8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream

[kabutz]

Since Java 10, spliterators for the ConcurrentSkipListMap were pointing to the head, which has item == null, rather than to the first element. The trySplit() method no longer worked, and always returned null. Therefore, parallel streams have not worked for ConcurrentSkipListMap and ConcurrentSkipListSet since Java 10. It worked correctly in Java 8 and 9.

The problem lies in the constructor calls for the various spliterators. In Java 9, we pass in head.node.next as "origin" into the constructor. In Java 10, this was changed to just head.node as "origin". Since the "item" field is always null on head.node, we never enter the first if() statement in the trySplit() method and thus it always returns null.

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Issue

• JDK-8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream (Bug - P3)

Reviewers

• Viktor Klang (@viktorklang-ora - Reviewer)

Contributors

• Doug Lea <dl@openjdk.org>

Reviewing

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[bridgekeeper]

👋 Welcome back kabutz! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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

8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream

Co-authored-by: Doug Lea <dl@openjdk.org>
Reviewed-by: vklang

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 22 new commits pushed to the master branch:

• 7be7772: 8344112: Remove code to support security manager execution mode from DatagramChannel implementation
• bd3fec3: 8344086: Remove security manager dependency in FFM
• 916694f: 8343317: Extend test generation tool to handle APX NDD/NF flavor of instructions
• eb240a7: 8344051: Problemlist jdk/jfr/event/runtime/TestNativeMemoryUsageEvents.java with ZGC until JDK-8343893 is fixed
• c00e20c: 8343285: java.lang.Process is unresponsive and CPU usage spikes to 100%
• cc2acd1: 8343286: Missing unchecked cast warning in polymorphic method call
• b80ca49: 8344124: JDK-8341411 Broke the build
• a08d67c: 8344080: Return type mismatch for jfr_unregister_stack_filter
• 4c5bc5f: 8343923: GHA: Switch to Xcode 15 on MacOS AArch64 runners
• 8af304c: 8341411: C2: remove slice parameter from GraphKit::make_load() and GraphKit::store_to_memory()
• ... and 12 more: https://git.openjdk.org/jdk/compare/c12b386d1916af9a04b4c6698838c2b40c6cdd86...master

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[openjdk]

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

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[mlbridge]

Webrevs

• 02: Full - Incremental (d167b88f)
• 01: Full - Incremental (7edb48c8)
• 00: Full (28658230)

[viktorklang-ora]

Hi @kabutz,
Interesting catch!
A regression test (splitability) and a test which verifies correct operation under parallel evaluation would be appropriate here.

[kabutz]

Sure, where should I add that test?

[viktorklang-ora]

@kabutz I'd say either under its own directory test/jdk/java/util/concurrent/ConcurrentSkipListMap/ or possibly in test/jdk/java/util/concurrent/tck/ConcurrentSkipListMapTest.java.

[viktorklang-ora]

@kabutz I think @DougLea identified some potential edge-cases with the proposed solution, so I added his suggested diff to the JBS Issue for reference.

[kabutz]

@kabutz I think @DougLea identified some potential edge-cases with the proposed solution, so I added his suggested diff to the JBS Issue for reference.

Indeed, I didn't check what happens when we create a spliterator on an empty collection.

[viktorklang-ora]

@kabutz Let me know how you want to proceed. 👍

[kabutz]

@kabutz Let me know how you want to proceed. 👍

've made the changes and sent another PR to the branch holding the changes. Hope that's the right way of doing it...

[viktorklang-ora]

@kabutz Ah, so then you can close this PR? I'll have a look at the other PR.

[viktorklang-ora]

@kabutz Might actually be easier to drop the other PR and add the commits to your branch 8343426-cslm-spliterator-bug so this PR is updated.

[kabutz]

/integrate

[openjdk]

@kabutz This pull request has not yet been marked as ready for integration.

[viktorklang-ora]

@kabutz The update for CSLM is based on @DougLea's proposal on the JBS issue, right? (Assuming that's the case I will add him as a co-contributor)

[kabutz]

@kabutz The update for CSLM is based on @DougLea's proposal on the JBS issue, right? (Assuming that's the case I will add him as a co-contributor)

Yes, correct.

[viktorklang-ora]

/contributor add @DougLea

[openjdk]

@viktorklang-ora Only the author (@kabutz) is allowed to issue the contributor command.

[viktorklang-ora]

@kabutz The OpenJDK bot doesn't trust me :-) would you mind adding Doug as a contributor? :)

[kabutz]

/contributor add @DougLea

[openjdk]

@kabutz
Contributor Doug Lea <dl@openjdk.org> successfully added.

[viktorklang-ora]

Nice catch, @kabutz !

[kabutz]

/integrate

[openjdk]

@kabutz
Your change (at version d167b88) is now ready to be sponsored by a Committer.

[viktorklang-ora]

/sponsor

[viktorklang-ora]

Thanks @kabutz & @DougLea!

[openjdk]

Going to push as commit 2b57f40.
Since your change was applied there have been 43 commits pushed to the master branch:

• a8152bd: 8343941: IGV: dump graph at different register allocation steps
• bd6152f: 8343855: HTTP/2 ConnectionWindowUpdateSender may miss some unprocessed DataFrames from closed streams
• c3776db: 8342936: Enhance java.io.IO with parameter-less println() and readln()
• b54bd82: 8344025: Remove unused ISO2022.Encoder.maximumDesignatorLength
• abacece: 8344011: Remove usage of security manager from Class and reflective APIs
• c977ef7: 8342047: Create Template Assertion Predicates with Halt nodes only instead of uncommon traps
• 23a8c71: 8341790: Fix ExceptionOccurred in java.desktop
• 1e97c1c: 8335989: Implement JEP 494: Module Import Declarations (Second Preview)
• e7d90b9: 8343460: ZGC: Crash in ZRemembered::scan_page_and_clear_remset
• 95a00f8: 8343875: Minor improvements of jpackage test library
• ... and 33 more: https://git.openjdk.org/jdk/compare/c12b386d1916af9a04b4c6698838c2b40c6cdd86...master

Your commit was automatically rebased without conflicts.

[openjdk]

@viktorklang-ora @kabutz Pushed as commit 2b57f40.

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