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8364111: InstanceMirrorKlass iterators should handle CDS and hidden classes consistently

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Reviewed-by: stuefe, ayang, coleenp
This commit is contained in:
Aleksey Shipilev 2025-07-31 06:07:17 +00:00
parent 05c63e8009
commit ebb7f5d39b
2 changed files with 34 additions and 32 deletions
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3
src/hotspot/share/oops/instanceMirrorKlass.hpp
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@ -52,6 +52,9 @@ class InstanceMirrorKlass: public InstanceKlass {
InstanceMirrorKlass(const ClassFileParser& parser) : InstanceKlass(parser, Kind) {}
template <class OopClosureType>
inline void do_metadata(oop obj, OopClosureType* closure);
public:
InstanceMirrorKlass();

63
src/hotspot/share/oops/instanceMirrorKlass.inline.hpp
View File

@ -46,38 +46,41 @@ void InstanceMirrorKlass::oop_oop_iterate_statics(oop obj, OopClosureType* closu
}
}
template <class OopClosureType>
void InstanceMirrorKlass::do_metadata(oop obj, OopClosureType* closure) {
Klass* klass = java_lang_Class::as_Klass(obj);
if (klass != nullptr) {
if (klass->class_loader_data() == nullptr) {
// This is a mirror that belongs to a shared class that has not been loaded yet.
assert(klass->is_shared(), "Must be");
} else if (klass->is_instance_klass() && klass->class_loader_data()->has_class_mirror_holder()) {
// A non-strong hidden class doesn't have its own class loader,
// so when handling the java mirror for the class we need to make sure its class
// loader data is claimed, this is done by calling do_cld explicitly.
// For non-strong hidden classes the call to do_cld is made when the class
// loader itself is handled.
Devirtualizer::do_cld(closure, klass->class_loader_data());
} else {
Devirtualizer::do_klass(closure, klass);
}
} else {
// Java mirror -> Klass* "nullptr" backlink means either:
// 1. This is a Java mirror for a primitive class. We do not need to follow it,
// these mirrors are always strong roots.
// 2. This is a Java mirror for a newly allocated non-primitive class, and we
// somehow managed to reach the newly allocated Java mirror with not yet
// installed backlink. We cannot do anything here, this case would be handled
// separately by GC, e.g. by keeping the relevant metadata alive during the GC.
// Unfortunately, the existence of corner case (2) prevents us from asserting (1).
}
}
template <typename T, class OopClosureType>
void InstanceMirrorKlass::oop_oop_iterate(oop obj, OopClosureType* closure) {
InstanceKlass::oop_oop_iterate<T>(obj, closure);
if (Devirtualizer::do_metadata(closure)) {
Klass* klass = java_lang_Class::as_Klass(obj);
// We'll get null for primitive mirrors.
if (klass != nullptr) {
if (klass->class_loader_data() == nullptr) {
// This is a mirror that belongs to a shared class that has not be loaded yet.
assert(klass->is_shared(), "must be");
} else if (klass->is_instance_klass() && klass->class_loader_data()->has_class_mirror_holder()) {
// A non-strong hidden class doesn't have its own class loader,
// so when handling the java mirror for the class we need to make sure its class
// loader data is claimed, this is done by calling do_cld explicitly.
// For non-strong hidden classes the call to do_cld is made when the class
// loader itself is handled.
Devirtualizer::do_cld(closure, klass->class_loader_data());
} else {
Devirtualizer::do_klass(closure, klass);
}
} else {
// We would like to assert here (as below) that if klass has been null, then
// this has been a mirror for a primitive type that we do not need to follow
// as they are always strong roots.
// However, we might get across a klass that just changed during CMS concurrent
// marking if allocation occurred in the old generation.
// This is benign here, as we keep alive all CLDs that were loaded during the
// CMS concurrent phase in the class loading, i.e. they will be iterated over
// and kept alive during remark.
// assert(java_lang_Class::is_primitive(obj), "Sanity check");
}
do_metadata<OopClosureType>(obj, closure);
}
oop_oop_iterate_statics<T>(obj, closure);
@ -121,11 +124,7 @@ void InstanceMirrorKlass::oop_oop_iterate_bounded(oop obj, OopClosureType* closu
if (Devirtualizer::do_metadata(closure)) {
if (mr.contains(obj)) {
Klass* klass = java_lang_Class::as_Klass(obj);
// We'll get null for primitive mirrors.
if (klass != nullptr) {
Devirtualizer::do_klass(closure, klass);
}
do_metadata<OopClosureType>(obj, closure);
}
}