src/hotspot/share/gc/shared/markBitMap.hpp

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#ifndef SHARE_GC_SHARED_MARKBITMAP_HPP
#define SHARE_GC_SHARED_MARKBITMAP_HPP

#include "memory/memRegion.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/bitMap.hpp"

// A generic mark bitmap for concurrent marking.  This is essentially a wrapper
// around the BitMap class that is based on HeapWords, with one bit per (1 << _shifter) HeapWords.
class MarkBitMap {
protected:
  MemRegion _covered;    // The heap area covered by this bitmap.

  const int _shifter;    // Shift amount from heap index to bit index in the bitmap.

  BitMapView _bm;        // The actual bitmap.

  virtual void check_mark(HeapWord* addr) NOT_DEBUG_RETURN;

  // Convert from bit offset to address.
  HeapWord* offset_to_addr(size_t offset) const {
    return _covered.start() + (offset << _shifter);
  }
  // Convert from address to bit offset.
  size_t addr_to_offset(const HeapWord* addr) const {
    return pointer_delta(addr, _covered.start()) >> _shifter;
  }

  // Clear bitmap range
  void do_clear(MemRegion mr, bool large);

  // Returns the amount of bytes on the heap between two marks in the bitmap.
  static size_t mark_distance();

public:
  static size_t compute_size(size_t heap_size);
  // Returns how many bytes (or bits) of the heap a single byte (or bit) of the
  // mark bitmap corresponds to. This is the same as the mark distance above.
  static size_t heap_map_factor() {
    return mark_distance();
  }

  MarkBitMap() : _covered(), _shifter(LogMinObjAlignment), _bm() {}

  // Initializes the underlying BitMap to cover the given area.
  void initialize(MemRegion heap, MemRegion storage);

  // Read marks
  bool is_marked(oop obj) const;
  bool is_marked(HeapWord* addr) const {
    assert(_covered.contains(addr),
           "Address " PTR_FORMAT " is outside underlying space from " PTR_FORMAT " to " PTR_FORMAT,
           p2i(addr), p2i(_covered.start()), p2i(_covered.end()));
    return _bm.at(addr_to_offset(addr));
  }

  // Return the address corresponding to the next marked bit at or after
  // "addr", and before "limit", if "limit" is non-null.  If there is no
  // such bit, returns "limit" if that is non-null, or else "endWord()".
  inline HeapWord* get_next_marked_addr(const HeapWord* addr,
                                        HeapWord* limit) const;

  void print_on(outputStream* st, const char* prefix) const;

  // Write marks.
  inline void mark(HeapWord* addr);
  inline void mark(oop obj);
  inline void clear(HeapWord* addr);
  inline void clear(oop obj);
  inline bool par_mark(HeapWord* addr);
  inline bool par_mark(oop obj);

  // Clear bitmap.
  void clear()                         { do_clear(_covered, true); }
  void clear_range(MemRegion mr)       { do_clear(mr, false);      }
  void clear_range_large(MemRegion mr) { do_clear(mr, true);       }
};

#endif // SHARE_GC_SHARED_MARKBITMAP_HPP