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1 /* |
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2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
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22 * |
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23 */ |
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24 |
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25 #ifndef SHARE_VM_OOPS_MARKOOP_HPP |
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26 #define SHARE_VM_OOPS_MARKOOP_HPP |
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27 |
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28 #include "oops/oop.hpp" |
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29 |
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30 // The markOop describes the header of an object. |
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31 // |
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32 // Note that the mark is not a real oop but just a word. |
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33 // It is placed in the oop hierarchy for historical reasons. |
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34 // |
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35 // Bit-format of an object header (most significant first, big endian layout below): |
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36 // |
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37 // 32 bits: |
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38 // -------- |
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39 // hash:25 ------------>| age:4 biased_lock:1 lock:2 (normal object) |
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40 // JavaThread*:23 epoch:2 age:4 biased_lock:1 lock:2 (biased object) |
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41 // size:32 ------------------------------------------>| (CMS free block) |
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42 // PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object) |
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43 // |
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44 // 64 bits: |
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45 // -------- |
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46 // unused:25 hash:31 -->| unused:1 age:4 biased_lock:1 lock:2 (normal object) |
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47 // JavaThread*:54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased object) |
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48 // PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object) |
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49 // size:64 ----------------------------------------------------->| (CMS free block) |
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50 // |
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51 // unused:25 hash:31 -->| cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && normal object) |
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52 // JavaThread*:54 epoch:2 cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && biased object) |
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53 // narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object) |
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54 // unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block) |
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55 // |
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56 // - hash contains the identity hash value: largest value is |
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57 // 31 bits, see os::random(). Also, 64-bit vm's require |
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58 // a hash value no bigger than 32 bits because they will not |
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59 // properly generate a mask larger than that: see library_call.cpp |
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60 // and c1_CodePatterns_sparc.cpp. |
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61 // |
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62 // - the biased lock pattern is used to bias a lock toward a given |
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63 // thread. When this pattern is set in the low three bits, the lock |
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64 // is either biased toward a given thread or "anonymously" biased, |
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65 // indicating that it is possible for it to be biased. When the |
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66 // lock is biased toward a given thread, locking and unlocking can |
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67 // be performed by that thread without using atomic operations. |
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68 // When a lock's bias is revoked, it reverts back to the normal |
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69 // locking scheme described below. |
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70 // |
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71 // Note that we are overloading the meaning of the "unlocked" state |
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72 // of the header. Because we steal a bit from the age we can |
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73 // guarantee that the bias pattern will never be seen for a truly |
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74 // unlocked object. |
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75 // |
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76 // Note also that the biased state contains the age bits normally |
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77 // contained in the object header. Large increases in scavenge |
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78 // times were seen when these bits were absent and an arbitrary age |
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79 // assigned to all biased objects, because they tended to consume a |
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80 // significant fraction of the eden semispaces and were not |
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81 // promoted promptly, causing an increase in the amount of copying |
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82 // performed. The runtime system aligns all JavaThread* pointers to |
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83 // a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM)) |
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84 // to make room for the age bits & the epoch bits (used in support of |
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85 // biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs). |
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86 // |
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87 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread |
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88 // [0 | epoch | age | 1 | 01] lock is anonymously biased |
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89 // |
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90 // - the two lock bits are used to describe three states: locked/unlocked and monitor. |
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91 // |
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92 // [ptr | 00] locked ptr points to real header on stack |
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93 // [header | 0 | 01] unlocked regular object header |
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94 // [ptr | 10] monitor inflated lock (header is wapped out) |
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95 // [ptr | 11] marked used by markSweep to mark an object |
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96 // not valid at any other time |
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97 // |
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98 // We assume that stack/thread pointers have the lowest two bits cleared. |
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99 |
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100 class BasicLock; |
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101 class ObjectMonitor; |
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102 class JavaThread; |
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103 |
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104 class markOopDesc: public oopDesc { |
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105 private: |
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106 // Conversion |
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107 uintptr_t value() const { return (uintptr_t) this; } |
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108 |
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109 public: |
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110 // Constants |
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111 enum { age_bits = 4, |
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112 lock_bits = 2, |
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113 biased_lock_bits = 1, |
