blob: 605d3009841f570a110ef62e63a01cc2e51c5b22 [file] [log] [blame]
// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#include "platform/assert.h"
#include "vm/allocation.h"
#include "vm/bitfield.h"
#include "vm/datastream.h"
#include "vm/finalizable_data.h"
#include "vm/globals.h"
#include "vm/growable_array.h"
#include "vm/isolate.h"
#include "vm/message.h"
#include "vm/visitor.h"
namespace dart {
// Forward declarations.
class AbstractType;
class Array;
class Class;
class ClassTable;
class Closure;
class Code;
class ExternalTypedData;
class GrowableObjectArray;
class Heap;
class Instructions;
class LanguageError;
class Library;
class LinkedHashMap;
class Object;
class PassiveObject;
class ObjectStore;
class MegamorphicCache;
class PageSpace;
class RawApiError;
class RawArray;
class RawBoundedType;
class RawCapability;
class RawClass;
class RawClosure;
class RawClosureData;
class RawCodeSourceMap;
class RawContext;
class RawContextScope;
class RawDouble;
class RawExceptionHandlers;
class RawField;
class RawFloat32x4;
class RawFloat64x2;
class RawFunction;
class RawGrowableObjectArray;
class RawICData;
class RawImmutableArray;
class RawInstructions;
class RawInt32x4;
class RawRegExp;
class RawLanguageError;
class RawLibrary;
class RawLibraryPrefix;
class RawLinkedHashMap;
class RawLiteralToken;
class RawLocalVarDescriptors;
class RawMegamorphicCache;
class RawMint;
class RawMixinAppType;
class RawNamespace;
class RawObject;
class RawObjectPool;
class RawOneByteString;
class RawPatchClass;
class RawPcDescriptors;
class RawReceivePort;
class RawRedirectionData;
class RawScript;
class RawSignatureData;
class RawSendPort;
class RawSmi;
class RawStackMap;
class RawStackTrace;
class RawSubtypeTestCache;
class RawTokenStream;
class RawTwoByteString;
class RawType;
class RawTypeArguments;
class RawTypedData;
class RawTypeParameter;
class RawTypeRef;
class RawUnhandledException;
class RawUnresolvedClass;
class RawWeakProperty;
class String;
class TokenStream;
class TypeArguments;
class TypedData;
class UnhandledException;
// Serialized object header encoding is as follows:
// - Smi: the Smi value is written as is (last bit is not tagged).
// - VM object (from VM isolate): (object id in vm isolate | 0x3)
// This valus is serialized as a negative number.
// (note VM objects are never serialized they are expected to be found
// using ths unique ID assigned to them).
// - Reference to object that has already been written: (object id | 0x3)
// This valus is serialized as a positive number.
// - Object that is seen for the first time (inlined in the stream):
// (a unique id for this object | 0x1)
enum SerializedHeaderType {
kInlined = 0x1,
kObjectId = 0x3,
static const int8_t kHeaderTagBits = 2;
static const int8_t kObjectIdBits = (kBitsPerInt32 - (kHeaderTagBits + 1));
static const intptr_t kMaxObjectId = (kMaxUint32 >> (kHeaderTagBits + 1));
static const bool kAsReference = true;
static const bool kAsInlinedObject = false;
static const intptr_t kInvalidPatchIndex = -1;
class SerializedHeaderTag
: public BitField<intptr_t, enum SerializedHeaderType, 0, kHeaderTagBits> {
class SerializedHeaderData
: public BitField<intptr_t, intptr_t, kHeaderTagBits, kObjectIdBits> {};
enum DeserializeState {
kIsDeserialized = 0,
kIsNotDeserialized = 1,
enum SerializeState {
kIsSerialized = 0,
kIsNotSerialized = 1,
#define HEAP_SPACE(kind) (kind == Snapshot::kMessage) ? Heap::kNew : Heap::kOld
// Structure capturing the raw snapshot.
