Another step on the way to context snapshots. We can now refer to

objects in the startup heap from a partial snapshot.  This happens
through the partial snapshot cache.  A startup snapshot and a
partial snapshot are created together so that the startup snapshot
contains the partial snapshot cache entries needed.
Review URL: http://codereview.chromium.org/548149

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3713 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -3344,6 +3344,11 @@ void Heap::IterateRSet(PagedSpace* space, ObjectSlotCallback copy_object_func) {
 
 void Heap::IterateRoots(ObjectVisitor* v, VisitMode mode) {
   IterateStrongRoots(v, mode);
+  IterateWeakRoots(v, mode);
+}
+
+
+void Heap::IterateWeakRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointer(reinterpret_cast<Object**>(&roots_[kSymbolTableRootIndex]));
   v->Synchronize("symbol_table");
   if (mode != VISIT_ALL_IN_SCAVENGE) {
@@ -3398,6 +3403,20 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   // Iterate over pointers being held by inactive threads.
   ThreadManager::Iterate(v);
   v->Synchronize("threadmanager");
+
+  // Iterate over the pointers the Serialization/Deserialization code is
+  // holding.
+  // During garbage collection this keeps the partial snapshot cache alive.
+  // During deserialization of the startup snapshot this creates the partial
+  // snapshot cache and deserializes the objects it refers to.  During
+  // serialization this does nothing, since the partial snapshot cache is
+  // empty.  However the next thing we do is create the partial snapshot,
+  // filling up the partial snapshot cache with objects it needs as we go.
+  SerializerDeserializer::Iterate(v);
+  // We don't do a v->Synchronize call here, because in debug mode that will
+  // output a flag to the snapshot.  However at this point the serializer and
+  // deserializer are deliberately a little unsynchronized (see above) so the
+  // checking of the sync flag in the snapshot would fail.
 }
 
 

src/heap.h

@@ -690,6 +690,8 @@ class Heap : public AllStatic {
   static void IterateRoots(ObjectVisitor* v, VisitMode mode);
   // Iterates over all strong roots in the heap.
   static void IterateStrongRoots(ObjectVisitor* v, VisitMode mode);
+  // Iterates over all the other roots in the heap.
+  static void IterateWeakRoots(ObjectVisitor* v, VisitMode mode);
 
   // Iterates remembered set of an old space.
   static void IterateRSet(PagedSpace* space, ObjectSlotCallback callback);

src/mksnapshot.cc

@@ -164,10 +164,10 @@ int main(int argc, char** argv) {
   }
   context.Dispose();
   CppByteSink sink(argv[1]);
-  i::Serializer ser(&sink);
   // This results in a somewhat smaller snapshot, probably because it gets rid
   // of some things that are cached between garbage collections.
   i::Heap::CollectAllGarbage(true);
+  i::StartupSerializer ser(&sink);
   ser.Serialize();
   return 0;
 }

src/serialize.cc

@@ -44,67 +44,6 @@
 namespace v8 {
 namespace internal {
 
-// Mapping objects to their location after deserialization.
-// This is used during building, but not at runtime by V8.
-class SerializationAddressMapper {
- public:
-  static bool IsMapped(HeapObject* obj) {
-    EnsureMapExists();
-    return serialization_map_->Lookup(Key(obj), Hash(obj), false) != NULL;
-  }
-
-  static int MappedTo(HeapObject* obj) {
-    ASSERT(IsMapped(obj));
-    return static_cast<int>(reinterpret_cast<intptr_t>(
-        serialization_map_->Lookup(Key(obj), Hash(obj), false)->value));
-  }
-
-  static void Map(HeapObject* obj, int to) {
-    EnsureMapExists();
-    ASSERT(!IsMapped(obj));
-    HashMap::Entry* entry =
-        serialization_map_->Lookup(Key(obj), Hash(obj), true);
-    entry->value = Value(to);
-  }
-
-  static void Zap() {
-    if (serialization_map_ != NULL) {
-      delete serialization_map_;
-    }
-    serialization_map_ = NULL;
-  }
-
- private:
-  static bool SerializationMatchFun(void* key1, void* key2) {
-    return key1 == key2;
-  }
-
-  static uint32_t Hash(HeapObject* obj) {
-    return static_cast<int32_t>(reinterpret_cast<intptr_t>(obj->address()));
-  }
-
-  static void* Key(HeapObject* obj) {
-    return reinterpret_cast<void*>(obj->address());
-  }
-
-  static void* Value(int v) {
-    return reinterpret_cast<void*>(v);
-  }
-
-  static void EnsureMapExists() {
-    if (serialization_map_ == NULL) {
-      serialization_map_ = new HashMap(&SerializationMatchFun);
-    }
-  }
-
-  static HashMap* serialization_map_;
-};
-
-
-HashMap* SerializationAddressMapper::serialization_map_ = NULL;
-
-
-
 
