heap.cc.svn-base

Google浏览器V8内核代码

void Heap::MarkCompact(GCTracer* tracer) {
  gc_state_ = MARK_COMPACT;
  mc_count_++;
  tracer->set_full_gc_count(mc_count_);
  LOG(ResourceEvent("markcompact", "begin"));

  MarkCompactPrologue();

  MarkCompactCollector::CollectGarbage(tracer);

  MarkCompactEpilogue();

  LOG(ResourceEvent("markcompact", "end"));

  gc_state_ = NOT_IN_GC;

  Shrink();

  Counters::objs_since_last_full.Set(0);
}


void Heap::MarkCompactPrologue() {
  CompilationCache::MarkCompactPrologue();
  RegExpImpl::OldSpaceCollectionPrologue();
  Top::MarkCompactPrologue();
  ThreadManager::MarkCompactPrologue();
}


void Heap::MarkCompactEpilogue() {
  Top::MarkCompactEpilogue();
  ThreadManager::MarkCompactEpilogue();
}


Object* Heap::FindCodeObject(Address a) {
  Object* obj = code_space_->FindObject(a);
  if (obj->IsFailure()) {
    obj = lo_space_->FindObject(a);
  }
  ASSERT(!obj->IsFailure());
  return obj;
}


// Helper class for copying HeapObjects
class CopyVisitor: public ObjectVisitor {
 public:

  void VisitPointer(Object** p) {
    CopyObject(p);
  }

  void VisitPointers(Object** start, Object** end) {
    // Copy all HeapObject pointers in [start, end)
    for (Object** p = start; p < end; p++) CopyObject(p);
  }

 private:
  void CopyObject(Object** p) {
    if (!Heap::InFromSpace(*p)) return;
    Heap::CopyObject(reinterpret_cast<HeapObject**>(p));
  }
};


// Shared state read by the scavenge collector and set by CopyObject.
static Address promoted_top = NULL;


#ifdef DEBUG
// Visitor class to verify pointers in code or data space do not point into
// new space.
class VerifyNonPointerSpacePointersVisitor: public ObjectVisitor {
 public:
  void VisitPointers(Object** start, Object**end) {
    for (Object** current = start; current < end; current++) {
      if ((*current)->IsHeapObject()) {
        ASSERT(!Heap::InNewSpace(HeapObject::cast(*current)));
      }
    }
  }
};
#endif

void Heap::Scavenge() {
#ifdef DEBUG
  if (FLAG_enable_slow_asserts) {
    VerifyNonPointerSpacePointersVisitor v;
    HeapObjectIterator it(code_space_);
    while (it.has_next()) {
      HeapObject* object = it.next();
      if (object->IsCode()) {
        Code::cast(object)->ConvertICTargetsFromAddressToObject();
      }
      object->Iterate(&v);
      if (object->IsCode()) {
        Code::cast(object)->ConvertICTargetsFromObjectToAddress();
      }
    }
  }
#endif

  gc_state_ = SCAVENGE;

  // Implements Cheney's copying algorithm
  LOG(ResourceEvent("scavenge", "begin"));

  scavenge_count_++;
  if (new_space_->Capacity() < new_space_->MaximumCapacity() &&
      scavenge_count_ > new_space_growth_limit_) {
    // Double the size of the new space, and double the limit.  The next
    // doubling attempt will occur after the current new_space_growth_limit_
    // more collections.
    // TODO(1240712): NewSpace::Double has a return value which is
    // ignored here.
    new_space_->Double();
    new_space_growth_limit_ *= 2;
  }

  // Flip the semispaces.  After flipping, to space is empty, from space has
  // live objects.
  new_space_->Flip();
  new_space_->ResetAllocationInfo();

  // We need to sweep newly copied objects which can be in either the to space
  // or the old space.  For to space objects, we use a mark.  Newly copied
  // objects lie between the mark and the allocation top.  For objects
  // promoted to old space, we write their addresses downward from the top of
  // the new space.  Sweeping newly promoted objects requires an allocation
  // pointer and a mark.  Note that the allocation pointer 'top' actually
  // moves downward from the high address in the to space.
  //
  // There is guaranteed to be enough room at the top of the to space for the
  // addresses of promoted objects: every object promoted frees up its size in
  // bytes from the top of the new space, and objects are at least one pointer
  // in size.  Using the new space to record promoted addresses makes the
  // scavenge collector agnostic to the allocation strategy (eg, linear or
  // free-list) used in old space.
  Address new_mark = new_space_->ToSpaceLow();
  Address promoted_mark = new_space_->ToSpaceHigh();
  promoted_top = new_space_->ToSpaceHigh();

