mark-compact.cc.svn-base

Google浏览器V8内核代码

#endif
  }
};


void MarkCompactCollector::UpdatePointers() {
#ifdef DEBUG
  ASSERT(state_ == ENCODE_FORWARDING_ADDRESSES);
  state_ = UPDATE_POINTERS;
#endif
  UpdatingVisitor updating_visitor;
  Heap::IterateRoots(&updating_visitor);
  GlobalHandles::IterateWeakRoots(&updating_visitor);

  int live_maps = IterateLiveObjects(Heap::map_space(),
                                     &UpdatePointersInOldObject);
  int live_pointer_olds = IterateLiveObjects(Heap::old_pointer_space(),
                                             &UpdatePointersInOldObject);
  int live_data_olds = IterateLiveObjects(Heap::old_data_space(),
                                          &UpdatePointersInOldObject);
  int live_codes = IterateLiveObjects(Heap::code_space(),
                                      &UpdatePointersInOldObject);
  int live_news = IterateLiveObjects(Heap::new_space(),
                                     &UpdatePointersInNewObject);

  // Large objects do not move, the map word can be updated directly.
  LargeObjectIterator it(Heap::lo_space());
  while (it.has_next()) UpdatePointersInNewObject(it.next());

  USE(live_maps);
  USE(live_pointer_olds);
  USE(live_data_olds);
  USE(live_codes);
  USE(live_news);

#ifdef DEBUG
  ASSERT(live_maps == live_map_objects_);
  ASSERT(live_data_olds == live_old_data_objects_);
  ASSERT(live_pointer_olds == live_old_pointer_objects_);
  ASSERT(live_codes == live_code_objects_);
  ASSERT(live_news == live_young_objects_);

  if (FLAG_verify_global_gc) VerifyHeapAfterUpdatingPointers();
#endif
}


int MarkCompactCollector::UpdatePointersInNewObject(HeapObject* obj) {
  // Keep old map pointers
  Map* old_map = obj->map();
  ASSERT(old_map->IsHeapObject());

  Address forwarded = GetForwardingAddressInOldSpace(old_map);

  ASSERT(Heap::map_space()->Contains(old_map));
  ASSERT(Heap::map_space()->Contains(forwarded));
#ifdef DEBUG
  if (FLAG_gc_verbose) {
    PrintF("update %p : %p -> %p\n", obj->address(), old_map->address(),
           forwarded);
  }
#endif
  // Update the map pointer.
  obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(forwarded)));

  // We have to compute the object size relying on the old map because
  // map objects are not relocated yet.
  int obj_size = obj->SizeFromMap(old_map);

  // Update pointers in the object body.
  UpdatingVisitor updating_visitor;
  obj->IterateBody(old_map->instance_type(), obj_size, &updating_visitor);
  return obj_size;
}


int MarkCompactCollector::UpdatePointersInOldObject(HeapObject* obj) {
  // Decode the map pointer.
  MapWord encoding = obj->map_word();
  Address map_addr = encoding.DecodeMapAddress(Heap::map_space());
  ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr)));

  // At this point, the first word of map_addr is also encoded, cannot
  // cast it to Map* using Map::cast.
  Map* map = reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr));
  int obj_size = obj->SizeFromMap(map);
  InstanceType type = map->instance_type();

  // Update map pointer.
  Address new_map_addr = GetForwardingAddressInOldSpace(map);
  int offset = encoding.DecodeOffset();
  obj->set_map_word(MapWord::EncodeAddress(new_map_addr, offset));

#ifdef DEBUG
  if (FLAG_gc_verbose) {
    PrintF("update %p : %p -> %p\n", obj->address(),
           map_addr, new_map_addr);
  }
#endif

  // Update pointers in the object body.
  UpdatingVisitor updating_visitor;
  obj->IterateBody(type, obj_size, &updating_visitor);
  return obj_size;
}


Address MarkCompactCollector::GetForwardingAddressInOldSpace(HeapObject* obj) {
  // Object should either in old or map space.
  MapWord encoding = obj->map_word();

  // Offset to the first live object's forwarding address.
  int offset = encoding.DecodeOffset();
  Address obj_addr = obj->address();

  // Find the first live object's forwarding address.
  Page* p = Page::FromAddress(obj_addr);
  Address first_forwarded = p->mc_first_forwarded;

  // Page start address of forwarded address.
  Page* forwarded_page = Page::FromAddress(first_forwarded);
  int forwarded_offset = forwarded_page->Offset(first_forwarded);

  // Find end of allocation of in the page of first_forwarded.
  Address mc_top = forwarded_page->mc_relocation_top;
  int mc_top_offset = forwarded_page->Offset(mc_top);

  // Check if current object's forward pointer is in the same page
  // as the first live object's forwarding pointer
  if (forwarded_offset + offset < mc_top_offset) {
    // In the same page.
    return first_forwarded + offset;
  }

  // Must be in the next page, NOTE: this may cross chunks.
  Page* next_page = forwarded_page->next_page();
  ASSERT(next_page->is_valid());

  offset -= (mc_top_offset - forwarded_offset);
  offset += Page::kObjectStartOffset;

