src/hotspot/share/utilities/objectBitSet.hpp

/*
 * Copyright (c) 2014, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
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 */

#ifndef SHARE_UTILITIES_OBJECTBITSET_HPP
#define SHARE_UTILITIES_OBJECTBITSET_HPP

#include "memory/allocation.hpp"
#include "oops/oop.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/bitMap.hpp"
#include "utilities/resizeableResourceHash.hpp"

class MemRegion;

/*
 * ObjectBitSet is a sparse bitmap for marking objects in the Java heap.
 * It holds one bit per ObjAlignmentInBytes-aligned address. Its underlying backing memory is
 * allocated on-demand only, in fragments covering 64M heap ranges. Fragments are never deleted
 * during the lifetime of the ObjectBitSet. The underlying memory is allocated from C-Heap.
 */
template<MEMFLAGS F>
class ObjectBitSet : public CHeapObj<F> {
  const static size_t _bitmap_granularity_shift = 26; // 64M
  const static size_t _bitmap_granularity_size = (size_t)1 << _bitmap_granularity_shift;
  const static size_t _bitmap_granularity_mask = _bitmap_granularity_size - 1;

  class BitMapFragment;

  static unsigned hash_segment(const uintptr_t& key) {
    unsigned hash = (unsigned)key;
    return hash ^ (hash >> 3);
  }

  typedef ResizeableResourceHashtable<uintptr_t, CHeapBitMap*, AnyObj::C_HEAP, F,
                                      hash_segment> BitMapFragmentTable;

  CHeapBitMap* get_fragment_bits(uintptr_t addr);

  BitMapFragmentTable _bitmap_fragments;
  BitMapFragment* _fragment_list;
  CHeapBitMap* _last_fragment_bits;
  uintptr_t _last_fragment_granule;

 public:
  ObjectBitSet();
  ~ObjectBitSet();

  BitMap::idx_t addr_to_bit(uintptr_t addr) const;

  void mark_obj(uintptr_t addr);

  void mark_obj(oop obj) {
    return mark_obj(cast_from_oop<uintptr_t>(obj));
  }

  bool is_marked(uintptr_t addr);

  bool is_marked(oop obj) {
    return is_marked(cast_from_oop<uintptr_t>(obj));
  }
};

template<MEMFLAGS F>
class ObjectBitSet<F>::BitMapFragment : public CHeapObj<F> {
  CHeapBitMap _bits;
  BitMapFragment* _next;

public:
  BitMapFragment(uintptr_t granule, BitMapFragment* next);

  BitMapFragment* next() const {
    return _next;
  }

  CHeapBitMap* bits() {
    return &_bits;
  }
};

#endif // SHARE_UTILITIES_OBJECTBITSET_HPP