src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
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rev 5917 : [mq]: cleanup-parcopyclosure
*** 4532,4542 ****
}
G1ParGCAllocBuffer::G1ParGCAllocBuffer(size_t gclab_word_size) :
ParGCAllocBuffer(gclab_word_size), _retired(false) { }
! G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h, uint queue_num)
: _g1h(g1h),
_refs(g1h->task_queue(queue_num)),
_dcq(&g1h->dirty_card_queue_set()),
_ct_bs(g1h->g1_barrier_set()),
_g1_rem(g1h->g1_rem_set()),
--- 4532,4631 ----
}
G1ParGCAllocBuffer::G1ParGCAllocBuffer(size_t gclab_word_size) :
ParGCAllocBuffer(gclab_word_size), _retired(false) { }
! inline oop G1ParScanThreadState::copy_to_survivor_space(oop old) {
! size_t word_sz = old->size();
! HeapRegion* from_region = _g1h->heap_region_containing_raw(old);
! // +1 to make the -1 indexes valid...
! int young_index = from_region->young_index_in_cset()+1;
! assert( (from_region->is_young() && young_index > 0) ||
! (!from_region->is_young() && young_index == 0), "invariant" );
! G1CollectorPolicy* g1p = _g1h->g1_policy();
! markOop m = old->mark();
! int age = m->has_displaced_mark_helper() ? m->displaced_mark_helper()->age()
! : m->age();
! GCAllocPurpose alloc_purpose = g1p->evacuation_destination(from_region, age,
! word_sz);
! HeapWord* obj_ptr = allocate(alloc_purpose, word_sz);
! #ifndef PRODUCT
! // Should this evacuation fail?
! if (_g1h->evacuation_should_fail()) {
! if (obj_ptr != NULL) {
! undo_allocation(alloc_purpose, obj_ptr, word_sz);
! obj_ptr = NULL;
! }
! }
! #endif // !PRODUCT
!
! if (obj_ptr == NULL) {
! // This will either forward-to-self, or detect that someone else has
! // installed a forwarding pointer.
! return _g1h->handle_evacuation_failure_par(this, old);
! }
!
! oop obj = oop(obj_ptr);
!
! // We're going to allocate linearly, so might as well prefetch ahead.
! Prefetch::write(obj_ptr, PrefetchCopyIntervalInBytes);
!
! oop forward_ptr = old->forward_to_atomic(obj);
! if (forward_ptr == NULL) {
! Copy::aligned_disjoint_words((HeapWord*) old, obj_ptr, word_sz);
! if (g1p->track_object_age(alloc_purpose)) {
! // We could simply do obj->incr_age(). However, this causes a
! // performance issue. obj->incr_age() will first check whether
! // the object has a displaced mark by checking its mark word;
! // getting the mark word from the new location of the object
! // stalls. So, given that we already have the mark word and we
! // are about to install it anyway, it's better to increase the
! // age on the mark word, when the object does not have a
! // displaced mark word. We're not expecting many objects to have
! // a displaced marked word, so that case is not optimized
! // further (it could be...) and we simply call obj->incr_age().
!
! if (m->has_displaced_mark_helper()) {
! // in this case, we have to install the mark word first,
! // otherwise obj looks to be forwarded (the old mark word,
! // which contains the forward pointer, was copied)
! obj->set_mark(m);
! obj->incr_age();
! } else {
! m = m->incr_age();
! obj->set_mark(m);
! }
! age_table()->add(obj, word_sz);
! } else {
! obj->set_mark(m);
! }
!
! size_t* surv_young_words = surviving_young_words();
! surv_young_words[young_index] += word_sz;
!
! if (!obj_needs_chunking(obj, word_sz)) {
! // No point in using the slower heap_region_containing() method,
! // given that we know obj is in the heap.
! HeapRegion* obj_region = _g1h->heap_region_containing_raw(obj);
! _scanner.set_region(obj_region);
! obj->oop_iterate_backwards(&_scanner);
! } else {
! // We keep track of the next start index in the length field of
! // the to-space object. The actual length can be found in the
! // length field of the from-space object.
! arrayOop(obj)->set_length(0);
! oop* old_p = set_partial_array_mask(old);
! push_on_queue(old_p);
! }
! } else {
! undo_allocation(alloc_purpose, obj_ptr, word_sz);
! obj = forward_ptr;
! }
! return obj;
! }
!