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114 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits, |
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115 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits, |
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116 cms_bits = LP64_ONLY(1) NOT_LP64(0), |
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117 epoch_bits = 2 |
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118 }; |
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119 |
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120 // The biased locking code currently requires that the age bits be |
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121 // contiguous to the lock bits. |
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122 enum { lock_shift = 0, |
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123 biased_lock_shift = lock_bits, |
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124 age_shift = lock_bits + biased_lock_bits, |
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125 cms_shift = age_shift + age_bits, |
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126 hash_shift = cms_shift + cms_bits, |
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127 epoch_shift = hash_shift |
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128 }; |
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129 |
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130 enum { lock_mask = right_n_bits(lock_bits), |
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131 lock_mask_in_place = lock_mask << lock_shift, |
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132 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits), |
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133 biased_lock_mask_in_place= biased_lock_mask << lock_shift, |
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134 biased_lock_bit_in_place = 1 << biased_lock_shift, |
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135 age_mask = right_n_bits(age_bits), |
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136 age_mask_in_place = age_mask << age_shift, |
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137 epoch_mask = right_n_bits(epoch_bits), |
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138 epoch_mask_in_place = epoch_mask << epoch_shift, |
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139 cms_mask = right_n_bits(cms_bits), |
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140 cms_mask_in_place = cms_mask << cms_shift |
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141 #ifndef _WIN64 |
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142 ,hash_mask = right_n_bits(hash_bits), |
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143 hash_mask_in_place = (address_word)hash_mask << hash_shift |
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144 #endif |
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145 }; |
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146 |
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147 // Alignment of JavaThread pointers encoded in object header required by biased locking |
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148 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) |
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149 }; |
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150 |
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151 #ifdef _WIN64 |
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152 // These values are too big for Win64 |
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153 const static uintptr_t hash_mask = right_n_bits(hash_bits); |
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154 const static uintptr_t hash_mask_in_place = |
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155 (address_word)hash_mask << hash_shift; |
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156 #endif |
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157 |
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158 enum { locked_value = 0, |
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159 unlocked_value = 1, |
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160 monitor_value = 2, |
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161 marked_value = 3, |
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162 biased_lock_pattern = 5 |
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163 }; |
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164 |
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165 enum { no_hash = 0 }; // no hash value assigned |
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166 |
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167 enum { no_hash_in_place = (address_word)no_hash << hash_shift, |
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168 no_lock_in_place = unlocked_value |
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169 }; |
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170 |
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171 enum { max_age = age_mask }; |
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172 |
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173 enum { max_bias_epoch = epoch_mask }; |
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174 |
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175 // Biased Locking accessors. |
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176 // These must be checked by all code which calls into the |
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177 // ObjectSynchronizer and other code. The biasing is not understood |
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178 // by the lower-level CAS-based locking code, although the runtime |
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179 // fixes up biased locks to be compatible with it when a bias is |
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180 // revoked. |
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181 bool has_bias_pattern() const { |
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182 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern); |
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183 } |
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184 JavaThread* biased_locker() const { |
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185 assert(has_bias_pattern(), "should not call this otherwise"); |
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186 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place)))); |
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187 } |
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188 // Indicates that the mark has the bias bit set but that it has not |
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189 // yet been biased toward a particular thread |
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190 bool is_biased_anonymously() const { |
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191 return (has_bias_pattern() && (biased_locker() == NULL)); |
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192 } |
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193 // Indicates epoch in which this bias was acquired. If the epoch |
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194 // changes due to too many bias revocations occurring, the biases |
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195 // from the previous epochs are all considered invalid. |
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196 int bias_epoch() const { |
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197 assert(has_bias_pattern(), "should not call this otherwise"); |
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198 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift); |
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199 } |
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200 markOop set_bias_epoch(int epoch) { |
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201 assert(has_bias_pattern(), "should not call this otherwise"); |
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202 assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); |
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203 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); |
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204 } |
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205 markOop incr_bias_epoch() { |
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206 return set_bias_epoch((1 + bias_epoch()) & epoch_mask); |
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207 } |
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208 // Prototype mark for initialization |
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209 static markOop biased_locking_prototype() { |
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210 return markOop( biased_lock_pattern ); |
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211 } |
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212 |
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213 // lock accessors (note that these assume lock_shift == 0) |