// TODO(turnidge): Remove this class once the snapshot does not have a
// header anymore. This is pending on making the embedder pass in the
// length of their snapshot.
class Snapshot {
enum Kind {
// N.B. The order of these values must be preserved to give proper error
// messages for old snapshots.
kFull = 0, // Full snapshot of core libraries or an application.
kScript, // A partial snapshot of only the application script.
kMessage, // A partial snapshot used only for isolate messaging.
kFullJIT, // Full + JIT code
kFullAOT, // Full + AOT code
kNone, // dart_bootstrap/gen_snapshot
static const char* KindToCString(Kind kind);
static const Snapshot* SetupFromBuffer(const void* raw_memory);
static const int32_t kMagicValue = 0xdcdcf5f5;
static const intptr_t kMagicOffset = 0;
static const intptr_t kMagicSize = sizeof(int32_t);
static const intptr_t kLengthOffset = kMagicOffset + kMagicSize;
static const intptr_t kLengthSize = sizeof(int64_t);
static const intptr_t kKindOffset = kLengthOffset + kLengthSize;
static const intptr_t kKindSize = sizeof(int64_t);
static const intptr_t kHeaderSize = kKindOffset + kKindSize;
// Accessors.
bool check_magic() const {
return Read<int32_t>(kMagicOffset) == kMagicValue;
void set_magic() { return Write<int32_t>(kMagicOffset, kMagicValue); }
// Excluding the magic value from the size written in the buffer is needed
// so we give a proper version mismatch error for snapshots create before
// magic value was written by the VM instead of the embedder.
int64_t large_length() const {
return Read<int64_t>(kLengthOffset) + kMagicSize;
intptr_t length() const { return static_cast<intptr_t>(large_length()); }
void set_length(intptr_t value) {
return Write<int64_t>(kLengthOffset, value - kMagicSize);
Kind kind() const { return static_cast<Kind>(Read<int64_t>(kKindOffset)); }
void set_kind(Kind value) { return Write<int64_t>(kKindOffset, value); }
const uint8_t* content() const {
return reinterpret_cast<const uint8_t*>(this) + kHeaderSize;
static bool IsFull(Kind kind) {
return (kind == kFull) || (kind == kFullJIT) || (kind == kFullAOT);
static bool IncludesCode(Kind kind) {
return (kind == kFullJIT) || (kind == kFullAOT);
const uint8_t* Addr() const { return reinterpret_cast<const uint8_t*>(this); }
const uint8_t* DataImage() const {
if (!IncludesCode(kind())) {
return NULL;
uword offset = Utils::RoundUp(length(), OS::kMaxPreferredCodeAlignment);
return Addr() + offset;
// Prevent Snapshot from ever being allocated directly.
template <typename T>
T Read(intptr_t offset) const {
return ReadUnaligned(
reinterpret_cast<const T*>(reinterpret_cast<uword>(this) + offset));
template <typename T>
void Write(intptr_t offset, T value) {
return StoreUnaligned(
reinterpret_cast<T*>(reinterpret_cast<uword>(this) + offset), value);
class BaseReader {
BaseReader(const uint8_t* buffer, intptr_t size) : stream_(buffer, size) {}
// Reads raw data (for basic types).
// sizeof(T) must be in {1,2,4,8}.
template <typename T>
T Read() {
return ReadStream::Raw<sizeof(T), T>::Read(&stream_);
classid_t ReadClassIDValue() {
uint32_t value = Read<uint32_t>();
return static_cast<classid_t>(value);
COMPILE_ASSERT(sizeof(uint32_t) >= sizeof(classid_t));
void ReadBytes(uint8_t* addr, intptr_t len) { stream_.ReadBytes(addr, len); }
double ReadDouble() {
double result;
stream_.ReadBytes(reinterpret_cast<uint8_t*>(&result), sizeof(result));
return result;
intptr_t ReadTags() {
const intptr_t tags = static_cast<intptr_t>(Read<int8_t>()) & 0xff;
return tags;
const uint8_t* CurrentBufferAddress() const {
return stream_.AddressOfCurrentPosition();
void Advance(intptr_t value) { stream_.Advance(value); }
intptr_t PendingBytes() const { return stream_.PendingBytes(); }
RawSmi* ReadAsSmi();
intptr_t ReadSmiValue();
// Negative header value indicates VM isolate object id.
bool IsVMIsolateObject(intptr_t header_value) { return (header_value < 0); }
intptr_t GetVMIsolateObjectId(intptr_t header_val) {
intptr_t value = -header_val; // Header is negative for VM isolate objects.