! G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h, uint queue_num, ReferenceProcessor* rp)
: _g1h(g1h),
_refs(g1h->task_queue(queue_num)),
_dcq(&g1h->dirty_card_queue_set()),
_ct_bs(g1h->g1_barrier_set()),
_g1_rem(g1h->g1_rem_set()),
*** 4544,4554 ****
_term_attempts(0),
_surviving_alloc_buffer(g1h->desired_plab_sz(GCAllocForSurvived)),
_tenured_alloc_buffer(g1h->desired_plab_sz(GCAllocForTenured)),
_age_table(false),
_strong_roots_time(0), _term_time(0),
! _alloc_buffer_waste(0), _undo_waste(0) {
// we allocate G1YoungSurvRateNumRegions plus one entries, since
// we "sacrifice" entry 0 to keep track of surviving bytes for
// non-young regions (where the age is -1)
// We also add a few elements at the beginning and at the end in
// an attempt to eliminate cache contention
--- 4633,4644 ----
_term_attempts(0),
_surviving_alloc_buffer(g1h->desired_plab_sz(GCAllocForSurvived)),
_tenured_alloc_buffer(g1h->desired_plab_sz(GCAllocForTenured)),
_age_table(false),
_strong_roots_time(0), _term_time(0),
! _alloc_buffer_waste(0), _undo_waste(0),
! _scanner(g1h, this, rp) {
// we allocate G1YoungSurvRateNumRegions plus one entries, since
// we "sacrifice" entry 0 to keep track of surviving bytes for
// non-young regions (where the age is -1)
// We also add a few elements at the beginning and at the end in
// an attempt to eliminate cache contention
*** 4632,4644 ****
}
}
#endif // ASSERT
void G1ParScanThreadState::trim_queue() {
- assert(_evac_cl != NULL, "not set");
assert(_evac_failure_cl != NULL, "not set");
- assert(_partial_scan_cl != NULL, "not set");
StarTask ref;
do {
// Drain the overflow stack first, so other threads can steal.
while (refs()->pop_overflow(ref)) {
--- 4722,4732 ----
*** 4651,4681 ****
} while (!refs()->is_empty());
}
G1ParClosureSuper::G1ParClosureSuper(G1CollectedHeap* g1,
G1ParScanThreadState* par_scan_state) :
! _g1(g1), _g1_rem(_g1->g1_rem_set()), _cm(_g1->concurrent_mark()),
! _par_scan_state(par_scan_state),
! _worker_id(par_scan_state->queue_num()),
! _during_initial_mark(_g1->g1_policy()->during_initial_mark_pause()),
! _mark_in_progress(_g1->mark_in_progress()) { }
! template <G1Barrier barrier, bool do_mark_object>
! void G1ParCopyClosure<barrier, do_mark_object>::mark_object(oop obj) {
#ifdef ASSERT
HeapRegion* hr = _g1->heap_region_containing(obj);
assert(hr != NULL, "sanity");
assert(!hr->in_collection_set(), "should not mark objects in the CSet");
#endif // ASSERT
// We know that the object is not moving so it's safe to read its size.
_cm->grayRoot(obj, (size_t) obj->size(), _worker_id);
}
! template <G1Barrier barrier, bool do_mark_object>
! void G1ParCopyClosure<barrier, do_mark_object>
! ::mark_forwarded_object(oop from_obj, oop to_obj) {
#ifdef ASSERT
assert(from_obj->is_forwarded(), "from obj should be forwarded");
assert(from_obj->forwardee() == to_obj, "to obj should be the forwardee");
assert(from_obj != to_obj, "should not be self-forwarded");
--- 4739,4763 ----
} while (!refs()->is_empty());
}
G1ParClosureSuper::G1ParClosureSuper(G1CollectedHeap* g1,
G1ParScanThreadState* par_scan_state) :
! _g1(g1), _par_scan_state(par_scan_state),
! _worker_id(par_scan_state->queue_num()) { }
! void G1ParCopyHelper::mark_object(oop obj) {
#ifdef ASSERT
HeapRegion* hr = _g1->heap_region_containing(obj);
assert(hr != NULL, "sanity");
assert(!hr->in_collection_set(), "should not mark objects in the CSet");
#endif // ASSERT
// We know that the object is not moving so it's safe to read its size.
