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8321619: Generational ZGC: ZColorStoreGoodOopClosure is only valid fo…
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…r young objects

Reviewed-by: stefank, sjohanss
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fisk committed Dec 19, 2023
1 parent ac968c3 commit be49dab
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Showing 3 changed files with 30 additions and 5 deletions.
13 changes: 13 additions & 0 deletions src/hotspot/share/gc/z/zBarrierSet.cpp
Expand Up @@ -152,6 +152,19 @@ void ZBarrierSet::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) {

void ZBarrierSet::clone_obj_array(objArrayOop src_obj, objArrayOop dst_obj, size_t size) {
volatile zpointer* src = (volatile zpointer*)src_obj->base();
volatile zpointer* dst = (volatile zpointer*)dst_obj->base();

for (const zpointer* const end = cast_from_oop<const zpointer*>(src_obj) + size; src < end; src++, dst++) {
zaddress elem = ZBarrier::load_barrier_on_oop_field(src);
// We avoid healing here because the store below colors the pointer store good,
// hence avoiding the cost of a CAS.
ZBarrier::store_barrier_on_heap_oop_field(dst, false /* heal */);
Atomic::store(dst, ZAddress::store_good(elem));

void ZBarrierSet::print_on(outputStream* st) const {
2 changes: 2 additions & 0 deletions src/hotspot/share/gc/z/zBarrierSet.hpp
Expand Up @@ -39,6 +39,8 @@ class ZBarrierSet : public BarrierSet {
static ZBarrierSetAssembler* assembler();
static bool barrier_needed(DecoratorSet decorators, BasicType type);

static void clone_obj_array(objArrayOop src, objArrayOop dst, size_t size);

virtual void on_thread_create(Thread* thread);
virtual void on_thread_destroy(Thread* thread);
virtual void on_thread_attach(Thread* thread);
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20 changes: 15 additions & 5 deletions src/hotspot/share/gc/z/zBarrierSet.inline.hpp
Expand Up @@ -403,14 +403,13 @@ inline bool ZBarrierSet::AccessBarrier<decorators, BarrierSetT>::oop_arraycopy_i
return oop_arraycopy_in_heap_no_check_cast(dst, src, length);

class ZStoreBarrierOopClosure : public BasicOopIterateClosure {
class ZColorStoreGoodOopClosure : public BasicOopIterateClosure {
virtual void do_oop(oop* p_) {
volatile zpointer* const p = (volatile zpointer*)p_;
const zpointer ptr = ZBarrier::load_atomic(p);
const zaddress addr = ZPointer::uncolor(ptr);
ZBarrier::store_barrier_on_heap_oop_field(p, false /* heal */);
*p = ZAddress::store_good(addr);
Atomic::store(p, ZAddress::store_good(addr));

virtual void do_oop(narrowOop* p) {
Expand All @@ -433,17 +432,28 @@ template <DecoratorSet decorators, typename BarrierSetT>
inline void ZBarrierSet::AccessBarrier<decorators, BarrierSetT>::clone_in_heap(oop src, oop dst, size_t size) {

if (dst->is_objArray()) {
// Cloning an object array is similar to performing array copy.
// If an array is large enough to have its allocation segmented,
// this operation might require GC barriers. However, the intrinsics
// for cloning arrays transform the clone to an optimized allocation
// and arraycopy sequence, so the performance of this runtime call
// does not matter for object arrays.
clone_obj_array(objArrayOop(src), objArrayOop(dst), size);

// Fix the oops
ZLoadBarrierOopClosure cl;
ZIterator::oop_iterate(src, &cl);

// Clone the object
Raw::clone_in_heap(src, dst, size);

assert(ZHeap::heap()->is_young(to_zaddress(dst)), "ZColorStoreGoodOopClosure is only valid for young objects");
assert(dst->is_typeArray() || ZHeap::heap()->is_young(to_zaddress(dst)), "ZColorStoreGoodOopClosure is only valid for young objects");

// Color store good before handing out
ZStoreBarrierOopClosure cl_sg;
ZColorStoreGoodOopClosure cl_sg;
ZIterator::oop_iterate(dst, &cl_sg);

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