ASSERT(SerializedHeaderTag::decode(value) == kObjectId);
return SerializedHeaderData::decode(value);
ReadStream stream_; // input stream.
class BackRefNode : public ValueObject {
BackRefNode(Object* reference,
DeserializeState state,
bool defer_canonicalization)
: reference_(reference),
patch_records_(NULL) {}
Object* reference() const { return reference_; }
bool is_deserialized() const { return state_ == kIsDeserialized; }
void set_state(DeserializeState state) { state_ = state; }
bool defer_canonicalization() const { return defer_canonicalization_; }
ZoneGrowableArray<intptr_t>* patch_records() const { return patch_records_; }
BackRefNode& operator=(const BackRefNode& other) {
reference_ = other.reference_;
state_ = other.state_;
defer_canonicalization_ = other.defer_canonicalization_;
patch_records_ = other.patch_records_;
return *this;
void AddPatchRecord(intptr_t patch_object_id, intptr_t patch_offset) {
if (defer_canonicalization_) {
if (patch_records_ == NULL) {
patch_records_ = new ZoneGrowableArray<intptr_t>();
Object* reference_;
DeserializeState state_;
bool defer_canonicalization_;
ZoneGrowableArray<intptr_t>* patch_records_;
// Reads a snapshot into objects.
class SnapshotReader : public BaseReader {
Thread* thread() const { return thread_; }
Zone* zone() const { return zone_; }
Isolate* isolate() const { return thread_->isolate(); }
Heap* heap() const { return heap_; }
ObjectStore* object_store() const { return isolate()->object_store(); }
ClassTable* class_table() const { return isolate()->class_table(); }
PassiveObject* PassiveObjectHandle() { return &pobj_; }
Array* ArrayHandle() { return &array_; }
Class* ClassHandle() { return &cls_; }
Code* CodeHandle() { return &code_; }
Instructions* InstructionsHandle() { return &instructions_; }
String* StringHandle() { return &str_; }
AbstractType* TypeHandle() { return &type_; }
TypeArguments* TypeArgumentsHandle() { return &type_arguments_; }
GrowableObjectArray* TokensHandle() { return &tokens_; }
TokenStream* StreamHandle() { return &stream_; }
ExternalTypedData* DataHandle() { return &data_; }
TypedData* TypedDataHandle() { return &typed_data_; }
Function* FunctionHandle() { return &function_; }
Snapshot::Kind kind() const { return kind_; }
// Reads an object.
RawObject* ReadObject();
// Add object to backward references.
void AddBackRef(intptr_t id,
Object* obj,
DeserializeState state,
bool defer_canonicalization = false);
// Get an object from the backward references list.
Object* GetBackRef(intptr_t id);
// Read a script snapshot.
RawObject* ReadScriptSnapshot();
// Read version number of snapshot and verify.
RawApiError* VerifyVersionAndFeatures(Isolate* isolate);
RawObject* NewInteger(int64_t value);
SnapshotReader(const uint8_t* buffer,
intptr_t size,
Snapshot::Kind kind,
ZoneGrowableArray<BackRefNode>* backward_references,
Thread* thread);
~SnapshotReader() {}
ZoneGrowableArray<BackRefNode>* GetBackwardReferenceTable() const {
return backward_references_;
void ResetBackwardReferenceTable() { backward_references_ = NULL; }
PageSpace* old_space() const { return old_space_; }
void EnqueueTypePostprocessing(const AbstractType& type);
void RunDelayedTypePostprocessing();
void EnqueueRehashingOfMap(const LinkedHashMap& map);
RawObject* RunDelayedRehashingOfMaps();
RawClass* ReadClassId(intptr_t object_id);
RawFunction* ReadFunctionId(intptr_t object_id);
RawObject* ReadStaticImplicitClosure(intptr_t object_id, intptr_t cls_header);
// Implementation to read an object.
RawObject* ReadObjectImpl(bool as_reference,
intptr_t patch_object_id = kInvalidPatchIndex,
intptr_t patch_offset = 0);
RawObject* ReadObjectImpl(intptr_t header,
bool as_reference,
intptr_t patch_object_id,
intptr_t patch_offset);
// Read a Dart Instance object.
RawObject* ReadInstance(intptr_t object_id, intptr_t tags, bool as_reference);
// Read a VM isolate object that was serialized as an Id.
RawObject* ReadVMIsolateObject(intptr_t object_id);
// Read an object that was serialized as an Id (singleton in object store,
// or an object that was already serialized before).