_cm->grayRoot(obj, (size_t) obj->size(), _worker_id);
}
! void G1ParCopyHelper::mark_forwarded_object(oop from_obj, oop to_obj) {
#ifdef ASSERT
assert(from_obj->is_forwarded(), "from obj should be forwarded");
assert(from_obj->forwardee() == to_obj, "to obj should be the forwardee");
assert(from_obj != to_obj, "should not be self-forwarded");
*** 4693,4814 ****
// well-formed. So we have to read its size from its from-space
// image which we know should not be changing.
_cm->grayRoot(to_obj, (size_t) from_obj->size(), _worker_id);
}
- template <G1Barrier barrier, bool do_mark_object>
- oop G1ParCopyClosure<barrier, do_mark_object>
- ::copy_to_survivor_space(oop old) {
- size_t word_sz = old->size();
- HeapRegion* from_region = _g1->heap_region_containing_raw(old);
- // +1 to make the -1 indexes valid...
- int young_index = from_region->young_index_in_cset()+1;
- assert( (from_region->is_young() && young_index > 0) ||
- (!from_region->is_young() && young_index == 0), "invariant" );
- G1CollectorPolicy* g1p = _g1->g1_policy();
- markOop m = old->mark();
- int age = m->has_displaced_mark_helper() ? m->displaced_mark_helper()->age()
- : m->age();
- GCAllocPurpose alloc_purpose = g1p->evacuation_destination(from_region, age,
- word_sz);
- HeapWord* obj_ptr = _par_scan_state->allocate(alloc_purpose, word_sz);
- #ifndef PRODUCT
- // Should this evacuation fail?
- if (_g1->evacuation_should_fail()) {
- if (obj_ptr != NULL) {
- _par_scan_state->undo_allocation(alloc_purpose, obj_ptr, word_sz);
- obj_ptr = NULL;
- }
- }
- #endif // !PRODUCT
-
- if (obj_ptr == NULL) {
- // This will either forward-to-self, or detect that someone else has
- // installed a forwarding pointer.
- return _g1->handle_evacuation_failure_par(_par_scan_state, old);
- }
-
- oop obj = oop(obj_ptr);
-
- // We're going to allocate linearly, so might as well prefetch ahead.
- Prefetch::write(obj_ptr, PrefetchCopyIntervalInBytes);
-
- oop forward_ptr = old->forward_to_atomic(obj);
- if (forward_ptr == NULL) {
- Copy::aligned_disjoint_words((HeapWord*) old, obj_ptr, word_sz);
- if (g1p->track_object_age(alloc_purpose)) {
- // We could simply do obj->incr_age(). However, this causes a
- // performance issue. obj->incr_age() will first check whether
- // the object has a displaced mark by checking its mark word;
- // getting the mark word from the new location of the object
- // stalls. So, given that we already have the mark word and we
- // are about to install it anyway, it's better to increase the
- // age on the mark word, when the object does not have a
- // displaced mark word. We're not expecting many objects to have
- // a displaced marked word, so that case is not optimized
- // further (it could be...) and we simply call obj->incr_age().
-
- if (m->has_displaced_mark_helper()) {
- // in this case, we have to install the mark word first,
- // otherwise obj looks to be forwarded (the old mark word,
- // which contains the forward pointer, was copied)
- obj->set_mark(m);
- obj->incr_age();
- } else {
- m = m->incr_age();
- obj->set_mark(m);
- }
- _par_scan_state->age_table()->add(obj, word_sz);
- } else {
- obj->set_mark(m);
- }
-
- size_t* surv_young_words = _par_scan_state->surviving_young_words();
- surv_young_words[young_index] += word_sz;
-
- if (obj->is_objArray() && arrayOop(obj)->length() >= ParGCArrayScanChunk) {
- // We keep track of the next start index in the length field of
- // the to-space object. The actual length can be found in the
- // length field of the from-space object.
- arrayOop(obj)->set_length(0);
- oop* old_p = set_partial_array_mask(old);
- _par_scan_state->push_on_queue(old_p);
- } else {
- // No point in using the slower heap_region_containing() method,
- // given that we know obj is in the heap.
