src/hotspot/share/gc/g1/g1CardTable.hpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#ifndef SHARE_GC_G1_G1CARDTABLE_HPP
#define SHARE_GC_G1_G1CARDTABLE_HPP

#include "gc/g1/g1RegionToSpaceMapper.hpp"
#include "gc/shared/cardTable.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/macros.hpp"

class G1CardTable;
class G1RegionToSpaceMapper;

class G1CardTableChangedListener : public G1MappingChangedListener {
 private:
  G1CardTable* _card_table;
 public:
  G1CardTableChangedListener() : _card_table(nullptr) { }

  void set_card_table(G1CardTable* card_table) { _card_table = card_table; }

  void on_commit(uint start_idx, size_t num_regions, bool zero_filled) override;
};

class G1CardTable : public CardTable {
  friend class VMStructs;
  friend class G1CardTableChangedListener;

  G1CardTableChangedListener _listener;

public:
  enum G1CardValues {
    g1_young_gen = CT_MR_BS_last_reserved << 1,

    // During evacuation we use the card table to consolidate the cards we need to
    // scan for roots onto the card table from the various sources. Further it is
    // used to record already completely scanned cards to avoid re-scanning them
    // when incrementally evacuating the old gen regions of a collection set.
    // This means that already scanned cards should be preserved.
    //
    // The merge at the start of each evacuation round simply sets cards to dirty
    // that are clean; scanned cards are set to 0x1.
    //
    // This means that the LSB determines what to do with the card during evacuation
    // given the following possible values:
    //
    // 11111111 - clean, do not scan
    // 00000001 - already scanned, do not scan
    // 00000000 - dirty, needs to be scanned.
    //
    g1_card_already_scanned = 0x1
  };

  static const size_t WordAllClean = SIZE_MAX;
  static const size_t WordAllDirty = 0;

  STATIC_ASSERT(BitsPerByte == 8);
  static const size_t WordAlreadyScanned = (SIZE_MAX / 255) * g1_card_already_scanned;

  G1CardTable(MemRegion whole_heap): CardTable(whole_heap), _listener() {
    _listener.set_card_table(this);
  }

  static CardValue g1_young_card_val() { return g1_young_gen; }
  static CardValue g1_scanned_card_val() { return g1_card_already_scanned; }

  void verify_g1_young_region(MemRegion mr) PRODUCT_RETURN;
  void g1_mark_as_young(const MemRegion& mr);

  size_t index_for_cardvalue(CardValue const* p) const {
    return pointer_delta(p, _byte_map, sizeof(CardValue));
  }

  // Mark the given card as Dirty if it is Clean. Returns whether the card was
  // Clean before this operation. This result may be inaccurate as it does not
  // perform the dirtying atomically.
  inline bool mark_clean_as_dirty(CardValue* card);

  // Change Clean cards in a (large) area on the card table as Dirty, preserving
  // already scanned cards. Assumes that most cards in that area are Clean.
  inline void mark_range_dirty(size_t start_card_index, size_t num_cards);

  // Change the given range of dirty cards to "which". All of these cards must be Dirty.
  inline void change_dirty_cards_to(CardValue* start_card, CardValue* end_card, CardValue which);

  inline uint region_idx_for(CardValue* p);

  static size_t compute_size(size_t mem_region_size_in_words) {
    size_t number_of_slots = (mem_region_size_in_words / _card_size_in_words);
    return ReservedSpace::allocation_align_size_up(number_of_slots);
  }

  // Returns how many bytes of the heap a single byte of the Card Table corresponds to.
  static size_t heap_map_factor() { return _card_size; }

  void initialize(G1RegionToSpaceMapper* mapper);

  bool is_in_young(const void* p) const override;
};

#endif // SHARE_GC_G1_G1CARDTABLE_HPP