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0
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1 /*
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2 * Copyright 2001-2007 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 # include "incls/_precompiled.incl"
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26 # include "incls/_referenceProcessor.cpp.incl"
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27
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28 // List of discovered references.
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29 class DiscoveredList {
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30 public:
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31 DiscoveredList() : _head(NULL), _len(0) { }
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32 oop head() const { return _head; }
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33 oop* head_ptr() { return &_head; }
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34 void set_head(oop o) { _head = o; }
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35 bool empty() const { return _head == ReferenceProcessor::_sentinelRef; }
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36 size_t length() { return _len; }
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37 void set_length(size_t len) { _len = len; }
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38 private:
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39 size_t _len;
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40 oop _head;
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41 };
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42
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43 oop ReferenceProcessor::_sentinelRef = NULL;
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44
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45 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
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46
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47 void referenceProcessor_init() {
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48 ReferenceProcessor::init_statics();
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49 }
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50
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51 void ReferenceProcessor::init_statics() {
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52 assert(_sentinelRef == NULL, "should be initialized precsiely once");
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53 EXCEPTION_MARK;
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54 _sentinelRef = instanceKlass::cast(
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55 SystemDictionary::object_klass())->
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56 allocate_permanent_instance(THREAD);
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57
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58 // Initialize the master soft ref clock.
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59 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
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60
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61 if (HAS_PENDING_EXCEPTION) {
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62 Handle ex(THREAD, PENDING_EXCEPTION);
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63 vm_exit_during_initialization(ex);
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64 }
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65 assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
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66 "Just constructed it!");
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67 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
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68 RefDiscoveryPolicy == ReferentBasedDiscovery,
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69 "Unrecongnized RefDiscoveryPolicy");
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70 }
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71
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72
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73 ReferenceProcessor* ReferenceProcessor::create_ref_processor(
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74 MemRegion span,
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75 bool atomic_discovery,
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76 bool mt_discovery,
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77 BoolObjectClosure* is_alive_non_header,
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78 int parallel_gc_threads,
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79 bool mt_processing)
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80 {
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81 int mt_degree = 1;
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82 if (parallel_gc_threads > 1) {
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83 mt_degree = parallel_gc_threads;
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84 }
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85 ReferenceProcessor* rp =
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86 new ReferenceProcessor(span, atomic_discovery,
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87 mt_discovery, mt_degree,
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88 mt_processing);
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89 if (rp == NULL) {
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90 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
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91 }
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92 rp->set_is_alive_non_header(is_alive_non_header);
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93 return rp;
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94 }
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95
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96
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97 ReferenceProcessor::ReferenceProcessor(MemRegion span,
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98 bool atomic_discovery, bool mt_discovery, int mt_degree,
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99 bool mt_processing) :
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100 _discovering_refs(false),
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101 _enqueuing_is_done(false),
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102 _is_alive_non_header(NULL),
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103 _processing_is_mt(mt_processing),
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104 _next_id(0)
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105 {
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106 _span = span;
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107 _discovery_is_atomic = atomic_discovery;
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108 _discovery_is_mt = mt_discovery;
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109 _num_q = mt_degree;
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110 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref);
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111 if (_discoveredSoftRefs == NULL) {
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112 vm_exit_during_initialization("Could not allocated RefProc Array");
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113 }
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114 _discoveredWeakRefs = &_discoveredSoftRefs[_num_q];
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115 _discoveredFinalRefs = &_discoveredWeakRefs[_num_q];
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116 _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q];
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117 assert(_sentinelRef != NULL, "_sentinelRef is NULL");
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118 // Initialized all entries to _sentinelRef
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119 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
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120 _discoveredSoftRefs[i].set_head(_sentinelRef);
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121 _discoveredSoftRefs[i].set_length(0);
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122 }
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123 }
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124
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125 #ifndef PRODUCT
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126 void ReferenceProcessor::verify_no_references_recorded() {
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127 guarantee(!_discovering_refs, "Discovering refs?");
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128 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
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129 guarantee(_discoveredSoftRefs[i].empty(),
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130 "Found non-empty discovered list");
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131 }
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132 }
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133 #endif
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134
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135 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
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136 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
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137 f->do_oop(_discoveredSoftRefs[i].head_ptr());
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138 }
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139 }
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140
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141 void ReferenceProcessor::oops_do(OopClosure* f) {
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142 f->do_oop(&_sentinelRef);
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143 }
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144
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145 void ReferenceProcessor::update_soft_ref_master_clock()
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146 {
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147 // Update (advance) the soft ref master clock field. This must be done
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148 // after processing the soft ref list.
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149 jlong now = os::javaTimeMillis();
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150 jlong clock = java_lang_ref_SoftReference::clock();
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151 NOT_PRODUCT(
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152 if (now < clock) {
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153 warning("time warp: %d to %d", clock, now);
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154 }
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155 )
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156 // In product mode, protect ourselves from system time being adjusted
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157 // externally and going backward; see note in the implementation of
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158 // GenCollectedHeap::time_since_last_gc() for the right way to fix
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159 // this uniformly throughout the VM; see bug-id 4741166. XXX
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160 if (now > clock) {
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161 java_lang_ref_SoftReference::set_clock(now);
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162 }
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163 // Else leave clock stalled at its old value until time progresses
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164 // past clock value.
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165 }
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166
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167
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168 void
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169 ReferenceProcessor::process_discovered_references(
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170 ReferencePolicy* policy,
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171 BoolObjectClosure* is_alive,
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172 OopClosure* keep_alive,
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173 VoidClosure* complete_gc,
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174 AbstractRefProcTaskExecutor* task_executor) {
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175 NOT_PRODUCT(verify_ok_to_handle_reflists());
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176
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177 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
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178 // Stop treating discovered references specially.
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179 disable_discovery();
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180
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181 bool trace_time = PrintGCDetails && PrintReferenceGC;
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182 // Soft references
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183 {
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184 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
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185 process_discovered_reflist(_discoveredSoftRefs, policy, true,
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186 is_alive, keep_alive, complete_gc, task_executor);
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187 }
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188
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189 update_soft_ref_master_clock();
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190
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191 // Weak references
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192 {
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193 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);
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194 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
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195 is_alive, keep_alive, complete_gc, task_executor);
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196 }
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197
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198 // Final references
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199 {
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200 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty);
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201 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
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202 is_alive, keep_alive, complete_gc, task_executor);
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203 }
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204
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205 // Phantom references
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206 {
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207 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty);
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208 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
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209 is_alive, keep_alive, complete_gc, task_executor);
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210 }
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211
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212 // Weak global JNI references. It would make more sense (semantically) to
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213 // traverse these simultaneously with the regular weak references above, but
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214 // that is not how the JDK1.2 specification is. See #4126360. Native code can
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215 // thus use JNI weak references to circumvent the phantom references and
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216 // resurrect a "post-mortem" object.