- _scanner.set_region(_g1->heap_region_containing_raw(obj));
- obj->oop_iterate_backwards(&_scanner);
- }
- } else {
- _par_scan_state->undo_allocation(alloc_purpose, obj_ptr, word_sz);
- obj = forward_ptr;
- }
- return obj;
- }
-
template <class T>
void G1ParCopyHelper::do_klass_barrier(T* p, oop new_obj) {
if (_g1->heap_region_containing_raw(new_obj)->is_young()) {
_scanned_klass->record_modified_oops();
}
}
template <G1Barrier barrier, bool do_mark_object>
template <class T>
! void G1ParCopyClosure<barrier, do_mark_object>
! ::do_oop_work(T* p) {
! oop obj = oopDesc::load_decode_heap_oop(p);
assert(_worker_id == _par_scan_state->queue_num(), "sanity");
- // here the null check is implicit in the cset_fast_test() test
if (_g1->in_cset_fast_test(obj)) {
oop forwardee;
if (obj->is_forwarded()) {
forwardee = obj->forwardee();
} else {
! forwardee = copy_to_survivor_space(obj);
}
assert(forwardee != NULL, "forwardee should not be NULL");
oopDesc::encode_store_heap_oop(p, forwardee);
if (do_mark_object && forwardee != obj) {
// If the object is self-forwarded we don't need to explicitly
--- 4775,4807 ----
// well-formed. So we have to read its size from its from-space
// image which we know should not be changing.
_cm->grayRoot(to_obj, (size_t) from_obj->size(), _worker_id);
}
template <class T>
void G1ParCopyHelper::do_klass_barrier(T* p, oop new_obj) {
if (_g1->heap_region_containing_raw(new_obj)->is_young()) {
_scanned_klass->record_modified_oops();
}
}
template <G1Barrier barrier, bool do_mark_object>
template <class T>
! void G1ParCopyClosure<barrier, do_mark_object>::do_oop_work(T* p) {
! T heap_oop = oopDesc::load_heap_oop(p);
!
! if (!oopDesc::is_null(heap_oop)) {
! oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
assert(_worker_id == _par_scan_state->queue_num(), "sanity");
if (_g1->in_cset_fast_test(obj)) {
oop forwardee;
if (obj->is_forwarded()) {
forwardee = obj->forwardee();
} else {
! forwardee = _par_scan_state->copy_to_survivor_space(obj);
}
assert(forwardee != NULL, "forwardee should not be NULL");
oopDesc::encode_store_heap_oop(p, forwardee);
if (do_mark_object && forwardee != obj) {
// If the object is self-forwarded we don't need to explicitly
*** 4821,4892 ****
}
} else {
// The object is not in collection set. If we're a root scanning
// closure during an initial mark pause (i.e. do_mark_object will
// be true) then attempt to mark the object.
! if (do_mark_object && _g1->is_in_g1_reserved(obj)) {
mark_object(obj);
}
}
! if (barrier == G1BarrierEvac && obj != NULL) {
_par_scan_state->update_rs(_from, p, _worker_id);
}
}
template void G1ParCopyClosure<G1BarrierEvac, false>::do_oop_work(oop* p);
template void G1ParCopyClosure<G1BarrierEvac, false>::do_oop_work(narrowOop* p);
- template <class T> void G1ParScanPartialArrayClosure::do_oop_nv(T* p) {
- assert(has_partial_array_mask(p), "invariant");
- oop from_obj = clear_partial_array_mask(p);
-
- assert(Universe::heap()->is_in_reserved(from_obj), "must be in heap.");
- assert(from_obj->is_objArray(), "must be obj array");
- objArrayOop from_obj_array = objArrayOop(from_obj);
- // The from-space object contains the real length.
- int length = from_obj_array->length();
-
- assert(from_obj->is_forwarded(), "must be forwarded");
- oop to_obj = from_obj->forwardee();
- assert(from_obj != to_obj, "should not be chunking self-forwarded objects");
- objArrayOop to_obj_array = objArrayOop(to_obj);
- // We keep track of the next start index in the length field of the
- // to-space object.
