> 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.
Ioi Lam has updated the pull request incrementally with three additional commits since the last revision: - Refactored code - Fixed error when running "make test JTREG=AOT_JDK=true TEST=open/test/hotspot/jtreg/runtime/invokedynamic" - Work around hotspot/jtreg/sources/TestNoNULL.java ------------- Changes: - all: https://git.openjdk.org/jdk/pull/24757/files - new: https://git.openjdk.org/jdk/pull/24757/files/6678482b..2c31ca7c Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=24757&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24757&range=00-01 Stats: 56 lines in 4 files changed: 35 ins; 12 del; 9 mod Patch: https://git.openjdk.org/jdk/pull/24757.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24757/head:pull/24757 PR: https://git.openjdk.org/jdk/pull/24757
