JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2018 SAP SE. 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
 * questions.
 *
 */

#ifndef SHARE_MEMORY_METASPACE_OCCUPANCYMAP_HPP
#define SHARE_MEMORY_METASPACE_OCCUPANCYMAP_HPP

#include "memory/allocation.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"


namespace metaspace {

class Metachunk;

// Helper for Occupancy Bitmap. A type trait to give an all-bits-are-one-unsigned constant.
template <typename T> struct all_ones  { static const T value; };
template <> struct all_ones <uint64_t> { static const uint64_t value = 0xFFFFFFFFFFFFFFFFULL; };
template <> struct all_ones <uint32_t> { static const uint32_t value = 0xFFFFFFFF; };

// The OccupancyMap is a bitmap which, for a given VirtualSpaceNode,
// keeps information about
// - where a chunk starts
// - whether a chunk is in-use or free
// A bit in this bitmap represents one range of memory in the smallest
// chunk size (SpecializedChunk or ClassSpecializedChunk).
class OccupancyMap : public CHeapObj<mtInternal> {

  // The address range this map covers.
  const MetaWord* const _reference_address;
  const size_t _word_size;

  // The word size of a specialized chunk, aka the number of words one
  // bit in this map represents.
  const size_t _smallest_chunk_word_size;

  // map data
  // Data are organized in two bit layers:
  // The first layer is the chunk-start-map. Here, a bit is set to mark
  // the corresponding region as the head of a chunk.
  // The second layer is the in-use-map. Here, a set bit indicates that
  // the corresponding belongs to a chunk which is in use.
  uint8_t* _map[2];

  enum { layer_chunk_start_map = 0, layer_in_use_map = 1 };

  // length, in bytes, of bitmap data
  size_t _map_size;

  // Returns true if bit at position pos at bit-layer layer is set.
  bool get_bit_at_position(unsigned pos, unsigned layer) const {
    assert(layer == 0 || layer == 1, "Invalid layer %d", layer);
    const unsigned byteoffset = pos / 8;
    assert(byteoffset < _map_size,
           "invalid byte offset (%u), map size is " SIZE_FORMAT ".", byteoffset, _map_size);
    const unsigned mask = 1 << (pos % 8);
    return (_map[layer][byteoffset] & mask) > 0;
  }

  // Changes bit at position pos at bit-layer layer to value v.
  void set_bit_at_position(unsigned pos, unsigned layer, bool v) {
    assert(layer == 0 || layer == 1, "Invalid layer %d", layer);
    const unsigned byteoffset = pos / 8;
    assert(byteoffset < _map_size,
           "invalid byte offset (%u), map size is " SIZE_FORMAT ".", byteoffset, _map_size);
    const unsigned mask = 1 << (pos % 8);
    if (v) {
      _map[layer][byteoffset] |= mask;
    } else {
      _map[layer][byteoffset] &= ~mask;
    }
  }

  // Optimized case of is_any_bit_set_in_region for 32/64bit aligned access:
  // pos is 32/64 aligned and num_bits is 32/64.
  // This is the typical case when coalescing to medium chunks, whose size is
  // 32 or 64 times the specialized chunk size (depending on class or non class
  // case), so they occupy 64 bits which should be 64bit aligned, because
  // chunks are chunk-size aligned.
  template <typename T>
  bool is_any_bit_set_in_region_3264(unsigned pos, unsigned num_bits, unsigned layer) const {
    assert(_map_size > 0, "not initialized");
    assert(layer == 0 || layer == 1, "Invalid layer %d.", layer);
    assert(pos % (sizeof(T) * 8) == 0, "Bit position must be aligned (%u).", pos);
    assert(num_bits == (sizeof(T) * 8), "Number of bits incorrect (%u).", num_bits);
    const size_t byteoffset = pos / 8;
    assert(byteoffset <= (_map_size - sizeof(T)),
           "Invalid byte offset (" SIZE_FORMAT "), map size is " SIZE_FORMAT ".", byteoffset, _map_size);
    const T w = *(T*)(_map[layer] + byteoffset);
    return w > 0 ? true : false;
  }

  // Returns true if any bit in region [pos1, pos1 + num_bits) is set in bit-layer layer.
  bool is_any_bit_set_in_region(unsigned pos, unsigned num_bits, unsigned layer) const {
    if (pos % 32 == 0 && num_bits == 32) {
      return is_any_bit_set_in_region_3264<uint32_t>(pos, num_bits, layer);
    } else if (pos % 64 == 0 && num_bits == 64) {
      return is_any_bit_set_in_region_3264<uint64_t>(pos, num_bits, layer);
    } else {
      for (unsigned n = 0; n < num_bits; n ++) {
        if (get_bit_at_position(pos + n, layer)) {
          return true;
        }
      }
    }
    return false;
  }

