1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
// 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 &&
heap->mark_compact_collector()->is_compacting();
}
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 = nullptr;
bool record_slots = MustRecordSlots(heap);
while (list != undefined) {
// Check whether to keep the candidate in the list.
T* candidate = reinterpret_cast<T*>(list);
Object* retained = retainer->RetainAs(list);
// Move to the next element before the WeakNext is cleared.
list = WeakListVisitor<T>::WeakNext(candidate);
if (retained != nullptr) {
if (head == undefined) {
// First element in the list.
head = retained;
} else {
// Subsequent elements in the list.
DCHECK_NOT_NULL(tail);
WeakListVisitor<T>::SetWeakNext(tail, retained);
if (record_slots) {
HeapObject* slot_holder = WeakListVisitor<T>::WeakNextHolder(tail);
int slot_offset = WeakListVisitor<T>::WeakNextOffset();
Object** slot = HeapObject::RawField(slot_holder, slot_offset);
MarkCompactCollector::RecordSlot(slot_holder, slot,
HeapObject::cast(retained));
}
}
// Retained object is new tail.
DCHECK(!retained->IsUndefined(heap->isolate()));
candidate = reinterpret_cast<T*>(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 != nullptr) 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 = reinterpret_cast<T*>(list);
list = WeakListVisitor<T>::WeakNext(candidate);
WeakListVisitor<T>::SetWeakNext(candidate, undefined);
}
}
template <>
struct WeakListVisitor<Code> {
static void SetWeakNext(Code* code, Object* next) {
code->code_data_container()->set_next_code_link(next,
UPDATE_WEAK_WRITE_BARRIER);
}
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) {
context->set(Context::NEXT_CONTEXT_LINK, next, UPDATE_WEAK_WRITE_BARRIER);
}
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) {
Object** slot = Context::cast(context)->RawFieldOfElementAt(idx);
MarkCompactCollector::RecordSlot(context, slot,
HeapObject::cast(*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.
Object** head_slot =
HeapObject::RawField(context, FixedArray::SizeFor(index));
heap->mark_compact_collector()->RecordSlot(context, head_slot,
HeapObject::cast(list_head));
}
}
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
|