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214 bool is_locked() const { |
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215 return (mask_bits(value(), lock_mask_in_place) != unlocked_value); |
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216 } |
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217 bool is_unlocked() const { |
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218 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); |
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219 } |
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220 bool is_marked() const { |
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221 return (mask_bits(value(), lock_mask_in_place) == marked_value); |
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222 } |
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223 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); } |
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224 |
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225 // Special temporary state of the markOop while being inflated. |
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226 // Code that looks at mark outside a lock need to take this into account. |
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227 bool is_being_inflated() const { return (value() == 0); } |
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228 |
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229 // Distinguished markword value - used when inflating over |
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230 // an existing stacklock. 0 indicates the markword is "BUSY". |
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231 // Lockword mutators that use a LD...CAS idiom should always |
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232 // check for and avoid overwriting a 0 value installed by some |
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233 // other thread. (They should spin or block instead. The 0 value |
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234 // is transient and *should* be short-lived). |
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235 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress |
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236 |
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237 // Should this header be preserved during GC? |
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238 inline bool must_be_preserved(oop obj_containing_mark) const; |
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239 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const; |
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240 |
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241 // Should this header (including its age bits) be preserved in the |
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242 // case of a promotion failure during scavenge? |
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243 // Note that we special case this situation. We want to avoid |
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244 // calling BiasedLocking::preserve_marks()/restore_marks() (which |
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245 // decrease the number of mark words that need to be preserved |
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246 // during GC) during each scavenge. During scavenges in which there |
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247 // is no promotion failure, we actually don't need to call the above |
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248 // routines at all, since we don't mutate and re-initialize the |
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249 // marks of promoted objects using init_mark(). However, during |
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250 // scavenges which result in promotion failure, we do re-initialize |
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251 // the mark words of objects, meaning that we should have called |
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252 // these mark word preservation routines. Currently there's no good |
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253 // place in which to call them in any of the scavengers (although |
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254 // guarded by appropriate locks we could make one), but the |
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255 // observation is that promotion failures are quite rare and |
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256 // reducing the number of mark words preserved during them isn't a |
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257 // high priority. |
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258 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const; |
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259 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const; |
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260 |
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261 // Should this header be preserved during a scavenge where CMS is |
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262 // the old generation? |
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263 // (This is basically the same body as must_be_preserved_for_promotion_failure(), |
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264 // but takes the Klass* as argument instead) |
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265 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const; |
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266 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const; |
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267 |
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268 // WARNING: The following routines are used EXCLUSIVELY by |
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269 // synchronization functions. They are not really gc safe. |
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270 // They must get updated if markOop layout get changed. |
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271 markOop set_unlocked() const { |
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272 return markOop(value() | unlocked_value); |
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273 } |
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274 bool has_locker() const { |
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275 return ((value() & lock_mask_in_place) == locked_value); |
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276 } |
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277 BasicLock* locker() const { |
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278 assert(has_locker(), "check"); |
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279 return (BasicLock*) value(); |
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280 } |
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281 bool has_monitor() const { |
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282 return ((value() & monitor_value) != 0); |
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283 } |
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284 ObjectMonitor* monitor() const { |
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285 assert(has_monitor(), "check"); |
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286 // Use xor instead of &~ to provide one extra tag-bit check. |
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287 return (ObjectMonitor*) (value() ^ monitor_value); |
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288 } |
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289 bool has_displaced_mark_helper() const { |
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290 return ((value() & unlocked_value) == 0); |
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291 } |
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292 markOop displaced_mark_helper() const { |
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293 assert(has_displaced_mark_helper(), "check"); |
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294 intptr_t ptr = (value() & ~monitor_value); |
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295 return *(markOop*)ptr; |
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296 } |
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297 void set_displaced_mark_helper(markOop m) const { |
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298 assert(has_displaced_mark_helper(), "check"); |
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299 intptr_t ptr = (value() & ~monitor_value); |
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300 *(markOop*)ptr = m; |
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301 } |
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302 markOop copy_set_hash(intptr_t hash) const { |
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303 intptr_t tmp = value() & (~hash_mask_in_place); |
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304 tmp |= ((hash & hash_mask) << hash_shift); |