RawObject* ReadIndexedObject(intptr_t object_id,
intptr_t patch_object_id,
intptr_t patch_offset);
// Add a patch record for the object so that objects whose canonicalization
// is deferred can be back patched after they are canonicalized.
void AddPatchRecord(intptr_t object_id,
intptr_t patch_object_id,
intptr_t patch_offset);
// Process all the deferred canonicalization entries and patch all references.
void ProcessDeferredCanonicalizations();
// Update subclasses array and is implemented bit for interfaces/superclass in
// the core snapshot.
void FixSubclassesAndImplementors();
// Decode class id from the header field.
intptr_t LookupInternalClass(intptr_t class_header);
void ArrayReadFrom(intptr_t object_id,
const Array& result,
intptr_t len,
intptr_t tags);
intptr_t NextAvailableObjectId() const;
void SetReadException(const char* msg);
RawObject* VmIsolateSnapshotObject(intptr_t index) const;
bool is_vm_isolate() const;
Snapshot::Kind kind_; // Indicates type of the snapshot.
Thread* thread_; // Current thread.
Zone* zone_; // Zone for allocations while reading.
Heap* heap_; // Heap of the current isolate.
PageSpace* old_space_; // Old space of the current isolate.
Class& cls_; // Temporary Class handle.
Code& code_; // Temporary Code handle.
Instructions& instructions_; // Temporary Instructions handle
Object& obj_; // Temporary Object handle.
PassiveObject& pobj_; // Temporary PassiveObject handle.
Array& array_; // Temporary Array handle.
Field& field_; // Temporary Field handle.
String& str_; // Temporary String handle.
Library& library_; // Temporary library handle.
AbstractType& type_; // Temporary type handle.
TypeArguments& type_arguments_; // Temporary type argument handle.
GrowableObjectArray& tokens_; // Temporary tokens handle.
TokenStream& stream_; // Temporary token stream handle.
ExternalTypedData& data_; // Temporary stream data handle.
TypedData& typed_data_; // Temporary typed data handle.
Function& function_; // Temporary function handle.
UnhandledException& error_; // Error handle.
intptr_t max_vm_isolate_object_id_;
ZoneGrowableArray<BackRefNode>* backward_references_;
GrowableObjectArray& types_to_postprocess_;
GrowableObjectArray& objects_to_rehash_;
friend class ApiError;
friend class Array;
friend class BoundedType;
friend class Class;
friend class Closure;
friend class ClosureData;
friend class Context;
friend class ContextScope;
friend class ExceptionHandlers;
friend class Field;
friend class Function;
friend class GrowableObjectArray;
friend class ICData;
friend class ImmutableArray;
friend class KernelProgramInfo;
friend class LanguageError;
friend class Library;
friend class LibraryPrefix;
friend class LinkedHashMap;
friend class LiteralToken;
friend class MirrorReference;
friend class MixinAppType;
friend class Namespace;
friend class PatchClass;
friend class RedirectionData;
friend class RegExp;
friend class Script;
friend class SignatureData;
friend class SubtypeTestCache;
friend class TokenStream;
friend class Type;
friend class TypeArguments;
friend class TypeParameter;
friend class TypeRef;
friend class UnhandledException;
friend class UnresolvedClass;
friend class WeakProperty;
class ScriptSnapshotReader : public SnapshotReader {
ScriptSnapshotReader(const uint8_t* buffer, intptr_t size, Thread* thread);
class MessageSnapshotReader : public SnapshotReader {
MessageSnapshotReader(Message* message, Thread* thread);
MessageFinalizableData* finalizable_data() const { return finalizable_data_; }
MessageFinalizableData* finalizable_data_;
class BaseWriter : public StackResource {
uint8_t* buffer() { return stream_.buffer(); }
intptr_t BytesWritten() const { return stream_.bytes_written(); }
// Writes raw data to the stream (basic type).
// sizeof(T) must be in {1,2,4,8}.
template <typename T>
void Write(T value) {
WriteStream::Raw<sizeof(T), T>::Write(&stream_, value);
void WriteClassIDValue(classid_t value) { Write<uint32_t>(value); }
COMPILE_ASSERT(sizeof(uint32_t) >= sizeof(classid_t));
// Write an object that is serialized as an Id (singleton in object store,
// or an object that was already serialized before).
void WriteIndexedObject(intptr_t object_id) {
ASSERT(object_id <= kMaxObjectId);
intptr_t value = 0;
value = SerializedHeaderTag::update(kObjectId, value);
value = SerializedHeaderData::update(object_id, value);
// Write a VM Isolateobject that is serialized as an Id.
void WriteVMIsolateObject(intptr_t object_id) {
ASSERT(object_id <= kMaxObjectId);
intptr_t value = 0;
value = SerializedHeaderTag::update(kObjectId, value);
value = SerializedHeaderData::update(object_id, value);
Write<int32_t>(-value); // Write as a negative value.
