342
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1 /*
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2 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 // The CollectedHeap type requires subtypes to implement a method
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26 // "block_start". For some subtypes, notably generational
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27 // systems using card-table-based write barriers, the efficiency of this
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28 // operation may be important. Implementations of the "BlockOffsetArray"
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29 // class may be useful in providing such efficient implementations.
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30 //
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31 // While generally mirroring the structure of the BOT for GenCollectedHeap,
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32 // the following types are tailored more towards G1's uses; these should,
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33 // however, be merged back into a common BOT to avoid code duplication
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34 // and reduce maintenance overhead.
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35 //
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36 // G1BlockOffsetTable (abstract)
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37 // -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray)
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38 // -- G1BlockOffsetArrayContigSpace
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39 //
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40 // A main impediment to the consolidation of this code might be the
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41 // effect of making some of the block_start*() calls non-const as
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42 // below. Whether that might adversely affect performance optimizations
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43 // that compilers might normally perform in the case of non-G1
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44 // collectors needs to be carefully investigated prior to any such
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45 // consolidation.
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46
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47 // Forward declarations
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48 class ContiguousSpace;
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49 class G1BlockOffsetSharedArray;
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50
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51 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
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52 friend class VMStructs;
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53 protected:
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54 // These members describe the region covered by the table.
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55
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56 // The space this table is covering.
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57 HeapWord* _bottom; // == reserved.start
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58 HeapWord* _end; // End of currently allocated region.
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59
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60 public:
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61 // Initialize the table to cover the given space.
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62 // The contents of the initial table are undefined.
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63 G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
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64 _bottom(bottom), _end(end)
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65 {
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66 assert(_bottom <= _end, "arguments out of order");
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67 }
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68
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69 // Note that the committed size of the covered space may have changed,
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70 // so the table size might also wish to change.
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71 virtual void resize(size_t new_word_size) = 0;
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72
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73 virtual void set_bottom(HeapWord* new_bottom) {
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74 assert(new_bottom <= _end, "new_bottom > _end");
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75 _bottom = new_bottom;
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76 resize(pointer_delta(_end, _bottom));
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77 }
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78
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79 // Requires "addr" to be contained by a block, and returns the address of
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80 // the start of that block. (May have side effects, namely updating of
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81 // shared array entries that "point" too far backwards. This can occur,
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82 // for example, when LAB allocation is used in a space covered by the
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83 // table.)
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84 virtual HeapWord* block_start_unsafe(const void* addr) = 0;
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85 // Same as above, but does not have any of the possible side effects
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86 // discussed above.
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87 virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
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88
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89 // Returns the address of the start of the block containing "addr", or
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90 // else "null" if it is covered by no block. (May have side effects,
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91 // namely updating of shared array entries that "point" too far
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92 // backwards. This can occur, for example, when lab allocation is used
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93 // in a space covered by the table.)
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94 inline HeapWord* block_start(const void* addr);
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95 // Same as above, but does not have any of the possible side effects
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96 // discussed above.
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97 inline HeapWord* block_start_const(const void* addr) const;
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98 };
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99
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100 // This implementation of "G1BlockOffsetTable" divides the covered region
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101 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
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102 // for each such subregion indicates how far back one must go to find the
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103 // start of the chunk that includes the first word of the subregion.
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104 //
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105 // Each BlockOffsetArray is owned by a Space. However, the actual array
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106 // may be shared by several BlockOffsetArrays; this is useful
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107 // when a single resizable area (such as a generation) is divided up into
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108 // several spaces in which contiguous allocation takes place,
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109 // such as, for example, in G1 or in the train generation.)
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110
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111 // Here is the shared array type.
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112
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113 class G1BlockOffsetSharedArray: public CHeapObj {
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114 friend class G1BlockOffsetArray;
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115 friend class G1BlockOffsetArrayContigSpace;
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116 friend class VMStructs;
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117
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118 private:
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119 // The reserved region covered by the shared array.
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120 MemRegion _reserved;
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121
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122 // End of the current committed region.
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123 HeapWord* _end;
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124
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125 // Array for keeping offsets for retrieving object start fast given an
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126 // address.
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127 VirtualSpace _vs;
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128 u_char* _offset_array; // byte array keeping backwards offsets
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129
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130 // Bounds checking accessors:
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131 // For performance these have to devolve to array accesses in product builds.