  // Returns true if any bit in region [p, p+word_size) is set in bit-layer layer.
  bool is_any_bit_set_in_region(MetaWord* p, size_t word_size, unsigned layer) const {
    assert(word_size % _smallest_chunk_word_size == 0,
        "Region size " SIZE_FORMAT " not a multiple of smallest chunk size.", word_size);
    const unsigned pos = get_bitpos_for_address(p);
    const unsigned num_bits = (unsigned) (word_size / _smallest_chunk_word_size);
    return is_any_bit_set_in_region(pos, num_bits, layer);
  }

  // Optimized case of set_bits_of_region for 32/64bit aligned access:
  // pos is 32/64 aligned and num_bits is 32/64.
  // This is the typical case when coalescing to medium chunks, whose size
  // is 32 or 64 times the specialized chunk size (depending on class or non
  // class case), so they occupy 64 bits which should be 64bit aligned,
  // because chunks are chunk-size aligned.
  template <typename T>
  void set_bits_of_region_T(unsigned pos, unsigned num_bits, unsigned layer, bool v) {
    assert(pos % (sizeof(T) * 8) == 0, "Bit position must be aligned to %u (%u).",
           (unsigned)(sizeof(T) * 8), pos);
    assert(num_bits == (sizeof(T) * 8), "Number of bits incorrect (%u), expected %u.",
           num_bits, (unsigned)(sizeof(T) * 8));
    const size_t byteoffset = pos / 8;
    assert(byteoffset <= (_map_size - sizeof(T)),
           "invalid byte offset (" SIZE_FORMAT "), map size is " SIZE_FORMAT ".", byteoffset, _map_size);
    T* const pw = (T*)(_map[layer] + byteoffset);
    *pw = v ? all_ones<T>::value : (T) 0;
  }

  // Set all bits in a region starting at pos to a value.
  void set_bits_of_region(unsigned pos, unsigned num_bits, unsigned layer, bool v) {
    assert(_map_size > 0, "not initialized");
    assert(layer == 0 || layer == 1, "Invalid layer %d.", layer);
    if (pos % 32 == 0 && num_bits == 32) {
      set_bits_of_region_T<uint32_t>(pos, num_bits, layer, v);
    } else if (pos % 64 == 0 && num_bits == 64) {
      set_bits_of_region_T<uint64_t>(pos, num_bits, layer, v);
    } else {
      for (unsigned n = 0; n < num_bits; n ++) {
        set_bit_at_position(pos + n, layer, v);
      }
    }
  }

  // Helper: sets all bits in a region [p, p+word_size).
  void set_bits_of_region(MetaWord* p, size_t word_size, unsigned layer, bool v) {
    assert(word_size % _smallest_chunk_word_size == 0,
        "Region size " SIZE_FORMAT " not a multiple of smallest chunk size.", word_size);
    const unsigned pos = get_bitpos_for_address(p);
    const unsigned num_bits = (unsigned) (word_size / _smallest_chunk_word_size);
    set_bits_of_region(pos, num_bits, layer, v);
  }

  // Helper: given an address, return the bit position representing that address.
  unsigned get_bitpos_for_address(const MetaWord* p) const {
    assert(_reference_address != NULL, "not initialized");
    assert(p >= _reference_address && p < _reference_address + _word_size,
           "Address %p out of range for occupancy map [%p..%p).",
            p, _reference_address, _reference_address + _word_size);
    assert(is_aligned(p, _smallest_chunk_word_size * sizeof(MetaWord)),
           "Address not aligned (%p).", p);
    const ptrdiff_t d = (p - _reference_address) / _smallest_chunk_word_size;
    assert(d >= 0 && (size_t)d < _map_size * 8, "Sanity.");
    return (unsigned) d;
  }

 public:

  OccupancyMap(const MetaWord* reference_address, size_t word_size, size_t smallest_chunk_word_size);
  ~OccupancyMap();

  // Returns true if at address x a chunk is starting.
  bool chunk_starts_at_address(MetaWord* p) const {
    const unsigned pos = get_bitpos_for_address(p);
    return get_bit_at_position(pos, layer_chunk_start_map);
  }

  void set_chunk_starts_at_address(MetaWord* p, bool v) {
    const unsigned pos = get_bitpos_for_address(p);
    set_bit_at_position(pos, layer_chunk_start_map, v);
  }

  // Removes all chunk-start-bits inside a region, typically as a
  // result of a chunk merge.

/**代码未完, 请加载全部代码(NowJava.com).**/