// Write serialization header information for an object.
void WriteInlinedObjectHeader(intptr_t id) {
ASSERT(id <= kMaxObjectId);
intptr_t value = 0;
value = SerializedHeaderTag::update(kInlined, value);
value = SerializedHeaderData::update(id, value);
void WriteTags(intptr_t tags) {
const intptr_t flags = tags & 0xff;
// Write out a buffer of bytes.
void WriteBytes(const uint8_t* addr, intptr_t len) {
stream_.WriteBytes(addr, len);
void WriteDouble(double value) {
stream_.WriteBytes(reinterpret_cast<const uint8_t*>(&value), sizeof(value));
BaseWriter(ReAlloc alloc, DeAlloc dealloc, intptr_t initial_size)
: StackResource(Thread::Current()),
stream_(&buffer_, alloc, initial_size),
dealloc_(dealloc) {
ASSERT(alloc != NULL);
~BaseWriter() {}
void ReserveHeader() {
// Make room for recording snapshot buffer size.
void FillHeader(Snapshot::Kind kind) {
Snapshot* header = reinterpret_cast<Snapshot*>(stream_.buffer());
void FreeBuffer() {
uint8_t* buffer_;
WriteStream stream_;
DeAlloc dealloc_;
class ForwardList {
explicit ForwardList(Thread* thread, intptr_t first_object_id);
class Node : public ZoneAllocated {
Node(const Object* obj, SerializeState state) : obj_(obj), state_(state) {}
const Object* obj() const { return obj_; }
bool is_serialized() const { return state_ == kIsSerialized; }
// Private to ensure the invariant of first_unprocessed_object_id_.
void set_state(SerializeState value) { state_ = value; }
const Object* obj_;
SerializeState state_;
friend class ForwardList;
Node* NodeForObjectId(intptr_t object_id) const {
return nodes_[object_id - first_object_id_];
// Returns the id for the added object.
intptr_t AddObject(Zone* zone, RawObject* raw, SerializeState state);
// Returns the id for the object it it exists in the list.
intptr_t FindObject(RawObject* raw);
// Exhaustively processes all unserialized objects in this list. 'writer' may
// concurrently add more objects.
void SerializeAll(ObjectVisitor* writer);
// Set state of object in forward list.
void SetState(intptr_t object_id, SerializeState state) {
intptr_t first_object_id() const { return first_object_id_; }
intptr_t next_object_id() const { return nodes_.length() + first_object_id_; }
Heap* heap() const { return thread_->isolate()->heap(); }
Thread* thread_;
const intptr_t first_object_id_;
GrowableArray<Node*> nodes_;
intptr_t first_unprocessed_object_id_;
class SnapshotWriter : public BaseWriter {
SnapshotWriter(Thread* thread,
Snapshot::Kind kind,
ReAlloc alloc,
DeAlloc dealloc,
intptr_t initial_size,
ForwardList* forward_list,
bool can_send_any_object);
// Snapshot kind.
Snapshot::Kind kind() const { return kind_; }
Thread* thread() const { return thread_; }
Zone* zone() const { return thread_->zone(); }
Isolate* isolate() const { return thread_->isolate(); }
Heap* heap() const { return isolate()->heap(); }
// Serialize an object into the buffer.
void WriteObject(RawObject* raw);
static uint32_t GetObjectTags(RawObject* raw);
static uword GetObjectTagsAndHash(RawObject* raw);
Exceptions::ExceptionType exception_type() const { return exception_type_; }
void set_exception_type(Exceptions::ExceptionType type) {
exception_type_ = type;
const char* exception_msg() const { return exception_msg_; }
void set_exception_msg(const char* msg) { exception_msg_ = msg; }
bool can_send_any_object() const { return can_send_any_object_; }
void ThrowException(Exceptions::ExceptionType type, const char* msg);
// Write a version string for the snapshot.
