On Wed, 4 Feb 2026 10:03:55 GMT, Paul Hübner <[email protected]> wrote:
> Hi all, > > The main ideas of this patch are to highlight and enforce the invariant we > enforce when it comes to value objects' identity hash code. > > The original JBS issues addresses the following points, which have been > addressed to various extents: > > 1. Adding assertions to the CAS-setting of the hash in the markWord. This is > vital to enforce the invariant and was added. > 2. Breaking the loop if the CAS results in a conflict. Putting the identity > hash in the markWord is an optimization, so one could break out of the loop > whenever. With the assertion, there's a good confidence that CAS will > eventually succeed, namely once other threads stop poking at the markWord > bits. **If there is demand, I can add a fixed upper bound.** > 3. SSA-ing the hash variable. Done. > 4. Possibly introducing a markWord::has_hash to improve legibility. I did not > do this as it would yield multiple `obj->mark()` calls in the fast path and > the current form is (in my opinion) sufficiently legible. > > Testing: tiers 1-3 on Linux (x64, AArch64), macOS (x64, AArch64), Windows > (x64). I think this looks good. From offline discussions I think I saw that the calculation of the identity hashcode could give a result of `0`, which means that`has_no_hash()` will return `true`. I wonder if it would be helpful to add a comment about that and why that is OK? ------------- Marked as reviewed by stefank (Committer). PR Review: https://git.openjdk.org/valhalla/pull/2029#pullrequestreview-3784694838
