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1 /*
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2 * Copyright 2000-2006 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 // A "SharedHeap" is an implementation of a java heap for HotSpot. This
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26 // is an abstract class: there may be many different kinds of heaps. This
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27 // class defines the functions that a heap must implement, and contains
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28 // infrastructure common to all heaps.
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29
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30 class PermGen;
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31 class Generation;
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32 class BarrierSet;
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33 class GenRemSet;
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34 class Space;
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35 class SpaceClosure;
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36 class OopClosure;
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37 class OopsInGenClosure;
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38 class ObjectClosure;
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39 class SubTasksDone;
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40 class WorkGang;
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41 class CollectorPolicy;
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42 class KlassHandle;
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43
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44 class SharedHeap : public CollectedHeap {
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45 friend class VMStructs;
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46
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47 private:
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48 // For claiming strong_roots tasks.
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49 SubTasksDone* _process_strong_tasks;
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50
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51 protected:
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52 // There should be only a single instance of "SharedHeap" in a program.
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53 // This is enforced with the protected constructor below, which will also
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54 // set the static pointer "_sh" to that instance.
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55 static SharedHeap* _sh;
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56
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57 // All heaps contain a "permanent generation." This is some ways
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58 // similar to a generation in a generational system, in other ways not.
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59 // See the "PermGen" class.
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60 PermGen* _perm_gen;
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61
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62 // and the Gen Remembered Set, at least one good enough to scan the perm
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63 // gen.
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64 GenRemSet* _rem_set;
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65
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66 // A gc policy, controls global gc resource issues
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67 CollectorPolicy *_collector_policy;
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68
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69 // See the discussion below, in the specification of the reader function
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70 // for this variable.
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71 int _strong_roots_parity;
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72
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73 // If we're doing parallel GC, use this gang of threads.
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74 WorkGang* _workers;
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75
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76 // Number of parallel threads currently working on GC tasks.
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77 // O indicates use sequential code; 1 means use parallel code even with
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78 // only one thread, for performance testing purposes.
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79 int _n_par_threads;
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80
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81 // Full initialization is done in a concrete subtype's "initialize"
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82 // function.
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83 SharedHeap(CollectorPolicy* policy_);
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84
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85 public:
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86 static SharedHeap* heap() { return _sh; }
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87
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88 CollectorPolicy *collector_policy() const { return _collector_policy; }
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89
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90 void set_barrier_set(BarrierSet* bs);
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91
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92 // Does operations required after initialization has been done.
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93 virtual void post_initialize();
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94
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95 // Initialization of ("weak") reference processing support
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96 virtual void ref_processing_init();
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97
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98 void set_perm(PermGen* perm_gen) { _perm_gen = perm_gen; }
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99
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100 // A helper function that fills an allocated-but-not-yet-initialized
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101 // region with a garbage object.
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102 static void fill_region_with_object(MemRegion mr);
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103
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104 // Minimum garbage fill object size
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105 static size_t min_fill_size() { return (size_t)align_object_size(oopDesc::header_size()); }
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106 static size_t min_fill_size_in_bytes() { return min_fill_size() * HeapWordSize; }
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107
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108 // This function returns the "GenRemSet" object that allows us to scan
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109 // generations; at least the perm gen, possibly more in a fully
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110 // generational heap.
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111 GenRemSet* rem_set() { return _rem_set; }
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112
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113 // These function return the "permanent" generation, in which
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114 // reflective objects are allocated and stored. Two versions, the second
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115 // of which returns the view of the perm gen as a generation.
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116 PermGen* perm() const { return _perm_gen; }
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117 Generation* perm_gen() const { return _perm_gen->as_gen(); }
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118
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119 // Iteration functions.
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120 void oop_iterate(OopClosure* cl) = 0;
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121
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122 // Same as above, restricted to a memory region.
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123 virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;
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124
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125 // Iterate over all objects allocated since the last collection, calling
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126 // "cl->do_object" on each. The heap must have been initialized properly
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127 // to support this function, or else this call will fail.
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128 virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0;
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129
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130 // Iterate over all spaces in use in the heap, in an undefined order.
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131 virtual void space_iterate(SpaceClosure* cl) = 0;
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132
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133 // A SharedHeap will contain some number of spaces. This finds the
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134 // space whose reserved area contains the given address, or else returns
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135 // NULL.
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136 virtual Space* space_containing(const void* addr) const = 0;
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137
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138 bool no_gc_in_progress() { return !is_gc_active(); }
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139
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140 // Some collectors will perform "process_strong_roots" in parallel.
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141 // Such a call will involve claiming some fine-grained tasks, such as
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142 // scanning of threads. To make this process simpler, we provide the
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143 // "strong_roots_parity()" method. Collectors that start parallel tasks
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144 // whose threads invoke "process_strong_roots" must
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145 // call "change_strong_roots_parity" in sequential code starting such a
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146 // task. (This also means that a parallel thread may only call
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147 // process_strong_roots once.)