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305 return (markOop)tmp; |
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306 } |
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307 // it is only used to be stored into BasicLock as the |
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308 // indicator that the lock is using heavyweight monitor |
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309 static markOop unused_mark() { |
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310 return (markOop) marked_value; |
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311 } |
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312 // the following two functions create the markOop to be |
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313 // stored into object header, it encodes monitor info |
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314 static markOop encode(BasicLock* lock) { |
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315 return (markOop) lock; |
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316 } |
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317 static markOop encode(ObjectMonitor* monitor) { |
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318 intptr_t tmp = (intptr_t) monitor; |
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319 return (markOop) (tmp | monitor_value); |
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320 } |
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321 static markOop encode(JavaThread* thread, uint age, int bias_epoch) { |
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322 intptr_t tmp = (intptr_t) thread; |
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323 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer"); |
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324 assert(age <= max_age, "age too large"); |
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325 assert(bias_epoch <= max_bias_epoch, "bias epoch too large"); |
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326 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); |
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327 } |
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328 |
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329 // used to encode pointers during GC |
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330 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } |
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331 |
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332 // age operations |
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333 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } |
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334 markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); } |
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335 |
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336 uint age() const { return mask_bits(value() >> age_shift, age_mask); } |
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337 markOop set_age(uint v) const { |
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338 assert((v & ~age_mask) == 0, "shouldn't overflow age field"); |
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339 return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift)); |
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340 } |
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341 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); } |
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342 |
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343 // hash operations |
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344 intptr_t hash() const { |
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345 return mask_bits(value() >> hash_shift, hash_mask); |
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346 } |
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347 |
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348 bool has_no_hash() const { |
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349 return hash() == no_hash; |
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350 } |
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351 |
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352 // Prototype mark for initialization |
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353 static markOop prototype() { |
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354 return markOop( no_hash_in_place | no_lock_in_place ); |
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355 } |
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356 |
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357 // Helper function for restoration of unmarked mark oops during GC |
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358 static inline markOop prototype_for_object(oop obj); |
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359 |
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360 // Debugging |
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361 void print_on(outputStream* st) const; |
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362 |
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363 // Prepare address of oop for placement into mark |
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364 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); } |
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365 |
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366 // Recover address of oop from encoded form used in mark |
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367 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); } |
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368 |
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369 // These markOops indicate cms free chunk blocks and not objects. |
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370 // In 64 bit, the markOop is set to distinguish them from oops. |
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371 // These are defined in 32 bit mode for vmStructs. |
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372 const static uintptr_t cms_free_chunk_pattern = 0x1; |
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373 |
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374 // Constants for the size field. |
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375 enum { size_shift = cms_shift + cms_bits, |
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376 size_bits = 35 // need for compressed oops 32G |
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377 }; |
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378 // These values are too big for Win64 |
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379 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits)) |
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380 NOT_LP64(0); |
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381 const static uintptr_t size_mask_in_place = |
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382 (address_word)size_mask << size_shift; |
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383 |
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384 #ifdef _LP64 |
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385 static markOop cms_free_prototype() { |
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386 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) | |
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387 ((cms_free_chunk_pattern & cms_mask) << cms_shift)); |
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388 } |
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389 uintptr_t cms_encoding() const { |
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390 return mask_bits(value() >> cms_shift, cms_mask); |
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391 } |
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392 bool is_cms_free_chunk() const { |
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393 return is_neutral() && |
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394 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern; |
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395 } |
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396 |
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397 size_t get_size() const { return (size_t)(value() >> size_shift); } |
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398 static markOop set_size_and_free(size_t size) { |
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399 assert((size & ~size_mask) == 0, "shouldn't overflow size field"); |
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400 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) | |
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401 (((intptr_t)size & size_mask) << size_shift)); |
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402 } |
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403 #endif // _LP64 |
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404 }; |
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405 |
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406 #endif // SHARE_VM_OOPS_MARKOOP_HPP |