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8217855: ZGC: Clean up ZReferenceProcessor

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Reviewed-by: stefank, kbarrett
This commit is contained in:
Per Lidén 2019-01-29 10:23:38 +01:00
parent 6962adcbb1
commit c97eccd24a
2 changed files with 184 additions and 144 deletions
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303
src/hotspot/share/gc/z/zReferenceProcessor.cpp
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@ -39,45 +39,11 @@
static const ZStatSubPhase ZSubPhaseConcurrentReferencesProcess("Concurrent References Process");
static const ZStatSubPhase ZSubPhaseConcurrentReferencesEnqueue("Concurrent References Enqueue");
ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :
_workers(workers),
_soft_reference_policy(NULL),
_encountered_count(),
_discovered_count(),
_enqueued_count(),
_discovered_list(NULL),
_pending_list(NULL),
_pending_list_tail(_pending_list.addr()) {}
void ZReferenceProcessor::set_soft_reference_policy(bool clear) {
static AlwaysClearPolicy always_clear_policy;
static LRUMaxHeapPolicy lru_max_heap_policy;
if (clear) {
log_info(gc, ref)("Clearing All Soft References");
_soft_reference_policy = &always_clear_policy;
} else {
_soft_reference_policy = &lru_max_heap_policy;
}
_soft_reference_policy->setup();
static ReferenceType reference_type(oop reference) {
return InstanceKlass::cast(reference->klass())->reference_type();
}
void ZReferenceProcessor::update_soft_reference_clock() const {
const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
java_lang_ref_SoftReference::set_clock(now);
}
bool ZReferenceProcessor::is_inactive_final_reference(oop obj, ReferenceType type) const {
// A non-null next field for a FinalReference means the reference is inactive.
return (type == REF_FINAL) && (java_lang_ref_Reference::next(obj) != NULL);
}
ReferenceType ZReferenceProcessor::reference_type(oop obj) const {
return InstanceKlass::cast(obj->klass())->reference_type();
}
const char* ZReferenceProcessor::reference_type_name(ReferenceType type) const {
static const char* reference_type_name(ReferenceType type) {
switch (type) {
case REF_SOFT:
return "Soft";
@ -97,53 +63,134 @@ const char* ZReferenceProcessor::reference_type_name(ReferenceType type) const {
}
}
volatile oop* ZReferenceProcessor::reference_referent_addr(oop obj) const {
return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(obj);
static volatile oop* reference_referent_addr(oop reference) {
return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(reference);
}
oop ZReferenceProcessor::reference_referent(oop obj) const {
return *reference_referent_addr(obj);
static oop reference_referent(oop reference) {
return *reference_referent_addr(reference);
}
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().
//
static void reference_set_referent(oop reference, oop referent) {
java_lang_ref_Reference::set_referent_raw(reference, referent);
}
static oop* reference_discovered_addr(oop reference) {
return (oop*)java_lang_ref_Reference::discovered_addr_raw(reference);
}
static oop reference_discovered(oop reference) {
return *reference_discovered_addr(reference);
}
static void reference_set_discovered(oop reference, oop discovered) {
java_lang_ref_Reference::set_discovered_raw(reference, discovered);
}
static oop* reference_next_addr(oop reference) {
return (oop*)java_lang_ref_Reference::next_addr_raw(reference);
}
static oop reference_next(oop reference) {
return *reference_next_addr(reference);
}
static void reference_set_next(oop reference, oop next) {
java_lang_ref_Reference::set_next_raw(reference, next);
}
static void soft_reference_update_clock() {
const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
java_lang_ref_SoftReference::set_clock(now);
}
ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :
_workers(workers),
_soft_reference_policy(NULL),
_encountered_count(),
_discovered_count(),
_enqueued_count(),
_discovered_list(NULL),
_pending_list(NULL),
_pending_list_tail(_pending_list.addr()) {}
void ZReferenceProcessor::set_soft_reference_policy(bool clear) {
static AlwaysClearPolicy always_clear_policy;
static LRUMaxHeapPolicy lru_max_heap_policy;
if (clear) {
log_info(gc, ref)("Clearing All SoftReferences");
_soft_reference_policy = &always_clear_policy;
} else {
_soft_reference_policy = &lru_max_heap_policy;
}
_soft_reference_policy->setup();
}
bool ZReferenceProcessor::is_inactive(oop reference, oop referent, ReferenceType type) const {
if (type == REF_FINAL) {
// A FinalReference is inactive if its next field is non-null. An application can't
// call enqueue() or clear() on a FinalReference.
