v8/src/serialize.h

// Copyright 2006-2008 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
// met:
//
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//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
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//       with the distribution.
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#ifndef V8_SERIALIZE_H_
#define V8_SERIALIZE_H_

#include "hashmap.h"

namespace v8 { namespace internal {

// A TypeCode is used to distinguish different kinds of external reference.
// It is a single bit to make testing for types easy.
enum TypeCode {
  UNCLASSIFIED,        // One-of-a-kind references.
  BUILTIN,
  RUNTIME_FUNCTION,
  IC_UTILITY,
  DEBUG_ADDRESS,
  STATS_COUNTER,
  TOP_ADDRESS,
  C_BUILTIN,
  EXTENSION,
  ACCESSOR,
  RUNTIME_ENTRY,
  STUB_CACHE_TABLE
};

const int kTypeCodeCount = STUB_CACHE_TABLE + 1;
const int kFirstTypeCode = UNCLASSIFIED;

const int kReferenceIdBits = 16;
const int kReferenceIdMask = (1 << kReferenceIdBits) - 1;
const int kReferenceTypeShift = kReferenceIdBits;
const int kDebugRegisterBits = 4;
const int kDebugIdShift = kDebugRegisterBits;


class ExternalReferenceEncoder {
 public:
  ExternalReferenceEncoder();

  uint32_t Encode(Address key) const;

  const char* NameOfAddress(Address key) const;

 private:
  HashMap encodings_;
  static uint32_t Hash(Address key) {
    return reinterpret_cast<uint32_t>(key) >> 2;
  }

  int IndexOf(Address key) const;

  static bool Match(void* key1, void* key2) { return key1 == key2; }

  void Put(Address key, int index);
};


class ExternalReferenceDecoder {
 public:
  ExternalReferenceDecoder();
  ~ExternalReferenceDecoder();

  Address Decode(uint32_t key) const {
    if (key == 0) return NULL;
    return *Lookup(key);
  }

 private:
  Address** encodings_;

  Address* Lookup(uint32_t key) const {
    int type = key >> kReferenceTypeShift;
    ASSERT(kFirstTypeCode <= type && type < kTypeCodeCount);
    int id = key & kReferenceIdMask;
    return &encodings_[type][id];
  }

  void Put(uint32_t key, Address value) {
    *Lookup(key) = value;
  }
};


// A Serializer recursively visits objects to construct a serialized
// representation of the Heap stored in a string. Serialization is
// destructive. We use a similar mechanism to the GC to ensure that
// each object is visited once, namely, we modify the map pointer of
// each visited object to contain the relative address in the
// appropriate space where that object will be allocated when the heap
// is deserialized.


// Helper classes defined in serialize.cc.
class RelativeAddress;
class SimulatedHeapSpace;
class SnapshotWriter;
class ReferenceUpdater;


class Serializer: public ObjectVisitor {
 public:
  Serializer();

  virtual ~Serializer();

  // Serialize the current state of the heap. This operation destroys the
  // heap contents and the contents of the roots into the heap.
  void Serialize();

  // Returns the serialized buffer. Ownership is transferred to the
  // caller. Only the destructor and getters may be called after this call.
  void Finalize(byte** str, int* len);

  int roots() { return roots_; }
  int objects() { return objects_; }

#ifdef DEBUG
  // insert "tag" into the serialized stream
  virtual void Synchronize(const char* tag);
#endif

  static bool enabled() { return serialization_enabled_; }

  static void Enable() { serialization_enabled_ = true; }
  static void Disable() { serialization_enabled_ = false; }

 private:
  friend class ReferenceUpdater;

  virtual void VisitPointers(Object** start, Object** end);

  bool IsVisited(HeapObject* obj);

  Address GetSavedAddress(HeapObject* obj);

  void SaveAddress(HeapObject* obj, Address addr);

  void PutEncodedAddress(Address addr);
  // Write the global flags into the file.
  void PutFlags();
  // Write global information into the header of the file.
  void PutHeader();
  // Write the contents of the log into the file.
  void PutLog();
  // Serialize 'obj', and return its encoded RelativeAddress.
  Address PutObject(HeapObject* obj);
  // Write a stack of handles to the file bottom first.
  void PutGlobalHandleStack(const List<Handle<Object> >& stack);
  // Write the context stack into the file.
  void PutContextStack();

  // Return the encoded RelativeAddress where this object will be
  // allocated on deserialization. On the first visit of 'o',
  // serialize its contents. On return, *serialized will be true iff
  // 'o' has just been serialized.
  Address Encode(Object* o, bool* serialized);

  // Simulate the allocation of 'obj', returning the address where it will
  // be allocated on deserialization
  RelativeAddress Allocate(HeapObject* obj);

  void InitializeAllocators();

  SnapshotWriter* writer_;
  bool root_;  // serializing a root?
  int roots_;  // number of roots visited
  int objects_;  // number of objects serialized

  static bool serialization_enabled_;

  int flags_end_;  // The position right after the flags.