- int next_index = to_obj_array->length();
- assert(0 <= next_index && next_index < length,
- err_msg("invariant, next index: %d, length: %d", next_index, length));
-
- int start = next_index;
- int end = length;
- int remainder = end - start;
- // We'll try not to push a range that's smaller than ParGCArrayScanChunk.
- if (remainder > 2 * ParGCArrayScanChunk) {
- end = start + ParGCArrayScanChunk;
- to_obj_array->set_length(end);
- // Push the remainder before we process the range in case another
- // worker has run out of things to do and can steal it.
- oop* from_obj_p = set_partial_array_mask(from_obj);
- _par_scan_state->push_on_queue(from_obj_p);
- } else {
- assert(length == end, "sanity");
- // We'll process the final range for this object. Restore the length
- // so that the heap remains parsable in case of evacuation failure.
- to_obj_array->set_length(end);
- }
- _scanner.set_region(_g1->heap_region_containing_raw(to_obj));
- // Process indexes [start,end). It will also process the header
- // along with the first chunk (i.e., the chunk with start == 0).
- // Note that at this point the length field of to_obj_array is not
- // correct given that we are using it to keep track of the next
- // start index. oop_iterate_range() (thankfully!) ignores the length
- // field and only relies on the start / end parameters. It does
- // however return the size of the object which will be incorrect. So
- // we have to ignore it even if we wanted to use it.
- to_obj_array->oop_iterate_range(&_scanner, start, end);
- }
-
class G1ParEvacuateFollowersClosure : public VoidClosure {
protected:
G1CollectedHeap* _g1h;
G1ParScanThreadState* _par_scan_state;
RefToScanQueueSet* _queues;
--- 4814,4839 ----
}
} else {
// The object is not in collection set. If we're a root scanning
// closure during an initial mark pause (i.e. do_mark_object will
// be true) then attempt to mark the object.
! if (do_mark_object) {
! assert(_g1->is_in_g1_reserved(obj), "Must reference an object within the heap");
mark_object(obj);
}
}
! if (barrier == G1BarrierEvac) {
! assert(obj != NULL, "Must be");
_par_scan_state->update_rs(_from, p, _worker_id);
}
+ }
}
template void G1ParCopyClosure<G1BarrierEvac, false>::do_oop_work(oop* p);
template void G1ParCopyClosure<G1BarrierEvac, false>::do_oop_work(narrowOop* p);
class G1ParEvacuateFollowersClosure : public VoidClosure {
protected:
G1CollectedHeap* _g1h;
G1ParScanThreadState* _par_scan_state;
RefToScanQueueSet* _queues;
*** 5023,5040 ****
ResourceMark rm;
HandleMark hm;
ReferenceProcessor* rp = _g1h->ref_processor_stw();
! G1ParScanThreadState pss(_g1h, worker_id);
! G1ParScanHeapEvacClosure scan_evac_cl(_g1h, &pss, rp);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, rp);
- G1ParScanPartialArrayClosure partial_scan_cl(_g1h, &pss, rp);
- pss.set_evac_closure(&scan_evac_cl);
pss.set_evac_failure_closure(&evac_failure_cl);
- pss.set_partial_scan_closure(&partial_scan_cl);
G1ParScanExtRootClosure only_scan_root_cl(_g1h, &pss, rp);
G1ParScanMetadataClosure only_scan_metadata_cl(_g1h, &pss, rp);
G1ParScanAndMarkExtRootClosure scan_mark_root_cl(_g1h, &pss, rp);
--- 4970,4983 ----
ResourceMark rm;
HandleMark hm;
ReferenceProcessor* rp = _g1h->ref_processor_stw();
! G1ParScanThreadState pss(_g1h, worker_id, rp);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, rp);
pss.set_evac_failure_closure(&evac_failure_cl);
G1ParScanExtRootClosure only_scan_root_cl(_g1h, &pss, rp);
G1ParScanMetadataClosure only_scan_metadata_cl(_g1h, &pss, rp);
G1ParScanAndMarkExtRootClosure scan_mark_root_cl(_g1h, &pss, rp);
*** 5454,5472 ****
ResourceMark rm;
HandleMark hm;
