8364111: InstanceMirrorKlass iterators should handle CDS and hidden classes consistently

[shipilev]

See the bug for more investigation. I think the root cause is already fixed in one of the InstanceMirrorKlass iterators, but not in the other one. Additionally, only one iterator handles the hidden classes. Also, there is a stale comment about CMS that apparently prevents us from asserting is_primitive, which is not relevant anymore.

So this PR commons out the metadata handling on both iterators, which fixes the GenShen+CDS bug, likely fixes hidden classes bug somewhere, and prevents the omission like this from happening again.

Additional testing:

• Linux x86_64 server fastdebug, Generational Shenandoah + CDS bugs are not reproducing now
• Linux x86_64 server fastdebug, tier1
• Linux x86_64 server fastdebug, all

---

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Issue

• JDK-8364111: InstanceMirrorKlass iterators should handle CDS and hidden classes consistently (Bug - P4)

Reviewers

• Coleen Phillimore (@coleenp - Reviewer) Review applies to 5e4153ae
• Thomas Stuefe (@tstuefe - Reviewer)
• Albert Mingkun Yang (@albertnetymk - Reviewer)

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[openjdk]

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8364111: InstanceMirrorKlass iterators should handle CDS and hidden classes consistently

Reviewed-by: stuefe, ayang, coleenp

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At the time when this comment was updated there had been 61 new commits pushed to the master branch:

• c6d64ed: 8364325: ProblemList com/sun/management/HotSpotDiagnosticMXBean/DumpThreads.java
• 1be412d: 8363920: JVMTI Documentation for GetLocalDouble is wrong: refers to long
• 164d036: 8364202: CDS without G1 gives build error in slowdebug, asserts in fastdebug
• ... and 58 more: https://git.openjdk.org/jdk/compare/594c080b2bde81a48ecccda85ac765218fc93856...master

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[openjdk]

@shipilev The following label will be automatically applied to this pull request:

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[mlbridge]

Webrevs

• 02: Full - Incremental (40761ecc)
• 01: Full - Incremental (bc853287)
• 00: Full (5e4153ae)

[coleenp]

This looks like a good cleanup but need someone who knows GC better to also review.

/reviewers add 2

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@coleenp Usage: /reviewers <n> [<role>] where <n> is the number of required reviewers. If role is set, the reviewers need to have that project role. If omitted, role defaults to authors.

[coleenp]

/reviewers 2

[openjdk]

@coleenp
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

[tstuefe]

The new comment is a lot better, thanks.

[tstuefe]

I wondered briefly whether the allowance ("CLD = null is okay for newly-loaded classes") should be also made in

jdk/src/hotspot/share/memory/iterator.inline.hpp

Lines 57 to 59 in 4669005

	} else {
	assert(AOTLinkedClassBulkLoader::is_pending_aot_linked_class(k), "sanity");
	}

But since we now handle mirror->referee Klass correctly in IMK, this only path affects oop->its Klass, and no instances exist yet for that Klass, right?

[shipilev]

I wondered briefly whether the allowance ("CLD = null is okay for newly-loaded classes") should be also made in

jdk/src/hotspot/share/memory/iterator.inline.hpp

Lines 57 to 59 in 4669005

	} else {
	assert(AOTLinkedClassBulkLoader::is_pending_aot_linked_class(k), "sanity");
	}

But since we now handle mirror->referee Klass correctly in IMK, this only path affects oop->its Klass, and no instances exist yet for that Klass, right?

ClaimMetadataVisitingOopIterateClosure::do_klass called from other places, not only IMK. So I believe those asserts could be reached through other means. What we handle here is only IMK.

[shipilev]

Thanks! If there are no more comments, I will integrate this soon.

[shipilev]

There we go.

/integrate

[openjdk]

Going to push as commit ebb7f5d.
Since your change was applied there have been 75 commits pushed to the master branch:

• 05c63e8: 8361524: [XWayland] possible JavaFX interop hang
• 559795b: 8362501: Update test/hotspot/jtreg/applications/jcstress/README
• 413ac74: 8357682: sun.security.provider.certpath.Builder#getMatchingPolicies always returns null
• ... and 72 more: https://git.openjdk.org/jdk/compare/594c080b2bde81a48ecccda85ac765218fc93856...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit ebb7f5d.

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