src/heap/objects-visiting.h

   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.
   4
   5 #ifndef V8_OBJECTS_VISITING_H_
   6 #define V8_OBJECTS_VISITING_H_
   7
   8 #include "src/allocation.h"
   9 #include "src/layout-descriptor.h"
  10
  11 // This file provides base classes and auxiliary methods for defining
  12 // static object visitors used during GC.
  13 // Visiting HeapObject body with a normal ObjectVisitor requires performing
  14 // two switches on object's instance type to determine object size and layout
  15 // and one or more virtual method calls on visitor itself.
  16 // Static visitor is different: it provides a dispatch table which contains
  17 // pointers to specialized visit functions. Each map has the visitor_id
  18 // field which contains an index of specialized visitor to use.
  19
  20 namespace v8 {
  21 namespace internal {
  22
  23
  24 // Base class for all static visitors.
  25 class StaticVisitorBase : public AllStatic {
  26  public:
  27 #define VISITOR_ID_LIST(V) \
  28   V(SeqOneByteString)      \
  29   V(SeqTwoByteString)      \
  30   V(ShortcutCandidate)     \
  31   V(ByteArray)             \
  32   V(FreeSpace)             \
  33   V(FixedArray)            \
  34   V(FixedDoubleArray)      \
  35   V(FixedTypedArray)       \
  36   V(FixedFloat64Array)     \
  37   V(ConstantPoolArray)     \
  38   V(NativeContext)         \
  39   V(AllocationSite)        \
  40   V(DataObject2)           \
  41   V(DataObject3)           \
  42   V(DataObject4)           \
  43   V(DataObject5)           \
  44   V(DataObject6)           \
  45   V(DataObject7)           \
  46   V(DataObject8)           \
  47   V(DataObject9)           \
  48   V(DataObjectGeneric)     \
  49   V(JSObject2)             \
  50   V(JSObject3)             \
  51   V(JSObject4)             \
  52   V(JSObject5)             \
  53   V(JSObject6)             \
  54   V(JSObject7)             \
  55   V(JSObject8)             \
  56   V(JSObject9)             \
  57   V(JSObjectGeneric)       \
  58   V(Struct2)               \
  59   V(Struct3)               \
  60   V(Struct4)               \
  61   V(Struct5)               \
  62   V(Struct6)               \
  63   V(Struct7)               \
  64   V(Struct8)               \
  65   V(Struct9)               \
  66   V(StructGeneric)         \
  67   V(ConsString)            \
  68   V(SlicedString)          \
  69   V(Symbol)                \
  70   V(Oddball)               \
  71   V(Code)                  \
  72   V(Map)                   \
  73   V(Cell)                  \
  74   V(PropertyCell)          \
  75   V(WeakCell)              \
  76   V(SharedFunctionInfo)    \
  77   V(JSFunction)            \
  78   V(JSWeakCollection)      \
  79   V(JSArrayBuffer)         \
  80   V(JSTypedArray)          \
  81   V(JSDataView)            \
  82   V(JSRegExp)
  83
  84   // For data objects, JS objects and structs along with generic visitor which
  85   // can visit object of any size we provide visitors specialized by
  86   // object size in words.
  87   // Ids of specialized visitors are declared in a linear order (without
  88   // holes) starting from the id of visitor specialized for 2 words objects
  89   // (base visitor id) and ending with the id of generic visitor.
  90   // Method GetVisitorIdForSize depends on this ordering to calculate visitor
  91   // id of specialized visitor from given instance size, base visitor id and
  92   // generic visitor's id.
  93   enum VisitorId {
  94 #define VISITOR_ID_ENUM_DECL(id) kVisit##id,
  95     VISITOR_ID_LIST(VISITOR_ID_ENUM_DECL)
  96 #undef VISITOR_ID_ENUM_DECL
  97     kVisitorIdCount,
  98     kVisitDataObject = kVisitDataObject2,
  99     kVisitJSObject = kVisitJSObject2,
 100     kVisitStruct = kVisitStruct2,
 101     kMinObjectSizeInWords = 2
 102   };
 103
 104   // Visitor ID should fit in one byte.
 105   STATIC_ASSERT(kVisitorIdCount <= 256);
 106
 107   // Determine which specialized visitor should be used for given instance type
 108   // and instance type.
