// Copyright 2011 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "src/heap/objects-visiting.h"
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#include "src/heap/heap-inl.h"
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#include "src/heap/mark-compact-inl.h"
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#include "src/heap/objects-visiting-inl.h"
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namespace v8 {
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namespace internal {
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// We don't record weak slots during marking or scavenges. Instead we do it
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// once when we complete mark-compact cycle. Note that write barrier has no
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// effect if we are already in the middle of compacting mark-sweep cycle and we
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// have to record slots manually.
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static bool MustRecordSlots(Heap* heap) {
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return heap->gc_state() == Heap::MARK_COMPACT &&
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heap->mark_compact_collector()->is_compacting();
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}
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template <class T>
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struct WeakListVisitor;
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template <class T>
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Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer) {
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Object* undefined = ReadOnlyRoots(heap).undefined_value();
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Object* head = undefined;
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T* tail = nullptr;
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bool record_slots = MustRecordSlots(heap);
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while (list != undefined) {
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// Check whether to keep the candidate in the list.
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T* candidate = reinterpret_cast<T*>(list);
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Object* retained = retainer->RetainAs(list);
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// Move to the next element before the WeakNext is cleared.
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list = WeakListVisitor<T>::WeakNext(candidate);
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if (retained != nullptr) {
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if (head == undefined) {
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// First element in the list.
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head = retained;
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} else {
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// Subsequent elements in the list.
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DCHECK_NOT_NULL(tail);
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WeakListVisitor<T>::SetWeakNext(tail, retained);
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if (record_slots) {
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HeapObject* slot_holder = WeakListVisitor<T>::WeakNextHolder(tail);
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int slot_offset = WeakListVisitor<T>::WeakNextOffset();
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Object** slot = HeapObject::RawField(slot_holder, slot_offset);
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MarkCompactCollector::RecordSlot(slot_holder, slot,
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HeapObject::cast(retained));
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}
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}
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// Retained object is new tail.
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DCHECK(!retained->IsUndefined(heap->isolate()));
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candidate = reinterpret_cast<T*>(retained);
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tail = candidate;
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// tail is a live object, visit it.
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WeakListVisitor<T>::VisitLiveObject(heap, tail, retainer);
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} else {
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WeakListVisitor<T>::VisitPhantomObject(heap, candidate);
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}
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}
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// Terminate the list if there is one or more elements.
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if (tail != nullptr) WeakListVisitor<T>::SetWeakNext(tail, undefined);
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return head;
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}
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template <class T>
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static void ClearWeakList(Heap* heap, Object* list) {
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Object* undefined = ReadOnlyRoots(heap).undefined_value();
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while (list != undefined) {
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T* candidate = reinterpret_cast<T*>(list);
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list = WeakListVisitor<T>::WeakNext(candidate);
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WeakListVisitor<T>::SetWeakNext(candidate, undefined);
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}
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}
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template <>
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struct WeakListVisitor<Code> {
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static void SetWeakNext(Code* code, Object* next) {
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code->code_data_container()->set_next_code_link(next,
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UPDATE_WEAK_WRITE_BARRIER);
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}
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static Object* WeakNext(Code* code) {
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return code->code_data_container()->next_code_link();
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}
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static HeapObject* WeakNextHolder(Code* code) {
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return code->code_data_container();
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}
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static int WeakNextOffset() { return CodeDataContainer::kNextCodeLinkOffset; }
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static void VisitLiveObject(Heap*, Code*, WeakObjectRetainer*) {}
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static void VisitPhantomObject(Heap* heap, Code* code) {
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// Even though the code is dying, its code_data_container can still be
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// alive. Clear the next_code_link slot to avoid a dangling pointer.
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SetWeakNext(code, ReadOnlyRoots(heap).undefined_value());
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}
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};
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template <>
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struct WeakListVisitor<Context> {
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static void SetWeakNext(Context* context, Object* next) {
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context->set(Context::NEXT_CONTEXT_LINK, next, UPDATE_WEAK_WRITE_BARRIER);
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}
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static Object* WeakNext(Context* context) {
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return context->next_context_link();
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}
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static HeapObject* WeakNextHolder(Context* context) { return context; }
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static int WeakNextOffset() {
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return FixedArray::SizeFor(Context::NEXT_CONTEXT_LINK);
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}
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static void VisitLiveObject(Heap* heap, Context* context,
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WeakObjectRetainer* retainer) {
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if (heap->gc_state() == Heap::MARK_COMPACT) {
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// Record the slots of the weak entries in the native context.
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for (int idx = Context::FIRST_WEAK_SLOT;
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idx < Context::NATIVE_CONTEXT_SLOTS; ++idx) {
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Object** slot = Context::cast(context)->RawFieldOfElementAt(idx);
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MarkCompactCollector::RecordSlot(context, slot,
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HeapObject::cast(*slot));
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}
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// Code objects are always allocated in Code space, we do not have to
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// visit them during scavenges.
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DoWeakList<Code>(heap, context, retainer, Context::OPTIMIZED_CODE_LIST);
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DoWeakList<Code>(heap, context, retainer, Context::DEOPTIMIZED_CODE_LIST);
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}
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}
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template <class T>
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static void DoWeakList(Heap* heap, Context* context,
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WeakObjectRetainer* retainer, int index) {
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// Visit the weak list, removing dead intermediate elements.
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Object* list_head = VisitWeakList<T>(heap, context->get(index), retainer);
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// Update the list head.
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context->set(index, list_head, UPDATE_WRITE_BARRIER);
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if (MustRecordSlots(heap)) {
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// Record the updated slot if necessary.
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Object** head_slot =
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HeapObject::RawField(context, FixedArray::SizeFor(index));
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heap->mark_compact_collector()->RecordSlot(context, head_slot,
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HeapObject::cast(list_head));
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}
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}
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static void VisitPhantomObject(Heap* heap, Context* context) {
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ClearWeakList<Code>(heap, context->get(Context::OPTIMIZED_CODE_LIST));
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ClearWeakList<Code>(heap, context->get(Context::DEOPTIMIZED_CODE_LIST));
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}
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};
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template <>
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struct WeakListVisitor<AllocationSite> {
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static void SetWeakNext(AllocationSite* obj, Object* next) {
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obj->set_weak_next(next, UPDATE_WEAK_WRITE_BARRIER);
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}
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static Object* WeakNext(AllocationSite* obj) { return obj->weak_next(); }
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static HeapObject* WeakNextHolder(AllocationSite* obj) { return obj; }
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static int WeakNextOffset() { return AllocationSite::kWeakNextOffset; }
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static void VisitLiveObject(Heap*, AllocationSite*, WeakObjectRetainer*) {}
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static void VisitPhantomObject(Heap*, AllocationSite*) {}
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};
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template Object* VisitWeakList<Context>(Heap* heap, Object* list,
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WeakObjectRetainer* retainer);
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template Object* VisitWeakList<AllocationSite>(Heap* heap, Object* list,
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WeakObjectRetainer* retainer);
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} // namespace internal
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} // namespace v8
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