RFR: 8351996: Behavioral updates for ClassValue::remove [v11]

[Shaojin Wen]

On Wed, 30 Apr 2025 20:26:33 GMT, Chen Liang <liach at openjdk.org> wrote:

>> The recent patch #23866 makes calling `ClassValue::remove()` from `ClassValue::computeValue()` end up in infinite loops while fixing the stale value risk from the method.
>> 
>> The proposed fix is to preserve the stale value risk fix, and update the remove-from-compute behavior from the original designated no-op behavior to throwing an exception, as the original behavior conflicts with the stale value fix.
>> 
>> The implementation track the owner thread in promises (accessed in locked section); as a result, we can fail-fast on recursive removals from `computeValue`. I did not choose to use `ThreadTracker` as it is designed for single tracker and multiple threads, while this case here sees often just one thread, and the threads outlive the promise objects.
>> 
>> Also updated the API specs for `remove` to more concisely describe the memory effects. Please review the associated CSR as well.
>
> Chen Liang 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 19 additional commits since the last revision:
> 
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/classvalue-compute-remove
>  - Reviews from viktor
>  - Rewrite impl to follow the new simplified spec
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/classvalue-compute-remove
>  - Try to simplify the model - use the finish of computeValue
>    
>  - Test updates - remove repetition, test case for no stale installation
>  - Fix incorrect promise removal when unnecessary and add regression test
>  - Cannot test for recursion eagerly - add test case
>  - More spec, eager exception, finish with existing, thanks John
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/classvalue-compute-remove
>  - ... and 9 more: https://git.openjdk.org/jdk/compare/b679d9c3...2292212b

src/java.base/share/classes/java/lang/ClassValue.java line 371:

> 369:             Version<T> v = version();
> 370:             if (v == null)  return false;
> 371:             if (v.isLive())  return true;

Suggestion:

            if (v == null)  return false;
            if (v.isLive()) return true;

Remove a space to align the code

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PR Review Comment: https://git.openjdk.org/jdk/pull/24043#discussion_r2071561616