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

[Dmitry Chuyko]

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

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Commit messages:
 - RC_MASK and TC_MASK instead of UC_MASK

Changes: https://git.openjdk.org/jdk17u-dev/pull/3354/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3354&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351933
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3354.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3354/head:pull/3354

PR: https://git.openjdk.org/jdk17u-dev/pull/3354