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132 u_char offset_array(size_t index) const {
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133 assert(index < _vs.committed_size(), "index out of range");
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134 return _offset_array[index];
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135 }
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136
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137 void set_offset_array(size_t index, u_char offset) {
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138 assert(index < _vs.committed_size(), "index out of range");
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139 assert(offset <= N_words, "offset too large");
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140 _offset_array[index] = offset;
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141 }
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142
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143 void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
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144 assert(index < _vs.committed_size(), "index out of range");
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145 assert(high >= low, "addresses out of order");
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146 assert(pointer_delta(high, low) <= N_words, "offset too large");
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147 _offset_array[index] = (u_char) pointer_delta(high, low);
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148 }
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149
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150 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
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151 assert(index_for(right - 1) < _vs.committed_size(),
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152 "right address out of range");
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153 assert(left < right, "Heap addresses out of order");
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154 size_t num_cards = pointer_delta(right, left) >> LogN_words;
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155 memset(&_offset_array[index_for(left)], offset, num_cards);
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156 }
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157
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158 void set_offset_array(size_t left, size_t right, u_char offset) {
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159 assert(right < _vs.committed_size(), "right address out of range");
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160 assert(left <= right, "indexes out of order");
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161 size_t num_cards = right - left + 1;
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162 memset(&_offset_array[left], offset, num_cards);
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163 }
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164
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165 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
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166 assert(index < _vs.committed_size(), "index out of range");
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167 assert(high >= low, "addresses out of order");
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168 assert(pointer_delta(high, low) <= N_words, "offset too large");
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169 assert(_offset_array[index] == pointer_delta(high, low),
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170 "Wrong offset");
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171 }
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172
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173 bool is_card_boundary(HeapWord* p) const;
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174
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175 // Return the number of slots needed for an offset array
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176 // that covers mem_region_words words.
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177 // We always add an extra slot because if an object
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178 // ends on a card boundary we put a 0 in the next
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179 // offset array slot, so we want that slot always
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180 // to be reserved.
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181
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182 size_t compute_size(size_t mem_region_words) {
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183 size_t number_of_slots = (mem_region_words / N_words) + 1;
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184 return ReservedSpace::page_align_size_up(number_of_slots);
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185 }
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186
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187 public:
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188 enum SomePublicConstants {
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189 LogN = 9,
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190 LogN_words = LogN - LogHeapWordSize,
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191 N_bytes = 1 << LogN,
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192 N_words = 1 << LogN_words
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193 };
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194
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195 // Initialize the table to cover from "base" to (at least)
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196 // "base + init_word_size". In the future, the table may be expanded
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197 // (see "resize" below) up to the size of "_reserved" (which must be at
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198 // least "init_word_size".) The contents of the initial table are
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199 // undefined; it is the responsibility of the constituent
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200 // G1BlockOffsetTable(s) to initialize cards.
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201 G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
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202
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203 // Notes a change in the committed size of the region covered by the
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204 // table. The "new_word_size" may not be larger than the size of the
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205 // reserved region this table covers.
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206 void resize(size_t new_word_size);
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207
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208 void set_bottom(HeapWord* new_bottom);
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209
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210 // Updates all the BlockOffsetArray's sharing this shared array to
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211 // reflect the current "top"'s of their spaces.
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212 void update_offset_arrays();
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213
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214 // Return the appropriate index into "_offset_array" for "p".
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215 inline size_t index_for(const void* p) const;
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216
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217 // Return the address indicating the start of the region corresponding to
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218 // "index" in "_offset_array".
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219 inline HeapWord* address_for_index(size_t index) const;
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220 };
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221
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222 // And here is the G1BlockOffsetTable subtype that uses the array.
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223
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224 class G1BlockOffsetArray: public G1BlockOffsetTable {
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225 friend class G1BlockOffsetSharedArray;
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226 friend class G1BlockOffsetArrayContigSpace;
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227 friend class VMStructs;
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228 private:
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229 enum SomePrivateConstants {
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230 N_words = G1BlockOffsetSharedArray::N_words,
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231 LogN = G1BlockOffsetSharedArray::LogN
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232 };
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233
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234 // The following enums are used by do_block_helper
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235 enum Action {
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236 Action_single, // BOT records a single block (see single_block())
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237 Action_mark, // BOT marks the start of a block (see mark_block())
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238 Action_check // Check that BOT records block correctly
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239 // (see verify_single_block()).
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240 };
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241
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242 // This is the array, which can be shared by several BlockOffsetArray's
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243 // servicing different
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244 G1BlockOffsetSharedArray* _array;
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245
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246 // The space that owns this subregion.
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247 Space* _sp;
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248
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249 // If "_sp" is a contiguous space, the field below is the view of "_sp"
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250 // as a contiguous space, else NULL.
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251 ContiguousSpace* _csp;
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252
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253 // If true, array entries are initialized to 0; otherwise, they are
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254 // initialized to point backwards to the beginning of the covered region.