 109   static VisitorId GetVisitorId(int instance_type, int instance_size,
 110                                 bool has_unboxed_fields);
 111
 112   // Determine which specialized visitor should be used for given map.
 113   static VisitorId GetVisitorId(Map* map) {
 114     return GetVisitorId(
 115         map->instance_type(), map->instance_size(),
 116         FLAG_unbox_double_fields && !map->HasFastPointerLayout());
 117   }
 118
 119   // For visitors that allow specialization by size calculate VisitorId based
 120   // on size, base visitor id and generic visitor id.
 121   static VisitorId GetVisitorIdForSize(VisitorId base, VisitorId generic,
 122                                        int object_size,
 123                                        bool has_unboxed_fields) {
 124     DCHECK((base == kVisitDataObject) || (base == kVisitStruct) ||
 125            (base == kVisitJSObject));
 126     DCHECK(IsAligned(object_size, kPointerSize));
 127     DCHECK(kMinObjectSizeInWords * kPointerSize <= object_size);
 128     DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
 129     DCHECK(!has_unboxed_fields || (base == kVisitJSObject));
 130
 131     if (has_unboxed_fields) return generic;
 132
 133     int visitor_id =
 134         Min(base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords,
 135             static_cast<int>(generic));
 136
 137     return static_cast<VisitorId>(visitor_id);
 138   }
 139 };
 140
 141
 142 template <typename Callback>
 143 class VisitorDispatchTable {
 144  public:
 145   void CopyFrom(VisitorDispatchTable* other) {
 146     // We are not using memcpy to guarantee that during update
 147     // every element of callbacks_ array will remain correct
 148     // pointer (memcpy might be implemented as a byte copying loop).
 149     for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
 150       base::NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
 151     }
 152   }
 153
 154   inline Callback GetVisitorById(StaticVisitorBase::VisitorId id) {
 155     return reinterpret_cast<Callback>(callbacks_[id]);
 156   }
 157
 158   inline Callback GetVisitor(Map* map) {
 159     return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
 160   }
 161
 162   void Register(StaticVisitorBase::VisitorId id, Callback callback) {
 163     DCHECK(id < StaticVisitorBase::kVisitorIdCount);  // id is unsigned.
 164     callbacks_[id] = reinterpret_cast<base::AtomicWord>(callback);
 165   }
 166
 167   template <typename Visitor, StaticVisitorBase::VisitorId base,
 168             StaticVisitorBase::VisitorId generic, int object_size_in_words>
 169   void RegisterSpecialization() {
 170     static const int size = object_size_in_words * kPointerSize;
 171     Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size, false),
 172              &Visitor::template VisitSpecialized<size>);
 173   }
 174
 175
 176   template <typename Visitor, StaticVisitorBase::VisitorId base,
 177             StaticVisitorBase::VisitorId generic>
 178   void RegisterSpecializations() {
 179     STATIC_ASSERT((generic - base + StaticVisitorBase::kMinObjectSizeInWords) ==
 180                   10);
 181     RegisterSpecialization<Visitor, base, generic, 2>();
 182     RegisterSpecialization<Visitor, base, generic, 3>();
 183     RegisterSpecialization<Visitor, base, generic, 4>();
 184     RegisterSpecialization<Visitor, base, generic, 5>();
 185     RegisterSpecialization<Visitor, base, generic, 6>();
 186     RegisterSpecialization<Visitor, base, generic, 7>();
 187     RegisterSpecialization<Visitor, base, generic, 8>();
 188     RegisterSpecialization<Visitor, base, generic, 9>();
 189     Register(generic, &Visitor::Visit);
 190   }
 191
 192  private:
 193   base::AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
 194 };
 195
 196
 197 template <typename StaticVisitor>
 198 class BodyVisitorBase : public AllStatic {
 199  public:
 200   INLINE(static void IteratePointers(Heap* heap, HeapObject* object,
 201                                      int start_offset, int end_offset)) {
 202     DCHECK(!FLAG_unbox_double_fields || object->map()->HasFastPointerLayout());
 203     IterateRawPointers(heap, object, start_offset, end_offset);
 204   }
 205
 206   INLINE(static void IterateBody(Heap* heap, HeapObject* object,
 207                                  int start_offset, int end_offset)) {
 208     if (!FLAG_unbox_double_fields || object->map()->HasFastPointerLayout()) {