 // -----------------------------------------------------------------------------
 // Coding of external references.
@@ -647,10 +586,13 @@ void Deserializer::Deserialize() {
   ASSERT_EQ(NULL, ThreadState::FirstInUse());
   // No active handles.
   ASSERT(HandleScopeImplementer::instance()->blocks()->is_empty());
+  // Make sure the entire partial snapshot cache is traversed, filling it with
+  // valid object pointers.
+  partial_snapshot_cache_length_ = kPartialSnapshotCacheCapacity;
   ASSERT_EQ(NULL, external_reference_decoder_);
   external_reference_decoder_ = new ExternalReferenceDecoder();
-  Heap::IterateRoots(this, VISIT_ONLY_STRONG);
-  ASSERT(source_->AtEOF());
+  Heap::IterateStrongRoots(this, VISIT_ONLY_STRONG);
+  Heap::IterateWeakRoots(this, VISIT_ALL);
 }
 
 
@@ -666,7 +608,8 @@ void Deserializer::DeserializePartial(Object** root) {
 }
 
 
-void Deserializer::TearDown() {
+Deserializer::~Deserializer() {
+  ASSERT(source_->AtEOF());
   if (external_reference_decoder_ != NULL) {
     delete external_reference_decoder_;
     external_reference_decoder_ = NULL;
@@ -891,6 +834,16 @@ void Deserializer::ReadChunk(Object** current,
         *current++ = Heap::roots_address()[root_id];
         break;
       }
+      case PARTIAL_SNAPSHOT_CACHE_ENTRY: {
+        int cache_index = source_->GetInt();
+        *current++ = partial_snapshot_cache_[cache_index];
+        break;
+      }
+      case SYNCHRONIZE: {
+        // If we get here then that indicates that you have a mismatch between
+        // the number of GC roots when serializing and deserializing.
+        UNREACHABLE();
+      }
       default:
         UNREACHABLE();
     }
@@ -944,7 +897,6 @@ Serializer::Serializer(SnapshotByteSink* sink)
     : sink_(sink),
       current_root_index_(0),
       external_reference_encoder_(NULL),
-      partial_(false),
       large_object_total_(0) {
   for (int i = 0; i <= LAST_SPACE; i++) {
     fullness_[i] = 0;
@@ -952,7 +904,7 @@ Serializer::Serializer(SnapshotByteSink* sink)
 }
 
 
-void Serializer::Serialize() {
+void StartupSerializer::SerializeStrongReferences() {
   // No active threads.
   CHECK_EQ(NULL, ThreadState::FirstInUse());
   // No active or weak handles.
@@ -966,20 +918,30 @@ void Serializer::Serialize() {
     CHECK_NE(v8::INSTALLED, ext->state());
   }
   external_reference_encoder_ = new ExternalReferenceEncoder();
-  Heap::IterateRoots(this, VISIT_ONLY_STRONG);
+  Heap::IterateStrongRoots(this, VISIT_ONLY_STRONG);
   delete external_reference_encoder_;
   external_reference_encoder_ = NULL;
-  SerializationAddressMapper::Zap();
 }
 
 
-void Serializer::SerializePartial(Object** object) {
-  partial_ = true;
+void PartialSerializer::Serialize(Object** object) {
   external_reference_encoder_ = new ExternalReferenceEncoder();
   this->VisitPointer(object);
+
+  // After we have done the partial serialization the partial snapshot cache
+  // will contain some references needed to decode the partial snapshot.  We
+  // fill it up with undefineds so it has a predictable length so the
+  // deserialization code doesn't need to know the length.
+  for (int index = partial_snapshot_cache_length_;
+       index < kPartialSnapshotCacheCapacity;
+       index++) {
+    partial_snapshot_cache_[index] = Heap::undefined_value();
+    startup_serializer_->VisitPointer(&partial_snapshot_cache_[index]);
+  }
+  partial_snapshot_cache_length_ = kPartialSnapshotCacheCapacity;
+
   delete external_reference_encoder_;
   external_reference_encoder_ = NULL;
-  SerializationAddressMapper::Zap();
 }
 
 
@@ -998,7 +960,54 @@ void Serializer::VisitPointers(Object** start, Object** end) {
 }
 