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217 {
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218 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty);
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219 if (task_executor != NULL) {
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220 task_executor->set_single_threaded_mode();
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221 }
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222 process_phaseJNI(is_alive, keep_alive, complete_gc);
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223 }
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224 }
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225
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226
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227 #ifndef PRODUCT
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228 // Calculate the number of jni handles.
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229 unsigned int ReferenceProcessor::count_jni_refs()
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230 {
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231 class AlwaysAliveClosure: public BoolObjectClosure {
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232 public:
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233 bool do_object_b(oop obj) { return true; }
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234 void do_object(oop obj) { assert(false, "Don't call"); }
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235 };
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236
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237 class CountHandleClosure: public OopClosure {
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238 private:
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239 int _count;
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240 public:
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241 CountHandleClosure(): _count(0) {}
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242 void do_oop(oop* unused) {
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243 _count++;
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244 }
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245 int count() { return _count; }
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246 };
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247 CountHandleClosure global_handle_count;
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248 AlwaysAliveClosure always_alive;
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249 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
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250 return global_handle_count.count();
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251 }
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252 #endif
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253
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254 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
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255 OopClosure* keep_alive,
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256 VoidClosure* complete_gc) {
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257 #ifndef PRODUCT
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258 if (PrintGCDetails && PrintReferenceGC) {
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259 unsigned int count = count_jni_refs();
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260 gclog_or_tty->print(", %u refs", count);
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261 }
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262 #endif
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263 JNIHandles::weak_oops_do(is_alive, keep_alive);
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264 // Finally remember to keep sentinel around
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265 keep_alive->do_oop(&_sentinelRef);
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266 complete_gc->do_void();
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267 }
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268
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269 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
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270 NOT_PRODUCT(verify_ok_to_handle_reflists());
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271 // Remember old value of pending references list
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272 oop* pending_list_addr = java_lang_ref_Reference::pending_list_addr();
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273 oop old_pending_list_value = *pending_list_addr;
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274
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275 // Enqueue references that are not made active again, and
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276 // clear the decks for the next collection (cycle).
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277 enqueue_discovered_reflists(pending_list_addr, task_executor);
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278 // Do the oop-check on pending_list_addr missed in
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279 // enqueue_discovered_reflist. We should probably
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280 // do a raw oop_check so that future such idempotent
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281 // oop_stores relying on the oop-check side-effect
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282 // may be elided automatically and safely without
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283 // affecting correctness.
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284 oop_store(pending_list_addr, *(pending_list_addr));
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285
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286 // Stop treating discovered references specially.
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287 disable_discovery();
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288
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289 // Return true if new pending references were added
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290 return old_pending_list_value != *pending_list_addr;
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291 }
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292
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293 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
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294 oop* pending_list_addr) {
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295 // Given a list of refs linked through the "discovered" field
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296 // (java.lang.ref.Reference.discovered) chain them through the
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297 // "next" field (java.lang.ref.Reference.next) and prepend
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298 // to the pending list.
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299 if (TraceReferenceGC && PrintGCDetails) {
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300 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
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301 INTPTR_FORMAT, (address)refs_list.head());
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302 }
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303 oop obj = refs_list.head();
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304 // Walk down the list, copying the discovered field into
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305 // the next field and clearing it (except for the last
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306 // non-sentinel object which is treated specially to avoid
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307 // confusion with an active reference).
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308 while (obj != _sentinelRef) {
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309 assert(obj->is_instanceRef(), "should be reference object");
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310 oop next = java_lang_ref_Reference::discovered(obj);
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311 if (TraceReferenceGC && PrintGCDetails) {
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312 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
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313 (oopDesc*) obj, (oopDesc*) next);
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314 }
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315 assert(*java_lang_ref_Reference::next_addr(obj) == NULL,
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316 "The reference should not be enqueued");
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317 if (next == _sentinelRef) { // obj is last
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318 // Swap refs_list into pendling_list_addr and
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319 // set obj's next to what we read from pending_list_addr.
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320 oop old = (oop)Atomic::xchg_ptr(refs_list.head(), pending_list_addr);
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321 // Need oop_check on pending_list_addr above;
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322 // see special oop-check code at the end of
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323 // enqueue_discovered_reflists() further below.
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324 if (old == NULL) {
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325 // obj should be made to point to itself, since
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326 // pending list was empty.
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327 java_lang_ref_Reference::set_next(obj, obj);
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328 } else {
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329 java_lang_ref_Reference::set_next(obj, old);
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330 }
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331 } else {
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332 java_lang_ref_Reference::set_next(obj, next);
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333 }
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334 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
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335 obj = next;
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336 }
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337 }
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338
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339 // Parallel enqueue task
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340 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
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341 public:
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342 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
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343 DiscoveredList discovered_refs[],
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344 oop* pending_list_addr,
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345 oop sentinel_ref,
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346 int n_queues)
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347 : EnqueueTask(ref_processor, discovered_refs,
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348 pending_list_addr, sentinel_ref, n_queues)
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349 { }
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350
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351 virtual void work(unsigned int work_id)
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352 {
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353 assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds");
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354 // Simplest first cut: static partitioning.
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355 int index = work_id;
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356 for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) {
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357 _ref_processor.enqueue_discovered_reflist(
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358 _refs_lists[index], _pending_list_addr);
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359 _refs_lists[index].set_head(_sentinel_ref);
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360 _refs_lists[index].set_length(0);
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361 }
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362 }
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363 };
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364
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365 // Enqueue references that are not made active again
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366 void ReferenceProcessor::enqueue_discovered_reflists(oop* pending_list_addr,
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367 AbstractRefProcTaskExecutor* task_executor) {
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368 if (_processing_is_mt && task_executor != NULL) {
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369 // Parallel code
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370 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
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371 pending_list_addr, _sentinelRef, _num_q);
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372 task_executor->execute(tsk);
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373 } else {
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374 // Serial code: call the parent class's implementation
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375 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
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376 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
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377 _discoveredSoftRefs[i].set_head(_sentinelRef);
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378 _discoveredSoftRefs[i].set_length(0);
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379 }
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380 }
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381 }
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382
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383 // Iterator for the list of discovered references.
