objects.h.svn-base

Google浏览器V8内核代码

                                  PropertyAttributes* attributes);
  Object* GetProperty(Object* receiver,
                      LookupResult* result,
                      String* key,
                      PropertyAttributes* attributes);
  Object* GetPropertyWithCallback(Object* receiver,
                                  Object* structure,
                                  String* name,
                                  Object* holder);

  inline Object* GetElement(uint32_t index);
  Object* GetElementWithReceiver(Object* receiver, uint32_t index);

  // Return the object's prototype (might be Heap::null_value()).
  Object* GetPrototype();

  // Returns true if this is a JSValue containing a string and the index is
  // < the length of the string.  Used to implement [] on strings.
  inline bool IsStringObjectWithCharacterAt(uint32_t index);

#ifdef DEBUG
  // Prints this object with details.
  void Print();
  void PrintLn();
  // Verifies the object.
  void Verify();

  // Verify a pointer is a valid object pointer.
  static void VerifyPointer(Object* p);
#endif

  // Prints this object without details.
  void ShortPrint();

  // Prints this object without details to a message accumulator.
  void ShortPrint(StringStream* accumulator);

  // Casting: This cast is only needed to satisfy macros in objects-inl.h.
  static Object* cast(Object* value) { return value; }

  // Layout description.
  static const int kHeaderSize = 0;  // Object does not take up any space.

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(Object);
};


// Smi represents integer Numbers that can be stored in 31 bits.
// Smis are immediate which means they are NOT allocated in the heap.
// The this pointer has the following format: [31 bit signed int] 0
// Smi stands for small integer.
class Smi: public Object {
 public:
  // Returns the integer value.
  inline int value();

  // Convert a value to a Smi object.
  static inline Smi* FromInt(int value);

  // Returns whether value can be represented in a Smi.
  static inline bool IsValid(int value);

  // Casting.
  static inline Smi* cast(Object* object);

  // Dispatched behavior.
  void SmiPrint();
  void SmiPrint(StringStream* accumulator);
#ifdef DEBUG
  void SmiVerify();
#endif

  // Min and max limits for Smi values.
  static const int kMinValue = -(1 << (kBitsPerPointer - (kSmiTagSize + 1)));
  static const int kMaxValue = (1 << (kBitsPerPointer - (kSmiTagSize + 1))) - 1;

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(Smi);
};


// Failure is used for reporing out of memory situations and
// propagating exceptions through the runtime system.  Failure objects
// are transient and cannot occur as part of the objects graph.
//
// Failures are a single word, encoded as follows:
// +-------------------------+---+--+--+
// |rrrrrrrrrrrrrrrrrrrrrrrrr|sss|tt|11|
// +-------------------------+---+--+--+
//
// The low two bits, 0-1, are the failure tag, 11.  The next two bits,
// 2-3, are a failure type tag 'tt' with possible values:
//   00 RETRY_AFTER_GC
//   01 EXCEPTION
//   10 INTERNAL_ERROR
//   11 OUT_OF_MEMORY_EXCEPTION
//
// The next three bits, 4-6, are an allocation space tag 'sss'.  The
// allocation space tag is 000 for all failure types except
// RETRY_AFTER_GC.  For RETRY_AFTER_GC, the possible values are
// (the encoding is found in globals.h):
//   000 NEW_SPACE
//   001 OLD_SPACE
//   010 CODE_SPACE
//   011 MAP_SPACE
//   100 LO_SPACE
//
// The remaining bits is the number of words requested by the
// allocation request that failed, and is zeroed except for
// RETRY_AFTER_GC failures.  The 25 bits (on a 32 bit platform) gives
// a representable range of 2^27 bytes (128MB).

// Failure type tag info.
const int kFailureTypeTagSize = 2;
const int kFailureTypeTagMask = (1 << kFailureTypeTagSize) - 1;

class Failure: public Object {
 public:
  // RuntimeStubs assumes EXCEPTION = 1 in the compiler-generated code.
  enum Type {
    RETRY_AFTER_GC = 0,
    EXCEPTION = 1,       // Returning this marker tells the real exception
                         // is in Top::pending_exception.
    INTERNAL_ERROR = 2,
    OUT_OF_MEMORY_EXCEPTION = 3
  };

  inline Type type() const;

  // Returns the space that needs to be collected for RetryAfterGC failures.
  inline AllocationSpace allocation_space() const;

  // Returns the number of bytes requested (up to the representable maximum)
  // for RetryAfterGC failures.
  inline int requested() const;

  inline bool IsInternalError() const;
  inline bool IsOutOfMemoryException() const;

  static Failure* RetryAfterGC(int requested_bytes, AllocationSpace space);
  static inline Failure* Exception();
  static inline Failure* InternalError();
  static inline Failure* OutOfMemoryException();
  // Casting.
  static inline Failure* cast(Object* object);

  // Dispatched behavior.
  void FailurePrint();
  void FailurePrint(StringStream* accumulator);
#ifdef DEBUG
  void FailureVerify();
#endif

 private:
  inline int value() const;
  static inline Failure* Construct(Type type, int value = 0);

  DISALLOW_IMPLICIT_CONSTRUCTORS(Failure);
};


// Heap objects typically have a map pointer in their first word.  However,
// during GC other data (eg, mark bits, forwarding addresses) is sometimes
// encoded in the first word.  The class MapWord is an abstraction of the
// value in a heap object's first word.
class MapWord BASE_EMBEDDED {
 public:
  // Normal state: the map word contains a map pointer.

