8276696: ParallelObjectIterator freed at the wrong time in VM_HeapDumper

[fisk]

The VM_HeapDumper code uses a C heap allocated ParallelObjectIterator. It is constructed right before running a parallel operation with a work gang, but freed in the destructor of the VM_HeapDumper. This means it is created on one thread and deleted on another thread. This becomes a bit problematic when a parallel object iterator implementation uses a ThreadsListHandle (which is indeed the case for ZGC). This patch changes ParallelObjectIterator to be a StackObj, carrying a ParallelObjectIteratorImpl object, which is never exposed publicly. This ensures that construction and destruction of the internal object iterator is scoped like RAII objects, hence complying with how ThreadsListHandle is supposed to be used.

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Progress

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Issue

• JDK-8276696: ParallelObjectIterator freed at the wrong time in VM_HeapDumper

Reviewers

• Per Liden (@pliden - Reviewer)
• Stefan Karlsson (@stefank - Reviewer)

Reviewing

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[openjdk]

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[mlbridge]

Webrevs

• 00: Full (929f2868)

[pliden]

Looks good.

[openjdk]

@fisk This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8276696: ParallelObjectIterator freed at the wrong time in VM_HeapDumper

Reviewed-by: pliden, stefank

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At the time when this comment was updated there had been 18 new commits pushed to the master branch:

• 79350b9: 8276216: Negated character classes performance regression in Pattern
• e3243ee: 8277087: ZipException: zip END header not found at ZipFile#Source.findEND
• 12f08ba: 8277507: Add jlink.debug system property while launching jpackage tests to help diagonize recent intermittent failures
• bb11c55: 8277542: G1: Move G1CardSetFreePool and related classes to separate files
• f62b81c: 8273095: vmTestbase/vm/mlvm/anonloader/stress/oome/heap/Test.java fails with "wrong OOME"
• 05a9a51: 8277423: ciReplay: hidden class with comment expected error
• 1049aba: 8277576: ProblemList runtime/ErrorHandling/CreateCoredumpOnCrash.java on macosx-X64
• 851a362: 8264297: Create implementation for NSAccessibilityProgressIndicator protocol peer
• 6cf4cd1: 8273341: Update Siphash to version 1.0
• e3911a8: 8277429: Conflicting jpackage static library name
• ... and 8 more: https://git.openjdk.java.net/jdk/compare/3f847fe89a088d6921107ca887a7a1bace871bd6...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[fisk]

Thanks for the reviews, @pliden and @stefank!

[fisk]

/integrate

[openjdk]

Going to push as commit f4dc03e.
Since your change was applied there have been 22 commits pushed to the master branch:

• 90f96fb: 8277441: CompileQueue::add fails with assert(_last->next() == __null) failed: not last
• 66eaf65: 8277413: Remove unused local variables in jdk.hotspot.agent
• 36b887a: 8277560: Remove WorkerDataArray::_is_serial
• 017df14: 8277556: Call ReferenceProcessorPhaseTimes::set_processing_is_mt once
• 79350b9: 8276216: Negated character classes performance regression in Pattern
• e3243ee: 8277087: ZipException: zip END header not found at ZipFile#Source.findEND
• 12f08ba: 8277507: Add jlink.debug system property while launching jpackage tests to help diagonize recent intermittent failures
• bb11c55: 8277542: G1: Move G1CardSetFreePool and related classes to separate files
• f62b81c: 8273095: vmTestbase/vm/mlvm/anonloader/stress/oome/heap/Test.java fails with "wrong OOME"
• 05a9a51: 8277423: ciReplay: hidden class with comment expected error
• ... and 12 more: https://git.openjdk.java.net/jdk/compare/3f847fe89a088d6921107ca887a7a1bace871bd6...master

Your commit was automatically rebased without conflicts.

[openjdk]

@fisk Pushed as commit f4dc03e.

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