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

mandy chung mandy.chung at oracle.com
Tue May 22 22:09:36 UTC 2018


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.

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

"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.

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.

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.

* Transitions: * clear * active/registered ------> inactive/registered * 
| | enqueue [2] * | GC enqueue [2] v * | ------> inactive/enqueued * v * 
pending/registered --- * | | * | enqueue [2] |-> inactive/enqueued 
(pending list processing) * v | | * pending/enqueued --| | * | | 
poll/remove * | poll/remove | * v v * pending/dequeued -----> 
inactive/dequeued * * clear/enqueue * active/unregistered -----> 
inactive/unregistered * | * | GC * v * pending/unregistered -> 
inactive/unregistered - pending list processing


114 * -> inactive/unregistered - GC, clear, enqueue

Under what circumstance does GC make a reference from 
active/unregistered -> inactive/unregistered?

Mandy

On 5/20/18 8:12 AM, Kim Barrett wrote:
>> On May 15, 2018, at 12:09 AM, Kim Barrett <kim.barrett at oracle.com> wrote:
>> New webrev, rebased to include JDK-8201491:
>> http://cr.openjdk.java.net/~kbarrett/8203028/open.01/
>>
>> New webrevs with above changes:
>> full: http://cr.openjdk.java.net/~kbarrett/8203028/open.02/
>> incr: http://cr.openjdk.java.net/~kbarrett/8203028/open.02.inc/
> Following up on a suggestion from Mark Reinhold in the discussion of JDK-8203327
> on the core-libs list, I’ve added the following comment to the Reference.queue field.
>
> diff -r 98982cddbac0 -r 2429129c4d48 src/java.base/share/classes/java/lang/ref/Reference.java
> --- a/src/java.base/share/classes/java/lang/ref/Reference.java	Mon May 14 18:01:36 2018 -0400
> +++ b/src/java.base/share/classes/java/lang/ref/Reference.java	Sun May 20 11:06:48 2018 -0400
> @@ -131,6 +131,14 @@
>   
>       private T referent;         /* Treated specially by GC */
>   
> +    /* The queue this reference gets enqueued to by GC notification or by
> +     * calling enqueue().
> +     *
> +     * When registered: the queue with which this reference is registered.
> +     *        enqueued: ReferenceQueue.ENQUEUE
> +     *        dequeued: ReferenceQueue.NULL
> +     *    unregistered: ReferenceQueue.NULL
> +     */
>       volatile ReferenceQueue<? super T> queue;
>   
>       /* The link in a ReferenceQueue's list of Reference objects.
>

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