On Fri, 18 Apr 2025 18:31:05 GMT, Ioi Lam <ik...@openjdk.org> wrote: > This PR contains 2 parts > > - Upstream of Soft/Weak Reference support authored by @macarte from [the > Leyden > repo](https://github.com/openjdk/leyden/commit/4ca75d156519596e23abc8a312496b7c2f0e0ca5) > - New C++ class `AOTReferenceObjSupport` and new Java method > `ReferencedKeyMap::prepareForAOTCache()` developed by @iklam on the advice of > @fisk from the GC team. These control the lifecycles of reference objects > during the assembly phase to simplify the implementation. > > One problem we faced in this PR is the handling of Reference objects that are > waiting for clean up. Currently, the only cached Reference objects that > require clean up are the `WeakReferenceKey`s used by `ReferencedKeyMap` > (which is used by `MethodType::internTable`): > > - When the referent of a `WeakReferenceKey` K has been collected, the key > will be placed on `Universe::reference_pending_list()`. It's linked to other > pending references with the `Reference::discovered` field. At this point, K > is still stored in the `ReferencedKeyMap`. > - When heapShared.cpp discovered the `ReferencedKeyMap`, it will discover K, > and it may also discover other pending references that are not intended for > the AOT cache. As a result, we end up caching unnecessary objects. > > `ReferencedKeyMap::prepareForAOTCache()` avoids the above problem. It goes > over all entries in the table: > > - If an entry has not yet been collected, we make sure it will never be > collected. > - If an entry has been collected, we remove it from the table > > Therefore, by the time heapShared.cpp starts scanning the `ReferencedKeyMap`, > it will never see any keys that are on the pending list, so we will not see > unintended objects. > > This implementation is the very first step of Reference support in the AOT > cache, so we chose a simplified approach that makes no assumptions on when > the pending reference list is processed. This is sufficient for the current > set of references objects in the AOT cache. > > In the future, we may relax the implementation to allow for other use cases.
This pull request has now been integrated. Changeset: 1ff7e813 Author: Mat Carter <maca...@openjdk.org> Committer: Ioi Lam <ik...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/1ff7e813e39d16376baccdbd9e7075035248319d Stats: 981 lines in 23 files changed: 804 ins; 107 del; 70 mod 8354897: Support Soft/Weak Reference in AOT cache Co-authored-by: Ioi Lam <ik...@openjdk.org> Reviewed-by: liach, eosterlund ------------- PR: https://git.openjdk.org/jdk/pull/24757