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384 class DiscoveredListIterator {
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385 public:
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386 inline DiscoveredListIterator(DiscoveredList& refs_list,
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387 OopClosure* keep_alive,
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388 BoolObjectClosure* is_alive);
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389
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390 // End Of List.
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391 inline bool has_next() const
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392 { return _next != ReferenceProcessor::_sentinelRef; }
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393
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394 // Get oop to the Reference object.
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395 inline oop obj() const { return _ref; }
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396
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397 // Get oop to the referent object.
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398 inline oop referent() const { return _referent; }
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399
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400 // Returns true if referent is alive.
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401 inline bool is_referent_alive() const;
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402
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403 // Loads data for the current reference.
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404 // The "allow_null_referent" argument tells us to allow for the possibility
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405 // of a NULL referent in the discovered Reference object. This typically
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406 // happens in the case of concurrent collectors that may have done the
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407 // discovery concurrently or interleaved with mutator execution.
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408 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
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409
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410 // Move to the next discovered reference.
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411 inline void next();
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412
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413 // Remove the current reference from the list and move to the next.
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414 inline void remove();
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415
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416 // Make the Reference object active again.
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417 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); }
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418
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419 // Make the referent alive.
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420 inline void make_referent_alive() { _keep_alive->do_oop(_referent_addr); }
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421
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422 // Update the discovered field.
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423 inline void update_discovered() { _keep_alive->do_oop(_prev_next); }
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424
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425 // NULL out referent pointer.
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426 inline void clear_referent() { *_referent_addr = NULL; }
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427
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428 // Statistics
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429 NOT_PRODUCT(
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430 inline size_t processed() const { return _processed; }
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431 inline size_t removed() const { return _removed; }
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432 )
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433
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434 private:
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435 inline void move_to_next();
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436
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437 private:
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438 DiscoveredList& _refs_list;
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439 oop* _prev_next;
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440 oop _ref;
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441 oop* _discovered_addr;
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442 oop _next;
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443 oop* _referent_addr;
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444 oop _referent;
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445 OopClosure* _keep_alive;
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446 BoolObjectClosure* _is_alive;
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447 DEBUG_ONLY(
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448 oop _first_seen; // cyclic linked list check
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449 )
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450 NOT_PRODUCT(
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451 size_t _processed;
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452 size_t _removed;
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453 )
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454 };
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455
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456 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list,
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457 OopClosure* keep_alive,
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458 BoolObjectClosure* is_alive)
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459 : _refs_list(refs_list),
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460 _prev_next(refs_list.head_ptr()),
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461 _ref(refs_list.head()),
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462 #ifdef ASSERT
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463 _first_seen(refs_list.head()),
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464 #endif
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465 #ifndef PRODUCT
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466 _processed(0),
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467 _removed(0),
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468 #endif
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469 _next(refs_list.head()),
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470 _keep_alive(keep_alive),
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471 _is_alive(is_alive)
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472 { }
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473
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474 inline bool DiscoveredListIterator::is_referent_alive() const
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475 {
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476 return _is_alive->do_object_b(_referent);
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477 }
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478
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479 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent))
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480 {
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481 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
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482 assert(_discovered_addr && (*_discovered_addr)->is_oop_or_null(),
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483 "discovered field is bad");
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484 _next = *_discovered_addr;
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485 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
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486 _referent = *_referent_addr;
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487 assert(Universe::heap()->is_in_reserved_or_null(_referent),
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488 "Wrong oop found in java.lang.Reference object");
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489 assert(allow_null_referent ?
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490 _referent->is_oop_or_null()
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491 : _referent->is_oop(),
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492 "bad referent");
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493 }
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494
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495 inline void DiscoveredListIterator::next()
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496 {
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497 _prev_next = _discovered_addr;
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498 move_to_next();
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499 }
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500
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501 inline void DiscoveredListIterator::remove()
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502 {
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503 assert(_ref->is_oop(), "Dropping a bad reference");
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504 // Clear the discovered_addr field so that the object does
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505 // not look like it has been discovered.
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506 *_discovered_addr = NULL;
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507 // Remove Reference object from list.
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508 *_prev_next = _next;
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509 NOT_PRODUCT(_removed++);
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510 move_to_next();
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511 }
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512
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513 inline void DiscoveredListIterator::move_to_next()
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514 {
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515 _ref = _next;
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516 assert(_ref != _first_seen, "cyclic ref_list found");
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517 NOT_PRODUCT(_processed++);
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518 }
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519
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520
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521 // NOTE: process_phase*() are largely similar, and at a high level
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522 // merely iterate over the extant list applying a predicate to
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523 // each of its elements and possibly removing that element from the
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524 // list and applying some further closures to that element.
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525 // We should consider the possibility of replacing these
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526 // process_phase*() methods by abstracting them into
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527 // a single general iterator invocation that receives appropriate
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528 // closures that accomplish this work.
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529
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530 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
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531 // referents are not alive, but that should be kept alive for policy reasons.
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532 // Keep alive the transitive closure of all such referents.
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533 void
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534 ReferenceProcessor::process_phase1(DiscoveredList& refs_list_addr,
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535 ReferencePolicy* policy,
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536 BoolObjectClosure* is_alive,
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537 OopClosure* keep_alive,
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538 VoidClosure* complete_gc) {
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539 assert(policy != NULL, "Must have a non-NULL policy");
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540 DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
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541 // Decide which softly reachable refs should be kept alive.
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542 while (iter.has_next()) {
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543 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
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544 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
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545 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) {
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546 if (TraceReferenceGC) {
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547 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
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548 (address)iter.obj(), iter.obj()->blueprint()->internal_name());
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549 }
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550 // Make the Reference object active again
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551 iter.make_active();
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552 // keep the referent around
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553 iter.make_referent_alive();
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554 // Remove Reference object from list
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555 iter.remove();
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556 } else {
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557 iter.next();
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558 }
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559 }
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560 // Close the reachable set
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561 complete_gc->do_void();
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562 NOT_PRODUCT(
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563 if (PrintGCDetails && TraceReferenceGC) {
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564 gclog_or_tty->print(" Dropped %d dead Refs out of %d "
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565 "discovered Refs by policy ", iter.removed(), iter.processed());
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566 }
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567 )
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568 }
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569
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570 // Traverse the list and remove any Refs that are not active, or
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571 // whose referents are either alive or NULL.
