer than the text description.  What do you think?  If we like this, I can clean that up and send you a revised version.

I've adopted your suggestion of ASCII-art to describe the state
transitions.  I've fixed a couple of errors and made some other
changes to (I hope) improve readability.

I've also made some naming changes for consistency and clarity,
including:

- "pending list" => "pending-Reference list" (both were being used)
- "pending list process(or|ing)" => ReferenceHandler [thread]

> 114 * -> inactive/unregistered - GC, clear, enqueue
> 
> Under what circumstance does GC make a reference from active/unregistered -> inactive/unregistered?

The GC may bypass the [active/unregistered] -> [pending/unregistered] transition, as an optimization.

New webrevs (only comment updates in Reference.java):
full: http://cr.openjdk.java.net/~kbarrett/8203028/open.04/
incr: http://cr.openjdk.java.net/~kbarrett/8203028/open.04.inc/