 
-int Serializer::RootIndex(HeapObject* heap_object) {
+Object* SerializerDeserializer::partial_snapshot_cache_[
+    kPartialSnapshotCacheCapacity];
+int SerializerDeserializer::partial_snapshot_cache_length_ = 0;
+
+
+// This ensures that the partial snapshot cache keeps things alive during GC and
+// tracks their movement.  When it is called during serialization of the startup
+// snapshot the partial snapshot is empty, so nothing happens.  When the partial
+// (context) snapshot is created, this array is populated with the pointers that
+// the partial snapshot will need. As that happens we emit serialized objects to
+// the startup snapshot that correspond to the elements of this cache array.  On
+// deserialization we therefore need to visit the cache array.  This fills it up
+// with pointers to deserialized objects.
+void SerializerDeserializer::Iterate(ObjectVisitor *visitor) {
+  visitor->VisitPointers(
+      &partial_snapshot_cache_[0],
+      &partial_snapshot_cache_[partial_snapshot_cache_length_]);
+}
+
+
+// When deserializing we need to set the size of the snapshot cache.  This means
+// the root iteration code (above) will iterate over array elements, writing the
+// references to deserialized objects in them.
+void SerializerDeserializer::SetSnapshotCacheSize(int size) {
+  partial_snapshot_cache_length_ = size;
+}
+
+
+int PartialSerializer::PartialSnapshotCacheIndex(HeapObject* heap_object) {
+  for (int i = 0; i < partial_snapshot_cache_length_; i++) {
+    Object* entry = partial_snapshot_cache_[i];
+    if (entry == heap_object) return i;
+  }
+  // We didn't find the object in the cache.  So we add it to the cache and
+  // then visit the pointer so that it becomes part of the startup snapshot
+  // and we can refer to it from the partial snapshot.
+  int length = partial_snapshot_cache_length_;
+  CHECK(length < kPartialSnapshotCacheCapacity);
+  partial_snapshot_cache_[length] = heap_object;
+  startup_serializer_->VisitPointer(&partial_snapshot_cache_[length]);
+  // We don't recurse from the startup snapshot generator into the partial
+  // snapshot generator.
+  ASSERT(length == partial_snapshot_cache_length_);
+  return partial_snapshot_cache_length_++;
+}
+
+
+int PartialSerializer::RootIndex(HeapObject* heap_object) {
   for (int i = 0; i < Heap::kRootListLength; i++) {
     Object* root = Heap::roots_address()[i];
     if (root == heap_object) return i;
@@ -1007,33 +1016,26 @@ int Serializer::RootIndex(HeapObject* heap_object) {
 }
 
 
-void Serializer::SerializeObject(
-    Object* o,
+// Encode the location of an already deserialized object in order to write its
+// location into a later object.  We can encode the location as an offset from
+// the start of the deserialized objects or as an offset backwards from the
+// current allocation pointer.
+void Serializer::SerializeReferenceToPreviousObject(
+    int space,
+    int address,
     ReferenceRepresentation reference_representation) {
-  CHECK(o->IsHeapObject());
-  HeapObject* heap_object = HeapObject::cast(o);
-  if (partial_) {
-    int root_index = RootIndex(heap_object);
-    if (root_index != kInvalidRootIndex) {
-      sink_->Put(ROOT_SERIALIZATION, "RootSerialization");
-      sink_->PutInt(root_index, "root_index");
-      return;
-    }
-    // All the symbols that the snapshot needs should be in the root table.
-    ASSERT(!heap_object->IsSymbol());
-  }
-  if (SerializationAddressMapper::IsMapped(heap_object)) {
-    int space = SpaceOfAlreadySerializedObject(heap_object);
-    int address = SerializationAddressMapper::MappedTo(heap_object);
   int offset = CurrentAllocationAddress(space) - address;
   bool from_start = true;
   if (SpaceIsPaged(space)) {
+    // For paged space it is simple to encode back from current allocation if
+    // the object is on the same page as the current allocation pointer.
     if ((CurrentAllocationAddress(space) >> kPageSizeBits) ==
         (address >> kPageSizeBits)) {
       from_start = false;
       address = offset;
     }
   } else if (space == NEW_SPACE) {
+    // For new space it is always simple to encode back from current allocation.
     if (offset < address) {
       from_start = false;
       address = offset;
@@ -1042,6 +1044,9 @@ void Serializer::SerializeObject(
   // If we are actually dealing with real offsets (and not a numbering of
   // all objects) then we should shift out the bits that are always 0.
   if (!SpaceIsLarge(space)) address >>= kObjectAlignmentBits;
+  // On some architectures references between code objects are encoded
+  // specially (as relative offsets).  Such references have their own
+  // special tags to simplify the deserializer.
   if (reference_representation == CODE_TARGET_REPRESENTATION) {
     if (from_start) {
       sink_->Put(CODE_REFERENCE_SERIALIZATION + space, "RefCodeSer");
@@ -1051,8 +1056,10 @@ void Serializer::SerializeObject(
       sink_->PutInt(address, "address");
     }
   } else {
+    // Regular absolute references.
     CHECK_EQ(TAGGED_REPRESENTATION, reference_representation);
     if (from_start) {
+      // There are some common offsets that have their own specialized encoding.
 #define COMMON_REFS_CASE(tag, common_space, common_offset)               \
       if (space == common_space && address == common_offset) {           \
         sink_->PutSection(tag + REFERENCE_SERIALIZATION, "RefSer");      \
@@ -1068,6 +1075,77 @@ void Serializer::SerializeObject(
       sink_->PutInt(address, "address");
     }
   }
+}
+
+
+void StartupSerializer::SerializeObject(
+    Object* o,
+    ReferenceRepresentation reference_representation) {
+  CHECK(o->IsHeapObject());
+  HeapObject* heap_object = HeapObject::cast(o);
+
+  if (address_mapper_.IsMapped(heap_object)) {
+    int space = SpaceOfAlreadySerializedObject(heap_object);
+    int address = address_mapper_.MappedTo(heap_object);
+    SerializeReferenceToPreviousObject(space,
+                                       address,
+                                       reference_representation);
+  } else {
+    // Object has not yet been serialized.  Serialize it here.
+    ObjectSerializer object_serializer(this,
+                                       heap_object,
+                                       sink_,
+                                       reference_representation);
+    object_serializer.Serialize();
+  }
+}
+
+
+void StartupSerializer::SerializeWeakReferences() {
+  for (int i = partial_snapshot_cache_length_;
+       i < kPartialSnapshotCacheCapacity;
+       i++) {
+    sink_->Put(ROOT_SERIALIZATION, "RootSerialization");
+    sink_->PutInt(Heap::kUndefinedValueRootIndex, "root_index");
+  }
+  Heap::IterateWeakRoots(this, VISIT_ALL);
+}
+
+
+void PartialSerializer::SerializeObject(
+    Object* o,
+    ReferenceRepresentation reference_representation) {
+  CHECK(o->IsHeapObject());
+  HeapObject* heap_object = HeapObject::cast(o);
+
+  int root_index;
+  if ((root_index = RootIndex(heap_object)) != kInvalidRootIndex) {
+    sink_->Put(ROOT_SERIALIZATION, "RootSerialization");
+    sink_->PutInt(root_index, "root_index");
+    return;
+  }
+
+  if (ShouldBeInThePartialSnapshotCache(heap_object)) {
+    int cache_index = PartialSnapshotCacheIndex(heap_object);
+    sink_->Put(PARTIAL_SNAPSHOT_CACHE_ENTRY, "PartialSnapshotCache");
+    sink_->PutInt(cache_index, "partial_snapshot_cache_index");
+    return;
+  }
+
+  // Pointers from the partial snapshot to the objects in the startup snapshot
+  // should go through the root array or through the partial snapshot cache.
+  // If this is not the case you may have to add something to the root array.
+  ASSERT(!startup_serializer_->address_mapper()->IsMapped(heap_object));
+  // All the symbols that the partial snapshot needs should be either in the
+  // root table or in the partial snapshot cache.
+  ASSERT(!heap_object->IsSymbol());
+
+  if (address_mapper_.IsMapped(heap_object)) {
+    int space = SpaceOfAlreadySerializedObject(heap_object);
+    int address = address_mapper_.MappedTo(heap_object);
+    SerializeReferenceToPreviousObject(space,
+                                       address,
+                                       reference_representation);
   } else {
     // Object has not yet been serialized.  Serialize it here.
     ObjectSerializer serializer(this,
@@ -1079,7 +1157,6 @@ void Serializer::SerializeObject(
 }
 
