[jdk21u-dev] RFR: 8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool

Thu Apr 3 15:03:09 UTC 2025

On Thu, 13 Mar 2025 14:31:42 GMT, Dmitry Chuyko <dchuyko at openjdk.org> wrote:

> This a backport of JDK-8351933 [0] (PR [1]) for 21u. At one of code paths the TC subfield of ctl field is decremented and the result is not masked correctly. The target code is also in tryTrim() but the surrounding 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

Please get a second review for this. Maybe @DougLea can help?

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/1485#issuecomment-2776085087