8371740 : LinkedTransferQueue.poll() returns null even though queue is not empty #28479

viktorklang-ora · 2025-11-24T17:31:20Z

Adds the patch by @DougLea

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JDK-8371740: LinkedTransferQueue.poll() returns null even though queue is not empty (Bug - P3)

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Alan Bateman (@AlanBateman - Reviewer)

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Doug Lea <dl@openjdk.org>
Dr Heinz M. Kabutz <heinz@javaspecialists.eu>

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viktorklang-ora · 2025-11-24T17:32:31Z

/contributor add @DougLea

bridgekeeper · 2025-11-24T17:32:40Z

👋 Welcome back vklang! 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 · 2025-11-24T17:33:36Z

@viktorklang-ora 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:

8371740: LinkedTransferQueue.poll() returns null even though queue is not empty

Co-authored-by: Doug Lea <dl@openjdk.org>
Co-authored-by: Dr Heinz M. Kabutz <heinz@javaspecialists.eu>
Reviewed-by: alanb

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 34 new commits pushed to the master branch:

5291e1c: 8372513: Shenandoah: ShenandoahMaxRegionSize can produce an unaligned heap alignment
5fe731d: 8349835: C2: Simplify IGV property printing
275cb9f: 8360510: C2: Template Assertion Predicates are not cloned to the inner counted loop with -XX:+StressDuplicateBackedge
... and 31 more: https://git.openjdk.org/jdk/compare/67b57f4f758f2fea647a3b6a68c0372a8f9e121b...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.

openjdk · 2025-11-24T17:34:27Z

@viktorklang-ora
Contributor Doug Lea <dl@openjdk.org> successfully added.

openjdk · 2025-11-24T17:35:22Z

@viktorklang-ora The following label will be automatically applied to this pull request:

core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-11-24T17:39:39Z

Webrevs

01: Full - Incremental (73c646ae)
00: Full (2b32c4fa)

kabutz · 2025-11-24T17:51:23Z

Would you like me to add some test code to make sure something like this does not happen again?

test/jdk/java/util/concurrent/BlockingQueue/MissedPoll.java

kabutz · 2025-11-24T20:47:19Z

Good work everyone :-)

viktorklang-ora · 2025-11-24T22:48:20Z

Thanks for reporting, @kabutz!

viktorklang-ora · 2025-11-24T17:34:21Z

test/jdk/java/util/concurrent/BlockingQueue/MissedPoll.java

+        System.out.println(q.getClass());
+        try (var pool = Executors.newCachedThreadPool()) {
+            var futures = new ArrayList<Future<Integer>>();
+            var phaser = new Phaser(4);


@DougLea Would it make sense to do the following, and then only keep a single phaser.arriveAndAwaitAdvance(); ? (and skip the explicit q.clear())

Suggested change

var phaser = new Phaser(4);

var phaser = new Phaser(4) {

@Override

protected boolean onAdvance(int phase, int registeredParties) {

q.clear();

return super.onAdvance(phase, registeredParties);

}

};

Sure. I was just trying to minimally adapt the submitter's bug report as test, so left this as-is.

It was primarily to validate my own understanding of equivalence :)

test/jdk/java/util/concurrent/BlockingQueue/MissedPoll.java

kabutz · 2025-11-25T16:43:45Z

Seeing that the original test was written by me, could we perhaps add me as contributor as well?

viktorklang-ora · 2025-11-25T17:14:43Z

@kabutz Of course, I missed that when I added Doug. Thanks for the reminder, Heinz. 👍

viktorklang-ora · 2025-11-25T17:14:59Z

/contributor add @kabutz

openjdk · 2025-11-25T17:46:19Z

@viktorklang-ora @kabutz was not found in the census.

Syntax: /contributor (add|remove) [@user | openjdk-user | Full Name <email@address>]. For example:

/contributor add @openjdk-bot
/contributor add duke
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kabutz · 2025-11-25T17:55:41Z

Maybe /contributor Dr Heinz M. Kabutz heinz@javaspecialists.eu ? I'm surprised that @kabutz did not work, since I have contributed before.

viktorklang-ora · 2025-11-26T09:52:11Z

/contributor add Dr Heinz M. Kabutz heinz@javaspecialists.eu

openjdk · 2025-11-26T09:53:06Z

@viktorklang-ora
Contributor Dr Heinz M. Kabutz <heinz@javaspecialists.eu> successfully added.

viktorklang-ora · 2025-11-26T09:54:59Z

@kabutz Adding that worked.

viktorklang-ora · 2025-11-27T09:42:04Z

/integrate

openjdk · 2025-11-27T09:42:52Z

Going to push as commit d350158.
Since your change was applied there have been 56 commits pushed to the master branch:

4ac3395: 8372150: Parallel: Tighten requirements around heap sizes with NUMA and Large Pages
1f417e7: 8371887: HttpClient: SSLParameters with no protocols configured disable HTTP2+ support
86aae12: 8367487: Test compiler/loopopts/superword/TestReinterpretAndCast.java fails on Linux aarch64 with Cavium CPU
... and 53 more: https://git.openjdk.org/jdk/compare/67b57f4f758f2fea647a3b6a68c0372a8f9e121b...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-11-27T09:43:05Z

@viktorklang-ora Pushed as commit d350158.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

viktorklang-ora · 2025-12-01T09:10:27Z

/backport jdk25u

openjdk · 2025-12-01T09:12:54Z

@viktorklang-ora the backport was successfully created on the branch backport-viktorklang-ora-d350158e-master in my personal fork of openjdk/jdk25u. To create a pull request with this backport targeting openjdk/jdk25u:master, just click the following link:

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Hi all,

This pull request contains a backport of commit d350158e from the openjdk/jdk repository.

The commit being backported was authored by Viktor Klang on 27 Nov 2025 and was reviewed by Alan Bateman.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk25u:

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$ git checkout backport-viktorklang-ora-d350158e-master
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk25u.git backport-viktorklang-ora-d350158e-master

8371740 - removes the risk of missed polls in LinkedTransferQueue

2b32c4f

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viktorklang-ora commented Nov 24, 2025

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73c646a

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-            var phaser = new Phaser(4);
+            var phaser = new Phaser(4) {
+                @Override
+                protected boolean onAdvance(int phase, int registeredParties) {
+                    q.clear();
+                    return super.onAdvance(phase, registeredParties);
+                }
+            };

8371740 : LinkedTransferQueue.poll() returns null even though queue is not empty #28479

8371740 : LinkedTransferQueue.poll() returns null even though queue is not empty #28479

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