 
-
 void Serializer::ObjectSerializer::Serialize() {
   int space = Serializer::SpaceOfObject(object_);
   int size = object_->Size();
@@ -1096,9 +1173,8 @@ void Serializer::ObjectSerializer::Serialize() {
 
   // Mark this object as already serialized.
   bool start_new_page;
-  SerializationAddressMapper::Map(
-    object_,
-    serializer_->Allocate(space, size, &start_new_page));
+  int offset = serializer_->Allocate(space, size, &start_new_page);
+  serializer_->address_mapper()->AddMapping(object_, offset);
   if (start_new_page) {
     sink_->Put(START_NEW_PAGE_SERIALIZATION, "NewPage");
     sink_->PutSection(space, "NewPageSpace");

src/serialize.h

@@ -185,9 +185,14 @@ class SnapshotByteSource {
   f(14, 32) \
   f(15, 36)
 
-// The SerDes class is a common superclass for Serializer and Deserializer
-// which is used to store common constants and methods used by both.
-class SerDes: public ObjectVisitor {
+// The Serializer/Deserializer class is a common superclass for Serializer and
+// Deserializer which is used to store common constants and methods used by
+// both.
+class SerializerDeserializer: public ObjectVisitor {
+ public:
+  static void Iterate(ObjectVisitor* visitor);
+  static void SetSnapshotCacheSize(int size);
+
  protected:
   enum DataType {
     RAW_DATA_SERIALIZATION = 0,
@@ -202,7 +207,8 @@ class SerDes: public ObjectVisitor {
     START_NEW_PAGE_SERIALIZATION = 37,
     NATIVES_STRING_RESOURCE = 38,
     ROOT_SERIALIZATION = 39,
-    // Free: 40-47.
+    PARTIAL_SNAPSHOT_CACHE_ENTRY = 40,
+    // Free: 41-47.
     BACKREF_SERIALIZATION = 48,
     // One per space, must be kSpaceMask aligned.
     // Free: 57-63.
@@ -227,17 +233,21 @@ class SerDes: public ObjectVisitor {
   static inline bool SpaceIsPaged(int space) {
     return space >= FIRST_PAGED_SPACE && space <= LAST_PAGED_SPACE;
   }
+
+  static int partial_snapshot_cache_length_;
+  static const int kPartialSnapshotCacheCapacity = 1024;
+  static Object* partial_snapshot_cache_[];
 };
 