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572 void
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573 ReferenceProcessor::pp2_work(DiscoveredList& refs_list_addr,
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574 BoolObjectClosure* is_alive,
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575 OopClosure* keep_alive)
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576 {
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577 assert(discovery_is_atomic(), "Error");
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578 DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
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579 while (iter.has_next()) {
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580 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
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581 DEBUG_ONLY(oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());)
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582 assert(*next_addr == NULL, "Should not discover inactive Reference");
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583 if (iter.is_referent_alive()) {
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584 if (TraceReferenceGC) {
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585 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
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586 (address)iter.obj(), iter.obj()->blueprint()->internal_name());
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587 }
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588 // The referent is reachable after all.
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589 // Update the referent pointer as necessary: Note that this
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590 // should not entail any recursive marking because the
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591 // referent must already have been traversed.
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592 iter.make_referent_alive();
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593 // Remove Reference object from list
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594 iter.remove();
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595 } else {
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596 iter.next();
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597 }
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598 }
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599 NOT_PRODUCT(
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600 if (PrintGCDetails && TraceReferenceGC) {
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601 gclog_or_tty->print(" Dropped %d active Refs out of %d "
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602 "Refs in discovered list ", iter.removed(), iter.processed());
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603 }
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604 )
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605 }
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606
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607 void
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|
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608 ReferenceProcessor::pp2_work_concurrent_discovery(
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|
|
609 DiscoveredList& refs_list_addr,
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|
|
610 BoolObjectClosure* is_alive,
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611 OopClosure* keep_alive,
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|
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612 VoidClosure* complete_gc)
|
|
|
613 {
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614 assert(!discovery_is_atomic(), "Error");
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|
615 DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
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616 while (iter.has_next()) {
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617 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
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|
618 oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
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619 if ((iter.referent() == NULL || iter.is_referent_alive() ||
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620 *next_addr != NULL)) {
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|
621 assert((*next_addr)->is_oop_or_null(), "bad next field");
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622 // Remove Reference object from list
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623 iter.remove();
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|
624 // Trace the cohorts
|
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|
625 iter.make_referent_alive();
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|
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626 keep_alive->do_oop(next_addr);
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|
627 } else {
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|
628 iter.next();
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|
629 }
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|
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630 }
|
|
|
631 // Now close the newly reachable set
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|
|
632 complete_gc->do_void();
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|
633 NOT_PRODUCT(
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|
634 if (PrintGCDetails && TraceReferenceGC) {
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|
635 gclog_or_tty->print(" Dropped %d active Refs out of %d "
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636 "Refs in discovered list ", iter.removed(), iter.processed());
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637 }
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|
638 )
|
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639 }
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640
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641 // Traverse the list and process the referents, by either
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642 // either clearing them or keeping them (and their reachable
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643 // closure) alive.
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644 void
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645 ReferenceProcessor::process_phase3(DiscoveredList& refs_list_addr,
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|
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646 bool clear_referent,
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|
|
647 BoolObjectClosure* is_alive,
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|
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648 OopClosure* keep_alive,
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|
|
649 VoidClosure* complete_gc) {
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|
|
650 DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
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651 while (iter.has_next()) {
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652 iter.update_discovered();
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|
653 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
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654 if (clear_referent) {
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655 // NULL out referent pointer
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656 iter.clear_referent();
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657 } else {
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|
658 // keep the referent around
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|
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659 iter.make_referent_alive();
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660 }
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661 if (TraceReferenceGC) {
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662 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
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|
|
663 clear_referent ? "cleared " : "",
|
|
|
664 (address)iter.obj(), iter.obj()->blueprint()->internal_name());
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|
|
665 }
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666 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
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|
667 // If discovery is concurrent, we may have objects with null referents,
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|
668 // being those that were concurrently cleared after they were discovered
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|
|
669 // (and not subsequently precleaned).
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|
|
670 assert( (discovery_is_atomic() && iter.referent()->is_oop())
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|
671 || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)),
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|
672 "Adding a bad referent");
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|
673 iter.next();
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|
674 }
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|
|
675 // Remember to keep sentinel pointer around
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|
|
676 iter.update_discovered();
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|
|
677 // Close the reachable set
|
|
|
678 complete_gc->do_void();
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|
|
679 }
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|
|
680
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|
|
681 void
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|
|
682 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& ref_list) {
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|
|
683 oop obj = ref_list.head();
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|
|
684 while (obj != _sentinelRef) {
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|
|
685 oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
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|
|
686 obj = *discovered_addr;
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|
|
687 *discovered_addr = NULL;
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|
|
688 }
|
|
|
689 ref_list.set_head(_sentinelRef);
|
|
|
690 ref_list.set_length(0);
|
|
|
691 }
|
|
|
692
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|
|
693 void
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|
|
694 ReferenceProcessor::abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]) {
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|
|
695 for (int i = 0; i < _num_q; i++) {
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|
|
696 abandon_partial_discovered_list(refs_lists[i]);
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|
|
697 }
|
|
|
698 }
|
|
|
699
|
|
|
700 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
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|
|
701 public:
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|
|
702 RefProcPhase1Task(ReferenceProcessor& ref_processor,
|
|
|
703 DiscoveredList refs_lists[],
|
|
|
704 ReferencePolicy* policy,
|
|
|
705 bool marks_oops_alive)
|
|
|
706 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
|
|
|
707 _policy(policy)
|
|
|
708 { }
|
|
|
709 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
|
710 OopClosure& keep_alive,
|
|
|
711 VoidClosure& complete_gc)
|
|
|
712 {
|
|
|
713 _ref_processor.process_phase1(_refs_lists[i], _policy,
|
|
|
714 &is_alive, &keep_alive, &complete_gc);
|
|
|
715 }
|
|
|
716 private:
|
|
|
717 ReferencePolicy* _policy;
|
|
|
718 };
|
|
|
719
|
|
|
720 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
|
|
|
721 public:
|
|
|
722 RefProcPhase2Task(ReferenceProcessor& ref_processor,
|
|
|
723 DiscoveredList refs_lists[],
|
|
|
724 bool marks_oops_alive)
|
|
|
725 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
|
|
|
726 { }
|
|
|
727 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
|
728 OopClosure& keep_alive,
|
|
|
729 VoidClosure& complete_gc)
|
|
|
730 {
|
|
|
731 _ref_processor.process_phase2(_refs_lists[i],
|
|
|
732 &is_alive, &keep_alive, &complete_gc);
|
|
|
733 }
|
|
|
734 };
|
|
|
735
|
|
|
736 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
|
|
|
737 public:
|
|
|
738 RefProcPhase3Task(ReferenceProcessor& ref_processor,
|
|
|
739 DiscoveredList refs_lists[],
|
|
|
740 bool clear_referent,
|
|
|
741 bool marks_oops_alive)
|
|
|
742 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
|
|
|
743 _clear_referent(clear_referent)
|
|
|
744 { }
|
|
|
745 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
|
746 OopClosure& keep_alive,
|
|
|
747 VoidClosure& complete_gc)
|
|
|
748 {
|
|
|
749 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
|
|
|
750 &is_alive, &keep_alive, &complete_gc);
|
|
|
751 }
|
|
|
752 private:
|
|
|
753 bool _clear_referent;
|
|
|
754 };
|
|
|
755
|
|
|
756 // Balances reference queues.