  CopyVisitor copy_visitor;
  // Copy roots.
  IterateRoots(&copy_visitor);

  // Copy objects reachable from the old generation.  By definition, there
  // are no intergenerational pointers in code or data spaces.
  IterateRSet(old_pointer_space_, &CopyObject);
  IterateRSet(map_space_, &CopyObject);
  lo_space_->IterateRSet(&CopyObject);

  bool has_processed_weak_pointers = false;

  while (true) {
    ASSERT(new_mark <= new_space_->top());
    ASSERT(promoted_mark >= promoted_top);

    // Copy objects reachable from newly copied objects.
    while (new_mark < new_space_->top() || promoted_mark > promoted_top) {
      // Sweep newly copied objects in the to space.  The allocation pointer
      // can change during sweeping.
      Address previous_top = new_space_->top();
      SemiSpaceIterator new_it(new_space_, new_mark);
      while (new_it.has_next()) {
        new_it.next()->Iterate(&copy_visitor);
      }
      new_mark = previous_top;

      // Sweep newly copied objects in the old space.  The promotion 'top'
      // pointer could change during sweeping.
      previous_top = promoted_top;
      for (Address current = promoted_mark - kPointerSize;
           current >= previous_top;
           current -= kPointerSize) {
        HeapObject* object = HeapObject::cast(Memory::Object_at(current));
        object->Iterate(&copy_visitor);
        UpdateRSet(object);
      }
      promoted_mark = previous_top;
    }

    if (has_processed_weak_pointers) break;  // We are done.
    // Copy objects reachable from weak pointers.
    GlobalHandles::IterateWeakRoots(&copy_visitor);
    has_processed_weak_pointers = true;
  }

  // Set age mark.
  new_space_->set_age_mark(new_mark);

  LOG(ResourceEvent("scavenge", "end"));

  gc_state_ = NOT_IN_GC;
}


void Heap::ClearRSetRange(Address start, int size_in_bytes) {
  uint32_t start_bit;
  Address start_word_address =
      Page::ComputeRSetBitPosition(start, 0, &start_bit);
  uint32_t end_bit;
  Address end_word_address =
      Page::ComputeRSetBitPosition(start + size_in_bytes - kIntSize,
                                   0,
                                   &end_bit);

  // We want to clear the bits in the starting word starting with the
  // first bit, and in the ending word up to and including the last
  // bit.  Build a pair of bitmasks to do that.
  uint32_t start_bitmask = start_bit - 1;
  uint32_t end_bitmask = ~((end_bit << 1) - 1);

  // If the start address and end address are the same, we mask that
  // word once, otherwise mask the starting and ending word
  // separately and all the ones in between.
  if (start_word_address == end_word_address) {
    Memory::uint32_at(start_word_address) &= (start_bitmask | end_bitmask);
  } else {
    Memory::uint32_at(start_word_address) &= start_bitmask;
    Memory::uint32_at(end_word_address) &= end_bitmask;
    start_word_address += kIntSize;
    memset(start_word_address, 0, end_word_address - start_word_address);
  }
}


class UpdateRSetVisitor: public ObjectVisitor {
 public:

  void VisitPointer(Object** p) {
    UpdateRSet(p);
  }

  void VisitPointers(Object** start, Object** end) {
    // Update a store into slots [start, end), used (a) to update remembered
    // set when promoting a young object to old space or (b) to rebuild
    // remembered sets after a mark-compact collection.
    for (Object** p = start; p < end; p++) UpdateRSet(p);
  }
 private:

  void UpdateRSet(Object** p) {
    // The remembered set should not be set.  It should be clear for objects
    // newly copied to old space, and it is cleared before rebuilding in the
    // mark-compact collector.
    ASSERT(!Page::IsRSetSet(reinterpret_cast<Address>(p), 0));
    if (Heap::InNewSpace(*p)) {
      Page::SetRSet(reinterpret_cast<Address>(p), 0);
    }
  }
};


