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// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_MARK_COMPACT_INL_H_
#define V8_HEAP_MARK_COMPACT_INL_H_
#include "src/base/bits.h"
#include "src/heap/mark-compact.h"
#include "src/heap/objects-visiting-inl.h"
#include "src/heap/remembered-set.h"
#include "src/objects/js-collection-inl.h"
namespace v8 {
namespace internal {
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::MarkingVisitor(MarkCompactCollector* collector,
MarkingState* marking_state)
: heap_(collector->heap()),
collector_(collector),
marking_state_(marking_state) {}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitAllocationSite(Map* map,
AllocationSite* object) {
int size = AllocationSite::BodyDescriptorWeak::SizeOf(map, object);
AllocationSite::BodyDescriptorWeak::IterateBody(map, object, size, this);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitBytecodeArray(Map* map,
BytecodeArray* array) {
int size = BytecodeArray::BodyDescriptor::SizeOf(map, array);
BytecodeArray::BodyDescriptor::IterateBody(map, array, size, this);
array->MakeOlder();
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode, MarkingState>::
VisitCodeDataContainer(Map* map, CodeDataContainer* object) {
int size = CodeDataContainer::BodyDescriptorWeak::SizeOf(map, object);
CodeDataContainer::BodyDescriptorWeak::IterateBody(map, object, size, this);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitFixedArray(Map* map,
FixedArray* object) {
return (fixed_array_mode == FixedArrayVisitationMode::kRegular)
? Parent::VisitFixedArray(map, object)
: VisitFixedArrayIncremental(map, object);
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitJSApiObject(Map* map, JSObject* object) {
if (heap_->local_embedder_heap_tracer()->InUse()) {
DCHECK(object->IsJSObject());
heap_->TracePossibleWrapper(object);
}
int size = JSObject::BodyDescriptor::SizeOf(map, object);
JSObject::BodyDescriptor::IterateBody(map, object, size, this);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitJSFunction(Map* map,
JSFunction* object) {
int size = JSFunction::BodyDescriptorWeak::SizeOf(map, object);
JSFunction::BodyDescriptorWeak::IterateBody(map, object, size, this);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode, MarkingState>::
VisitEphemeronHashTable(Map* map, EphemeronHashTable* table) {
collector_->AddEphemeronHashTable(table);
for (int i = 0; i < table->Capacity(); i++) {
Object** key_slot =
table->RawFieldOfElementAt(EphemeronHashTable::EntryToIndex(i));
HeapObject* key = HeapObject::cast(table->KeyAt(i));
collector_->RecordSlot(table, key_slot, key);
Object** value_slot =
table->RawFieldOfElementAt(EphemeronHashTable::EntryToValueIndex(i));
if (marking_state()->IsBlackOrGrey(key)) {
VisitPointer(table, value_slot);
} else {
Object* value_obj = *value_slot;
if (value_obj->IsHeapObject()) {
HeapObject* value = HeapObject::cast(value_obj);
collector_->RecordSlot(table, value_slot, value);
// Revisit ephemerons with both key and value unreachable at end
// of concurrent marking cycle.
if (marking_state()->IsWhite(value)) {
collector_->AddEphemeron(key, value);
}
}
}
}
return table->SizeFromMap(map);
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitMap(Map* map, Map* object) {
// When map collection is enabled we have to mark through map's transitions
// and back pointers in a special way to make these links weak.
int size = Map::BodyDescriptor::SizeOf(map, object);
if (object->CanTransition()) {
MarkMapContents(object);
} else {
Map::BodyDescriptor::IterateBody(map, object, size, this);
}
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitNativeContext(Map* map,
Context* context) {
int size = Context::BodyDescriptorWeak::SizeOf(map, context);
Context::BodyDescriptorWeak::IterateBody(map, context, size, this);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitTransitionArray(Map* map,
TransitionArray* array) {
int size = TransitionArray::BodyDescriptor::SizeOf(map, array);
TransitionArray::BodyDescriptor::IterateBody(map, array, size, this);
collector_->AddTransitionArray(array);
return size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitWeakCell(Map* map, WeakCell* weak_cell) {
// Enqueue weak cell in linked list of encountered weak collections.
// We can ignore weak cells with cleared values because they will always
// contain smi zero.
if (!weak_cell->cleared()) {
HeapObject* value = HeapObject::cast(weak_cell->value());
if (marking_state()->IsBlackOrGrey(value)) {
// Weak cells with live values are directly processed here to reduce
// the processing time of weak cells during the main GC pause.
Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
collector_->RecordSlot(weak_cell, slot, HeapObject::cast(*slot));
} else {
// If we do not know about liveness of values of weak cells, we have to
// process them when we know the liveness of the whole transitive
// closure.
collector_->AddWeakCell(weak_cell);
}
}
return WeakCell::BodyDescriptor::SizeOf(map, weak_cell);
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitPointer(HeapObject* host, Object** p) {
if (!(*p)->IsHeapObject()) return;
HeapObject* target_object = HeapObject::cast(*p);
collector_->RecordSlot(host, p, target_object);
MarkObject(host, target_object);
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitPointer(HeapObject* host,
MaybeObject** p) {
HeapObject* target_object;
if ((*p)->ToStrongHeapObject(&target_object)) {
collector_->RecordSlot(host, reinterpret_cast<HeapObjectReference**>(p),
target_object);
MarkObject(host, target_object);
} else if ((*p)->ToWeakHeapObject(&target_object)) {
if (marking_state()->IsBlackOrGrey(target_object)) {
// Weak references with live values are directly processed here to reduce
// the processing time of weak cells during the main GC pause.
collector_->RecordSlot(host, reinterpret_cast<HeapObjectReference**>(p),
target_object);
} else {
// If we do not know about liveness of values of weak cells, we have to
// process them when we know the liveness of the whole transitive
// closure.
collector_->AddWeakReference(host,
reinterpret_cast<HeapObjectReference**>(p));
}
}
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitPointers(HeapObject* host,
Object** start, Object** end) {
for (Object** p = start; p < end; p++) {
VisitPointer(host, p);
}
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitPointers(HeapObject* host,
MaybeObject** start,
MaybeObject** end) {
for (MaybeObject** p = start; p < end; p++) {
VisitPointer(host, p);
}
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitEmbeddedPointer(Code* host,
RelocInfo* rinfo) {
DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
HeapObject* object = HeapObject::cast(rinfo->target_object());
collector_->RecordRelocSlot(host, rinfo, object);
if (!host->IsWeakObject(object)) {
MarkObject(host, object);
} else if (!marking_state()->IsBlackOrGrey(object)) {
collector_->AddWeakObjectInCode(object, host);
}
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::VisitCodeTarget(Code* host,
RelocInfo* rinfo) {
DCHECK(RelocInfo::IsCodeTargetMode(rinfo->rmode()));
Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
collector_->RecordRelocSlot(host, rinfo, target);
MarkObject(host, target);
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
bool MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::MarkObjectWithoutPush(HeapObject* host,
HeapObject* object) {
if (marking_state()->WhiteToBlack(object)) {
if (retaining_path_mode == TraceRetainingPathMode::kEnabled &&
V8_UNLIKELY(FLAG_track_retaining_path)) {
heap_->AddRetainer(host, object);
}
return true;
}
return false;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::MarkObject(HeapObject* host,
HeapObject* object) {
if (marking_state()->WhiteToGrey(object)) {
marking_worklist()->Push(object);
if (retaining_path_mode == TraceRetainingPathMode::kEnabled &&
V8_UNLIKELY(FLAG_track_retaining_path)) {
heap_->AddRetainer(host, object);
}
}
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
int MarkingVisitor<fixed_array_mode, retaining_path_mode, MarkingState>::
VisitFixedArrayIncremental(Map* map, FixedArray* object) {
MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);
if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
DCHECK(!FLAG_use_marking_progress_bar ||
chunk->owner()->identity() == LO_SPACE);
// When using a progress bar for large fixed arrays, scan only a chunk of
// the array and try to push it onto the marking deque again until it is
// fully scanned. Fall back to scanning it through to the end in case this
// fails because of a full deque.
int start_offset =
Max(FixedArray::BodyDescriptor::kStartOffset, chunk->progress_bar());
if (start_offset < object_size) {
// Ensure that the object is either grey or black before pushing it
// into marking worklist.
marking_state()->WhiteToGrey(object);
if (FLAG_concurrent_marking) {
marking_worklist()->PushBailout(object);
} else {
marking_worklist()->Push(object);
}
DCHECK(marking_state()->IsGrey(object) ||
marking_state()->IsBlack(object));
int end_offset =
Min(object_size, start_offset + kProgressBarScanningChunk);
int already_scanned_offset = start_offset;
VisitPointers(object, HeapObject::RawField(object, start_offset),
HeapObject::RawField(object, end_offset));
start_offset = end_offset;
end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);
chunk->set_progress_bar(start_offset);
if (start_offset < object_size) {
heap_->incremental_marking()->NotifyIncompleteScanOfObject(
object_size - (start_offset - already_scanned_offset));
}
}
} else {
FixedArray::BodyDescriptor::IterateBody(map, object, object_size, this);
}
return object_size;
}
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
void MarkingVisitor<fixed_array_mode, retaining_path_mode,
MarkingState>::MarkMapContents(Map* map) {
// Since descriptor arrays are potentially shared, ensure that only the
// descriptors that belong to this map are marked. The first time a non-empty
// descriptor array is marked, its header is also visited. The slot holding
// the descriptor array will be implicitly recorded when the pointer fields of
// this map are visited. Prototype maps don't keep track of transitions, so
// just mark the entire descriptor array.