|
|
|
757 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
|
|
|
758 {
|
|
|
759 // calculate total length
|
|
|
760 size_t total_refs = 0;
|
|
|
761 for (int i = 0; i < _num_q; ++i) {
|
|
|
762 total_refs += ref_lists[i].length();
|
|
|
763 }
|
|
|
764 size_t avg_refs = total_refs / _num_q + 1;
|
|
|
765 int to_idx = 0;
|
|
|
766 for (int from_idx = 0; from_idx < _num_q; from_idx++) {
|
|
|
767 while (ref_lists[from_idx].length() > avg_refs) {
|
|
|
768 assert(to_idx < _num_q, "Sanity Check!");
|
|
|
769 if (ref_lists[to_idx].length() < avg_refs) {
|
|
|
770 // move superfluous refs
|
|
|
771 size_t refs_to_move =
|
|
|
772 MIN2(ref_lists[from_idx].length() - avg_refs,
|
|
|
773 avg_refs - ref_lists[to_idx].length());
|
|
|
774 oop move_head = ref_lists[from_idx].head();
|
|
|
775 oop move_tail = move_head;
|
|
|
776 oop new_head = move_head;
|
|
|
777 // find an element to split the list on
|
|
|
778 for (size_t j = 0; j < refs_to_move; ++j) {
|
|
|
779 move_tail = new_head;
|
|
|
780 new_head = *java_lang_ref_Reference::discovered_addr(new_head);
|
|
|
781 }
|
|
|
782 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head());
|
|
|
783 ref_lists[to_idx].set_head(move_head);
|
|
|
784 ref_lists[to_idx].set_length(ref_lists[to_idx].length() + refs_to_move);
|
|
|
785 ref_lists[from_idx].set_head(new_head);
|
|
|
786 ref_lists[from_idx].set_length(ref_lists[from_idx].length() - refs_to_move);
|
|
|
787 } else {
|
|
|
788 ++to_idx;
|
|
|
789 }
|
|
|
790 }
|
|
|
791 }
|
|
|
792 }
|
|
|
793
|
|
|
794 void
|
|
|
795 ReferenceProcessor::process_discovered_reflist(
|
|
|
796 DiscoveredList refs_lists[],
|
|
|
797 ReferencePolicy* policy,
|
|
|
798 bool clear_referent,
|
|
|
799 BoolObjectClosure* is_alive,
|
|
|
800 OopClosure* keep_alive,
|
|
|
801 VoidClosure* complete_gc,
|
|
|
802 AbstractRefProcTaskExecutor* task_executor)
|
|
|
803 {
|
|
|
804 bool mt = task_executor != NULL && _processing_is_mt;
|
|
|
805 if (mt && ParallelRefProcBalancingEnabled) {
|
|
|
806 balance_queues(refs_lists);
|
|
|
807 }
|
|
|
808 if (PrintReferenceGC && PrintGCDetails) {
|
|
|
809 size_t total = 0;
|
|
|
810 for (int i = 0; i < _num_q; ++i) {
|
|
|
811 total += refs_lists[i].length();
|
|
|
812 }
|
|
|
813 gclog_or_tty->print(", %u refs", total);
|
|
|
814 }
|
|
|
815
|
|
|
816 // Phase 1 (soft refs only):
|
|
|
817 // . Traverse the list and remove any SoftReferences whose
|
|
|
818 // referents are not alive, but that should be kept alive for
|
|
|
819 // policy reasons. Keep alive the transitive closure of all
|
|
|
820 // such referents.
|
|
|
821 if (policy != NULL) {
|
|
|
822 if (mt) {
|
|
|
823 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
|
|
|
824 task_executor->execute(phase1);
|
|
|
825 } else {
|
|
|
826 for (int i = 0; i < _num_q; i++) {
|
|
|
827 process_phase1(refs_lists[i], policy,
|
|
|
828 is_alive, keep_alive, complete_gc);
|
|
|
829 }
|
|
|
830 }
|
|
|
831 } else { // policy == NULL
|
|
|
832 assert(refs_lists != _discoveredSoftRefs,
|
|
|
833 "Policy must be specified for soft references.");
|
|
|
834 }
|
|
|
835
|
|
|
836 // Phase 2:
|
|
|
837 // . Traverse the list and remove any refs whose referents are alive.
|
|
|
838 if (mt) {
|
|
|
839 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
|
|
|
840 task_executor->execute(phase2);
|
|
|
841 } else {
|
|
|
842 for (int i = 0; i < _num_q; i++) {
|
|
|
843 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
|
|
|
844 }
|
|
|
845 }
|
|
|
846
|
|
|
847 // Phase 3:
|
|
|
848 // . Traverse the list and process referents as appropriate.
|
|
|
849 if (mt) {
|
|
|
850 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
|
|
|
851 task_executor->execute(phase3);
|
|
|
852 } else {
|
|
|
853 for (int i = 0; i < _num_q; i++) {
|
|
|
854 process_phase3(refs_lists[i], clear_referent,
|
|
|
855 is_alive, keep_alive, complete_gc);
|
|
|
856 }
|
|
|
857 }
|
|
|
858 }
|
|
|
859
|
|
|
860 void ReferenceProcessor::clean_up_discovered_references() {
|
|
|
861 // loop over the lists
|
|
|
862 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
|
|
|
863 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
|
|
|
864 gclog_or_tty->print_cr(
|
|
|
865 "\nScrubbing %s discovered list of Null referents",
|
|
|
866 list_name(i));
|
|
|
867 }
|
|
|
868 clean_up_discovered_reflist(_discoveredSoftRefs[i]);
|
|
|
869 }
|
|
|
870 }
|
|
|
871
|
|
|
872 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
|
|
|
873 assert(!discovery_is_atomic(), "Else why call this method?");
|
|
|
874 DiscoveredListIterator iter(refs_list, NULL, NULL);
|
|
|
875 size_t length = refs_list.length();
|
|
|
876 while (iter.has_next()) {
|
|
|
877 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
|
|
|
878 oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
|
|
|
879 assert((*next_addr)->is_oop_or_null(), "bad next field");
|
|
|
880 // If referent has been cleared or Reference is not active,
|
|
|
881 // drop it.
