src/hotspot/share/gc/g1/g1BlockOffsetTable.hpp

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#ifndef SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP
#define SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP

#include "gc/g1/g1RegionToSpaceMapper.hpp"
#include "gc/shared/blockOffsetTable.hpp"
#include "gc/shared/cardTable.hpp"
#include "memory/memRegion.hpp"
#include "utilities/globalDefinitions.hpp"

// This implementation of "G1BlockOffsetTable" divides the covered region
// into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
// for each such subregion indicates how far back one must go to find the
// start of the chunk that includes the first word of the subregion.
class G1BlockOffsetTable: public CHeapObj<mtGC> {
  friend class VMStructs;

private:
  // The reserved region covered by the table.
  MemRegion _reserved;

  // Biased array-start of BOT array for fast BOT entry translation
  volatile uint8_t* _offset_base;

  void check_offset(size_t offset, const char* msg) const {
    assert(offset < CardTable::card_size_in_words(),
           "%s - offset: %zu, N_words: %u",
           msg, offset, CardTable::card_size_in_words());
  }

  // Bounds checking accessors:
  // For performance these have to devolve to array accesses in product builds.
  inline uint8_t offset_array(uint8_t* addr) const;

  inline void set_offset_array(uint8_t* addr, uint8_t offset);

  inline void set_offset_array(uint8_t* addr, HeapWord* high, HeapWord* low);

  inline void set_offset_array(uint8_t* left, uint8_t* right, uint8_t offset);

  // Mapping from address to object start array entry
  inline uint8_t* entry_for_addr(const void* const p) const;

  // Mapping from object start array entry to address of first word
  inline HeapWord* addr_for_entry(const uint8_t* const p) const;

  void check_address(uint8_t* addr, const char* msg) const NOT_DEBUG_RETURN;

  // Sets the entries corresponding to the cards starting at "start" and ending
  // at "end" to point back to the card before "start"; [start, end]
  void set_remainder_to_point_to_start_incl(uint8_t* start, uint8_t* end);

  // Update BOT entries corresponding to the mem range [blk_start, blk_end).
  void update_for_block_work(HeapWord* blk_start, HeapWord* blk_end);

  void check_all_cards(uint8_t* left_card, uint8_t* right_card) const NOT_DEBUG_RETURN;

  void verify_offset(uint8_t* card_index, uint8_t upper) const NOT_DEBUG_RETURN;
  void verify_for_block(HeapWord* blk_start, HeapWord* blk_end) const NOT_DEBUG_RETURN;

  static HeapWord* align_up_by_card_size(HeapWord* const addr) {
    return align_up(addr, CardTable::card_size());
  }

public:

  // Return the number of slots needed for an offset array
  // that covers mem_region_words words.
  static size_t compute_size(size_t mem_region_words);

  // Returns how many bytes of the heap a single byte of the BOT corresponds to.
  static size_t heap_map_factor() {
    return CardTable::card_size();
  }

  // Initialize the Block Offset Table to cover the memory region passed
  // in the heap parameter.
  G1BlockOffsetTable(MemRegion heap, G1RegionToSpaceMapper* storage);

  static bool is_crossing_card_boundary(HeapWord* const obj_start,
                                        HeapWord* const obj_end) {
    HeapWord* cur_card_boundary = align_up_by_card_size(obj_start);
    // strictly greater-than
    return obj_end > cur_card_boundary;
  }

  // Returns the address of the start of the block reaching into the card containing
  // "addr".
  inline HeapWord* block_start_reaching_into_card(const void* addr) const;

  void update_for_block(HeapWord* blk_start, HeapWord* blk_end) {
    if (is_crossing_card_boundary(blk_start, blk_end)) {
      update_for_block_work(blk_start, blk_end);
    }
  }
};

#endif // SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP