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annotate src/share/vm/memory/sharedHeap.hpp @ 23286:dd9cc155639c

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Merge with jdk8u66-b17
author Gilles Duboscq <gilles.m.duboscq@oracle.com>
date Thu, 07 Jan 2016 17:28:46 +0100
parents 7848fc12602b 38d6febe66af
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1 /*
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2 * Copyright (c) 2000, 2013, 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_MEMORY_SHAREDHEAP_HPP
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26 #define SHARE_VM_MEMORY_SHAREDHEAP_HPP
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27
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28 #include "gc_interface/collectedHeap.hpp"
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29 #include "memory/generation.hpp"
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30
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31 // A "SharedHeap" is an implementation of a java heap for HotSpot. This
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32 // is an abstract class: there may be many different kinds of heaps. This
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33 // class defines the functions that a heap must implement, and contains
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34 // infrastructure common to all heaps.
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35
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36 class Generation;
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37 class BarrierSet;
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38 class GenRemSet;
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39 class Space;
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40 class SpaceClosure;
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41 class OopClosure;
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42 class OopsInGenClosure;
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43 class ObjectClosure;
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44 class SubTasksDone;
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45 class WorkGang;
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46 class FlexibleWorkGang;
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47 class CollectorPolicy;
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48 class KlassClosure;
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49
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50 // Note on use of FlexibleWorkGang's for GC.
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51 // There are three places where task completion is determined.
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52 // In
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53 // 1) ParallelTaskTerminator::offer_termination() where _n_threads
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54 // must be set to the correct value so that count of workers that
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55 // have offered termination will exactly match the number
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56 // working on the task. Tasks such as those derived from GCTask
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57 // use ParallelTaskTerminator's. Tasks that want load balancing
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58 // by work stealing use this method to gauge completion.
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59 // 2) SubTasksDone has a variable _n_threads that is used in
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60 // all_tasks_completed() to determine completion. all_tasks_complete()
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61 // counts the number of tasks that have been done and then reset
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62 // the SubTasksDone so that it can be used again. When the number of
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63 // tasks is set to the number of GC workers, then _n_threads must
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64 // be set to the number of active GC workers. G1RootProcessor and
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65 // GenCollectedHeap have SubTasksDone.
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66 // 3) SequentialSubTasksDone has an _n_threads that is used in
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67 // a way similar to SubTasksDone and has the same dependency on the
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68 // number of active GC workers. CompactibleFreeListSpace and Space
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69 // have SequentialSubTasksDone's.
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70 //
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71 // Examples of using SubTasksDone and SequentialSubTasksDone:
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72 // G1RootProcessor and GenCollectedHeap::process_roots() use
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73 // SubTasksDone* _process_strong_tasks to claim tasks for workers
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74 //
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75 // GenCollectedHeap::gen_process_roots() calls
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76 // rem_set()->younger_refs_iterate()
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77 // to scan the card table and which eventually calls down into
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78 // CardTableModRefBS::par_non_clean_card_iterate_work(). This method
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79 // uses SequentialSubTasksDone* _pst to claim tasks.
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80 // Both SubTasksDone and SequentialSubTasksDone call their method
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81 // all_tasks_completed() to count the number of GC workers that have
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82 // finished their work. That logic is "when all the workers are
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83 // finished the tasks are finished".
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84 //
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85 // The pattern that appears in the code is to set _n_threads
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86 // to a value > 1 before a task that you would like executed in parallel
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87 // and then to set it to 0 after that task has completed. A value of
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88 // 0 is a "special" value in set_n_threads() which translates to
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89 // setting _n_threads to 1.
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90 //
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91 // Some code uses _n_terminiation to decide if work should be done in
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92 // parallel. The notorious possibly_parallel_oops_do() in threads.cpp
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93 // is an example of such code. Look for variable "is_par" for other
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94 // examples.
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95 //
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96 // The active_workers is not reset to 0 after a parallel phase. It's
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97 // value may be used in later phases and in one instance at least
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98 // (the parallel remark) it has to be used (the parallel remark depends
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99 // on the partitioning done in the previous parallel scavenge).
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100
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101 class SharedHeap : public CollectedHeap {
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102 friend class VMStructs;
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103
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104 friend class VM_GC_Operation;
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105 friend class VM_CGC_Operation;
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106
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107 protected:
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108 // There should be only a single instance of "SharedHeap" in a program.
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109 // This is enforced with the protected constructor below, which will also
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110 // set the static pointer "_sh" to that instance.
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111 static SharedHeap* _sh;
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112
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113 // and the Gen Remembered Set, at least one good enough to scan the perm
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114 // gen.
