RFR: 8188055: (ref) Add Reference::refersTo predicate [v5]

[Kim Barrett]

On Fri, 16 Oct 2020 05:41:17 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev
>> excludes the unrelated changes brought in by the merge/rebase. The pull request contains 11 additional commits since
>> the last revision:
>>  - Merge branch 'master' into refersto
>>  - More explicit refersTo0 comment.
>>  - simplify test
>>  - cleanup nits from Mandy
>>  - use Object instead of TestObject
>>  - improve refersTo0 descriptions
>>  - basic functional test
>>  - change referent access
>>  - expand test
>>  - remove CMS comment
>>  - ... and 1 more: https://git.openjdk.java.net/jdk/compare/b5adeaad...ab4e519b
>
> src/java.base/share/classes/java/lang/ref/Reference.java line 348:
> 
>> 346:      * Tests if this reference object refers to {@code obj}.  If {@code obj} is
>> 347:      * {@code null}, this method returns {@code true} if this reference object
>> 348:      * refers to {@code null} or has been cleared.
> 
> Is there actually a distinction between clearing and referring to null?

A (not very useful) Reference can be created with a null referent.

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PR: https://git.openjdk.java.net/jdk/pull/498