blob: ec494715ba754b8a41665eefccd51c51cd0bf3f0 [file] [log] [blame]
// Copyright 2011 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.
#include "src/heap/objects-visiting.h"
#include "src/heap/heap-inl.h"
#include "src/heap/mark-compact-inl.h"
#include "src/heap/objects-visiting-inl.h"
namespace v8 {
namespace internal {
// We don't record weak slots during marking or scavenges. Instead we do it
// once when we complete mark-compact cycle. Note that write barrier has no
// effect if we are already in the middle of compacting mark-sweep cycle and we
// have to record slots manually.
static bool MustRecordSlots(Heap* heap) {
return heap->gc_state() == Heap::MARK_COMPACT &&
template <class T>
struct WeakListVisitor;
template <class T>
Object VisitWeakList(Heap* heap, Object list, WeakObjectRetainer* retainer) {
Object undefined = ReadOnlyRoots(heap).undefined_value();
Object head = undefined;
T tail;
bool record_slots = MustRecordSlots(heap);
while (list != undefined) {
// Check whether to keep the candidate in the list.
T candidate = T::cast(list);
Object retained = retainer->RetainAs(list);
// Move to the next element before the WeakNext is cleared.
list = WeakListVisitor<T>::WeakNext(candidate);
if (retained != Object()) {
if (head == undefined) {
// First element in the list.
head = retained;
} else {
// Subsequent elements in the list.
WeakListVisitor<T>::SetWeakNext(tail, retained);
if (record_slots) {
HeapObject slot_holder = WeakListVisitor<T>::WeakNextHolder(tail);
int slot_offset = WeakListVisitor<T>::WeakNextOffset();
ObjectSlot slot = slot_holder.RawField(slot_offset);
MarkCompactCollector::RecordSlot(slot_holder, slot,
// Retained object is new tail.
candidate = T::cast(retained);
tail = candidate;
// tail is a live object, visit it.
WeakListVisitor<T>::VisitLiveObject(heap, tail, retainer);
} else {
WeakListVisitor<T>::VisitPhantomObject(heap, candidate);
// Terminate the list if there is one or more elements.
if (!tail.is_null()) WeakListVisitor<T>::SetWeakNext(tail, undefined);
return head;
template <class T>
static void ClearWeakList(Heap* heap, Object list) {
Object undefined = ReadOnlyRoots(heap).undefined_value();
while (list != undefined) {
T candidate = T::cast(list);
list = WeakListVisitor<T>::WeakNext(candidate);
WeakListVisitor<T>::SetWeakNext(candidate, undefined);
template <>
struct WeakListVisitor<Code> {
static void SetWeakNext(Code code, Object next) {
static Object WeakNext(Code code) {
return code.code_data_container().next_code_link();
static HeapObject WeakNextHolder(Code code) {
return code.code_data_container();
static int WeakNextOffset() { return CodeDataContainer::kNextCodeLinkOffset; }
static void VisitLiveObject(Heap*, Code, WeakObjectRetainer*) {}
static void VisitPhantomObject(Heap* heap, Code code) {
// Even though the code is dying, its code_data_container can still be
// alive. Clear the next_code_link slot to avoid a dangling pointer.
SetWeakNext(code, ReadOnlyRoots(heap).undefined_value());
template <>
struct WeakListVisitor<Context> {
static void SetWeakNext(Context context, Object next) {
static Object WeakNext(Context context) {
return context.next_context_link();
static HeapObject WeakNextHolder(Context context) { return context; }
static int WeakNextOffset() {
return FixedArray::SizeFor(Context::NEXT_CONTEXT_LINK);
static void VisitLiveObject(Heap* heap, Context context,
WeakObjectRetainer* retainer) {
if (heap->gc_state() == Heap::MARK_COMPACT) {
// Record the slots of the weak entries in the native context.
for (int idx = Context::FIRST_WEAK_SLOT;
idx < Context::NATIVE_CONTEXT_SLOTS; ++idx) {
ObjectSlot slot = context.RawField(Context::OffsetOfElementAt(idx));
MarkCompactCollector::RecordSlot(context, slot,
// Code objects are always allocated in Code space, we do not have to
// visit them during scavenges.
DoWeakList<Code>(heap, context, retainer, Context::OPTIMIZED_CODE_LIST);
DoWeakList<Code>(heap, context, retainer, Context::DEOPTIMIZED_CODE_LIST);
template <class T>
static void DoWeakList(Heap* heap, Context context,
WeakObjectRetainer* retainer, int index) {
// Visit the weak list, removing dead intermediate elements.
Object list_head = VisitWeakList<T>(heap, context.get(index), retainer);
// Update the list head.
context.set(index, list_head, UPDATE_WRITE_BARRIER);
if (MustRecordSlots(heap)) {
// Record the updated slot if necessary.
ObjectSlot head_slot = context.RawField(FixedArray::SizeFor(index));
heap->mark_compact_collector()->RecordSlot(context, head_slot,
static void VisitPhantomObject(Heap* heap, Context context) {
ClearWeakList<Code>(heap, context.get(Context::OPTIMIZED_CODE_LIST));
ClearWeakList<Code>(heap, context.get(Context::DEOPTIMIZED_CODE_LIST));
template <>
struct WeakListVisitor<AllocationSite> {
static void SetWeakNext(AllocationSite obj, Object next) {
obj.set_weak_next(next, UPDATE_WEAK_WRITE_BARRIER);
static Object WeakNext(AllocationSite obj) { return obj.weak_next(); }
static HeapObject WeakNextHolder(AllocationSite obj) { return obj; }
static int WeakNextOffset() { return AllocationSite::kWeakNextOffset; }
static void VisitLiveObject(Heap*, AllocationSite, WeakObjectRetainer*) {}
static void VisitPhantomObject(Heap*, AllocationSite) {}
template Object VisitWeakList<Context>(Heap* heap, Object list,
WeakObjectRetainer* retainer);
template Object VisitWeakList<AllocationSite>(Heap* heap, Object list,
WeakObjectRetainer* retainer);
} // namespace internal
} // namespace v8