 
 
 // A Deserializer reads a snapshot and reconstructs the Object graph it defines.
-class Deserializer: public SerDes {
+class Deserializer: public SerializerDeserializer {
  public:
   // Create a deserializer from a snapshot byte source.
   explicit Deserializer(SnapshotByteSource* source);
 
-  virtual ~Deserializer() { }
+  virtual ~Deserializer();
 
   // Deserialize the snapshot into an empty heap.
   void Deserialize();
@@ -249,8 +259,6 @@ class Deserializer: public SerDes {
   virtual void Synchronize(const char* tag);
 #endif
 
-  static void TearDown();
-
  private:
   virtual void VisitPointers(Object** start, Object** end);
 
@@ -272,7 +280,7 @@ class Deserializer: public SerDes {
   // (In large object space we are keeping track of individual objects
   // rather than pages.)  In new space we just need the address of the
   // first object and the others will flow from that.
-  List<Address> pages_[SerDes::kNumberOfSpaces];
+  List<Address> pages_[SerializerDeserializer::kNumberOfSpaces];
 
   SnapshotByteSource* source_;
   static ExternalReferenceDecoder* external_reference_decoder_;
@@ -300,13 +308,62 @@ class SnapshotByteSink {
 };
 
 
-class Serializer : public SerDes {
+// Mapping objects to their location after deserialization.
+// This is used during building, but not at runtime by V8.
+class SerializationAddressMapper {
+ public:
+  SerializationAddressMapper()
+      : serialization_map_(new HashMap(&SerializationMatchFun)),
+        no_allocation_(new AssertNoAllocation()) { }
+
+  ~SerializationAddressMapper() {
+    delete serialization_map_;
+    delete no_allocation_;
+  }
+
+  bool IsMapped(HeapObject* obj) {
+    return serialization_map_->Lookup(Key(obj), Hash(obj), false) != NULL;
+  }
+
+  int MappedTo(HeapObject* obj) {
+    ASSERT(IsMapped(obj));
+    return static_cast<int>(reinterpret_cast<intptr_t>(
+        serialization_map_->Lookup(Key(obj), Hash(obj), false)->value));
+  }
+
+  void AddMapping(HeapObject* obj, int to) {
+    ASSERT(!IsMapped(obj));
+    HashMap::Entry* entry =
+        serialization_map_->Lookup(Key(obj), Hash(obj), true);
+    entry->value = Value(to);
+  }
+
+ private:
+  static bool SerializationMatchFun(void* key1, void* key2) {
+    return key1 == key2;
+  }
+
+  static uint32_t Hash(HeapObject* obj) {
+    return static_cast<int32_t>(reinterpret_cast<intptr_t>(obj->address()));
+  }
+
+  static void* Key(HeapObject* obj) {
+    return reinterpret_cast<void*>(obj->address());
+  }
+
+  static void* Value(int v) {
+    return reinterpret_cast<void*>(v);
+  }
+
+  HashMap* serialization_map_;
+  AssertNoAllocation* no_allocation_;
+  DISALLOW_COPY_AND_ASSIGN(SerializationAddressMapper);
+};
+
+
+class Serializer : public SerializerDeserializer {
  public:
   explicit Serializer(SnapshotByteSink* sink);
-  // Serialize the current state of the heap.
-  void Serialize();
-  // Serialize a single object and the objects reachable from it.
-  void SerializePartial(Object** obj);
   void VisitPointers(Object** start, Object** end);
   // You can call this after serialization to find out how much space was used
   // in each space.
@@ -327,15 +384,20 @@ class Serializer : public SerDes {
   // going on.
   static void TooLateToEnableNow() { too_late_to_enable_now_ = true; }
   static bool enabled() { return serialization_enabled_; }
+  SerializationAddressMapper* address_mapper() { return &address_mapper_; }
 #ifdef DEBUG
   virtual void Synchronize(const char* tag);
 #endif
 
- private:
+ protected:
   enum ReferenceRepresentation {
     TAGGED_REPRESENTATION,      // A tagged object reference.
     CODE_TARGET_REPRESENTATION  // A reference to first instruction in target.
   };
+  static const int kInvalidRootIndex = -1;
+  virtual int RootIndex(HeapObject* heap_object) = 0;
+  virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) = 0;
+
   class ObjectSerializer : public ObjectVisitor {
    public:
     ObjectSerializer(Serializer* serializer,
@@ -371,7 +433,12 @@ class Serializer : public SerDes {
     int bytes_processed_so_far_;
   };
 
