8354078: Implement JEP 521: Generational Shenandoah

[earthling-amzn]

Testing:

% ./build/linux-x86_64-server-fastdebug/jdk/bin/java -XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational --version
openjdk 25 2025-09-16
OpenJDK Runtime Environment (fastdebug build 25-make-genshen-non-experimental)
OpenJDK 64-Bit Server VM (fastdebug build 25-make-genshen-non-experimental, mixed mode)

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Change requires CSR request JDK-8354079 to be approved
• Commit message must refer to an issue
• Change requires a JEP request to be targeted

Issues

• JDK-8354078: Implement JEP 521: Generational Shenandoah (Enhancement - P4)
• JDK-8356990: JEP 521: Generational Shenandoah (JEP)
• JDK-8354079: JEP 521: Shenandoah: Make the generational mode be non-experimental (CSR)

Reviewers

• Y. Srinivas Ramakrishna (@ysramakrishna - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/25270/head:pull/25270
$ git checkout pull/25270

Update a local copy of the PR:
$ git checkout pull/25270
$ git pull https://git.openjdk.org/jdk.git pull/25270/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 25270

View PR using the GUI difftool:
$ git pr show -t 25270

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/25270.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back wkemper! 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]

@earthling-amzn 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:

8354078: Implement JEP 521: Generational Shenandoah

Reviewed-by: ysr

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 162 new commits pushed to the master branch:

• c1f066e: 8356888: (fs) FileSystems.newFileSystem that take an env must specify IllegalArgumentException
• c295377: 8357800: Initialize JvmtiThreadState bool fields with bool literals
• cdff7b9: 8357801: Parallel: Remove deprecated PSVirtualSpace methods
• ... and 159 more: https://git.openjdk.org/jdk/compare/d5245092249ed400f98711393e25e0ae97990daf...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]

@earthling-amzn The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

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

[mlbridge]

Webrevs

• 01: Full - Incremental (198fb3ba)
• 00: Full (719126e6)

[ysramakrishna]

Break out the production bubbly! 🍾

Reviewed!

[ysramakrishna]

Just noticed that gc/shenandoah/options/TestModeUnlock.java needs to be taught that "generational" is no longer experimental. It's failing in the GHA tests.

[rkennke]

Many tests specify -XX:+UseExperimentalVMOptions to be able to use generational mode. Those -XX:+UseExperimentalVMOptions should be removed.

[ysramakrishna]

Looks good, thanks!

[rkennke]

/jep JEP-521

[openjdk]

@rkennke
This pull request will not be integrated until the JEP-521 has been targeted.

[earthling-amzn]

/integrate

[openjdk]

Going to push as commit 2e8b195.
Since your change was applied there have been 166 commits pushed to the master branch:

• 11ad173: 8354944: Remove unnecessary PartiallyOrderedSet.nodes
• 4755276: 8357912: (fs) Remove @SInCE tag from java.nio.file.FileSystems.newFileSystem(Path,ClassLoader)
• da228e0: 8357145: CRC/Inflater/Deflater/Adler32 methods that take a ByteBuffer throw UOE if backed by shared memory segment
• ... and 163 more: https://git.openjdk.org/jdk/compare/d5245092249ed400f98711393e25e0ae97990daf...master

Your commit was automatically rebased without conflicts.

[openjdk]

@earthling-amzn Pushed as commit 2e8b195.

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