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8205163: ZGC: Keeps finalizable marked PhantomReference referents strongly alive

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Reviewed-by: pliden, kbarrett
This commit is contained in:
Stefan Karlsson 2018-06-19 08:44:31 +02:00
parent 3905df21f5
commit 14373f7ff8
4 changed files with 23 additions and 14 deletions
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1
src/hotspot/share/gc/z/zBarrier.hpp
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@ -83,6 +83,7 @@ public:
static oop load_barrier_on_phantom_oop_field_preloaded(volatile oop* p, oop o);
// Weak load barrier
static oop weak_load_barrier_on_oop_field(volatile oop* p);
static oop weak_load_barrier_on_oop_field_preloaded(volatile oop* p, oop o);
static oop weak_load_barrier_on_weak_oop(oop o);
static oop weak_load_barrier_on_weak_oop_field(volatile oop* p);

6
src/hotspot/share/gc/z/zBarrier.inline.hpp
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@ -191,6 +191,12 @@ inline oop ZBarrier::load_barrier_on_phantom_oop_field_preloaded(volatile oop* p
//
// Weak load barrier
//
inline oop ZBarrier::weak_load_barrier_on_oop_field(volatile oop* p) {
assert(!ZResurrection::is_blocked(), "Should not be called during resurrection blocked phase");
const oop o = *p;
return weak_load_barrier_on_oop_field_preloaded(p, o);
}
inline oop ZBarrier::weak_load_barrier_on_oop_field_preloaded(volatile oop* p, oop o) {
return weak_barrier<is_weak_good_or_null_fast_path, weak_load_barrier_on_oop_slow_path>(p, o);
}

26
src/hotspot/share/gc/z/zReferenceProcessor.cpp
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@ -105,20 +105,22 @@ oop ZReferenceProcessor::reference_referent(oop obj) const {
return *reference_referent_addr(obj);
}
bool ZReferenceProcessor::is_referent_alive_or_null(oop obj, ReferenceType type) const {
volatile oop* const p = reference_referent_addr(obj);
bool ZReferenceProcessor::is_referent_strongly_alive_or_null(oop obj, ReferenceType type) const {
// Check if the referent is strongly alive or null, in which case we don't want to
// discover the reference. It can only be null if the application called
// Reference.enqueue() or Reference.clear().
//
// PhantomReferences with finalizable marked referents should technically not have
// to be discovered. However, InstanceRefKlass::oop_oop_iterate_ref_processing()
// does not know about the finalizable mark concept, and will therefore mark
// referents in non-discovered PhantomReferences as strongly live. To prevent
// this, we always discover PhantomReferences with finalizable marked referents.
// They will automatically be dropped during the reference processing phase.
// Check if the referent is alive or null, in which case we don't want to discover
// the reference. It can only be null if the application called Reference.enqueue()
// or Reference.clear().
if (type == REF_PHANTOM) {
const oop o = ZBarrier::weak_load_barrier_on_phantom_oop_field(p);
return o == NULL || ZHeap::heap()->is_object_live(ZOop::to_address(o));
} else {
const oop o = ZBarrier::weak_load_barrier_on_weak_oop_field(p);
volatile oop* const p = reference_referent_addr(obj);
const oop o = ZBarrier::weak_load_barrier_on_oop_field(p);
return o == NULL || ZHeap::heap()->is_object_strongly_live(ZOop::to_address(o));
}
}
bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {
if (type != REF_SOFT) {
@ -191,7 +193,7 @@ bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
_encountered_count.get()[type]++;
if (is_reference_inactive(obj) ||
is_referent_alive_or_null(obj, type) ||
is_referent_strongly_alive_or_null(obj, type) ||
is_referent_softly_alive(obj, type)) {
// Not discovered
return false;

2
src/hotspot/share/gc/z/zReferenceProcessor.hpp
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@ -53,7 +53,7 @@ private:
volatile oop* reference_referent_addr(oop obj) const;
oop reference_referent(oop obj) const;
bool is_reference_inactive(oop obj) const;
bool is_referent_alive_or_null(oop obj, ReferenceType type) const;
bool is_referent_strongly_alive_or_null(oop obj, ReferenceType type) const;
bool is_referent_softly_alive(oop obj, ReferenceType type) const;
bool should_drop_reference(oop obj, ReferenceType type) const;
bool should_mark_referent(ReferenceType type) const;