On Wed, 26 Aug 2026 11:46:42 GMT, Axel Boldt-Christmas <[email protected]> wrote:
> Historically we have had displaced markWord's because locking (stack locks, > and inflated monitors). > > After the `UseObjectMonitorTable` removal there are no more need to protect > against displaced markWords. > > I suggest we simplify this logic and clean up the interface w.r.t. > `identity_hash`. > > Changes the `fast_no_hash_check` and `has_no_hash` into `has_identity_hash` > and `has_hash` checks. > As before it is invalid to read the hash on marked objects, added asserts to > ensure this. > Rewrote `oopDesc::slow_identity_hash` to not regenerate a new hash every time > it transiently fails to install the hash in the markWord due to some other > header change. > > There are a few places which right now calls `identity_hash` from develop > logging / introspection printing `InstanceStackChunkKlass::print_chunk` and > `Continuation::print`. It is a bit unfortunate that we have these > side-effects in debug VMs. But think we should handle these in a future RFE. > > Testing (in progress): > * Tier 1-3 Oracle supported platforms > * GHA > > --------- > - [x] I confirm that I make this contribution in accordance with the [OpenJDK > Interim AI Policy](https://openjdk.org/legal/ai). I won't dare to approve not my code, but I have a suggestion about a comment. src/hotspot/share/oops/markWord.hpp line 77: > 75: // > 76: // Inline types cannot be locked and have a deterministic identity > hash based > 77: // on the immutable payload, which may be cached in the markWord. [....]based on the immutable payload, and the identity hash of their `Class`. But I don't know if it's worth mentioning here (I surely have a bias...). ------------- PR Review: https://git.openjdk.org/jdk/pull/32535#pullrequestreview-5031821260 PR Review Comment: https://git.openjdk.org/jdk/pull/32535#discussion_r3863907425
