8314329: AgeTable: add is_clear() & allocation spec, and relax assert to allow use of 0-index slot

[ysramakrishna]

/issue JDK-8314329

I'd like to propose the following changes to the AgeTable (motivated by the uses in generational shenandoah):

/summary

1. add an allocation spec so the AgeTable can be allocated on the C-heap, and tracked
2. add an is_clear() method that checks whether the age table has only zero entries
3. relax the assertion that the 0th index of the age table is never used, so specific collectors may make use of the slot

Testing:

• the code has been active in the generational shenandoah repository for several months
• tested in the jdk repository with hotspot_gc tests
• code pipeline stress tests
• github actions (tier1) testing

---

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

Issue

• JDK-8314329: AgeTable: add is_clear() & allocation spec, and relax assert to allow use of 0-index slot (Task - P5)

Reviewers

• William Kemper (@earthling-amzn - Author) ⚠️ Review applies to ede84ca2
• Kelvin Nilsen (@kdnilsen - no project role) ⚠️ Review applies to ede84ca2
• Albert Mingkun Yang (@albertnetymk - Reviewer) ⚠️ Review applies to 3572babf
• Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 3572babf

Reviewing

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$ git checkout pull/17470

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/17470/head

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$ git pr checkout 17470

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Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back ysr! 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]

@ysramakrishna This issue is referenced in the PR title - it will now be updated.

[openjdk]

@ysramakrishna Setting summary to:

1. add an allocation spec so the AgeTable can be allocated on the C-heap, and tracked
2. add an `is_clear()` method that verifies that the age table has no non-zero entries
3. relax the assertion that the 0th index of the age table is never used, so specific collectors may make use of the slot

Testing:
- [x] the code has been active in the generational shenandoah repository for several months
- [x] tested in the jdk repository with hotspot_gc tests
- [ ] code pipeline stress tests
- [ ] github actions testing

[openjdk]

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

• hotspot-gc

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]

Webrevs

• 03: Full - Incremental (676e8950)
• 02: Full - Incremental (3572babf)
• 01: Full - Incremental (ede84ca2)
• 00: Full (d4b650a9)

[earthling-amzn]

Consider a minor optimization for is_clear test.

[kdnilsen]

LGTM

[ysramakrishna]

Thanks @earthling-amzn & @kdnilsen!

Could I please also have one of the G1 folk look over this and approve as a formal Reviewer, so I can push the change; may be @tschatzl or @stefank or @albertnetymk et al. Thanks!

[albertnetymk]

Thanks for the revision. I guess the new API can be const.

[openjdk]

@ysramakrishna 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:

8314329: AgeTable: add is_clear() & allocation spec, and relax assert to allow use of 0-index slot

AgeTable changes:
1. add CHeap allocation spec
2. add a non-product const is_clear() method to check if the age table has only zero entries
3. relax the assertion that the 0th index of the age table is never used, to allow use of that slot

Reviewed-by: wkemper, kdnilsen, ayang, shade

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 43 new commits pushed to the master branch:

• c9cacfb: 8323657: Compilation of snippet results in VerifyError at runtime with --release 9 (and above)
• bde650f: 8322282: Incorrect LoaderConstraintTable::add_entry after JDK-8298468
• be943a9: 8321984: IGV: Upgrade to Netbeans Platform 20
• d3b2ac1: 8314186: runtime/8176717/TestInheritFD.java failed with "Log file was leaked"
• 72f1990: 8323057: Recoverable errors may be reported before unrecoverable errors when annotation processing is skipped
• c84af49: 8324129: C2: Remove some ttyLocker usages in preparation for JDK-8306767
• fd37262: 8323748: RISC-V: Add Zfh probe code
• 76afa02: 8322572: AllocationMergesTests.java fails with "IRViolationException: There were one or multiple IR rule failures."
• 2003610: 8323108: BufferedImage.setData(Raster) should not cast float and double values to integers
• a474b37: 8324240: Remove unused GrowableArrayView::EMPTY
• ... and 33 more: https://git.openjdk.org/jdk/compare/de237fb058c74b87ea65a6020939264a5dfe3796...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.

[ysramakrishna]

/summary

AgeTable changes:

1. add CHeap allocation spec
2. add a non-product const is_clear() method to check if the age table has only zero entries
3. relax the assertion that the 0th index of the age table is never used, to allow use of that slot

[openjdk]

@ysramakrishna Updating existing summary to:

AgeTable changes:
1. add CHeap allocation spec
2. add a non-product const is_clear() method to check if the age table has only zero entries
3. relax the assertion that the 0th index of the age table is never used, to allow use of that slot

[ysramakrishna]

Thanks for your reviews!

/integrate

[openjdk]

Going to push as commit df370d7.
Since your change was applied there have been 44 commits pushed to the master branch:

• 0d8543d: 8324065: Daylight saving information for Africa/Casablanca are incorrect
• c9cacfb: 8323657: Compilation of snippet results in VerifyError at runtime with --release 9 (and above)
• bde650f: 8322282: Incorrect LoaderConstraintTable::add_entry after JDK-8298468
• be943a9: 8321984: IGV: Upgrade to Netbeans Platform 20
• d3b2ac1: 8314186: runtime/8176717/TestInheritFD.java failed with "Log file was leaked"
• 72f1990: 8323057: Recoverable errors may be reported before unrecoverable errors when annotation processing is skipped
• c84af49: 8324129: C2: Remove some ttyLocker usages in preparation for JDK-8306767
• fd37262: 8323748: RISC-V: Add Zfh probe code
• 76afa02: 8322572: AllocationMergesTests.java fails with "IRViolationException: There were one or multiple IR rule failures."
• 2003610: 8323108: BufferedImage.setData(Raster) should not cast float and double values to integers
• ... and 34 more: https://git.openjdk.org/jdk/compare/de237fb058c74b87ea65a6020939264a5dfe3796...master

Your commit was automatically rebased without conflicts.

[openjdk]

@ysramakrishna Pushed as commit df370d7.

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