1 // Copyright 2012 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef V8_OBJECTS_VISITING_H_
6 #define V8_OBJECTS_VISITING_H_
8 #include "src/allocation.h"
10 // This file provides base classes and auxiliary methods for defining
11 // static object visitors used during GC.
12 // Visiting HeapObject body with a normal ObjectVisitor requires performing
13 // two switches on object's instance type to determine object size and layout
14 // and one or more virtual method calls on visitor itself.
15 // Static visitor is different: it provides a dispatch table which contains
16 // pointers to specialized visit functions. Each map has the visitor_id
17 // field which contains an index of specialized visitor to use.
23 // Base class for all static visitors.
24 class StaticVisitorBase : public AllStatic {
26 #define VISITOR_ID_LIST(V) \
29 V(ShortcutCandidate) \
35 V(FixedFloat64Array) \
36 V(ConstantPoolArray) \
47 V(DataObjectGeneric) \
75 V(SharedFunctionInfo) \
83 // For data objects, JS objects and structs along with generic visitor which
84 // can visit object of any size we provide visitors specialized by
85 // object size in words.
86 // Ids of specialized visitors are declared in a linear order (without
87 // holes) starting from the id of visitor specialized for 2 words objects
88 // (base visitor id) and ending with the id of generic visitor.
89 // Method GetVisitorIdForSize depends on this ordering to calculate visitor
90 // id of specialized visitor from given instance size, base visitor id and
91 // generic visitor's id.
93 #define VISITOR_ID_ENUM_DECL(id) kVisit##id,
94 VISITOR_ID_LIST(VISITOR_ID_ENUM_DECL)
95 #undef VISITOR_ID_ENUM_DECL
97 kVisitDataObject = kVisitDataObject2,
98 kVisitJSObject = kVisitJSObject2,
99 kVisitStruct = kVisitStruct2,
100 kMinObjectSizeInWords = 2
103 // Visitor ID should fit in one byte.
104 STATIC_ASSERT(kVisitorIdCount <= 256);
106 // Determine which specialized visitor should be used for given instance type
107 // and instance type.
108 static VisitorId GetVisitorId(int instance_type, int instance_size);
110 static VisitorId GetVisitorId(Map* map) {
111 return GetVisitorId(map->instance_type(), map->instance_size());
114 // For visitors that allow specialization by size calculate VisitorId based
115 // on size, base visitor id and generic visitor id.
116 static VisitorId GetVisitorIdForSize(VisitorId base, VisitorId generic,
118 DCHECK((base == kVisitDataObject) || (base == kVisitStruct) ||
119 (base == kVisitJSObject));
120 DCHECK(IsAligned(object_size, kPointerSize));
121 DCHECK(kMinObjectSizeInWords * kPointerSize <= object_size);
122 DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
124 const VisitorId specialization = static_cast<VisitorId>(
125 base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords);
127 return Min(specialization, generic);
132 template <typename Callback>
133 class VisitorDispatchTable {
135 void CopyFrom(VisitorDispatchTable* other) {
136 // We are not using memcpy to guarantee that during update
137 // every element of callbacks_ array will remain correct
138 // pointer (memcpy might be implemented as a byte copying loop).
139 for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
140 base::NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
144 inline Callback GetVisitorById(StaticVisitorBase::VisitorId id) {
145 return reinterpret_cast<Callback>(callbacks_[id]);
