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1 /*
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2 * Copyright 1998-2005 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 // Recording and retrieval of oop relocations in compiled code.
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26
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27 class CodeBlob;
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28
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29 class OopRecorder : public ResourceObj {
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30 public:
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31 // A two-way mapping from positive indexes to oop handles.
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32 // The zero index is reserved for a constant (sharable) null.
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33 // Indexes may not be negative.
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34
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35 // Use the given arena to manage storage, if not NULL.
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36 // By default, uses the current ResourceArea.
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37 OopRecorder(Arena* arena = NULL);
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38
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39 // Generate a new index on which CodeBlob::oop_addr_at will work.
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40 // allocate_index and find_index never return the same index,
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41 // and allocate_index never returns the same index twice.
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42 // In fact, two successive calls to allocate_index return successive ints.
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43 int allocate_index(jobject h) {
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44 return add_handle(h, false);
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45 }
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46
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47 // For a given jobject, this will return the same index repeatedly.
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48 // The index can later be given to oop_at to retrieve the oop.
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49 // However, the oop must not be changed via CodeBlob::oop_addr_at.
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50 int find_index(jobject h) {
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51 int index = maybe_find_index(h);
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52 if (index < 0) { // previously unallocated
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53 index = add_handle(h, true);
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54 }
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55 return index;
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56 }
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57
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58 // variant of find_index which does not allocate if not found (yields -1)
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59 int maybe_find_index(jobject h);
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60
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61 // returns the size of the generated oop table, for sizing the CodeBlob.
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62 // must be called after all oops are allocated!
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63 int oop_size();
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64
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65 // Retrieve the oop handle at a given index.
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66 jobject handle_at(int index);
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67
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68 int element_count() {
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69 // there is always a NULL virtually present as first object
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70 return _handles->length() + first_index;
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71 }
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72
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73 // copy the generated oop table to CodeBlob
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74 void copy_to(CodeBlob* code); // => code->copy_oops(_handles)
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75
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76 bool is_unused() { return _handles == NULL && !_complete; }
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77 #ifdef ASSERT
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78 bool is_complete() { return _complete; }
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79 #endif
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80
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81 private:
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82 // leaky hash table of handle => index, to help detect duplicate insertion
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83 class IndexCache: public ResourceObj {
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84 // This class is only used by the OopRecorder class.
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85 friend class OopRecorder;
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86 enum {
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87 _log_cache_size = 9,
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88 _cache_size = (1<<_log_cache_size),
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89 // Index entries are ints. The LSBit is a collision indicator.
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90 _collision_bit_shift = 0,
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91 _collision_bit = 1,
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92 _index_shift = _collision_bit_shift+1
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93 };
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94 int _cache[_cache_size];
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95 static juint cache_index(jobject handle) {
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96 juint ci = (int) (intptr_t) handle;
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97 ci ^= ci >> (BitsPerByte*2);
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98 ci += ci >> (BitsPerByte*1);
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99 return ci & (_cache_size-1);
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100 }
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101 int* cache_location(jobject handle) {
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102 return &_cache[ cache_index(handle) ];
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103 }
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104 static bool cache_location_collision(int* cloc) {
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105 return ((*cloc) & _collision_bit) != 0;
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106 }
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107 static int cache_location_index(int* cloc) {
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108 return (*cloc) >> _index_shift;
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109 }
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110 static void set_cache_location_index(int* cloc, int index) {
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111 int cval0 = (*cloc);
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112 int cval1 = (index << _index_shift);
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113 if (cval0 != 0 && cval1 != cval0) cval1 += _collision_bit;
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114 (*cloc) = cval1;
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115 }
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116 IndexCache();
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117 };
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118
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119 // Helper function; returns false for NULL or Universe::non_oop_word().
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120 inline bool is_real_jobject(jobject h);
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121
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122 void maybe_initialize();
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123 int add_handle(jobject h, bool make_findable);
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124
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125 enum { null_index = 0, first_index = 1, index_cache_threshold = 20 };
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126
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127 GrowableArray<jobject>* _handles; // ordered list (first is always NULL)
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128 GrowableArray<int>* _no_finds; // all unfindable indexes; usually empty
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129 IndexCache* _indexes; // map: jobject -> its probable index
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130 Arena* _arena;
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131 bool _complete;
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132
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133 #ifdef ASSERT
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134 static int _find_index_calls, _hit_indexes, _missed_indexes;
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135 #endif
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136 };
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