|
|
|
882 if (iter.referent() == NULL || *next_addr != NULL) {
|
|
|
883 debug_only(
|
|
|
884 if (PrintGCDetails && TraceReferenceGC) {
|
|
|
885 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
|
|
|
886 INTPTR_FORMAT " with next field: " INTPTR_FORMAT
|
|
|
887 " and referent: " INTPTR_FORMAT,
|
|
|
888 (address)iter.obj(), (address)*next_addr, (address)iter.referent());
|
|
|
889 }
|
|
|
890 )
|
|
|
891 // Remove Reference object from list
|
|
|
892 iter.remove();
|
|
|
893 --length;
|
|
|
894 } else {
|
|
|
895 iter.next();
|
|
|
896 }
|
|
|
897 }
|
|
|
898 refs_list.set_length(length);
|
|
|
899 NOT_PRODUCT(
|
|
|
900 if (PrintGCDetails && TraceReferenceGC) {
|
|
|
901 gclog_or_tty->print(
|
|
|
902 " Removed %d Refs with NULL referents out of %d discovered Refs",
|
|
|
903 iter.removed(), iter.processed());
|
|
|
904 }
|
|
|
905 )
|
|
|
906 }
|
|
|
907
|
|
|
908 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
|
|
|
909 int id = 0;
|
|
|
910 // Determine the queue index to use for this object.
|
|
|
911 if (_discovery_is_mt) {
|
|
|
912 // During a multi-threaded discovery phase,
|
|
|
913 // each thread saves to its "own" list.
|
|
|
914 Thread* thr = Thread::current();
|
|
|
915 assert(thr->is_GC_task_thread(),
|
|
|
916 "Dubious cast from Thread* to WorkerThread*?");
|
|
|
917 id = ((WorkerThread*)thr)->id();
|
|
|
918 } else {
|
|
|
919 // single-threaded discovery, we save in round-robin
|
|
|
920 // fashion to each of the lists.
|
|
|
921 if (_processing_is_mt) {
|
|
|
922 id = next_id();
|
|
|
923 }
|
|
|
924 }
|
|
|
925 assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)");
|
|
|
926
|
|
|
927 // Get the discovered queue to which we will add
|
|
|
928 DiscoveredList* list = NULL;
|
|
|
929 switch (rt) {
|
|
|
930 case REF_OTHER:
|
|
|
931 // Unknown reference type, no special treatment
|
|
|
932 break;
|
|
|
933 case REF_SOFT:
|
|
|
934 list = &_discoveredSoftRefs[id];
|
|
|
935 break;
|
|
|
936 case REF_WEAK:
|
|
|
937 list = &_discoveredWeakRefs[id];
|
|
|
938 break;
|
|
|
939 case REF_FINAL:
|
|
|
940 list = &_discoveredFinalRefs[id];
|
|
|
941 break;
|
|
|
942 case REF_PHANTOM:
|
|
|
943 list = &_discoveredPhantomRefs[id];
|
|
|
944 break;
|
|
|
945 case REF_NONE:
|
|
|
946 // we should not reach here if we are an instanceRefKlass
|
|
|
947 default:
|
|
|
948 ShouldNotReachHere();
|
|
|
949 }
|
|
|
950 return list;
|
|
|
951 }
|
|
|
952
|
|
|
953 inline void ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& list,
|
|
|
954 oop obj, oop* discovered_addr) {
|
|
|
955 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
|
|
|
956 // First we must make sure this object is only enqueued once. CAS in a non null
|
|
|
957 // discovered_addr.
|
|
|
958 oop retest = (oop)Atomic::cmpxchg_ptr(list.head(), discovered_addr, NULL);
|
|
|
959 if (retest == NULL) {
|
|
|
960 // This thread just won the right to enqueue the object.
|
|
|
961 // We have separate lists for enqueueing so no synchronization
|
|
|
962 // is necessary.
|
|
|
963 list.set_head(obj);
|
|
|
964 list.set_length(list.length() + 1);
|
|
|
965 } else {
|
|
|
966 // If retest was non NULL, another thread beat us to it:
|
|
|
967 // The reference has already been discovered...
|
|
|
968 if (TraceReferenceGC) {
|
|
|
969 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
|
|
|
970 obj, obj->blueprint()->internal_name());
|
|
|
971 }
|
|
|
972 }
|
|
|
973 }
|
|
|
974
|
|
|
975
|
|
|
976 // We mention two of several possible choices here:
|
|
|
977 // #0: if the reference object is not in the "originating generation"
|
|
|
978 // (or part of the heap being collected, indicated by our "span"
|
|
|
979 // we don't treat it specially (i.e. we scan it as we would
|
|
|
980 // a normal oop, treating its references as strong references).
|
|
|
981 // This means that references can't be enqueued unless their
|
|
|
982 // referent is also in the same span. This is the simplest,
|
|
|
983 // most "local" and most conservative approach, albeit one
|
|
|
984 // that may cause weak references to be enqueued least promptly.
|
|
|
985 // We call this choice the "ReferenceBasedDiscovery" policy.
|
|
|
986 // #1: the reference object may be in any generation (span), but if
|
|
|
987 // the referent is in the generation (span) being currently collected
|
|
|
988 // then we can discover the reference object, provided
|
|
|
989 // the object has not already been discovered by
|
|
|
990 // a different concurrently running collector (as may be the
|
|
|
991 // case, for instance, if the reference object is in CMS and
|
|
|
992 // the referent in DefNewGeneration), and provided the processing
|
|
|
993 // of this reference object by the current collector will
|
|
|
994 // appear atomic to every other collector in the system.
|
|
|
995 // (Thus, for instance, a concurrent collector may not
|
|
|
996 // discover references in other generations even if the
|
|
|
997 // referent is in its own generation). This policy may,
|
|
|
998 // in certain cases, enqueue references somewhat sooner than
|
|
|
999 // might Policy #0 above, but at marginally increased cost
|
|
|
1000 // and complexity in processing these references.
|
|
|
1001 // We call this choice the "RefeferentBasedDiscovery" policy.
|
|
|
1002 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
|
|
|
1003 // We enqueue references only if we are discovering refs
|
|
|
1004 // (rather than processing discovered refs).
|
|
|
1005 if (!_discovering_refs || !RegisterReferences) {
|
|
|
1006 return false;
|
|
|
1007 }
|
|
|
1008 // We only enqueue active references.
|
|
|
1009 oop* next_addr = java_lang_ref_Reference::next_addr(obj);
|
|
|
1010 if (*next_addr != NULL) {
|
|
|
1011 return false;
|
|
|
1012 }
|
|
|
1013
|
|
|
1014 HeapWord* obj_addr = (HeapWord*)obj;
|
|
|
1015 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
|
|
|
1016 !_span.contains(obj_addr)) {
|
|
|
1017 // Reference is not in the originating generation;
|
|
|
1018 // don't treat it specially (i.e. we want to scan it as a normal
|
|
|
1019 // object with strong references).
|
|
|
1020 return false;
|
|
|
1021 }
|
|
|
1022
|
|
|
1023 // We only enqueue references whose referents are not (yet) strongly
|
|
|
1024 // reachable.
|
|
|
1025 if (is_alive_non_header() != NULL) {
|
|
|
1026 oop referent = java_lang_ref_Reference::referent(obj);
|
|
|
1027 // We'd like to assert the following:
|
|
|
1028 // assert(referent != NULL, "Refs with null referents already filtered");
|
|
|
1029 // However, since this code may be executed concurrently with
|
|
|
1030 // mutators, which can clear() the referent, it is not
|
|
|
1031 // guaranteed that the referent is non-NULL.
|
|
|
1032 if (is_alive_non_header()->do_object_b(referent)) {
|
|
|
1033 return false; // referent is reachable
|
|
|
1034 }
|
|
|
1035 }
|
|
|
1036
|
|
|
1037 oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
|
|
|
1038 assert(discovered_addr != NULL && (*discovered_addr)->is_oop_or_null(),
|
|
|
1039 "bad discovered field");
|
|
|
1040 if (*discovered_addr != NULL) {
|
|
|
1041 // The reference has already been discovered...
|
|
|
1042 if (TraceReferenceGC) {
|
|
|
1043 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
|
|
|
1044 (oopDesc*)obj, obj->blueprint()->internal_name());
|
|
|
1045 }
|
|
|
1046 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
|
|
|
1047 // assumes that an object is not processed twice;
|
|
|
1048 // if it's been already discovered it must be on another
|
|
|
1049 // generation's discovered list; so we won't discover it.
|
|
|
1050 return false;
|
|
|
1051 } else {
|
|
|
1052 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
|
|
|
1053 "Unrecognized policy");
|
|
|
1054 // Check assumption that an object is not potentially
|
|
|
1055 // discovered twice except by concurrent collectors that potentially
|
|
|
1056 // trace the same Reference object twice.
|
|
|
1057 assert(UseConcMarkSweepGC,
|
|
|
1058 "Only possible with a concurrent collector");
|
|
|
1059 return true;
|
|
|
1060 }
|
|
|
1061 }
|
|
|
1062
|
|
|
1063 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
|
|
|
1064 oop referent = java_lang_ref_Reference::referent(obj);
|
|
|
1065 assert(referent->is_oop(), "bad referent");
|
|
|
1066 // enqueue if and only if either:
|
|
|
1067 // reference is in our span or
|
|
|
1068 // we are an atomic collector and referent is in our span
|
|
|
1069 if (_span.contains(obj_addr) ||
|
|
|
1070 (discovery_is_atomic() && _span.contains(referent))) {
|
|
|
1071 // should_enqueue = true;
|
|
|
1072 } else {
|
|
|
1073 return false;
|
|
|
1074 }
|
|
|
1075 } else {
|
|
|
1076 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
|
|
|
1077 _span.contains(obj_addr), "code inconsistency");
|
|
|
1078 }
|
|
|
1079
|
|
|
1080 // Get the right type of discovered queue head.
|
|
|
1081 DiscoveredList* list = get_discovered_list(rt);
|
|
|
1082 if (list == NULL) {
|
|
|
1083 return false; // nothing special needs to be done
|
|
|
1084 }
|
|
|
1085
|
|
|
1086 // We do a raw store here, the field will be visited later when
|
|
|
1087 // processing the discovered references.
|
|
|
1088 if (_discovery_is_mt) {
|
|
|
1089 add_to_discovered_list_mt(*list, obj, discovered_addr);
|
|
|
1090 } else {
|
|
|
1091 *discovered_addr = list->head();
|
|
|
1092 list->set_head(obj);
|
|
|
1093 list->set_length(list->length() + 1);
|
|
|
1094 }
|
|
|
1095
|
|
|
1096 // In the MT discovery case, it is currently possible to see
|
|
|
1097 // the following message multiple times if several threads
|
|
|
1098 // discover a reference about the same time. Only one will
|
|
|
1099 // however have actually added it to the disocvered queue.
|
|
|
1100 // One could let add_to_discovered_list_mt() return an
|
|
|
1101 // indication for success in queueing (by 1 thread) or
|
|
|
1102 // failure (by all other threads), but I decided the extra
|
|
|
1103 // code was not worth the effort for something that is
|
|
|
1104 // only used for debugging support.
|
|
|
1105 if (TraceReferenceGC) {
|
|
|
1106 oop referent = java_lang_ref_Reference::referent(obj);
|
|
|
1107 if (PrintGCDetails) {
|
|
|
1108 gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
|
|
|
1109 (oopDesc*) obj, obj->blueprint()->internal_name());
|
|
|
1110 }
|
|
|
1111 assert(referent->is_oop(), "Enqueued a bad referent");
|
|
|
1112 }
|
|
|
1113 assert(obj->is_oop(), "Enqueued a bad reference");
|
|
|
1114 return true;
|
|
|
1115 }
|
|
|
1116
|
|
|
1117 // Preclean the discovered references by removing those
|
|
|
1118 // whose referents are alive, and by marking from those that
|
|
|
1119 // are not active. These lists can be handled here
|
|
|
1120 // in any order and, indeed, concurrently.
