8373941: Epsilon: Robust counter updates in early VM phases

[shipilev]

See more details in the bug. This PR makes the counters updated on allocation path more robust. New regression test captures the original failure (intermittently). This would be also backported to JDK 26.

Additional testing:

• Linux x86_64 server fastdebug, gc/epsilon, 100x
• Linux x86_64 server fastdebug, runtime/cds/appcds/TestEpsilonGCWithCDS.java, 100x
• Linux x86_64 server fastdebug, gc/epsilon/TestInitAllocs.java, 1000x

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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

Issue

• JDK-8373941: Epsilon: Robust counter updates in early VM phases (Bug - P3)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Thomas Schatzl (@tschatzl - Reviewer)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/29061/head:pull/29061
$ git checkout pull/29061

Update a local copy of the PR:
$ git checkout pull/29061
$ git pull https://git.openjdk.org/jdk.git pull/29061/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 29061

View PR using the GUI difftool:
$ git pr show -t 29061

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/29061.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

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[openjdk]

@shipilev 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:

8373941: Epsilon: Robust counter updates in early VM phases

Reviewed-by: stefank, tschatzl

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At the time when this comment was updated there had been 24 new commits pushed to the master branch:

• c8c6e70: 8374825: vmTestbase comment typo: lunch
• 2a965df: 8374377: PNGImageDecoder Slow For 8-bit PNGs
• a855224: 8373695: G1: Using a value near integer max for ActiveProcessorCount causes fatal crash
• ... and 21 more: https://git.openjdk.org/jdk/compare/067fd3cb2fa6a4a0484a922df8efbde03325ad3d...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]

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[mlbridge]

Webrevs

• 01: Full - Incremental (1c347b7d)
• 00: Full (9a450be5)

[shipilev]

@stefank -- is that what you had in mind as one of the solutions?

[stefank]

Looks good to me.

Kim would probably prefer if you changed the volatile bool _ready to use the new Atomic<bool> class.

[shipilev]

Kim would probably prefer if you changed the volatile bool _ready to use the new Atomic<bool> class.

Right. There are other cases in Epsilon that would enjoy this conversion. Tell you what, let's do this version (so that is also easily backportable), and then I'll do a cleanup that converts all Epsilon code to Atomic<T>: https://bugs.openjdk.org/browse/JDK-8374876

[shipilev]

Thanks for reviews, @stefank, @tschatzl! Here goes.

/integrate

[openjdk]

Going to push as commit 47e1935.
Since your change was applied there have been 24 commits pushed to the master branch:

• c8c6e70: 8374825: vmTestbase comment typo: lunch
• 2a965df: 8374377: PNGImageDecoder Slow For 8-bit PNGs
• a855224: 8373695: G1: Using a value near integer max for ActiveProcessorCount causes fatal crash
• ... and 21 more: https://git.openjdk.org/jdk/compare/067fd3cb2fa6a4a0484a922df8efbde03325ad3d...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit 47e1935.

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