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148 //
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149 // For calls to process_strong_roots by sequential code, the parity is
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150 // updated automatically.
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151 //
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152 // The idea is that objects representing fine-grained tasks, such as
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153 // threads, will contain a "parity" field. A task will is claimed in the
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154 // current "process_strong_roots" call only if its parity field is the
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155 // same as the "strong_roots_parity"; task claiming is accomplished by
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156 // updating the parity field to the strong_roots_parity with a CAS.
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157 //
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158 // If the client meats this spec, then strong_roots_parity() will have
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159 // the following properties:
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160 // a) to return a different value than was returned before the last
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161 // call to change_strong_roots_parity, and
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162 // c) to never return a distinguished value (zero) with which such
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163 // task-claiming variables may be initialized, to indicate "never
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164 // claimed".
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165 void change_strong_roots_parity();
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166 int strong_roots_parity() { return _strong_roots_parity; }
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167
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168 enum ScanningOption {
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169 SO_None = 0x0,
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170 SO_AllClasses = 0x1,
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171 SO_SystemClasses = 0x2,
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172 SO_Symbols = 0x4,
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173 SO_Strings = 0x8,
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174 SO_CodeCache = 0x10
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175 };
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176
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177 WorkGang* workers() const { return _workers; }
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178
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179 // Sets the number of parallel threads that will be doing tasks
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180 // (such as process strong roots) subsequently.
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181 virtual void set_par_threads(int t);
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182
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183 // Number of threads currently working on GC tasks.
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184 int n_par_threads() { return _n_par_threads; }
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185
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186 // Invoke the "do_oop" method the closure "roots" on all root locations.
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187 // If "collecting_perm_gen" is false, then roots that may only contain
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188 // references to permGen objects are not scanned. If true, the
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189 // "perm_gen" closure is applied to all older-to-younger refs in the
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190 // permanent generation. The "so" argument determines which of roots
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191 // the closure is applied to:
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192 // "SO_None" does none;
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193 // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
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194 // "SO_SystemClasses" to all the "system" classes and loaders;
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195 // "SO_Symbols" applies the closure to all entries in SymbolsTable;
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196 // "SO_Strings" applies the closure to all entries in StringTable;
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197 // "SO_CodeCache" applies the closure to all elements of the CodeCache.
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198 void process_strong_roots(bool collecting_perm_gen,
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199 ScanningOption so,
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200 OopClosure* roots,
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201 OopsInGenClosure* perm_blk);
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202
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203 // Apply "blk" to all the weak roots of the system. These include
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204 // JNI weak roots, the code cache, system dictionary, symbol table,
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205 // string table.
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206 void process_weak_roots(OopClosure* root_closure,
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207 OopClosure* non_root_closure);
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208
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209
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210 // Like CollectedHeap::collect, but assume that the caller holds the Heap_lock.
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211 virtual void collect_locked(GCCause::Cause cause) = 0;
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212
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213 // The functions below are helper functions that a subclass of
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214 // "SharedHeap" can use in the implementation of its virtual
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215 // functions.
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216
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217 protected:
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218
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219 // Do anything common to GC's.
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220 virtual void gc_prologue(bool full) = 0;
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221 virtual void gc_epilogue(bool full) = 0;
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222
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223 public:
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224 //
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225 // New methods from CollectedHeap
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226 //
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227
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228 size_t permanent_capacity() const {
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229 assert(perm_gen(), "NULL perm gen");
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230 return perm_gen()->capacity();
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231 }
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232
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233 size_t permanent_used() const {
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234 assert(perm_gen(), "NULL perm gen");
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235 return perm_gen()->used();
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236 }
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237
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238 bool is_in_permanent(const void *p) const {
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239 assert(perm_gen(), "NULL perm gen");
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240 return perm_gen()->is_in_reserved(p);
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241 }
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242
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243 // Different from is_in_permanent in that is_in_permanent
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244 // only checks if p is in the reserved area of the heap
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245 // and this checks to see if it in the commited area.
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246 // This is typically used by things like the forte stackwalker
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247 // during verification of suspicious frame values.
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248 bool is_permanent(const void *p) const {
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249 assert(perm_gen(), "NULL perm gen");
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250 return perm_gen()->is_in(p);
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251 }
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252
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253 HeapWord* permanent_mem_allocate(size_t size) {
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254 assert(perm_gen(), "NULL perm gen");
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255 return _perm_gen->mem_allocate(size);
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256 }
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257
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258 void permanent_oop_iterate(OopClosure* cl) {
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259 assert(perm_gen(), "NULL perm gen");
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260 _perm_gen->oop_iterate(cl);
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261 }
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262
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263 void permanent_object_iterate(ObjectClosure* cl) {
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264 assert(perm_gen(), "NULL perm gen");
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265 _perm_gen->object_iterate(cl);
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266 }
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267
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268 // Some utilities.
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269 void print_size_transition(size_t bytes_before,
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270 size_t bytes_after,
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271 size_t capacity);
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272 };
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