if (!map->is_prototype_map()) {
DescriptorArray* descriptors = map->instance_descriptors();
if (MarkObjectWithoutPush(map, descriptors) && descriptors->length() > 0) {
VisitPointers(descriptors, descriptors->GetFirstElementAddress(),
descriptors->GetDescriptorEndSlot(0));
}
int start = 0;
int end = map->NumberOfOwnDescriptors();
if (start < end) {
VisitPointers(descriptors, descriptors->GetDescriptorStartSlot(start),
descriptors->GetDescriptorEndSlot(end));
}
}
// Mark the pointer fields of the Map. Since the transitions array has
// been marked already, it is fine that one of these fields contains a
// pointer to it.
Map::BodyDescriptor::IterateBody(
map->map(), map, Map::BodyDescriptor::SizeOf(map->map(), map), this);
}
void MarkCompactCollector::MarkObject(HeapObject* host, HeapObject* obj) {
if (marking_state()->WhiteToGrey(obj)) {
marking_worklist()->Push(obj);
if (V8_UNLIKELY(FLAG_track_retaining_path)) {
heap_->AddRetainer(host, obj);
}
}
}
void MarkCompactCollector::MarkRootObject(Root root, HeapObject* obj) {
if (marking_state()->WhiteToGrey(obj)) {
marking_worklist()->Push(obj);
if (V8_UNLIKELY(FLAG_track_retaining_path)) {
heap_->AddRetainingRoot(root, obj);
}
}
}
#ifdef ENABLE_MINOR_MC
void MinorMarkCompactCollector::MarkRootObject(HeapObject* obj) {
if (Heap::InNewSpace(obj) && non_atomic_marking_state_.WhiteToGrey(obj)) {
worklist_->Push(kMainThread, obj);
}
}
#endif
void MarkCompactCollector::MarkExternallyReferencedObject(HeapObject* obj) {
if (marking_state()->WhiteToGrey(obj)) {
marking_worklist()->Push(obj);
if (V8_UNLIKELY(FLAG_track_retaining_path)) {
heap_->AddRetainingRoot(Root::kWrapperTracing, obj);
}
}
}
void MarkCompactCollector::RecordSlot(HeapObject* object, Object** slot,
HeapObject* target) {
RecordSlot(object, reinterpret_cast<HeapObjectReference**>(slot), target);
}
void MarkCompactCollector::RecordSlot(HeapObject* object,
HeapObjectReference** slot,
HeapObject* target) {
Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
Page* source_page = Page::FromAddress(reinterpret_cast<Address>(object));
if (target_page->IsEvacuationCandidate() &&
!source_page->ShouldSkipEvacuationSlotRecording()) {
RememberedSet<OLD_TO_OLD>::Insert(source_page,
reinterpret_cast<Address>(slot));
}
}
template <LiveObjectIterationMode mode>
LiveObjectRange<mode>::iterator::iterator(MemoryChunk* chunk, Bitmap* bitmap,
Address start)
: chunk_(chunk),
one_word_filler_map_(
ReadOnlyRoots(chunk->heap()).one_pointer_filler_map()),
two_word_filler_map_(
ReadOnlyRoots(chunk->heap()).two_pointer_filler_map()),
free_space_map_(ReadOnlyRoots(chunk->heap()).free_space_map()),
it_(chunk, bitmap) {
it_.Advance(Bitmap::IndexToCell(
Bitmap::CellAlignIndex(chunk_->AddressToMarkbitIndex(start))));
if (!it_.Done()) {
cell_base_ = it_.CurrentCellBase();
current_cell_ = *it_.CurrentCell();
AdvanceToNextValidObject();
} else {
current_object_ = nullptr;
}
}
template <LiveObjectIterationMode mode>
typename LiveObjectRange<mode>::iterator& LiveObjectRange<mode>::iterator::
operator++() {
AdvanceToNextValidObject();
return *this;
}
template <LiveObjectIterationMode mode>
typename LiveObjectRange<mode>::iterator LiveObjectRange<mode>::iterator::
operator++(int) {
iterator retval = *this;
++(*this);
return retval;
}
template <LiveObjectIterationMode mode>
void LiveObjectRange<mode>::iterator::AdvanceToNextValidObject() {
while (!it_.Done()) {
HeapObject* object = nullptr;
int size = 0;
while (current_cell_ != 0) {
uint32_t trailing_zeros = base::bits::CountTrailingZeros(current_cell_);
Address addr = cell_base_ + trailing_zeros * kPointerSize;
// Clear the first bit of the found object..