int Heap::UpdateRSet(HeapObject* obj) {
  ASSERT(!InNewSpace(obj));
  // Special handling of fixed arrays to iterate the body based on the start
  // address and offset.  Just iterating the pointers as in UpdateRSetVisitor
  // will not work because Page::SetRSet needs to have the start of the
  // object.
  if (obj->IsFixedArray()) {
    FixedArray* array = FixedArray::cast(obj);
    int length = array->length();
    for (int i = 0; i < length; i++) {
      int offset = FixedArray::kHeaderSize + i * kPointerSize;
      ASSERT(!Page::IsRSetSet(obj->address(), offset));
      if (Heap::InNewSpace(array->get(i))) {
        Page::SetRSet(obj->address(), offset);
      }
    }
  } else if (!obj->IsCode()) {
    // Skip code object, we know it does not contain inter-generational
    // pointers.
    UpdateRSetVisitor v;
    obj->Iterate(&v);
  }
  return obj->Size();
}


void Heap::RebuildRSets() {
  // By definition, we do not care about remembered set bits in code or data
  // spaces.
  map_space_->ClearRSet();
  RebuildRSets(map_space_);

  old_pointer_space_->ClearRSet();
  RebuildRSets(old_pointer_space_);

  Heap::lo_space_->ClearRSet();
  RebuildRSets(lo_space_);
}


void Heap::RebuildRSets(PagedSpace* space) {
  HeapObjectIterator it(space);
  while (it.has_next()) Heap::UpdateRSet(it.next());
}


void Heap::RebuildRSets(LargeObjectSpace* space) {
  LargeObjectIterator it(space);
  while (it.has_next()) Heap::UpdateRSet(it.next());
}


#if defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)
void Heap::RecordCopiedObject(HeapObject* obj) {
  bool should_record = false;
#ifdef DEBUG
  should_record = FLAG_heap_stats;
#endif
#ifdef ENABLE_LOGGING_AND_PROFILING
  should_record = should_record || FLAG_log_gc;
#endif
  if (should_record) {
    if (new_space_->Contains(obj)) {
      new_space_->RecordAllocation(obj);
    } else {
      new_space_->RecordPromotion(obj);
    }
  }
}
#endif  // defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)


HeapObject* Heap::MigrateObject(HeapObject** source_p,
                                HeapObject* target,
                                int size) {
  void** src = reinterpret_cast<void**>((*source_p)->address());
  void** dst = reinterpret_cast<void**>(target->address());
  int counter = size/kPointerSize - 1;
  do {
    *dst++ = *src++;
  } while (counter-- > 0);

  // Set the forwarding address.
  (*source_p)->set_map_word(MapWord::FromForwardingAddress(target));

  // Update NewSpace stats if necessary.
#if defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)
  RecordCopiedObject(target);
#endif

  return target;
}


void Heap::CopyObject(HeapObject** p) {
  ASSERT(InFromSpace(*p));

  HeapObject* object = *p;

  // We use the first word (where the map pointer usually is) of a heap
  // object to record the forwarding pointer.  A forwarding pointer can
  // point to an old space, the code space, or the to space of the new
  // generation.
  MapWord first_word = object->map_word();

  // If the first word is a forwarding address, the object has already been
  // copied.
  if (first_word.IsForwardingAddress()) {
    *p = first_word.ToForwardingAddress();
    return;
  }

  // Optimization: Bypass ConsString objects where the right-hand side is
  // Heap::empty_string().  We do not use object->IsConsString because we
  // already know that object has the heap object tag.
  InstanceType type = first_word.ToMap()->instance_type();
  if (type < FIRST_NONSTRING_TYPE &&
      String::cast(object)->representation_tag() == kConsStringTag &&
      ConsString::cast(object)->second() == Heap::empty_string()) {
    object = HeapObject::cast(ConsString::cast(object)->first());
    *p = object;
    // After patching *p we have to repeat the checks that object is in the
    // active semispace of the young generation and not already copied.
    if (!InFromSpace(object)) return;
    first_word = object->map_word();
    if (first_word.IsForwardingAddress()) {
      *p = first_word.ToForwardingAddress();
      return;
    }
    type = first_word.ToMap()->instance_type();
  }

  int object_size = object->SizeFromMap(first_word.ToMap());
  Object* result;
  // If the object should be promoted, we try to copy it to old space.
  if (ShouldBePromoted(object->address(), object_size)) {
    OldSpace* target_space = Heap::TargetSpace(object);
    ASSERT(target_space == Heap::old_pointer_space_ ||
           target_space == Heap::old_data_space_);
    result = target_space->AllocateRaw(object_size);

    if (!result->IsFailure()) {
      *p = MigrateObject(p, HeapObject::cast(result), object_size);
      if (target_space == Heap::old_pointer_space_) {