|
|
|
1121 void ReferenceProcessor::preclean_discovered_references(
|
|
|
1122 BoolObjectClosure* is_alive,
|
|
|
1123 OopClosure* keep_alive,
|
|
|
1124 VoidClosure* complete_gc,
|
|
|
1125 YieldClosure* yield) {
|
|
|
1126
|
|
|
1127 NOT_PRODUCT(verify_ok_to_handle_reflists());
|
|
|
1128
|
|
|
1129 // Soft references
|
|
|
1130 {
|
|
|
1131 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
|
|
|
1132 false, gclog_or_tty);
|
|
|
1133 for (int i = 0; i < _num_q; i++) {
|
|
|
1134 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
|
|
|
1135 keep_alive, complete_gc, yield);
|
|
|
1136 }
|
|
|
1137 }
|
|
|
1138 if (yield->should_return()) {
|
|
|
1139 return;
|
|
|
1140 }
|
|
|
1141
|
|
|
1142 // Weak references
|
|
|
1143 {
|
|
|
1144 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
|
|
|
1145 false, gclog_or_tty);
|
|
|
1146 for (int i = 0; i < _num_q; i++) {
|
|
|
1147 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
|
|
|
1148 keep_alive, complete_gc, yield);
|
|
|
1149 }
|
|
|
1150 }
|
|
|
1151 if (yield->should_return()) {
|
|
|
1152 return;
|
|
|
1153 }
|
|
|
1154
|
|
|
1155 // Final references
|
|
|
1156 {
|
|
|
1157 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
|
|
|
1158 false, gclog_or_tty);
|
|
|
1159 for (int i = 0; i < _num_q; i++) {
|
|
|
1160 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
|
|
|
1161 keep_alive, complete_gc, yield);
|
|
|
1162 }
|
|
|
1163 }
|
|
|
1164 if (yield->should_return()) {
|
|
|
1165 return;
|
|
|
1166 }
|
|
|
1167
|
|
|
1168 // Phantom references
|
|
|
1169 {
|
|
|
1170 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
|
|
|
1171 false, gclog_or_tty);
|
|
|
1172 for (int i = 0; i < _num_q; i++) {
|
|
|
1173 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
|
|
|
1174 keep_alive, complete_gc, yield);
|
|
|
1175 }
|
|
|
1176 }
|
|
|
1177 }
|
|
|
1178
|
|
|
1179 // Walk the given discovered ref list, and remove all reference objects
|
|
|
1180 // whose referents are still alive, whose referents are NULL or which
|
|
|
1181 // are not active (have a non-NULL next field). NOTE: For this to work
|
|
|
1182 // correctly, refs discovery can not be happening concurrently with this
|
|
|
1183 // step.
|
|
|
1184 void ReferenceProcessor::preclean_discovered_reflist(
|
|
|
1185 DiscoveredList& refs_list, BoolObjectClosure* is_alive,
|
|
|
1186 OopClosure* keep_alive, VoidClosure* complete_gc, YieldClosure* yield) {
|
|
|
1187
|
|
|
1188 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
|
1189 size_t length = refs_list.length();
|
|
|
1190 while (iter.has_next()) {
|
|
|
1191 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
|
|
|
1192 oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
|
|
|
1193 if (iter.referent() == NULL || iter.is_referent_alive() ||
|
|
|
1194 *next_addr != NULL) {
|
|
|
1195 // The referent has been cleared, or is alive, or the Reference is not
|
|
|
1196 // active; we need to trace and mark its cohort.
|
|
|
1197 if (TraceReferenceGC) {
|
|
|
1198 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
|
|
|
1199 iter.obj(), iter.obj()->blueprint()->internal_name());
|
|
|
1200 }
|
|
|
1201 // Remove Reference object from list
|
|
|
1202 iter.remove();
|
|
|
1203 --length;
|
|
|
1204 // Keep alive its cohort.
|
|
|
1205 iter.make_referent_alive();
|
|
|
1206 keep_alive->do_oop(next_addr);
|
|
|
1207 } else {
|
|
|
1208 iter.next();
|
|
|
1209 }
|
|
|
1210 }
|
|
|
1211 refs_list.set_length(length);
|
|
|
1212
|
|
|
1213 // Close the reachable set
|
|
|
1214 complete_gc->do_void();
|
|
|
1215
|
|
|
1216 NOT_PRODUCT(
|
|
|
1217 if (PrintGCDetails && PrintReferenceGC) {
|
|
|
1218 gclog_or_tty->print(" Dropped %d Refs out of %d "
|
|
|
1219 "Refs in discovered list ", iter.removed(), iter.processed());
|
|
|
1220 }
|
|
|
1221 )
|
|
|
1222 }
|
|
|
1223
|
|
|
1224 const char* ReferenceProcessor::list_name(int i) {
|
|
|
1225 assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index");
|
|
|
1226 int j = i / _num_q;
|
|
|
1227 switch (j) {
|
|
|
1228 case 0: return "SoftRef";
|
|
|
1229 case 1: return "WeakRef";
|
|
|
1230 case 2: return "FinalRef";
|
|
|
1231 case 3: return "PhantomRef";
|
|
|
1232 }
|
|
|
1233 ShouldNotReachHere();
|
|
|
1234 return NULL;
|
|
|
1235 }
|
|
|
1236
|
|
|
1237 #ifndef PRODUCT
|
|
|
1238 void ReferenceProcessor::verify_ok_to_handle_reflists() {
|
|
|
1239 // empty for now
|
|
|
1240 }
|
|
|
1241 #endif
|
|
|
1242
|
|
|
1243 void ReferenceProcessor::verify() {
|
|
|
1244 guarantee(_sentinelRef != NULL && _sentinelRef->is_oop(), "Lost _sentinelRef");
|
|
|
1245 }
|
|
|
1246
|
|
|
1247 #ifndef PRODUCT
|
|
|
1248 void ReferenceProcessor::clear_discovered_references() {
|
|
|
1249 guarantee(!_discovering_refs, "Discovering refs?");
|
|
|
1250 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
|
|
|
1251 oop obj = _discoveredSoftRefs[i].head();
|
|
|
1252 while (obj != _sentinelRef) {
|
|
|
1253 oop next = java_lang_ref_Reference::discovered(obj);
|
|
|
1254 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
|
|
|
1255 obj = next;
|
|
|
1256 }
|
|
|
1257 _discoveredSoftRefs[i].set_head(_sentinelRef);
|
|
|
1258 _discoveredSoftRefs[i].set_length(0);
|
|
|
1259 }
|
|
|
1260 }
|
|
|
1261 #endif // PRODUCT
|