-  void SerializeObject(Object* o, ReferenceRepresentation representation);
+  virtual void SerializeObject(Object* o,
+                               ReferenceRepresentation representation) = 0;
+  void SerializeReferenceToPreviousObject(
+      int space,
+      int address,
+      ReferenceRepresentation reference_representation);
   void InitializeAllocators();
   // This will return the space for an object.  If the object is in large
   // object space it may return kLargeCode or kLargeFixedArray in order
@@ -386,8 +453,6 @@ class Serializer : public SerDes {
   int EncodeExternalReference(Address addr) {
     return external_reference_encoder_->Encode(addr);
   }
-  int RootIndex(HeapObject* heap_object);
-  static const int kInvalidRootIndex = -1;
 
   // Keep track of the fullness of each space in order to generate
   // relative addresses for back references.  Large objects are
@@ -397,11 +462,11 @@ class Serializer : public SerDes {
   SnapshotByteSink* sink_;
   int current_root_index_;
   ExternalReferenceEncoder* external_reference_encoder_;
-  bool partial_;
   static bool serialization_enabled_;
   // Did we already make use of the fact that serialization was not enabled?
   static bool too_late_to_enable_now_;
   int large_object_total_;
+  SerializationAddressMapper address_mapper_;
 
   friend class ObjectSerializer;
   friend class Deserializer;
@@ -409,6 +474,62 @@ class Serializer : public SerDes {
   DISALLOW_COPY_AND_ASSIGN(Serializer);
 };
 
+
+class PartialSerializer : public Serializer {
+ public:
+  PartialSerializer(Serializer* startup_snapshot_serializer,
+                    SnapshotByteSink* sink)
+    : Serializer(sink),
+      startup_serializer_(startup_snapshot_serializer) {
+  }
+
+  // Serialize the objects reachable from a single object pointer.
+  virtual void Serialize(Object** o);
+  virtual void SerializeObject(Object* o,
+                               ReferenceRepresentation representation);
+
+ protected:
+  virtual int RootIndex(HeapObject* o);
+  virtual int PartialSnapshotCacheIndex(HeapObject* o);
+  virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
+    return o->IsString() || o->IsSharedFunctionInfo();
+  }
+
+ private:
+  Serializer* startup_serializer_;
+  DISALLOW_COPY_AND_ASSIGN(PartialSerializer);
+};
+
+
+class StartupSerializer : public Serializer {
+ public:
+  explicit StartupSerializer(SnapshotByteSink* sink) : Serializer(sink) {
+    // Clear the cache of objects used by the partial snapshot.  After the
+    // strong roots have been serialized we can create a partial snapshot
+    // which will repopulate the cache with objects neede by that partial
+    // snapshot.
+    partial_snapshot_cache_length_ = 0;
+  }
+  // Serialize the current state of the heap.  The order is:
+  // 1) Strong references.
+  // 2) Partial snapshot cache.
+  // 3) Weak references (eg the symbol table).
+  virtual void SerializeStrongReferences();
+  virtual void SerializeObject(Object* o,
+                               ReferenceRepresentation representation);
+  void SerializeWeakReferences();
+  void Serialize() {
+    SerializeStrongReferences();
+    SerializeWeakReferences();
+  }
+
+ private:
+  virtual int RootIndex(HeapObject* o) { return kInvalidRootIndex; }
+  virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
+    return false;
+  }
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_

src/snapshot-common.cc

@@ -59,42 +59,4 @@ bool Snapshot::Initialize(const char* snapshot_file) {
   return false;
 }
 
-
-class FileByteSink : public SnapshotByteSink {
- public:
-  explicit FileByteSink(const char* snapshot_file) {
-    fp_ = OS::FOpen(snapshot_file, "wb");
-    if (fp_ == NULL) {
-      PrintF("Unable to write to snapshot file \"%s\"\n", snapshot_file);
-      exit(1);
-    }
-  }
-  virtual ~FileByteSink() {
-    if (fp_ != NULL) {
-      fclose(fp_);
-    }
-  }
-  virtual void Put(int byte, const char* description) {
-    if (fp_ != NULL) {
-      fputc(byte, fp_);
-    }
-  }
-  virtual int Position() {
-    return ftell(fp_);
-  }
-
- private:
-  FILE* fp_;
-};
-
-
-bool Snapshot::WriteToFile(const char* snapshot_file) {
-  FileByteSink file(snapshot_file);
-  Serializer ser(&file);
-  ser.Serialize();
-  return true;
-}
-
-
-
 } }  // namespace v8::internal

src/v8.cc

@@ -146,7 +146,6 @@ void V8::TearDown() {
 
   Heap::TearDown();
   Logger::TearDown();
-  Deserializer::TearDown();
 
   is_running_ = false;
   has_been_disposed_ = true;

test/cctest/test-serialize.cc

@@ -39,6 +39,8 @@
 #include "cctest.h"
 #include "spaces.h"
 #include "objects.h"
+#include "natives.h"
+#include "bootstrapper.h"
 
 using namespace v8::internal;
 
