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

[Paul Hohensee]

On Thu, 13 Mar 2025 14:50:23 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

Marked as reviewed by phh (Reviewer).

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PR Review: https://git.openjdk.org/jdk17u-dev/pull/3354#pullrequestreview-2682731537