8350457: Implement JEP 519: Compact Object Headers

[rkennke]

As title says.

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change requires CSR request JDK-8354070 to be approved
• Change requires a JEP request to be targeted

Issues

• JDK-8350457: Implement JEP 519: Compact Object Headers (Enhancement - P3)
• JDK-8354672: JEP 519: Compact Object Headers (JEP)
• JDK-8354070: Support Compact Object Headers as product option (CSR)

Reviewers

• Zhengyu Gu (@zhengyu123 - Reviewer) Review applies to 31035040
• Martin Doerr (@TheRealMDoerr - Reviewer)
• Coleen Phillimore (@coleenp - Reviewer)

Reviewing

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Update a local copy of the PR:
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[bridgekeeper]

👋 Welcome back rkennke! 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]

@rkennke 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:

8350457: Implement JEP 519: Compact Object Headers

Reviewed-by: mdoerr, coleenp, zgu

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 8 new commits pushed to the master branch:

• 275cfd3: 8357280: (bf) Remove @requires tags from java/nio/Buffer/LimitDirectMemory[NegativeTest].java
• 254713a: 8338833: Error on reference not found for a snippet target
• 21c1282: 8333664: Decouple command line parsing and package building in jpackage
• ... and 5 more: https://git.openjdk.org/jdk/compare/2c126f1954435a5b4d6cdc367b7b5e8c91cfae63...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]

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

• hotspot-runtime

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[mlbridge]

Webrevs

• 03: Full - Incremental (0e3835a7)
• 02: Full - Incremental (ad389db3)
• 01: Full - Incremental (56a50df8)
• 00: Full (31035040)

[zhengyu123]

LGTM

[dholmes-ora]

Are there no tests that need -XX:+UnlockExperimentalVMOptions to be removed?

[liach]

I just noticed we missed this flag for https://docs.oracle.com/en/java/javase/24/docs/specs/man/java.html#advanced-runtime-options-for-java - if we add this option to java.md, should we do it in this patch or a separate patch?

[dholmes-ora]

I just noticed we missed this flag for https://docs.oracle.com/en/java/javase/24/docs/specs/man/java.html#advanced-runtime-options-for-java - if we add this option to java.md, should we do it in this patch or a separate patch?

It wasn't missed - we don't (generally - I'm not going to say never) document experimental flags in the command reference. Once it is a product flag then it probably should be documented.

[TheRealMDoerr]

LGTM. A bit unfortunate that we need so many CDS archives. Maybe some people are interested in e.g. using CDS only with COH. Just an idea for future enhancements (configure options).

[rkennke]

LGTM. A bit unfortunate that we need so many CDS archives. Maybe some people are interested in e.g. using CDS only with COH. Just an idea for future enhancements (configure options).

The plan is to get rid of options and combinations. The only option that will most likely remain is +/-UseCompressedOops.

[coleenp]

This looks good pending JEP targeting.

[rkennke]

/jep JEP-519

[openjdk]

@rkennke
This pull request will not be integrated until the JEP-519 has been targeted.

[rkennke]

JEP has been targeted, I think it is ready to go.

Thank you all!

/integrate

[openjdk]

Going to push as commit 1e57648.
Since your change was applied there have been 31 commits pushed to the master branch:

• 26053fe: 8357406: Remove usages of jdk.tracePinnedThreads system property from httpclient tests
• c0665ef: 8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler
• 85b24c3: 8350869: os::stat doesn't follow symlinks on Windows
• ... and 28 more: https://git.openjdk.org/jdk/compare/2c126f1954435a5b4d6cdc367b7b5e8c91cfae63...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rkennke Pushed as commit 1e57648.

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