  ASSERT_PAGE_OFFSET(offset);
  ASSERT(next_page->OffsetToAddress(offset) < next_page->mc_relocation_top);

  return next_page->OffsetToAddress(offset);
}


#ifdef DEBUG
void MarkCompactCollector::VerifyHeapAfterUpdatingPointers() {
  ASSERT(state_ == UPDATE_POINTERS);

  AllSpaces spaces;
  while (Space* space = spaces.next()) space->Verify();
  PagedSpaces paged_spaces;
  while (PagedSpace* space = paged_spaces.next()) VerifyPageHeaders(space);
}
#endif


// ----------------------------------------------------------------------------
// Phase 4: Relocate objects

void MarkCompactCollector::RelocateObjects() {
#ifdef DEBUG
  ASSERT(state_ == UPDATE_POINTERS);
  state_ = RELOCATE_OBJECTS;
#endif
  // Relocates objects, always relocate map objects first. Relocating
  // objects in other space relies on map objects to get object size.
  int live_maps = IterateLiveObjects(Heap::map_space(), &RelocateMapObject);
  int live_pointer_olds = IterateLiveObjects(Heap::old_pointer_space(),
                                             &RelocateOldPointerObject);
  int live_data_olds = IterateLiveObjects(Heap::old_data_space(),
                                          &RelocateOldDataObject);
  int live_codes = IterateLiveObjects(Heap::code_space(), &RelocateCodeObject);
  int live_news = IterateLiveObjects(Heap::new_space(), &RelocateNewObject);

  USE(live_maps);
  USE(live_data_olds);
  USE(live_pointer_olds);
  USE(live_codes);
  USE(live_news);
#ifdef DEBUG
  ASSERT(live_maps == live_map_objects_);
  ASSERT(live_data_olds == live_old_data_objects_);
  ASSERT(live_pointer_olds == live_old_pointer_objects_);
  ASSERT(live_codes == live_code_objects_);
  ASSERT(live_news == live_young_objects_);
#endif

  // Notify code object in LO to convert IC target to address
  // This must happen after lo_space_->Compact
  LargeObjectIterator it(Heap::lo_space());
  while (it.has_next()) { ConvertCodeICTargetToAddress(it.next()); }

  // Flips from and to spaces
  Heap::new_space()->Flip();

  // Sets age_mark to bottom in to space
  Address mark = Heap::new_space()->bottom();
  Heap::new_space()->set_age_mark(mark);

  Heap::new_space()->MCCommitRelocationInfo();
#ifdef DEBUG
  // It is safe to write to the remembered sets as remembered sets on a
  // page-by-page basis after committing the m-c forwarding pointer.
  Page::set_rset_state(Page::IN_USE);
#endif
  PagedSpaces spaces;
  while (PagedSpace* space = spaces.next()) space->MCCommitRelocationInfo();

#ifdef DEBUG
  if (FLAG_verify_global_gc) VerifyHeapAfterRelocatingObjects();
#endif
}


int MarkCompactCollector::ConvertCodeICTargetToAddress(HeapObject* obj) {
  if (obj->IsCode()) {
    Code::cast(obj)->ConvertICTargetsFromObjectToAddress();
  }
  return obj->Size();
}


int MarkCompactCollector::RelocateMapObject(HeapObject* obj) {
  // decode map pointer (forwarded address)
  MapWord encoding = obj->map_word();
  Address map_addr = encoding.DecodeMapAddress(Heap::map_space());
  ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr)));

  // Get forwarding address before resetting map pointer
  Address new_addr = GetForwardingAddressInOldSpace(obj);

  // recover map pointer
  obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr)));

  // The meta map object may not be copied yet.
  Address old_addr = obj->address();

  if (new_addr != old_addr) {
    memmove(new_addr, old_addr, Map::kSize);  // copy contents
  }

#ifdef DEBUG
  if (FLAG_gc_verbose) {
    PrintF("relocate %p -> %p\n", old_addr, new_addr);
  }
#endif

  return Map::kSize;
}


static inline int RelocateOldObject(HeapObject* obj,
                                    OldSpace* space,
                                    Address new_addr,
                                    Address map_addr) {
  // recover map pointer
  obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr)));

  // This is a non-map object, it relies on the assumption that the Map space
  // is compacted before the Old space (see RelocateObjects).
  int obj_size = obj->Size();
  ASSERT_OBJECT_SIZE(obj_size);

  ASSERT(space->MCSpaceOffsetForAddress(new_addr) <=
         space->MCSpaceOffsetForAddress(obj->address()));

  space->MCAdjustRelocationEnd(new_addr, obj_size);

#ifdef DEBUG
  if (FLAG_gc_verbose) {
    PrintF("relocate %p -> %p\n", obj->address(), new_addr);
  }
#endif

  return obj_size;
}


int MarkCompactCollector::RelocateOldNonCodeObject(HeapObject* obj,
                                                   OldSpace* space) {
  // decode map pointer (forwarded address)
  MapWord encoding = obj->map_word();
  Address map_addr = encoding.DecodeMapAddress(Heap::map_space());
  ASSERT(Heap::map_space()->Contains(map_addr));