 209       IterateRawPointers(heap, object, start_offset, end_offset);
 210     } else {
 211       IterateBodyUsingLayoutDescriptor(heap, object, start_offset, end_offset);
 212     }
 213   }
 214
 215  private:
 216   INLINE(static void IterateRawPointers(Heap* heap, HeapObject* object,
 217                                         int start_offset, int end_offset)) {
 218     StaticVisitor::VisitPointers(heap,
 219                                  HeapObject::RawField(object, start_offset),
 220                                  HeapObject::RawField(object, end_offset));
 221   }
 222
 223   static void IterateBodyUsingLayoutDescriptor(Heap* heap, HeapObject* object,
 224                                                int start_offset,
 225                                                int end_offset) {
 226     DCHECK(FLAG_unbox_double_fields);
 227     DCHECK(IsAligned(start_offset, kPointerSize) &&
 228            IsAligned(end_offset, kPointerSize));
 229
 230     LayoutDescriptorHelper helper(object->map());
 231     DCHECK(!helper.all_fields_tagged());
 232     for (int offset = start_offset; offset < end_offset;) {
 233       int end_of_region_offset;
 234       if (helper.IsTagged(offset, end_offset, &end_of_region_offset)) {
 235         IterateRawPointers(heap, object, offset, end_of_region_offset);
 236       }
 237       offset = end_of_region_offset;
 238     }
 239   }
 240 };
 241
 242
 243 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
 244 class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
 245  public:
 246   INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
 247     int object_size = BodyDescriptor::SizeOf(map, object);
 248     BodyVisitorBase<StaticVisitor>::IterateBody(
 249         map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
 250     return static_cast<ReturnType>(object_size);
 251   }
 252
 253   template <int object_size>
 254   static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
 255     DCHECK(BodyDescriptor::SizeOf(map, object) == object_size);
 256     BodyVisitorBase<StaticVisitor>::IteratePointers(
 257         map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
 258     return static_cast<ReturnType>(object_size);
 259   }
 260 };
 261
 262
 263 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
 264 class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
 265  public:
 266   INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
 267     BodyVisitorBase<StaticVisitor>::IterateBody(map->GetHeap(), object,
 268                                                 BodyDescriptor::kStartOffset,
 269                                                 BodyDescriptor::kEndOffset);
 270     return static_cast<ReturnType>(BodyDescriptor::kSize);
 271   }
 272 };
 273
 274
 275 // Base class for visitors used for a linear new space iteration.
 276 // IterateBody returns size of visited object.
 277 // Certain types of objects (i.e. Code objects) are not handled
 278 // by dispatch table of this visitor because they cannot appear
 279 // in the new space.
 280 //
 281 // This class is intended to be used in the following way:
 282 //
 283 //   class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
 284 //     ...
 285 //   }
 286 //
 287 // This is an example of Curiously recurring template pattern
 288 // (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
 289 // We use CRTP to guarantee aggressive compile time optimizations (i.e.
 290 // inlining and specialization of StaticVisitor::VisitPointers methods).
 291 template <typename StaticVisitor>
 292 class StaticNewSpaceVisitor : public StaticVisitorBase {
 293  public:
 294   static void Initialize();
 295
 296   INLINE(static int IterateBody(Map* map, HeapObject* obj)) {
 297     return table_.GetVisitor(map)(map, obj);
 298   }
 299
 300   INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
 301     for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(heap, p);
 302   }
 303
 304  private:
 305   INLINE(static int VisitJSFunction(Map* map, HeapObject* object)) {
 306     Heap* heap = map->GetHeap();
 307     VisitPointers(heap,
 308                   HeapObject::RawField(object, JSFunction::kPropertiesOffset),
 309                   HeapObject::RawField(object, JSFunction::kCodeEntryOffset));
 310
 311     // Don't visit code entry. We are using this visitor only during scavenges.