148 inline Callback GetVisitor(Map* map) {
149 return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
152 void Register(StaticVisitorBase::VisitorId id, Callback callback) {
153 DCHECK(id < StaticVisitorBase::kVisitorIdCount); // id is unsigned.
154 callbacks_[id] = reinterpret_cast<base::AtomicWord>(callback);
157 template <typename Visitor, StaticVisitorBase::VisitorId base,
158 StaticVisitorBase::VisitorId generic, int object_size_in_words>
159 void RegisterSpecialization() {
160 static const int size = object_size_in_words * kPointerSize;
161 Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size),
162 &Visitor::template VisitSpecialized<size>);
166 template <typename Visitor, StaticVisitorBase::VisitorId base,
167 StaticVisitorBase::VisitorId generic>
168 void RegisterSpecializations() {
169 STATIC_ASSERT((generic - base + StaticVisitorBase::kMinObjectSizeInWords) ==
171 RegisterSpecialization<Visitor, base, generic, 2>();
172 RegisterSpecialization<Visitor, base, generic, 3>();
173 RegisterSpecialization<Visitor, base, generic, 4>();
174 RegisterSpecialization<Visitor, base, generic, 5>();
175 RegisterSpecialization<Visitor, base, generic, 6>();
176 RegisterSpecialization<Visitor, base, generic, 7>();
177 RegisterSpecialization<Visitor, base, generic, 8>();
178 RegisterSpecialization<Visitor, base, generic, 9>();
179 Register(generic, &Visitor::Visit);
183 base::AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
187 template <typename StaticVisitor>
188 class BodyVisitorBase : public AllStatic {
190 INLINE(static void IteratePointers(Heap* heap, HeapObject* object,
191 int start_offset, int end_offset)) {
192 Object** start_slot =
193 reinterpret_cast<Object**>(object->address() + start_offset);
195 reinterpret_cast<Object**>(object->address() + end_offset);
196 StaticVisitor::VisitPointers(heap, start_slot, end_slot);
201 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
202 class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
204 INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
205 int object_size = BodyDescriptor::SizeOf(map, object);
206 BodyVisitorBase<StaticVisitor>::IteratePointers(
207 map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
208 return static_cast<ReturnType>(object_size);
211 template <int object_size>
212 static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
213 DCHECK(BodyDescriptor::SizeOf(map, object) == object_size);
214 BodyVisitorBase<StaticVisitor>::IteratePointers(
215 map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
216 return static_cast<ReturnType>(object_size);
221 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
222 class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
224 INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
225 BodyVisitorBase<StaticVisitor>::IteratePointers(
226 map->GetHeap(), object, BodyDescriptor::kStartOffset,
227 BodyDescriptor::kEndOffset);
228 return static_cast<ReturnType>(BodyDescriptor::kSize);
233 // Base class for visitors used for a linear new space iteration.
234 // IterateBody returns size of visited object.
235 // Certain types of objects (i.e. Code objects) are not handled
236 // by dispatch table of this visitor because they cannot appear
239 // This class is intended to be used in the following way:
241 // class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
245 // This is an example of Curiously recurring template pattern
246 // (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
247 // We use CRTP to guarantee aggressive compile time optimizations (i.e.
248 // inlining and specialization of StaticVisitor::VisitPointers methods).
249 template <typename StaticVisitor>
250 class StaticNewSpaceVisitor : public StaticVisitorBase {
252 static void Initialize();
254 INLINE(static int IterateBody(Map* map, HeapObject* obj)) {
255 return table_.GetVisitor(map)(map, obj);
258 INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
259 for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(heap, p);
263 INLINE(static int VisitJSFunction(Map* map, HeapObject* object)) {
264 Heap* heap = map->GetHeap();
266 HeapObject::RawField(object, JSFunction::kPropertiesOffset),
267 HeapObject::RawField(object, JSFunction::kCodeEntryOffset));
269 // Don't visit code entry. We are using this visitor only during scavenges.
272 heap, HeapObject::RawField(object,
273 JSFunction::kCodeEntryOffset + kPointerSize),
274 HeapObject::RawField(object, JSFunction::kNonWeakFieldsEndOffset));
275 return JSFunction::kSize;
278 INLINE(static int VisitByteArray(Map* map, HeapObject* object)) {
279 return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
282 INLINE(static int VisitFixedDoubleArray(Map* map, HeapObject* object)) {
283 int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
284 return FixedDoubleArray::SizeFor(length);
287 INLINE(static int VisitFixedTypedArray(Map* map, HeapObject* object)) {
288 return reinterpret_cast<FixedTypedArrayBase*>(object)->size();
291 INLINE(static int VisitJSObject(Map* map, HeapObject* object)) {
292 return JSObjectVisitor::Visit(map, object);
295 INLINE(static int VisitSeqOneByteString(Map* map, HeapObject* object)) {
296 return SeqOneByteString::cast(object)
297 ->SeqOneByteStringSize(map->instance_type());
300 INLINE(static int VisitSeqTwoByteString(Map* map, HeapObject* object)) {
301 return SeqTwoByteString::cast(object)
302 ->SeqTwoByteStringSize(map->instance_type());
305 INLINE(static int VisitFreeSpace(Map* map, HeapObject* object)) {
306 return FreeSpace::cast(object)->Size();
309 INLINE(static int VisitJSArrayBuffer(Map* map, HeapObject* object));
310 INLINE(static int VisitJSTypedArray(Map* map, HeapObject* object));
311 INLINE(static int VisitJSDataView(Map* map, HeapObject* object));
313 class DataObjectVisitor {
315 template <int object_size>
316 static inline int VisitSpecialized(Map* map, HeapObject* object) {
320 INLINE(static int Visit(Map* map, HeapObject* object)) {
321 return map->instance_size();
325 typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, int>
328 typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, int>
331 typedef int (*Callback)(Map* map, HeapObject* object);
333 static VisitorDispatchTable<Callback> table_;
337 template <typename StaticVisitor>
338 VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
339 StaticNewSpaceVisitor<StaticVisitor>::table_;
342 // Base class for visitors used to transitively mark the entire heap.
343 // IterateBody returns nothing.
344 // Certain types of objects might not be handled by this base class and
345 // no visitor function is registered by the generic initialization. A
346 // specialized visitor function needs to be provided by the inheriting
347 // class itself for those cases.