return reference_next(reference) != NULL;
} else {
// A non-FinalReference is inactive if the referent is null. The referent can only
// be null if the application called Reference.enqueue() or Reference.clear().
return referent == NULL;
}
}
bool ZReferenceProcessor::is_strongly_live(oop referent) const {
return ZHeap::heap()->is_object_strongly_live(ZOop::to_address(referent));
}
bool ZReferenceProcessor::is_softly_live(oop reference, ReferenceType type) const {
if (type != REF_SOFT) {
// Not a SoftReference
return false;
}
// Ask SoftReference policy
const jlong clock = java_lang_ref_SoftReference::clock();
assert(clock != 0, "Clock not initialized");
assert(_soft_reference_policy != NULL, "Policy not initialized");
return !_soft_reference_policy->should_clear_reference(reference, clock);
}
bool ZReferenceProcessor::should_discover(oop reference, ReferenceType type) const {
volatile oop* const referent_addr = reference_referent_addr(reference);
const oop referent = ZBarrier::weak_load_barrier_on_oop_field(referent_addr);
if (is_inactive(reference, referent, type)) {
return false;
}
if (is_strongly_live(referent)) {
return false;
}
if (is_softly_live(reference, type)) {
return false;
}
// 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.
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));
return true;
}
bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {
if (type != REF_SOFT) {
// Not a soft reference
return false;
}
// Ask soft reference policy
const jlong clock = java_lang_ref_SoftReference::clock();
assert(clock != 0, "Clock not initialized");
assert(_soft_reference_policy != NULL, "Policy not initialized");
return !_soft_reference_policy->should_clear_reference(obj, clock);
}
bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) const {
bool ZReferenceProcessor::should_drop(oop reference, ReferenceType type) const {
// This check is racing with a call to Reference.clear() from the application.
// If the application clears the reference after this check it will still end
// up on the pending list, and there's nothing we can do about that without
// changing the Reference.clear() API. This check is also racing with a call
// to Reference.enqueue() from the application, which is unproblematic, since
// the application wants the reference to be enqueued anyway.
const oop o = reference_referent(obj);
if (o == NULL) {
const oop referent = reference_referent(reference);
if (referent == NULL) {
// Reference has been cleared, by a call to Reference.enqueue()
// or Reference.clear() from the application, which means we
// should drop the reference.
@ -153,22 +200,14 @@ bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) con
// Check if the referent is still alive, in which case we should
// drop the reference.
if (type == REF_PHANTOM) {
return ZBarrier::is_alive_barrier_on_phantom_oop(o);
return ZBarrier::is_alive_barrier_on_phantom_oop(referent);
} else {
return ZBarrier::is_alive_barrier_on_weak_oop(o);
return ZBarrier::is_alive_barrier_on_weak_oop(referent);
}
}
bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {
// Referents of final references (and its reachable sub graph) are
// always marked finalizable during discovery. This avoids the problem
// of later having to mark those objects if the referent is still final
// reachable during processing.
return type == REF_FINAL;
}
void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {
volatile oop* const p = reference_referent_addr(obj);
void ZReferenceProcessor::keep_alive(oop reference, ReferenceType type) const {
volatile oop* const p = reference_referent_addr(reference);
if (type == REF_PHANTOM) {
ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);
} else {
@ -176,82 +215,86 @@ void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const
}
}
bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
void ZReferenceProcessor::make_inactive(oop reference, ReferenceType type) const {
if (type == REF_FINAL) {
// Don't clear referent. It is needed by the Finalizer thread to make the call
// to finalize(). A FinalReference is instead made inactive by self-looping the
// next field. An application can't call FinalReference.enqueue(), so there is
// no race to worry about when setting the next field.
assert(reference_next(reference) == NULL, "Already inactive");
reference_set_next(reference, reference);
} else {
// Clear referent
reference_set_referent(reference, NULL);
}
}
void ZReferenceProcessor::discover(oop reference, ReferenceType type) {
log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
// Update statistics
_discovered_count.get()[type]++;
if (type == REF_FINAL) {
// Mark referent (and its reachable subgraph) finalizable. This avoids
// the problem of later having to mark those objects if the referent is
// still final reachable during processing.