 312
 313     VisitPointers(
 314         heap, HeapObject::RawField(object,
 315                                    JSFunction::kCodeEntryOffset + kPointerSize),
 316         HeapObject::RawField(object, JSFunction::kNonWeakFieldsEndOffset));
 317     return JSFunction::kSize;
 318   }
 319
 320   INLINE(static int VisitByteArray(Map* map, HeapObject* object)) {
 321     return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
 322   }
 323
 324   INLINE(static int VisitFixedDoubleArray(Map* map, HeapObject* object)) {
 325     int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
 326     return FixedDoubleArray::SizeFor(length);
 327   }
 328
 329   INLINE(static int VisitFixedTypedArray(Map* map, HeapObject* object)) {
 330     return reinterpret_cast<FixedTypedArrayBase*>(object)->size();
 331   }
 332
 333   INLINE(static int VisitJSObject(Map* map, HeapObject* object)) {
 334     return JSObjectVisitor::Visit(map, object);
 335   }
 336
 337   INLINE(static int VisitSeqOneByteString(Map* map, HeapObject* object)) {
 338     return SeqOneByteString::cast(object)
 339         ->SeqOneByteStringSize(map->instance_type());
 340   }
 341
 342   INLINE(static int VisitSeqTwoByteString(Map* map, HeapObject* object)) {
 343     return SeqTwoByteString::cast(object)
 344         ->SeqTwoByteStringSize(map->instance_type());
 345   }
 346
 347   INLINE(static int VisitFreeSpace(Map* map, HeapObject* object)) {
 348     return FreeSpace::cast(object)->Size();
 349   }
 350
 351   INLINE(static int VisitJSArrayBuffer(Map* map, HeapObject* object));
 352   INLINE(static int VisitJSTypedArray(Map* map, HeapObject* object));
 353   INLINE(static int VisitJSDataView(Map* map, HeapObject* object));
 354
 355   class DataObjectVisitor {
 356    public:
 357     template <int object_size>
 358     static inline int VisitSpecialized(Map* map, HeapObject* object) {
 359       return object_size;
 360     }
 361
 362     INLINE(static int Visit(Map* map, HeapObject* object)) {
 363       return map->instance_size();
 364     }
 365   };
 366
 367   typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, int>
 368       StructVisitor;
 369
 370   typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, int>
 371       JSObjectVisitor;
 372
 373   typedef int (*Callback)(Map* map, HeapObject* object);
 374
 375   static VisitorDispatchTable<Callback> table_;
 376 };
 377
 378
 379 template <typename StaticVisitor>
 380 VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
 381     StaticNewSpaceVisitor<StaticVisitor>::table_;
 382
 383
 384 // Base class for visitors used to transitively mark the entire heap.
 385 // IterateBody returns nothing.
 386 // Certain types of objects might not be handled by this base class and
 387 // no visitor function is registered by the generic initialization. A
 388 // specialized visitor function needs to be provided by the inheriting
 389 // class itself for those cases.
 390 //
 391 // This class is intended to be used in the following way:
 392 //
 393 //   class SomeVisitor : public StaticMarkingVisitor<SomeVisitor> {
 394 //     ...
 395 //   }
 396 //
 397 // This is an example of Curiously recurring template pattern.
 398 template <typename StaticVisitor>
 399 class StaticMarkingVisitor : public StaticVisitorBase {
 400  public:
 401   static void Initialize();
 402
 403   INLINE(static void IterateBody(Map* map, HeapObject* obj)) {
 404     table_.GetVisitor(map)(map, obj);
 405   }
 406
 407   INLINE(static void VisitPropertyCell(Map* map, HeapObject* object));
 408   INLINE(static void VisitWeakCell(Map* map, HeapObject* object));
 409   INLINE(static void VisitCodeEntry(Heap* heap, Address entry_address));
 410   INLINE(static void VisitEmbeddedPointer(Heap* heap, RelocInfo* rinfo));
 411   INLINE(static void VisitCell(Heap* heap, RelocInfo* rinfo));
 412   INLINE(static void VisitDebugTarget(Heap* heap, RelocInfo* rinfo));
 413   INLINE(static void VisitCodeTarget(Heap* heap, RelocInfo* rinfo));
 414   INLINE(static void VisitCodeAgeSequence(Heap* heap, RelocInfo* rinfo));
 415   INLINE(static void VisitExternalReference(RelocInfo* rinfo)) {}
 416   INLINE(static void VisitInternalReference(RelocInfo* rinfo)) {}
 417   INLINE(static void VisitRuntimeEntry(RelocInfo* rinfo)) {}
 418   // Skip the weak next code link in a code object.