349 // This class is intended to be used in the following way:
351 // class SomeVisitor : public StaticMarkingVisitor<SomeVisitor> {
355 // This is an example of Curiously recurring template pattern.
356 template <typename StaticVisitor>
357 class StaticMarkingVisitor : public StaticVisitorBase {
359 static void Initialize();
361 INLINE(static void IterateBody(Map* map, HeapObject* obj)) {
362 table_.GetVisitor(map)(map, obj);
365 INLINE(static void VisitPropertyCell(Map* map, HeapObject* object));
366 INLINE(static void VisitWeakCell(Map* map, HeapObject* object));
367 INLINE(static void VisitCodeEntry(Heap* heap, Address entry_address));
368 INLINE(static void VisitEmbeddedPointer(Heap* heap, RelocInfo* rinfo));
369 INLINE(static void VisitCell(Heap* heap, RelocInfo* rinfo));
370 INLINE(static void VisitDebugTarget(Heap* heap, RelocInfo* rinfo));
371 INLINE(static void VisitCodeTarget(Heap* heap, RelocInfo* rinfo));
372 INLINE(static void VisitCodeAgeSequence(Heap* heap, RelocInfo* rinfo));
373 INLINE(static void VisitExternalReference(RelocInfo* rinfo)) {}
374 INLINE(static void VisitRuntimeEntry(RelocInfo* rinfo)) {}
375 // Skip the weak next code link in a code object.
376 INLINE(static void VisitNextCodeLink(Heap* heap, Object** slot)) {}
378 // TODO(mstarzinger): This should be made protected once refactoring is done.
379 // Mark non-optimize code for functions inlined into the given optimized
380 // code. This will prevent it from being flushed.
381 static void MarkInlinedFunctionsCode(Heap* heap, Code* code);
384 INLINE(static void VisitMap(Map* map, HeapObject* object));
385 INLINE(static void VisitCode(Map* map, HeapObject* object));
386 INLINE(static void VisitSharedFunctionInfo(Map* map, HeapObject* object));
387 INLINE(static void VisitConstantPoolArray(Map* map, HeapObject* object));
388 INLINE(static void VisitAllocationSite(Map* map, HeapObject* object));
389 INLINE(static void VisitWeakCollection(Map* map, HeapObject* object));
390 INLINE(static void VisitJSFunction(Map* map, HeapObject* object));
391 INLINE(static void VisitJSRegExp(Map* map, HeapObject* object));
392 INLINE(static void VisitJSArrayBuffer(Map* map, HeapObject* object));
393 INLINE(static void VisitJSTypedArray(Map* map, HeapObject* object));
394 INLINE(static void VisitJSDataView(Map* map, HeapObject* object));
395 INLINE(static void VisitNativeContext(Map* map, HeapObject* object));
397 // Mark pointers in a Map and its TransitionArray together, possibly
398 // treating transitions or back pointers weak.
399 static void MarkMapContents(Heap* heap, Map* map);
400 static void MarkTransitionArray(Heap* heap, TransitionArray* transitions);
402 // Code flushing support.
403 INLINE(static bool IsFlushable(Heap* heap, JSFunction* function));
404 INLINE(static bool IsFlushable(Heap* heap, SharedFunctionInfo* shared_info));
406 // Helpers used by code flushing support that visit pointer fields and treat
407 // references to code objects either strongly or weakly.
408 static void VisitSharedFunctionInfoStrongCode(Heap* heap, HeapObject* object);
409 static void VisitSharedFunctionInfoWeakCode(Heap* heap, HeapObject* object);
410 static void VisitJSFunctionStrongCode(Heap* heap, HeapObject* object);
411 static void VisitJSFunctionWeakCode(Heap* heap, HeapObject* object);
413 class DataObjectVisitor {
416 static inline void VisitSpecialized(Map* map, HeapObject* object) {}
418 INLINE(static void Visit(Map* map, HeapObject* object)) {}
421 typedef FlexibleBodyVisitor<StaticVisitor, FixedArray::BodyDescriptor, void>
424 typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, void>
427 typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, void>
430 typedef void (*Callback)(Map* map, HeapObject* object);
432 static VisitorDispatchTable<Callback> table_;
436 template <typename StaticVisitor>
437 VisitorDispatchTable<typename StaticMarkingVisitor<StaticVisitor>::Callback>
438 StaticMarkingVisitor<StaticVisitor>::table_;
441 class WeakObjectRetainer;
444 // A weak list is single linked list where each element has a weak pointer to
445 // the next element. Given the head of the list, this function removes dead
446 // elements from the list and if requested records slots for next-element
447 // pointers. The template parameter T is a WeakListVisitor that defines how to
448 // access the next-element pointers.
450 Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer);
452 } // namespace v8::internal
454 #endif // V8_OBJECTS_VISITING_H_