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115 GenRemSet* _rem_set;
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116
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117 // A gc policy, controls global gc resource issues
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118 CollectorPolicy *_collector_policy;
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119
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120 // See the discussion below, in the specification of the reader function
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121 // for this variable.
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122 int _strong_roots_parity;
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123
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124 // If we're doing parallel GC, use this gang of threads.
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125 FlexibleWorkGang* _workers;
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126
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127 // Full initialization is done in a concrete subtype's "initialize"
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128 // function.
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129 SharedHeap(CollectorPolicy* policy_);
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130
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131 // Returns true if the calling thread holds the heap lock,
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132 // or the calling thread is a par gc thread and the heap_lock is held
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133 // by the vm thread doing a gc operation.
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134 bool heap_lock_held_for_gc();
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135 // True if the heap_lock is held by the a non-gc thread invoking a gc
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136 // operation.
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137 bool _thread_holds_heap_lock_for_gc;
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138
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139 public:
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140 static SharedHeap* heap() { return _sh; }
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141
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142 void set_barrier_set(BarrierSet* bs);
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143
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144 // Does operations required after initialization has been done.
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145 virtual void post_initialize();
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146
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147 // Initialization of ("weak") reference processing support
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148 virtual void ref_processing_init();
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149
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150 // This function returns the "GenRemSet" object that allows us to scan
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151 // generations in a fully generational heap.
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152 GenRemSet* rem_set() { return _rem_set; }
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153
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154 // Iteration functions.
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155 void oop_iterate(ExtendedOopClosure* cl) = 0;
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156
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157 // Iterate over all spaces in use in the heap, in an undefined order.
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158 virtual void space_iterate(SpaceClosure* cl) = 0;
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159
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160 // A SharedHeap will contain some number of spaces. This finds the
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161 // space whose reserved area contains the given address, or else returns
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162 // NULL.
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163 virtual Space* space_containing(const void* addr) const = 0;
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164
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165 bool no_gc_in_progress() { return !is_gc_active(); }
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166
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167 // Some collectors will perform "process_strong_roots" in parallel.
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168 // Such a call will involve claiming some fine-grained tasks, such as
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169 // scanning of threads. To make this process simpler, we provide the
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170 // "strong_roots_parity()" method. Collectors that start parallel tasks
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171 // whose threads invoke "process_strong_roots" must
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172 // call "change_strong_roots_parity" in sequential code starting such a
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173 // task. (This also means that a parallel thread may only call
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174 // process_strong_roots once.)
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175 //
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176 // For calls to process_roots by sequential code, the parity is
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177 // updated automatically.
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178 //
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179 // The idea is that objects representing fine-grained tasks, such as
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180 // threads, will contain a "parity" field. A task will is claimed in the
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181 // current "process_roots" call only if its parity field is the
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182 // same as the "strong_roots_parity"; task claiming is accomplished by
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183 // updating the parity field to the strong_roots_parity with a CAS.
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184 //
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185 // If the client meats this spec, then strong_roots_parity() will have
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186 // the following properties:
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187 // a) to return a different value than was returned before the last
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188 // call to change_strong_roots_parity, and
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189 // c) to never return a distinguished value (zero) with which such
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190 // task-claiming variables may be initialized, to indicate "never
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191 // claimed".
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192 public:
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193 int strong_roots_parity() { return _strong_roots_parity; }
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194
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195 // Call these in sequential code around process_roots.
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196 // strong_roots_prologue calls change_strong_roots_parity, if
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197 // parallel tasks are enabled.
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198 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
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199 SharedHeap* _sh;
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200
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201 public:
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202 StrongRootsScope(SharedHeap* heap, bool activate = true);
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203 };
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204 friend class StrongRootsScope;
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205
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206 private:
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207 void change_strong_roots_parity();
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208
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209 public:
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210 FlexibleWorkGang* workers() const { return _workers; }
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211
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212 // The functions below are helper functions that a subclass of
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213 // "SharedHeap" can use in the implementation of its virtual
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214 // functions.
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215
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216 public:
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217
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218 // Do anything common to GC's.
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219 virtual void gc_prologue(bool full) = 0;
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220 virtual void gc_epilogue(bool full) = 0;
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221
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222 // Sets the number of parallel threads that will be doing tasks
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223 // (such as process roots) subsequently.
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224 virtual void set_par_threads(uint t);
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225
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226 //
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227 // New methods from CollectedHeap
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228 //
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229
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230 // Some utilities.
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231 void print_size_transition(outputStream* out,
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232 size_t bytes_before,
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233 size_t bytes_after,
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234 size_t capacity);
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235 };
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236
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237 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP