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1 /*
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2 * Copyright 2001-2005 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 //
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26 // Free block maintenance for Concurrent Mark Sweep Generation
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27 //
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28 // The main data structure for free blocks are
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29 // . an indexed array of small free blocks, and
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30 // . a dictionary of large free blocks
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31 //
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32
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33 // No virtuals in FreeChunk (don't want any vtables).
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34
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35 // A FreeChunk is merely a chunk that can be in a doubly linked list
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36 // and has a size field. NOTE: FreeChunks are distinguished from allocated
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37 // objects in two ways (by the sweeper). The second word (prev) has the
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38 // LSB set to indicate a free chunk; allocated objects' klass() pointers
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39 // don't have their LSB set. The corresponding bit in the CMSBitMap is
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40 // set when the chunk is allocated. There are also blocks that "look free"
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41 // but are not part of the free list and should not be coalesced into larger
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42 // free blocks. These free blocks have their two LSB's set.
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43
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44 class FreeChunk VALUE_OBJ_CLASS_SPEC {
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45 friend class VMStructs;
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46 FreeChunk* _next;
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47 FreeChunk* _prev;
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48 size_t _size;
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49
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50 public:
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51 NOT_PRODUCT(static const size_t header_size();)
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52 // Returns "true" if the "wrd", which is required to be the second word
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53 // of a block, indicates that the block represents a free chunk.
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54 static bool secondWordIndicatesFreeChunk(intptr_t wrd) {
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55 return (wrd & 0x1) == 0x1;
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56 }
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57 bool isFree() const {
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58 return secondWordIndicatesFreeChunk((intptr_t)_prev);
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59 }
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60 bool cantCoalesce() const { return (((intptr_t)_prev) & 0x3) == 0x3; }
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61 FreeChunk* next() const { return _next; }
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62 FreeChunk* prev() const { return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); }
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63 debug_only(void* prev_addr() const { return (void*)&_prev; })
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64
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65 void linkAfter(FreeChunk* ptr) {
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66 linkNext(ptr);
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67 if (ptr != NULL) ptr->linkPrev(this);
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68 }
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69 void linkAfterNonNull(FreeChunk* ptr) {
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70 assert(ptr != NULL, "precondition violation");
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71 linkNext(ptr);
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72 ptr->linkPrev(this);
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73 }
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74 void linkNext(FreeChunk* ptr) { _next = ptr; }
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75 void linkPrev(FreeChunk* ptr) { _prev = (FreeChunk*)((intptr_t)ptr | 0x1); }
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76 void clearPrev() { _prev = NULL; }
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77 void clearNext() { _next = NULL; }
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78 void dontCoalesce() {
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79 // the block should be free
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80 assert(isFree(), "Should look like a free block");
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81 _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2);
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82 }
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83 void markFree() { _prev = (FreeChunk*)((intptr_t)_prev | 0x1); }
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84 void markNotFree() { _prev = NULL; }
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85
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86 size_t size() const { return _size; }
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87 void setSize(size_t size) { _size = size; }
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88
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89 // For volatile reads:
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90 size_t* size_addr() { return &_size; }
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91
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92 // Return the address past the end of this chunk
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93 HeapWord* end() const { return ((HeapWord*) this) + _size; }
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94
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95 // debugging
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96 void verify() const PRODUCT_RETURN;
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97 void verifyList() const PRODUCT_RETURN;
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98 void mangleAllocated(size_t size) PRODUCT_RETURN;
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99 void mangleFreed(size_t size) PRODUCT_RETURN;
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100 };
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101
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102 // Alignment helpers etc.
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103 #define numQuanta(x,y) ((x+y-1)/y)
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104 enum AlignmentConstants {
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105 MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment
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106 };
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107
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108 // A FreeBlockDictionary is an abstract superclass that will allow
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109 // a number of alternative implementations in the future.
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110 class FreeBlockDictionary: public CHeapObj {
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111 public:
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112 enum Dither {
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113 atLeast,
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114 exactly,
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115 roughly
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116 };
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117 enum DictionaryChoice {
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118 dictionaryBinaryTree = 0,
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119 dictionarySplayTree = 1,
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120 dictionarySkipList = 2
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121 };
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122
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123 private:
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124 NOT_PRODUCT(Mutex* _lock;)
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125
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126 public:
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127 virtual void removeChunk(FreeChunk* fc) = 0;
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128 virtual FreeChunk* getChunk(size_t size, Dither dither = atLeast) = 0;
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129 virtual void returnChunk(FreeChunk* chunk) = 0;
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130 virtual size_t totalChunkSize(debug_only(const Mutex* lock)) const = 0;
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131 virtual size_t maxChunkSize() const = 0;
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132 virtual size_t minSize() const = 0;
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133 // Reset the dictionary to the initial conditions for a single
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134 // block.
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135 virtual void reset(HeapWord* addr, size_t size) = 0;
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136 virtual void reset() = 0;
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137
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138 virtual void dictCensusUpdate(size_t size, bool split, bool birth) = 0;
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139 virtual bool coalDictOverPopulated(size_t size) = 0;
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140 virtual void beginSweepDictCensus(double coalSurplusPercent,
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141 float sweep_current, float sweep_ewstimate) = 0;
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142 virtual void endSweepDictCensus(double splitSurplusPercent) = 0;
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143 virtual FreeChunk* findLargestDict() const = 0;
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144 // verify that the given chunk is in the dictionary.
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145 virtual bool verifyChunkInFreeLists(FreeChunk* tc) const = 0;
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146
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147 // Sigma_{all_free_blocks} (block_size^2)
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148 virtual double sum_of_squared_block_sizes() const = 0;
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149
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150 virtual FreeChunk* find_chunk_ends_at(HeapWord* target) const = 0;
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151 virtual void inc_totalSize(size_t v) = 0;
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152 virtual void dec_totalSize(size_t v) = 0;
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153
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154 NOT_PRODUCT (
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155 virtual size_t sumDictReturnedBytes() = 0;
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156 virtual void initializeDictReturnedBytes() = 0;
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157 virtual size_t totalCount() = 0;
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158 )
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159
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160 virtual void reportStatistics() const {
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161 gclog_or_tty->print("No statistics available");
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162 }
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163
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164 virtual void printDictCensus() const = 0;
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165
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166 virtual void verify() const = 0;
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167
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168 Mutex* par_lock() const PRODUCT_RETURN0;
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169 void set_par_lock(Mutex* lock) PRODUCT_RETURN;
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170 void verify_par_locked() const PRODUCT_RETURN;
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171 };
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