8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool

[dchuyko]

This a backport of JDK-8351933 [0] (PR [1]) for 17u. At one of code paths the TC subfield of ctl field is decremented and the result is not masked correctly. As a result, the FJP may stop executing tasks [2]. The target code is in awaitWork() instead of tryTrim() and the surrounding code is different from the current master, as well as the original mask name. The core change is the same, candidate for compareAndSetCtl() is constructed using '(c & RC_MASK) | ((c - TC_UNIT) & TC_MASK)' instead of '(UC_MASK & (c - TC_UNIT))' to correctly preserve the RC subfield.

[0] https://bugs.openjdk.org/browse/JDK-8351933
[1] openjdk/jdk#24034
[2] https://bugs.openjdk.org/browse/JDK-8330017

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Progress

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• JDK-8351933 needs maintainer approval

Issue

• JDK-8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool (Bug - P4 - Requested)

Reviewers

• Paul Hohensee (@phohensee - Reviewer)
• Doug Lea (@DougLea - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with the original issue, but not the original commit. If you have the original commit hash, please update the pull request title with Backport <hash>.

[mlbridge]

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[openjdk]

⚠️ @dchuyko This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[dchuyko]

/approval request This a tiny bugfix in ForkJoinPool. At one of code paths the TC subfield of ctl field is decremented and the result is not masked correctly, so the RC subfield is not preserved. That sometimes leads to a stopped pool in 17 and 11 [0].

Testing: full jtreg tier1-3 and JCK for multiple supported platforms in the internal Liberica CI.

[0] https://bugs.openjdk.org/browse/JDK-8330017

[openjdk]

@dchuyko
8351933: The approval request has been created successfully.

[DougLea]

Yes, this corrects in the same way as in other releases

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[dchuyko]

/keepalive

[openjdk]

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