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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 // This class can be used to locate the beginning of an object in the
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27 // covered region.
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28 //
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29
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30 class ObjectStartArray : public CHeapObj {
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31 friend class VerifyObjectStartArrayClosure;
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32
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33 private:
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34 PSVirtualSpace _virtual_space;
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35 MemRegion _reserved_region;
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36 MemRegion _covered_region;
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37 MemRegion _blocks_region;
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38 jbyte* _raw_base;
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39 jbyte* _offset_base;
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40
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41 public:
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42
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43 enum BlockValueConstants {
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44 clean_block = -1
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45 };
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46
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47 enum BlockSizeConstants {
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48 block_shift = 9,
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49 block_size = 1 << block_shift,
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50 block_size_in_words = block_size / sizeof(HeapWord)
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51 };
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52
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53 protected:
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54
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55 // Mapping from address to object start array entry
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56 jbyte* block_for_addr(void* p) const {
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57 assert(_covered_region.contains(p),
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58 "out of bounds access to object start array");
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59 jbyte* result = &_offset_base[uintptr_t(p) >> block_shift];
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60 assert(_blocks_region.contains(result),
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61 "out of bounds result in byte_for");
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62 return result;
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63 }
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64
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65 // Mapping from object start array entry to address of first word
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66 HeapWord* addr_for_block(jbyte* p) {
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67 assert(_blocks_region.contains(p),
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68 "out of bounds access to object start array");
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69 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
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70 HeapWord* result = (HeapWord*) (delta << block_shift);
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71 assert(_covered_region.contains(result),
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72 "out of bounds accessor from card marking array");
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73 return result;
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74 }
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75
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76 // Mapping that includes the derived offset.
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77 // If the block is clean, returns the last address in the covered region.
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78 // If the block is < index 0, returns the start of the covered region.
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79 HeapWord* offset_addr_for_block (jbyte* p) const {
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80 // We have to do this before the assert
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81 if (p < _raw_base) {
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82 return _covered_region.start();
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83 }
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84
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85 assert(_blocks_region.contains(p),
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86 "out of bounds access to object start array");
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87
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88 if (*p == clean_block) {
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89 return _covered_region.end();
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90 }
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91
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92 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
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93 HeapWord* result = (HeapWord*) (delta << block_shift);
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94 result += *p;
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95
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96 assert(_covered_region.contains(result),
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97 "out of bounds accessor from card marking array");
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98
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99 return result;
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100 }
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101
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102 public:
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103
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104 // This method is in lieu of a constructor, so that this class can be
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105 // embedded inline in other classes.
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106 void initialize(MemRegion reserved_region);
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107
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108 void set_covered_region(MemRegion mr);
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109
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110 void reset();
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111
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112 MemRegion covered_region() { return _covered_region; }
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113
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114 void allocate_block(HeapWord* p) {
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115 assert(_covered_region.contains(p), "Must be in covered region");
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116 jbyte* block = block_for_addr(p);
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117 HeapWord* block_base = addr_for_block(block);
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118 size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));
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119 assert(offset < 128, "Sanity");
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120 // When doing MT offsets, we can't assert this.
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121 //assert(offset > *block, "Found backwards allocation");
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122 *block = (jbyte)offset;
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123
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124 // tty->print_cr("[%p]", p);
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125 }
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126
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127 // Optimized for finding the first object that crosses into
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128 // a given block. The blocks contain the offset of the last
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129 // object in that block. Scroll backwards by one, and the first
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605
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130 // object hit should be at the beginning of the block
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0
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131 HeapWord* object_start(HeapWord* addr) const {
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132 assert(_covered_region.contains(addr), "Must be in covered region");
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133 jbyte* block = block_for_addr(addr);
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134 HeapWord* scroll_forward = offset_addr_for_block(block--);
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135 while (scroll_forward > addr) {
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136 scroll_forward = offset_addr_for_block(block--);
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137 }
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138
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139 HeapWord* next = scroll_forward;
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140 while (next <= addr) {
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141 scroll_forward = next;
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142 next += oop(next)->size();
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143 }
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144 assert(scroll_forward <= addr, "wrong order for current and arg");
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145 assert(addr <= next, "wrong order for arg and next");
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146 return scroll_forward;
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147 }
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148
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149 bool is_block_allocated(HeapWord* addr) {
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150 assert(_covered_region.contains(addr), "Must be in covered region");
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151 jbyte* block = block_for_addr(addr);
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152 if (*block == clean_block)
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153 return false;
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154
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155 return true;
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156 }
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157
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158 // Return true if an object starts in the range of heap addresses.
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159 // If an object starts at an address corresponding to
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160 // "start", the method will return true.
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161 bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const;
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162 };
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