@@ -169,6 +171,75 @@ TEST(ExternalReferenceDecoder) {
 }
 
 
+class FileByteSink : public SnapshotByteSink {
+ public:
+  explicit FileByteSink(const char* snapshot_file) {
+    fp_ = OS::FOpen(snapshot_file, "wb");
+    file_name_ = snapshot_file;
+    if (fp_ == NULL) {
+      PrintF("Unable to write to snapshot file \"%s\"\n", snapshot_file);
+      exit(1);
+    }
+  }
+  virtual ~FileByteSink() {
+    if (fp_ != NULL) {
+      fclose(fp_);
+    }
+  }
+  virtual void Put(int byte, const char* description) {
+    if (fp_ != NULL) {
+      fputc(byte, fp_);
+    }
+  }
+  virtual int Position() {
+    return ftell(fp_);
+  }
+  void WriteSpaceUsed(
+      int new_space_used,
+      int pointer_space_used,
+      int data_space_used,
+      int code_space_used,
+      int map_space_used,
+      int cell_space_used,
+      int large_space_used);
+
+ private:
+  FILE* fp_;
+  const char* file_name_;
+};
+
+
+void FileByteSink::WriteSpaceUsed(
+      int new_space_used,
+      int pointer_space_used,
+      int data_space_used,
+      int code_space_used,
+      int map_space_used,
+      int cell_space_used,
+      int large_space_used) {
+  int file_name_length = strlen(file_name_) + 10;
+  Vector<char> name = Vector<char>::New(file_name_length + 1);
+  OS::SNPrintF(name, "%s.size", file_name_);
+  FILE* fp = OS::FOpen(name.start(), "w");
+  fprintf(fp, "new %d\n", new_space_used);
+  fprintf(fp, "pointer %d\n", pointer_space_used);
+  fprintf(fp, "data %d\n", data_space_used);
+  fprintf(fp, "code %d\n", code_space_used);
+  fprintf(fp, "map %d\n", map_space_used);
+  fprintf(fp, "cell %d\n", cell_space_used);
+  fprintf(fp, "large %d\n", large_space_used);
+  fclose(fp);
+}
+
+
+static bool WriteToFile(const char* snapshot_file) {
+  FileByteSink file(snapshot_file);
+  StartupSerializer ser(&file);
+  ser.Serialize();
+  return true;
+}
+
+
 static void Serialize() {
   // We have to create one context.  One reason for this is so that the builtins
   // can be loaded from v8natives.js and their addresses can be processed.  This
@@ -176,7 +247,7 @@ static void Serialize() {
   // that would confuse the serialization/deserialization process.
   v8::Persistent<v8::Context> env = v8::Context::New();
   env.Dispose();
-  Snapshot::WriteToFile(FLAG_testing_serialization_file);
+  WriteToFile(FLAG_testing_serialization_file);
 }
 
 
@@ -273,95 +344,63 @@ DEPENDENT_TEST(DeserializeFromSecondSerializationAndRunScript2,
 }
 
 
-class FileByteSink : public SnapshotByteSink {
- public:
-  explicit FileByteSink(const char* snapshot_file) {
-    fp_ = OS::FOpen(snapshot_file, "wb");
-    file_name_ = snapshot_file;
-    if (fp_ == NULL) {
-      PrintF("Unable to write to snapshot file \"%s\"\n", snapshot_file);
-      exit(1);
-    }
-  }
-  virtual ~FileByteSink() {
-    if (fp_ != NULL) {
-      fclose(fp_);
-    }
-  }
-  virtual void Put(int byte, const char* description) {
-    if (fp_ != NULL) {
-      fputc(byte, fp_);
-    }
-  }
-  virtual int Position() {
-    return ftell(fp_);
-  }
-  void WriteSpaceUsed(
-      int new_space_used,
-      int pointer_space_used,
-      int data_space_used,
-      int code_space_used,
-      int map_space_used,
-      int cell_space_used,
-      int large_space_used);
-
- private:
-  FILE* fp_;
-  const char* file_name_;
-};
-
-
-void FileByteSink::WriteSpaceUsed(
-      int new_space_used,
-      int pointer_space_used,
-      int data_space_used,
-      int code_space_used,
-      int map_space_used,
-      int cell_space_used,
-      int large_space_used) {
-  int file_name_length = StrLength(file_name_) + 10;
-  Vector<char> name = Vector<char>::New(file_name_length + 1);
-  OS::SNPrintF(name, "%s.size", file_name_);
-  FILE* fp = OS::FOpen(name.start(), "w");
-  fprintf(fp, "new %d\n", new_space_used);
-  fprintf(fp, "pointer %d\n", pointer_space_used);
-  fprintf(fp, "data %d\n", data_space_used);
-  fprintf(fp, "code %d\n", code_space_used);
-  fprintf(fp, "map %d\n", map_space_used);
-  fprintf(fp, "cell %d\n", cell_space_used);
-  fprintf(fp, "large %d\n", large_space_used);
-  fclose(fp);
-}
-
-
 TEST(PartialSerialization) {
   Serializer::Enable();
   v8::V8::Initialize();
+
   v8::Persistent<v8::Context> env = v8::Context::New();
+  ASSERT(!env.IsEmpty());
   env->Enter();
+  // Make sure all builtin scripts are cached.
+  { HandleScope scope;
+    for (int i = 0; i < Natives::GetBuiltinsCount(); i++) {
+      Bootstrapper::NativesSourceLookup(i);
+    }
+  }
+  Heap::CollectAllGarbage(true);
+  Heap::CollectAllGarbage(true);
 