G1STWIsAliveClosure is_alive(_g1h);
! G1ParScanThreadState pss(_g1h, worker_id);
- G1ParScanHeapEvacClosure scan_evac_cl(_g1h, &pss, NULL);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, NULL);
- G1ParScanPartialArrayClosure partial_scan_cl(_g1h, &pss, NULL);
- pss.set_evac_closure(&scan_evac_cl);
pss.set_evac_failure_closure(&evac_failure_cl);
- pss.set_partial_scan_closure(&partial_scan_cl);
G1ParScanExtRootClosure only_copy_non_heap_cl(_g1h, &pss, NULL);
G1ParScanMetadataClosure only_copy_metadata_cl(_g1h, &pss, NULL);
G1ParScanAndMarkExtRootClosure copy_mark_non_heap_cl(_g1h, &pss, NULL);
--- 5397,5411 ----
ResourceMark rm;
HandleMark hm;
G1STWIsAliveClosure is_alive(_g1h);
! G1ParScanThreadState pss(_g1h, worker_id, NULL);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, NULL);
pss.set_evac_failure_closure(&evac_failure_cl);
G1ParScanExtRootClosure only_copy_non_heap_cl(_g1h, &pss, NULL);
G1ParScanMetadataClosure only_copy_metadata_cl(_g1h, &pss, NULL);
G1ParScanAndMarkExtRootClosure copy_mark_non_heap_cl(_g1h, &pss, NULL);
*** 5566,5583 ****
void work(uint worker_id) {
ResourceMark rm;
HandleMark hm;
! G1ParScanThreadState pss(_g1h, worker_id);
! G1ParScanHeapEvacClosure scan_evac_cl(_g1h, &pss, NULL);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, NULL);
- G1ParScanPartialArrayClosure partial_scan_cl(_g1h, &pss, NULL);
- pss.set_evac_closure(&scan_evac_cl);
pss.set_evac_failure_closure(&evac_failure_cl);
- pss.set_partial_scan_closure(&partial_scan_cl);
assert(pss.refs()->is_empty(), "both queue and overflow should be empty");
G1ParScanExtRootClosure only_copy_non_heap_cl(_g1h, &pss, NULL);
--- 5505,5518 ----
void work(uint worker_id) {
ResourceMark rm;
HandleMark hm;
! G1ParScanThreadState pss(_g1h, worker_id, NULL);
G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss, NULL);
pss.set_evac_failure_closure(&evac_failure_cl);
assert(pss.refs()->is_empty(), "both queue and overflow should be empty");
G1ParScanExtRootClosure only_copy_non_heap_cl(_g1h, &pss, NULL);
*** 5692,5713 ****
// of JNI refs is serial and performed serially by the current thread
// rather than by a worker. The following PSS will be used for processing
// JNI refs.
// Use only a single queue for this PSS.
! G1ParScanThreadState pss(this, 0);
// We do not embed a reference processor in the copying/scanning
// closures while we're actually processing the discovered
// reference objects.
- G1ParScanHeapEvacClosure scan_evac_cl(this, &pss, NULL);
G1ParScanHeapEvacFailureClosure evac_failure_cl(this, &pss, NULL);
- G1ParScanPartialArrayClosure partial_scan_cl(this, &pss, NULL);
- pss.set_evac_closure(&scan_evac_cl);
pss.set_evac_failure_closure(&evac_failure_cl);
- pss.set_partial_scan_closure(&partial_scan_cl);
assert(pss.refs()->is_empty(), "pre-condition");
G1ParScanExtRootClosure only_copy_non_heap_cl(this, &pss, NULL);
G1ParScanMetadataClosure only_copy_metadata_cl(this, &pss, NULL);
--- 5627,5644 ----
// of JNI refs is serial and performed serially by the current thread
// rather than by a worker. The following PSS will be used for processing
// JNI refs.
// Use only a single queue for this PSS.
! G1ParScanThreadState pss(this, 0, NULL);
// We do not embed a reference processor in the copying/scanning
// closures while we're actually processing the discovered
// reference objects.
G1ParScanHeapEvacFailureClosure evac_failure_cl(this, &pss, NULL);
pss.set_evac_failure_closure(&evac_failure_cl);
assert(pss.refs()->is_empty(), "pre-condition");
G1ParScanExtRootClosure only_copy_non_heap_cl(this, &pss, NULL);
G1ParScanMetadataClosure only_copy_metadata_cl(this, &pss, NULL);