  // Get forwarding address before resetting map pointer
  Address new_addr = GetForwardingAddressInOldSpace(obj);

  int obj_size = RelocateOldObject(obj, space, new_addr, map_addr);

  Address old_addr = obj->address();

  if (new_addr != old_addr) {
    memmove(new_addr, old_addr, obj_size);  // copy contents
  }

  ASSERT(!HeapObject::FromAddress(new_addr)->IsCode());

  return obj_size;
}


int MarkCompactCollector::RelocateOldPointerObject(HeapObject* obj) {
  return RelocateOldNonCodeObject(obj, Heap::old_pointer_space());
}


int MarkCompactCollector::RelocateOldDataObject(HeapObject* obj) {
  return RelocateOldNonCodeObject(obj, Heap::old_data_space());
}


int MarkCompactCollector::RelocateCodeObject(HeapObject* obj) {
  // decode map pointer (forwarded address)
  MapWord encoding = obj->map_word();
  Address map_addr = encoding.DecodeMapAddress(Heap::map_space());
  ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr)));

  // Get forwarding address before resetting map pointer
  Address new_addr = GetForwardingAddressInOldSpace(obj);

  int obj_size = RelocateOldObject(obj, Heap::code_space(), new_addr, map_addr);

  // convert inline cache target to address using old address
  if (obj->IsCode()) {
    // convert target to address first related to old_address
    Code::cast(obj)->ConvertICTargetsFromObjectToAddress();
  }

  Address old_addr = obj->address();

  if (new_addr != old_addr) {
    memmove(new_addr, old_addr, obj_size);  // copy contents
  }

  HeapObject* copied_to = HeapObject::FromAddress(new_addr);
  if (copied_to->IsCode()) {
    // may also update inline cache target.
    Code::cast(copied_to)->Relocate(new_addr - old_addr);
    // Notify the logger that compile code has moved.
    LOG(CodeMoveEvent(old_addr, new_addr));
  }

  return obj_size;
}


#ifdef DEBUG
class VerifyCopyingVisitor: public ObjectVisitor {
 public:
  void VisitPointers(Object** start, Object** end) {
    for (Object** p = start; p < end; p++) {
      MarkCompactCollector::VerifyCopyingObjects(p);
    }
  }
};

#endif

int MarkCompactCollector::RelocateNewObject(HeapObject* obj) {
  int obj_size = obj->Size();

  // Get forwarding address
  Address old_addr = obj->address();
  int offset = Heap::new_space()->ToSpaceOffsetForAddress(old_addr);

  Address new_addr =
    Memory::Address_at(Heap::new_space()->FromSpaceLow() + offset);

  if (Heap::new_space()->FromSpaceContains(new_addr)) {
    ASSERT(Heap::new_space()->FromSpaceOffsetForAddress(new_addr) <=
           Heap::new_space()->ToSpaceOffsetForAddress(old_addr));
  } else {
    OldSpace* target_space = Heap::TargetSpace(obj);
    ASSERT(target_space == Heap::old_pointer_space() ||
           target_space == Heap::old_data_space());
    target_space->MCAdjustRelocationEnd(new_addr, obj_size);
  }

  // New and old addresses cannot overlap.
  memcpy(reinterpret_cast<void*>(new_addr),
         reinterpret_cast<void*>(old_addr),
         obj_size);

#ifdef DEBUG
  if (FLAG_gc_verbose) {
    PrintF("relocate %p -> %p\n", old_addr, new_addr);
  }
  if (FLAG_verify_global_gc) {
    VerifyCopyingVisitor v;
    HeapObject* copied_to = HeapObject::FromAddress(new_addr);
    copied_to->Iterate(&v);
  }
#endif

  return obj_size;
}


#ifdef DEBUG
void MarkCompactCollector::VerifyHeapAfterRelocatingObjects() {
  ASSERT(state_ == RELOCATE_OBJECTS);

  Heap::new_space()->Verify();
  PagedSpaces spaces;
  while (PagedSpace* space = spaces.next()) {
    space->Verify();
    PageIterator it(space, PageIterator::PAGES_IN_USE);
    while (it.has_next()) {
      Page* p = it.next();
      ASSERT_PAGE_OFFSET(p->Offset(p->AllocationTop()));
    }
  }
}
#endif


#ifdef DEBUG
void MarkCompactCollector::VerifyCopyingObjects(Object** p) {
  if (!(*p)->IsHeapObject()) return;
  ASSERT(!Heap::InToSpace(*p));
}
#endif  // DEBUG


// -----------------------------------------------------------------------------
// Phase 5: rebuild remembered sets

void MarkCompactCollector::RebuildRSets() {
#ifdef DEBUG
  ASSERT(state_ == RELOCATE_OBJECTS);
  state_ = REBUILD_RSETS;
#endif
  Heap::RebuildRSets();
}

} }  // namespace v8::internal