volatile oop* const referent_addr = reference_referent_addr(reference);
ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
}
// Add reference to discovered list
assert(reference_discovered(reference) == NULL, "Already discovered");
oop* const list = _discovered_list.addr();
reference_set_discovered(reference, *list);
*list = reference;
}
bool ZReferenceProcessor::discover_reference(oop reference, ReferenceType type) {
if (!RegisterReferences) {
// Reference processing disabled
return false;
}
log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
// Update statistics
_encountered_count.get()[type]++;
if (is_referent_strongly_alive_or_null(obj, type) ||
is_inactive_final_reference(obj, type) ||
is_referent_softly_alive(obj, type)) {
if (!should_discover(reference, type)) {
// Not discovered
return false;
}
discover(obj, type);
discover(reference, type);
// Discovered
return true;
}
void ZReferenceProcessor::discover(oop obj, ReferenceType type) {
log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
// Update statistics
_discovered_count.get()[type]++;
// Mark referent finalizable
if (should_mark_referent(type)) {
oop* const referent_addr = (oop*)java_lang_ref_Reference::referent_addr_raw(obj);
ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
}
// Add reference to discovered list
assert(java_lang_ref_Reference::discovered(obj) == NULL, "Already discovered");
oop* const list = _discovered_list.addr();
java_lang_ref_Reference::set_discovered(obj, *list);
*list = obj;
}
oop ZReferenceProcessor::drop(oop obj, ReferenceType type) {
log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
oop ZReferenceProcessor::drop(oop reference, ReferenceType type) {
log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
// Keep referent alive
keep_referent_alive(obj, type);
keep_alive(reference, type);
// Unlink and return next in list
const oop next = java_lang_ref_Reference::discovered(obj);
java_lang_ref_Reference::set_discovered(obj, NULL);
const oop next = reference_discovered(reference);
reference_set_discovered(reference, NULL);
return next;
}
oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {
log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
oop* ZReferenceProcessor::keep(oop reference, ReferenceType type) {
log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
// Update statistics
_enqueued_count.get()[type]++;
if (type != REF_FINAL) {
// Clear referent
java_lang_ref_Reference::set_referent(obj, NULL);
} else {
// For a FinalReference, don't clear the referent, because it is
// needed for the finalize call. Instead, make the reference
// inactive by self-looping the 'next' field. FinalReference
// doesn't allow Reference.enqueue, so there's no race to worry
// about when setting 'next'.
assert(java_lang_ref_Reference::next(obj) == NULL, "enqueued FinalReference");
java_lang_ref_Reference::set_next_raw(obj, obj);
}
// Make reference inactive
make_inactive(reference, type);
// Return next in list
return (oop*)java_lang_ref_Reference::discovered_addr_raw(obj);
return reference_discovered_addr(reference);
}
void ZReferenceProcessor::work() {
@ -260,13 +303,13 @@ void ZReferenceProcessor::work() {
oop* p = list;
while (*p != NULL) {
const oop obj = *p;
const ReferenceType type = reference_type(obj);
const oop reference = *p;
const ReferenceType type = reference_type(reference);
if (should_drop_reference(obj, type)) {
*p = drop(obj, type);
if (should_drop(reference, type)) {
*p = drop(reference, type);
} else {
p = keep(obj, type);
p = keep(reference, type);
}
}
@ -390,8 +433,8 @@ void ZReferenceProcessor::process_references() {
ZReferenceProcessorTask task(this);
_workers->run_concurrent(&task);
// Update soft reference clock
update_soft_reference_clock();
// Update SoftReference clock
soft_reference_update_clock();
// Collect, log and trace statistics
collect_statistics();

25
src/hotspot/share/gc/z/zReferenceProcessor.hpp
View File

@ -46,22 +46,19 @@ private:
ZContended<oop> _pending_list;
oop* _pending_list_tail;
void update_soft_reference_clock() const;
bool is_inactive(oop reference, oop referent, ReferenceType type) const;
bool is_strongly_live(oop referent) const;
bool is_softly_live(oop reference, ReferenceType type) const;
ReferenceType reference_type(oop obj) const;
const char* reference_type_name(ReferenceType type) const;
volatile oop* reference_referent_addr(oop obj) const;
oop reference_referent(oop obj) const;
bool is_inactive_final_reference(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;
void keep_referent_alive(oop obj, ReferenceType type) const;
bool should_discover(oop reference, ReferenceType type) const;
bool should_drop(oop reference, ReferenceType type) const;
void keep_alive(oop reference, ReferenceType type) const;
void make_inactive(oop reference, ReferenceType type) const;
void discover(oop obj, ReferenceType type);
oop drop(oop obj, ReferenceType type);
oop* keep(oop obj, ReferenceType type);
void discover(oop reference, ReferenceType type);
oop drop(oop reference, ReferenceType type);
oop* keep(oop reference, ReferenceType type);
bool is_empty() const;