current_cell_ &= ~(1u << trailing_zeros);
uint32_t second_bit_index = 0;
if (trailing_zeros >= Bitmap::kBitIndexMask) {
second_bit_index = 0x1;
// The overlapping case; there has to exist a cell after the current
// cell.
// However, if there is a black area at the end of the page, and the
// last word is a one word filler, we are not allowed to advance. In
// that case we can return immediately.
if (!it_.Advance()) {
DCHECK(HeapObject::FromAddress(addr)->map() == one_word_filler_map_);
current_object_ = nullptr;
return;
}
cell_base_ = it_.CurrentCellBase();
current_cell_ = *it_.CurrentCell();
} else {
second_bit_index = 1u << (trailing_zeros + 1);
}
Map* map = nullptr;
if (current_cell_ & second_bit_index) {
// We found a black object. If the black object is within a black area,
// make sure that we skip all set bits in the black area until the
// object ends.
HeapObject* black_object = HeapObject::FromAddress(addr);
map =
base::AsAtomicPointer::Relaxed_Load(reinterpret_cast<Map**>(addr));
size = black_object->SizeFromMap(map);
Address end = addr + size - kPointerSize;
// One word filler objects do not borrow the second mark bit. We have
// to jump over the advancing and clearing part.
// Note that we know that we are at a one word filler when
// object_start + object_size - kPointerSize == object_start.
if (addr != end) {
DCHECK_EQ(chunk_, MemoryChunk::FromAddress(end));
uint32_t end_mark_bit_index = chunk_->AddressToMarkbitIndex(end);
unsigned int end_cell_index =
end_mark_bit_index >> Bitmap::kBitsPerCellLog2;
MarkBit::CellType end_index_mask =
1u << Bitmap::IndexInCell(end_mark_bit_index);
if (it_.Advance(end_cell_index)) {
cell_base_ = it_.CurrentCellBase();
current_cell_ = *it_.CurrentCell();
}
// Clear all bits in current_cell, including the end index.
current_cell_ &= ~(end_index_mask + end_index_mask - 1);
}
if (mode == kBlackObjects || mode == kAllLiveObjects) {
object = black_object;
}
} else if ((mode == kGreyObjects || mode == kAllLiveObjects)) {
map =
base::AsAtomicPointer::Relaxed_Load(reinterpret_cast<Map**>(addr));
object = HeapObject::FromAddress(addr);
size = object->SizeFromMap(map);
}
// We found a live object.
if (object != nullptr) {
// Do not use IsFiller() here. This may cause a data race for reading
// out the instance type when a new map concurrently is written into
// this object while iterating over the object.
if (map == one_word_filler_map_ || map == two_word_filler_map_ ||
map == free_space_map_) {
// There are two reasons why we can get black or grey fillers:
// 1) Black areas together with slack tracking may result in black one
// word filler objects.
// 2) Left trimming may leave black or grey fillers behind because we
// do not clear the old location of the object start.
// We filter these objects out in the iterator.
object = nullptr;
} else {
break;
}
}
}
if (current_cell_ == 0) {
if (it_.Advance()) {
cell_base_ = it_.CurrentCellBase();
current_cell_ = *it_.CurrentCell();
}
}
if (object != nullptr) {
current_object_ = object;
current_size_ = size;
return;
}
}
current_object_ = nullptr;
}
template <LiveObjectIterationMode mode>
typename LiveObjectRange<mode>::iterator LiveObjectRange<mode>::begin() {
return iterator(chunk_, bitmap_, start_);
}
template <LiveObjectIterationMode mode>
typename LiveObjectRange<mode>::iterator LiveObjectRange<mode>::end() {
return iterator(chunk_, bitmap_, end_);
}
Isolate* MarkCompactCollectorBase::isolate() { return heap()->isolate(); }
} // namespace internal
} // namespace v8
#endif // V8_HEAP_MARK_COMPACT_INL_H_