8274349: ForkJoinPool.commonPool() does not work with 1 CPU

[dholmes-ora]

A regression introduced in Java 17 will give the default FJ pool a parallelism of zero in a uniprocessor environment. The fix restores this to a value of 1. See bug report for details.

Testing:

• new regression test
• tiers 1-3

Thanks,
David

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8274349: ForkJoinPool.commonPool() does not work with 1 CPU

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 666f36f
• Martin Buchholz (@Martin-Buchholz - Reviewer) ⚠️ Review applies to 666f36f

Contributors

• Doug Lea <dl@openjdk.org>

Reviewing

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[dholmes-ora]

/contributor dl@cs.oswego.edu

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[dholmes-ora]

/contributor add @DougLea

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

[mlbridge]

Webrevs

• 02: Full - Incremental (1344903a)
• 01: Full - Incremental (666f36f4)
• 00: Full (7199b2b6)

[shipilev]

Oh wow. Looks good!

[openjdk]

@dholmes-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:

8274349: ForkJoinPool.commonPool() does not work with 1 CPU

Co-authored-by: Doug Lea <dl@openjdk.org>
Reviewed-by: shade, martin

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 26 new commits pushed to the master branch:

• 7e757f6: 8274559: JFR: Typo in 'jfr help configure' text
• 75d6688: 8274745: ProblemList TestSnippetTag.java
• 9914e5c: 8274610: Add linux-aarch64 to bootcycle build profiles
• 0ca094b: 8273244: Improve diagnostic output related to ErroneousTree
• 6f727d8: 8274666: rename HtmlStyle.descfrmTypeLabel to be less cryptic
• 139a833: 8268869: java in source-file mode suggests javac-only Xlint flags
• f63c4a8: 8274471: Verification of OCSP Response signed with RSASSA-PSS fails
• f2404d6: 8274658: ISO 4217 Amendment 170 Update
• 7eb0372: 8274606: Fix jaxp/javax/xml/jaxp/unittest/transform/SurrogateTest.java test
• 47bfc8a: 8274563: jfr/event/oldobject/TestClassLoaderLeak.java fails when GC cycles are not happening
• ... and 16 more: https://git.openjdk.java.net/jdk/compare/a8edd1b360d4e5f35aff371a91fda42eeb00d395...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.

[Martin-Buchholz]

I always try to avoid Thread.sleep or polling in tests, so I would write the test like this:

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ForkJoinPool;

public class ForkJoinUniProcessor {
public static void main(String[] args) throws InterruptedException {
// If the default parallelism were zero then this task would not
// complete and the test will timeout.
CountDownLatch ran = new CountDownLatch(1);
ForkJoinPool.commonPool().submit(() -> ran.countDown());
ran.await();
}
}

[dholmes-ora]

Thanks for the reviews @shipilev and @Martin-Buchholz !

Test updated per Martin's suggestion.

/integrate

[openjdk]

Going to push as commit 2e542e3.
Since your change was applied there have been 26 commits pushed to the master branch:

• 7e757f6: 8274559: JFR: Typo in 'jfr help configure' text
• 75d6688: 8274745: ProblemList TestSnippetTag.java
• 9914e5c: 8274610: Add linux-aarch64 to bootcycle build profiles
• 0ca094b: 8273244: Improve diagnostic output related to ErroneousTree
• 6f727d8: 8274666: rename HtmlStyle.descfrmTypeLabel to be less cryptic
• 139a833: 8268869: java in source-file mode suggests javac-only Xlint flags
• f63c4a8: 8274471: Verification of OCSP Response signed with RSASSA-PSS fails
• f2404d6: 8274658: ISO 4217 Amendment 170 Update
• 7eb0372: 8274606: Fix jaxp/javax/xml/jaxp/unittest/transform/SurrogateTest.java test
• 47bfc8a: 8274563: jfr/event/oldobject/TestClassLoaderLeak.java fails when GC cycles are not happening
• ... and 16 more: https://git.openjdk.java.net/jdk/compare/a8edd1b360d4e5f35aff371a91fda42eeb00d395...master

Your commit was automatically rebased without conflicts.

[openjdk]

@dholmes-ora Pushed as commit 2e542e3.

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