void WriteVersionAndFeatures();
void WriteFunctionId(RawFunction* func, bool owner_is_class);
RawFunction* IsSerializableClosure(RawClosure* closure);
void WriteStaticImplicitClosure(intptr_t object_id,
RawFunction* func,
intptr_t tags);
bool CheckAndWritePredefinedObject(RawObject* raw);
bool HandleVMIsolateObject(RawObject* raw);
void WriteClassId(RawClass* cls);
void WriteObjectImpl(RawObject* raw, bool as_reference);
void WriteMarkedObjectImpl(RawObject* raw,
intptr_t tags,
intptr_t object_id,
bool as_reference);
void WriteForwardedObjects();
void ArrayWriteTo(intptr_t object_id,
intptr_t array_kind,
intptr_t tags,
RawSmi* length,
RawTypeArguments* type_arguments,
RawObject* data[],
bool as_reference);
RawClass* GetFunctionOwner(RawFunction* func);
void CheckForNativeFields(RawClass* cls);
void SetWriteException(Exceptions::ExceptionType type, const char* msg);
void WriteInstance(RawObject* raw,
RawClass* cls,
intptr_t tags,
intptr_t object_id,
bool as_reference);
bool AllowObjectsInDartLibrary(RawLibrary* library);
intptr_t FindVmSnapshotObject(RawObject* rawobj);
ObjectStore* object_store() const { return object_store_; }
Thread* thread_;
Snapshot::Kind kind_;
ObjectStore* object_store_; // Object store for common classes.
ClassTable* class_table_; // Class table for the class index to class lookup.
ForwardList* forward_list_;
Exceptions::ExceptionType exception_type_; // Exception type.
const char* exception_msg_; // Message associated with exception.
bool can_send_any_object_; // True if any Dart instance can be sent.
friend class RawArray;
friend class RawClass;
friend class RawClosureData;
friend class RawCode;
friend class RawContextScope;
friend class RawExceptionHandlers;
friend class RawField;
friend class RawFunction;
friend class RawGrowableObjectArray;
friend class RawImmutableArray;
friend class RawInstructions;
friend class RawLibrary;
friend class RawLinkedHashMap;
friend class RawLiteralToken;
friend class RawLocalVarDescriptors;
friend class RawMirrorReference;
friend class RawObjectPool;
friend class RawReceivePort;
friend class RawRegExp;
friend class RawScript;
friend class RawStackTrace;
friend class RawSubtypeTestCache;
friend class RawTokenStream;
friend class RawType;
friend class RawTypeRef;
friend class RawBoundedType;
friend class RawTypeArguments;
friend class RawTypeParameter;
friend class RawUserTag;
friend class SnapshotWriterVisitor;
friend class WriteInlinedObjectVisitor;
class ScriptSnapshotWriter : public SnapshotWriter {
static const intptr_t kInitialSize = 64 * KB;
explicit ScriptSnapshotWriter(ReAlloc alloc);
~ScriptSnapshotWriter() {}
// Writes a partial snapshot of the script.
void WriteScriptSnapshot(const Library& lib);
ForwardList forward_list_;
class SerializedObjectBuffer : public StackResource {
SerializedObjectBuffer() : StackResource(Thread::Current()), message_(NULL) {}
virtual ~SerializedObjectBuffer() { delete message_; }
void set_message(Message* message) {
ASSERT(message_ == NULL);
message_ = message;
Message* StealMessage() {
Message* result = message_;
message_ = NULL;
return result;
Message* message_;
class MessageWriter : public SnapshotWriter {
static const intptr_t kInitialSize = 512;
explicit MessageWriter(bool can_send_any_object);
Message* WriteMessage(const Object& obj,
Dart_Port dest_port,
Message::Priority priority);
MessageFinalizableData* finalizable_data() const { return finalizable_data_; }
ForwardList forward_list_;
MessageFinalizableData* finalizable_data_;
// An object pointer visitor implementation which writes out
// objects to a snap shot.
class SnapshotWriterVisitor : public ObjectPointerVisitor {
SnapshotWriterVisitor(SnapshotWriter* writer, bool as_references)
: ObjectPointerVisitor(Isolate::Current()),
as_references_(as_references) {}
virtual void VisitPointers(RawObject** first, RawObject** last);
SnapshotWriter* writer_;
bool as_references_;
} // namespace dart