RFR: 8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool

[Dmitry Chuyko]

On Mon, 17 Mar 2025 14:43:05 GMT, Chen Liang <liach at openjdk.org> wrote:

> It seems this is an overflow for the TC part of the flag. The RC part seems to be able to overflow too, but because it occupies the higher bits its overflow will never affect the TC. And this is the only site where TC is masked with `UMASK` after overflow-capable addition.

Yes, from this point RC (in)accurate masking can be considered cosmetic, but this might be the source of this bug with TC.

> Should we reexamine all uses of `UMASK` to mask only RC/TC explicitly?

'(v.stackPred & SP_MASK) | (UC_MASK & c)' patterns seem ok to me, but for all subfield arithmetic it would be more clear to see all subfields recombined.

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PR Comment: https://git.openjdk.org/jdk/pull/24034#issuecomment-2729913449