  // Create a map word from a map pointer.
  static inline MapWord FromMap(Map* map);

  // View this map word as a map pointer.
  inline Map* ToMap();


  // Scavenge collection: the map word of live objects in the from space
  // contains a forwarding address (a heap object pointer in the to space).

  // True if this map word is a forwarding address for a scavenge
  // collection.  Only valid during a scavenge collection (specifically,
  // when all map words are heap object pointers, ie. not during a full GC).
  inline bool IsForwardingAddress();

  // Create a map word from a forwarding address.
  static inline MapWord FromForwardingAddress(HeapObject* object);

  // View this map word as a forwarding address.
  inline HeapObject* ToForwardingAddress();


  // Marking phase of full collection: the map word of live objects is
  // marked, and may be marked as overflowed (eg, the object is live, its
  // children have not been visited, and it does not fit in the marking
  // stack).

  // True if this map word's mark bit is set.
  inline bool IsMarked();

  // Return this map word but with its mark bit set.
  inline void SetMark();

  // Return this map word but with its mark bit cleared.
  inline void ClearMark();

  // True if this map word's overflow bit is set.
  inline bool IsOverflowed();

  // Return this map word but with its overflow bit set.
  inline void SetOverflow();

  // Return this map word but with its overflow bit cleared.
  inline void ClearOverflow();


  // Compacting phase of a full compacting collection: the map word of live
  // objects contains an encoding of the original map address along with the
  // forwarding address (represented as an offset from the first live object
  // in the same page as the (old) object address).

  // Create a map word from a map address and a forwarding address offset.
  static inline MapWord EncodeAddress(Address map_address, int offset);

  // Return the map address encoded in this map word.
  inline Address DecodeMapAddress(MapSpace* map_space);

  // Return the forwarding offset encoded in this map word.
  inline int DecodeOffset();


  // During serialization: the map word is used to hold an encoded
  // address, and possibly a mark bit (set and cleared with SetMark
  // and ClearMark).

  // Create a map word from an encoded address.
  static inline MapWord FromEncodedAddress(Address address);

  inline Address ToEncodedAddress();

 private:
  // HeapObject calls the private constructor and directly reads the value.
  friend class HeapObject;

  explicit MapWord(uintptr_t value) : value_(value) {}

  uintptr_t value_;

  // Bits used by the marking phase of the garbage collector.
  //
  // The first word of a heap object is normall a map pointer. The last two
  // bits are tagged as '01' (kHeapObjectTag). We reuse the last two bits to
  // mark an object as live and/or overflowed:
  //   last bit = 0, marked as alive
  //   second bit = 1, overflowed
  // An object is only marked as overflowed when it is marked as live while
  // the marking stack is overflowed.
  static const int kMarkingBit = 0;  // marking bit
  static const int kMarkingMask = (1 << kMarkingBit);  // marking mask
  static const int kOverflowBit = 1;  // overflow bit
  static const int kOverflowMask = (1 << kOverflowBit);  // overflow mask

  // Forwarding pointers and map pointer encoding
  //  31             21 20              10 9               0
  // +-----------------+------------------+-----------------+
  // |forwarding offset|page offset of map|page index of map|
  // +-----------------+------------------+-----------------+
  //  11 bits           11 bits            10 bits
  static const int kMapPageIndexBits = 10;
  static const int kMapPageOffsetBits = 11;
  static const int kForwardingOffsetBits = 11;

  static const int kMapPageIndexShift = 0;
  static const int kMapPageOffsetShift =
      kMapPageIndexShift + kMapPageIndexBits;
  static const int kForwardingOffsetShift =
      kMapPageOffsetShift + kMapPageOffsetBits;

  // 0x000003FF
  static const uint32_t kMapPageIndexMask =
      (1 << kMapPageOffsetShift) - 1;

  // 0x001FFC00
  static const uint32_t kMapPageOffsetMask =
      ((1 << kForwardingOffsetShift) - 1) & ~kMapPageIndexMask;

  // 0xFFE00000
  static const uint32_t kForwardingOffsetMask =
      ~(kMapPageIndexMask | kMapPageOffsetMask);
};


// HeapObject is the superclass for all classes describing heap allocated
// objects.
class HeapObject: public Object {
 public:
  // [map]: Contains a map which contains the object's reflective
  // information.
  inline Map* map();
  inline void set_map(Map* value);

  // During garbage collection, the map word of a heap object does not
  // necessarily contain a map pointer.
  inline MapWord map_word();
  inline void set_map_word(MapWord map_word);

  // Converts an address to a HeapObject pointer.
  static inline HeapObject* FromAddress(Address address);

  // Returns the address of this HeapObject.
  inline Address address();

  // Iterates over pointers contained in the object (including the Map)
  void Iterate(ObjectVisitor* v);

  // Iterates over all pointers contained in the object except the
  // first map pointer.  The object type is given in the first
  // parameter. This function does not access the map pointer in the
  // object, and so is safe to call while the map pointer is modified.
  void IterateBody(InstanceType type, int object_size, ObjectVisitor* v);

  // This method only applies to struct objects.  Iterates over all the fields
  // of this struct.
  void IterateStructBody(int object_size, ObjectVisitor* v);

  // Copy the body from the 'from' object to this.
  // Please note the two object must have the same map prior to the call.
  inline void CopyBody(JSObject* from);

  // Returns the heap object's size in bytes
  inline int Size();

  // Given a heap object's map pointer, returns the heap size in bytes