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255 bool _init_to_zero;
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256
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257 // The portion [_unallocated_block, _sp.end()) of the space that
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258 // is a single block known not to contain any objects.
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259 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
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260 HeapWord* _unallocated_block;
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261
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262 // Sets the entries
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263 // corresponding to the cards starting at "start" and ending at "end"
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264 // to point back to the card before "start": the interval [start, end)
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265 // is right-open.
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266 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
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267 // Same as above, except that the args here are a card _index_ interval
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268 // that is closed: [start_index, end_index]
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269 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
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270
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271 // A helper function for BOT adjustment/verification work
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272 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
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273
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274 protected:
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275
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276 ContiguousSpace* csp() const { return _csp; }
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277
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278 // Returns the address of a block whose start is at most "addr".
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279 // If "has_max_index" is true, "assumes "max_index" is the last valid one
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280 // in the array.
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281 inline HeapWord* block_at_or_preceding(const void* addr,
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282 bool has_max_index,
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283 size_t max_index) const;
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284
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285 // "q" is a block boundary that is <= "addr"; "n" is the address of the
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286 // next block (or the end of the space.) Return the address of the
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287 // beginning of the block that contains "addr". Does so without side
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288 // effects (see, e.g., spec of block_start.)
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289 inline HeapWord*
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290 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
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291 const void* addr) const;
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292
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293 // "q" is a block boundary that is <= "addr"; return the address of the
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294 // beginning of the block that contains "addr". May have side effects
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295 // on "this", by updating imprecise entries.
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296 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
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297 const void* addr);
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298
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299 // "q" is a block boundary that is <= "addr"; "n" is the address of the
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300 // next block (or the end of the space.) Return the address of the
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301 // beginning of the block that contains "addr". May have side effects
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302 // on "this", by updating imprecise entries.
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303 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
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304 HeapWord* n,
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305 const void* addr);
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306
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307 // Requires that "*threshold_" be the first array entry boundary at or
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308 // above "blk_start", and that "*index_" be the corresponding array
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309 // index. If the block starts at or crosses "*threshold_", records
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310 // "blk_start" as the appropriate block start for the array index
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311 // starting at "*threshold_", and for any other indices crossed by the
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312 // block. Updates "*threshold_" and "*index_" to correspond to the first
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313 // index after the block end.
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314 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
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315 HeapWord* blk_start, HeapWord* blk_end);
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316
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317 public:
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318 // The space may not have it's bottom and top set yet, which is why the
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319 // region is passed as a parameter. If "init_to_zero" is true, the
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320 // elements of the array are initialized to zero. Otherwise, they are
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321 // initialized to point backwards to the beginning.
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322 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
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323 bool init_to_zero);
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324
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325 // Note: this ought to be part of the constructor, but that would require
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326 // "this" to be passed as a parameter to a member constructor for
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327 // the containing concrete subtype of Space.
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328 // This would be legal C++, but MS VC++ doesn't allow it.
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329 void set_space(Space* sp);
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330
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331 // Resets the covered region to the given "mr".
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332 void set_region(MemRegion mr);
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333
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334 // Resets the covered region to one with the same _bottom as before but
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335 // the "new_word_size".
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336 void resize(size_t new_word_size);
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337
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338 // These must be guaranteed to work properly (i.e., do nothing)
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339 // when "blk_start" ("blk" for second version) is "NULL".
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340 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
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341 virtual void alloc_block(HeapWord* blk, size_t size) {
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342 alloc_block(blk, blk + size);
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343 }
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344
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345 // The following methods are useful and optimized for a
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346 // general, non-contiguous space.
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347
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348 // The given arguments are required to be the starts of adjacent ("blk1"
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349 // before "blk2") well-formed blocks covered by "this". After this call,
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350 // they should be considered to form one block.
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351 virtual void join_blocks(HeapWord* blk1, HeapWord* blk2);
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352
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353 // Given a block [blk_start, blk_start + full_blk_size), and
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354 // a left_blk_size < full_blk_size, adjust the BOT to show two
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355 // blocks [blk_start, blk_start + left_blk_size) and
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356 // [blk_start + left_blk_size, blk_start + full_blk_size).
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357 // It is assumed (and verified in the non-product VM) that the
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358 // BOT was correct for the original block.
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359 void split_block(HeapWord* blk_start, size_t full_blk_size,
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360 size_t left_blk_size);
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361
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362 // Adjust the BOT to show that it has a single block in the
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363 // range [blk_start, blk_start + size). All necessary BOT
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364 // cards are adjusted, but _unallocated_block isn't.
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365 void single_block(HeapWord* blk_start, HeapWord* blk_end);
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366 void single_block(HeapWord* blk, size_t size) {
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367 single_block(blk, blk + size);
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368 }
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369
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370 // Adjust BOT to show that it has a block in the range
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371 // [blk_start, blk_start + size). Only the first card
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372 // of BOT is touched. It is assumed (and verified in the
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373 // non-product VM) that the remaining cards of the block
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374 // are correct.
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375 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
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376 void mark_block(HeapWord* blk, size_t size) {
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377 mark_block(blk, blk + size);
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378 }
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379
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380 // Adjust _unallocated_block to indicate that a particular
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381 // block has been newly allocated or freed. It is assumed (and
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382 // verified in the non-product VM) that the BOT is correct for
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383 // the given block.
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384 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
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385 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
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386 verify_single_block(blk_start, blk_end);
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387 if (BlockOffsetArrayUseUnallocatedBlock) {
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388 _unallocated_block = MAX2(_unallocated_block, blk_end);
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389 }
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390 }
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391
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392 inline void allocated(HeapWord* blk, size_t size) {
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393 allocated(blk, blk + size);
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394 }
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395
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396 inline void freed(HeapWord* blk_start, HeapWord* blk_end);
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397
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398 inline void freed(HeapWord* blk, size_t size);
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399
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400 virtual HeapWord* block_start_unsafe(const void* addr);
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401 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
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402
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403 // Requires "addr" to be the start of a card and returns the
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404 // start of the block that contains the given address.
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405 HeapWord* block_start_careful(const void* addr) const;
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406
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407 // If true, initialize array slots with no allocated blocks to zero.
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408 // Otherwise, make them point back to the front.
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409 bool init_to_zero() { return _init_to_zero; }
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410
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411 // Verification & debugging - ensure that the offset table reflects the fact
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412 // that the block [blk_start, blk_end) or [blk, blk + size) is a
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413 // single block of storage. NOTE: can;t const this because of
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414 // call to non-const do_block_internal() below.
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415 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
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416 if (VerifyBlockOffsetArray) {
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417 do_block_internal(blk_start, blk_end, Action_check);
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418 }
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419 }
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420
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421 inline void verify_single_block(HeapWord* blk, size_t size) {
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422 verify_single_block(blk, blk + size);
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423 }
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424
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425 // Verify that the given block is before _unallocated_block
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426 inline void verify_not_unallocated(HeapWord* blk_start,
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427 HeapWord* blk_end) const {
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428 if (BlockOffsetArrayUseUnallocatedBlock) {
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429 assert(blk_start < blk_end, "Block inconsistency?");
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430 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
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431 }
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432 }
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433
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434 inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
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435 verify_not_unallocated(blk, blk + size);
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436 }
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437
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438 void check_all_cards(size_t left_card, size_t right_card) const;
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439 };
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440
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441 // A subtype of BlockOffsetArray that takes advantage of the fact
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442 // that its underlying space is a ContiguousSpace, so that its "active"
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443 // region can be more efficiently tracked (than for a non-contiguous space).
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444 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
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445 friend class VMStructs;
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446
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447 // allocation boundary at which offset array must be updated
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448 HeapWord* _next_offset_threshold;
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449 size_t _next_offset_index; // index corresponding to that boundary
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450
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451 // Work function to be called when allocation start crosses the next
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452 // threshold in the contig space.
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453 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
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454 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
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455 blk_start, blk_end);
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456 }
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457
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458
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459 public:
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460 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
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461
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462 // Initialize the threshold to reflect the first boundary after the
|
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463 // bottom of the covered region.
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464 HeapWord* initialize_threshold();
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465
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466 // Zero out the entry for _bottom (offset will be zero).
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467 void zero_bottom_entry();
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468
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469 // Return the next threshold, the point at which the table should be
|
|
470 // updated.
|
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471 HeapWord* threshold() const { return _next_offset_threshold; }
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472
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473 // These must be guaranteed to work properly (i.e., do nothing)
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474 // when "blk_start" ("blk" for second version) is "NULL". In this
|
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475 // implementation, that's true because NULL is represented as 0, and thus
|
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476 // never exceeds the "_next_offset_threshold".
|
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477 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
|
|
478 if (blk_end > _next_offset_threshold)
|
|
479 alloc_block_work1(blk_start, blk_end);
|
|
480 }
|
|
481 void alloc_block(HeapWord* blk, size_t size) {
|
|
482 alloc_block(blk, blk+size);
|
|
483 }
|
|
484
|
|
485 HeapWord* block_start_unsafe(const void* addr);
|
|
486 HeapWord* block_start_unsafe_const(const void* addr) const;
|
|
487 };
|