 419   INLINE(static void VisitNextCodeLink(Heap* heap, Object** slot)) {}
 420
 421   // TODO(mstarzinger): This should be made protected once refactoring is done.
 422   // Mark non-optimize code for functions inlined into the given optimized
 423   // code. This will prevent it from being flushed.
 424   static void MarkInlinedFunctionsCode(Heap* heap, Code* code);
 425
 426  protected:
 427   INLINE(static void VisitMap(Map* map, HeapObject* object));
 428   INLINE(static void VisitCode(Map* map, HeapObject* object));
 429   INLINE(static void VisitSharedFunctionInfo(Map* map, HeapObject* object));
 430   INLINE(static void VisitConstantPoolArray(Map* map, HeapObject* object));
 431   INLINE(static void VisitAllocationSite(Map* map, HeapObject* object));
 432   INLINE(static void VisitWeakCollection(Map* map, HeapObject* object));
 433   INLINE(static void VisitJSFunction(Map* map, HeapObject* object));
 434   INLINE(static void VisitJSRegExp(Map* map, HeapObject* object));
 435   INLINE(static void VisitJSArrayBuffer(Map* map, HeapObject* object));
 436   INLINE(static void VisitJSTypedArray(Map* map, HeapObject* object));
 437   INLINE(static void VisitJSDataView(Map* map, HeapObject* object));
 438   INLINE(static void VisitNativeContext(Map* map, HeapObject* object));
 439
 440   // Mark pointers in a Map and its TransitionArray together, possibly
 441   // treating transitions or back pointers weak.
 442   static void MarkMapContents(Heap* heap, Map* map);
 443   static void MarkTransitionArray(Heap* heap, TransitionArray* transitions);
 444
 445   // Code flushing support.
 446   INLINE(static bool IsFlushable(Heap* heap, JSFunction* function));
 447   INLINE(static bool IsFlushable(Heap* heap, SharedFunctionInfo* shared_info));
 448
 449   // Helpers used by code flushing support that visit pointer fields and treat
 450   // references to code objects either strongly or weakly.
 451   static void VisitSharedFunctionInfoStrongCode(Heap* heap, HeapObject* object);
 452   static void VisitSharedFunctionInfoWeakCode(Heap* heap, HeapObject* object);
 453   static void VisitJSFunctionStrongCode(Heap* heap, HeapObject* object);
 454   static void VisitJSFunctionWeakCode(Heap* heap, HeapObject* object);
 455
 456   class DataObjectVisitor {
 457    public:
 458     template <int size>
 459     static inline void VisitSpecialized(Map* map, HeapObject* object) {}
 460
 461     INLINE(static void Visit(Map* map, HeapObject* object)) {}
 462   };
 463
 464   typedef FlexibleBodyVisitor<StaticVisitor, FixedArray::BodyDescriptor, void>
 465       FixedArrayVisitor;
 466
 467   typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, void>
 468       JSObjectVisitor;
 469
 470   typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, void>
 471       StructObjectVisitor;
 472
 473   typedef void (*Callback)(Map* map, HeapObject* object);
 474
 475   static VisitorDispatchTable<Callback> table_;
 476 };
 477
 478
 479 template <typename StaticVisitor>
 480 VisitorDispatchTable<typename StaticMarkingVisitor<StaticVisitor>::Callback>
 481     StaticMarkingVisitor<StaticVisitor>::table_;
 482
 483
 484 class WeakObjectRetainer;
 485
 486
 487 // A weak list is single linked list where each element has a weak pointer to
 488 // the next element. Given the head of the list, this function removes dead
 489 // elements from the list and if requested records slots for next-element
 490 // pointers. The template parameter T is a WeakListVisitor that defines how to
 491 // access the next-element pointers.
 492 template <class T>
 493 Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer,
 494                       bool stop_after_young, Object** list_tail);
 495 Object* VisitNewArrayBufferViewsWeakList(Heap* heap, Object* list,
 496                                          WeakObjectRetainer* retainer);
 497 }
 498 }  // namespace v8::internal
 499
 500 #endif  // V8_OBJECTS_VISITING_H_