[jdk17u-dev] RFR: 8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool [v3]

[duke]

On Tue, 24 Jun 2025 11:12:25 GMT, Dmitry Chuyko <dchuyko at openjdk.org> wrote:

>> 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] https://github.com/openjdk/jdk/pull/24034
>> [2] https://bugs.openjdk.org/browse/JDK-8330017
>
> Dmitry Chuyko has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into JDK-8351935
>  - Merge branch 'openjdk:master' into JDK-8351935
>  - RC_MASK and TC_MASK instead of UC_MASK

@dchuyko 
Your change (at version 09d4316d6b074f1ab70acea5de1757e22148f0e4) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/3354#issuecomment-3012636079