8389452: Inherited @Contended annotation corrupts concrete value class layout

[caspernorrbin]

Hi everyone,

The @Contended notation is not supported on value classes. The intended behavior is for the annotation to be ignored without affecting the class layout. However, value classes are currently still marked as contended internally. When another class inherits from a value class marked as contended, this causes padding to be inserted between the inherited fields and the subclass fields, which causes a crash on debug builds.

To fix this, I have changed the handling so that a class is only marked as contended if it is an identity class. Since value classes cannot be contended, filtering the annotation when it is processed avoids carrying an invalid state that would require extra checks later on. With this change, contended and non-contended value classes behave identically, and inheriting from a value class annotated with @Contended no longer introduces padding.

Testing:

• Oracle tiers 1-3
• A new regression test covering value and identity subclasses inheriting from contended and non-contended base value classes.

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Progress

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Issue

• JDK-8389452: Inherited @Contended annotation corrupts concrete value class layout (Bug - P3)

Reviewers

• Frederic Parain (@fparain - Reviewer)
• Johan Sjölen (@johan-sjolen - Reviewer) 🔄 Re-review required (review applies to e4d0b235)

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[mlbridge]

Webrevs

• 01: Full - Incremental (300b7f18)
• 00: Full (e4d0b235)

[fparain]

Changes look good to me.
The fix just needs the update to the Javadoc of @contended we discussed.

[johan-sjolen]

This LGTM, but please address Frederic's comment.

[openjdk]

@caspernorrbin core-libs has been added to this pull request based on files touched in new commit(s).

[fparain]

LGTM
Thanks for the Javadoc update