+  Object* raw_foo;
+  {
     v8::HandleScope handle_scope;
     v8::Local<v8::String> foo = v8::String::New("foo");
+    ASSERT(!foo.IsEmpty());
+    raw_foo = *(v8::Utils::OpenHandle(*foo));
+  }
+
+  int file_name_length = strlen(FLAG_testing_serialization_file) + 10;
+  Vector<char> startup_name = Vector<char>::New(file_name_length + 1);
+  OS::SNPrintF(startup_name, "%s.startup", FLAG_testing_serialization_file);
+
+  env->Exit();
+  env.Dispose();
 
-  FileByteSink file(FLAG_testing_serialization_file);
-  Serializer ser(&file);
-  i::Handle<i::String> internal_foo = v8::Utils::OpenHandle(*foo);
-  Object* raw_foo = *internal_foo;
-  ser.SerializePartial(&raw_foo);
-  file.WriteSpaceUsed(ser.CurrentAllocationAddress(NEW_SPACE),
-                      ser.CurrentAllocationAddress(OLD_POINTER_SPACE),
-                      ser.CurrentAllocationAddress(OLD_DATA_SPACE),
-                      ser.CurrentAllocationAddress(CODE_SPACE),
-                      ser.CurrentAllocationAddress(MAP_SPACE),
-                      ser.CurrentAllocationAddress(CELL_SPACE),
-                      ser.CurrentAllocationAddress(LO_SPACE));
+  FileByteSink startup_sink(startup_name.start());
+  StartupSerializer startup_serializer(&startup_sink);
+  startup_serializer.SerializeStrongReferences();
+
+  FileByteSink partial_sink(FLAG_testing_serialization_file);
+  PartialSerializer p_ser(&startup_serializer, &partial_sink);
+  p_ser.Serialize(&raw_foo);
+  startup_serializer.SerializeWeakReferences();
+  partial_sink.WriteSpaceUsed(p_ser.CurrentAllocationAddress(NEW_SPACE),
+                              p_ser.CurrentAllocationAddress(OLD_POINTER_SPACE),
+                              p_ser.CurrentAllocationAddress(OLD_DATA_SPACE),
+                              p_ser.CurrentAllocationAddress(CODE_SPACE),
+                              p_ser.CurrentAllocationAddress(MAP_SPACE),
+                              p_ser.CurrentAllocationAddress(CELL_SPACE),
+                              p_ser.CurrentAllocationAddress(LO_SPACE));
 }
 
 
 DEPENDENT_TEST(PartialDeserialization, PartialSerialization) {
-  v8::V8::Initialize();
+  int file_name_length = strlen(FLAG_testing_serialization_file) + 10;
+  Vector<char> startup_name = Vector<char>::New(file_name_length + 1);
+  OS::SNPrintF(startup_name, "%s.startup", FLAG_testing_serialization_file);
+
+  CHECK(Snapshot::Initialize(startup_name.start()));
+
   const char* file_name = FLAG_testing_serialization_file;
-  int file_name_length = StrLength(file_name) + 10;
   Vector<char> name = Vector<char>::New(file_name_length + 1);
   OS::SNPrintF(name, "%s.size", file_name);
   FILE* fp = OS::FOpen(name.start(), "r");
@@ -392,11 +431,25 @@ DEPENDENT_TEST(PartialDeserialization, PartialSerialization) {
                      large_size);
   int snapshot_size = 0;
   byte* snapshot = ReadBytes(file_name, &snapshot_size);
+
+  Object* root;
+  {
     SnapshotByteSource source(snapshot, snapshot_size);
     Deserializer deserializer(&source);
-  Object* root;
     deserializer.DeserializePartial(&root);
     CHECK(root->IsString());
+  }
+  v8::HandleScope handle_scope;
+  Handle<Object>root_handle(root);
+
+  Object* root2;
+  {
+    SnapshotByteSource source(snapshot, snapshot_size);
+    Deserializer deserializer(&source);
+    deserializer.DeserializePartial(&root2);
+    CHECK(root2->IsString());
+    CHECK(*root_handle == root2);
+  }
 }