  // An array of per-space SimulatedHeapSpacees used as memory allocators.
  SimulatedHeapSpace* allocator_[LAST_SPACE+1];
  // A list of global handles at serialization time.
  List<Object**> global_handles_;

  ExternalReferenceEncoder* reference_encoder_;

  HashMap saved_addresses_;

  DISALLOW_COPY_AND_ASSIGN(Serializer);
};

// Helper class to read the bytes of the serialized heap.

class SnapshotReader {
 public:
  SnapshotReader(const byte* str, int len): str_(str), end_(str + len) {}

  void ExpectC(char expected) {
    int c = GetC();
    USE(c);
    ASSERT(c == expected);
  }

  int GetC() {
    if (str_ >= end_) return EOF;
    return *str_++;
  }

  int GetInt() {
    int result;
    GetBytes(reinterpret_cast<Address>(&result), sizeof(result));
    return result;
  }

  void GetBytes(Address a, int size) {
    ASSERT(str_ + size <= end_);
    memcpy(a, str_, size);
    str_ += size;
  }

  char* GetString() {
    ExpectC('[');
    int size = GetInt();
    ExpectC(']');
    char* s = NewArray<char>(size + 1);
    GetBytes(reinterpret_cast<Address>(s), size);
    s[size] = 0;
    return s;
  }

 private:
  const byte* str_;
  const byte* end_;
};


// A Deserializer reads a snapshot and reconstructs the Object graph it defines.

class Deserializer: public ObjectVisitor {
 public:
  // Create a deserializer. The snapshot is held in str and has size len.
  Deserializer(const byte* str, int len);

  virtual ~Deserializer();

  // Read the flags from the header of the file, and set those that
  // should be inherited from the snapshot.
  void GetFlags();

  // Read saved profiling information from the file and log it if required.
  void GetLog();

  // Deserialize the snapshot into an empty heap.
  void Deserialize();

  int roots() { return roots_; }
  int objects() { return objects_; }

#ifdef DEBUG
  // Check for the presence of "tag" in the serialized stream
  virtual void Synchronize(const char* tag);
#endif

 private:
  virtual void VisitPointers(Object** start, Object** end);
  virtual void VisitExternalReferences(Address* start, Address* end);
  virtual void VisitRuntimeEntry(RelocInfo* rinfo);

  Address GetEncodedAddress();

  // Read other global information (except flags) from the header of the file.
  void GetHeader();
  // Read a stack of handles from the file bottom first.
  void GetGlobalHandleStack(List<Handle<Object> >* stack);
  // Read the context stack from the file.
  void GetContextStack();

  Object* GetObject();

  // Get the encoded address. In debug mode we make sure
  // it matches the given expectations.
  void ExpectEncodedAddress(Address expected);

  // Given an encoded address (the result of
  // RelativeAddress::Encode), return the object to which it points,
  // which will be either an Smi or a HeapObject in the current heap.
  Object* Resolve(Address encoded_address);

  SnapshotReader reader_;
  bool root_;  // Deserializing a root?
  int roots_;  // number of roots visited
  int objects_;  // number of objects serialized

  bool has_log_;  // The file has log information.

  // Resolve caches the following:
  List<Page*> map_pages_;          // All pages in the map space.
  List<Page*> old_pointer_pages_;  // All pages in the old pointer space.
  List<Page*> old_data_pages_;     // All pages in the old data space.
  List<Page*> code_pages_;
  List<Object*> large_objects_;    // All known large objects.
  // A list of global handles at deserialization time.
  List<Object**> global_handles_;

  ExternalReferenceDecoder* reference_decoder_;

#ifdef DEBUG
  bool expect_debug_information_;
#endif

  DISALLOW_COPY_AND_ASSIGN(Deserializer);
};

} }  // namespace v8::internal

#endif  // V8_SERIALIZE_H_