Mercurial > hg > graal-compiler
annotate src/share/vm/memory/referenceProcessor.cpp @ 10408:836a62f43af9
Merge with http://hg.openjdk.java.net/hsx/hsx25/hotspot/
author | Doug Simon <doug.simon@oracle.com> |
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date | Wed, 19 Jun 2013 10:45:56 +0200 |
parents | 4a7dc38ae96b f2110083203d |
children | f22cbff51c12 |
rev | line source |
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0 | 1 /* |
10405 | 2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved. |
0 | 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
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. |
0 | 22 * |
23 */ | |
24 | |
1972 | 25 #include "precompiled.hpp" |
26 #include "classfile/javaClasses.hpp" | |
27 #include "classfile/systemDictionary.hpp" | |
10405 | 28 #include "gc_implementation/shared/gcTimer.hpp" |
29 #include "gc_implementation/shared/gcTraceTime.hpp" | |
1972 | 30 #include "gc_interface/collectedHeap.hpp" |
31 #include "gc_interface/collectedHeap.inline.hpp" | |
32 #include "memory/referencePolicy.hpp" | |
33 #include "memory/referenceProcessor.hpp" | |
34 #include "oops/oop.inline.hpp" | |
35 #include "runtime/java.hpp" | |
36 #include "runtime/jniHandles.hpp" | |
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37 #ifdef GRAAL |
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38 #include "code/codeCache.hpp" |
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39 #include "code/nmethod.hpp" |
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40 #endif |
0 | 41 |
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42 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
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43 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
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44 bool ReferenceProcessor::_pending_list_uses_discovered_field = false; |
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45 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; |
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46 |
0 | 47 void referenceProcessor_init() { |
48 ReferenceProcessor::init_statics(); | |
49 } | |
50 | |
51 void ReferenceProcessor::init_statics() { | |
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52 // We need a monotonically non-deccreasing time in ms but |
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53 // os::javaTimeMillis() does not guarantee monotonicity. |
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54 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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55 |
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56 // Initialize the soft ref timestamp clock. |
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57 _soft_ref_timestamp_clock = now; |
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58 // Also update the soft ref clock in j.l.r.SoftReference |
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59 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); |
0 | 60 |
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61 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
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62 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
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63 NOT_COMPILER2(LRUCurrentHeapPolicy()); |
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64 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
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65 vm_exit_during_initialization("Could not allocate reference policy object"); |
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66 } |
0 | 67 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
68 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
69 "Unrecongnized RefDiscoveryPolicy"); | |
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70 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field(); |
0 | 71 } |
72 | |
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73 void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) { |
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74 #ifdef ASSERT |
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75 // Verify that we're not currently discovering refs |
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76 assert(!verify_disabled || !_discovering_refs, "nested call?"); |
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77 |
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78 if (check_no_refs) { |
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79 // Verify that the discovered lists are empty |
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80 verify_no_references_recorded(); |
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81 } |
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82 #endif // ASSERT |
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83 |
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84 // Someone could have modified the value of the static |
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85 // field in the j.l.r.SoftReference class that holds the |
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86 // soft reference timestamp clock using reflection or |
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87 // Unsafe between GCs. Unconditionally update the static |
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88 // field in ReferenceProcessor here so that we use the new |
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89 // value during reference discovery. |
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90 |
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91 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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92 _discovering_refs = true; |
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93 } |
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94 |
0 | 95 ReferenceProcessor::ReferenceProcessor(MemRegion span, |
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96 bool mt_processing, |
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97 uint mt_processing_degree, |
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98 bool mt_discovery, |
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99 uint mt_discovery_degree, |
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100 bool atomic_discovery, |
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101 BoolObjectClosure* is_alive_non_header, |
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102 bool discovered_list_needs_barrier) : |
0 | 103 _discovering_refs(false), |
104 _enqueuing_is_done(false), | |
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105 _is_alive_non_header(is_alive_non_header), |
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106 _discovered_list_needs_barrier(discovered_list_needs_barrier), |
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107 _bs(NULL), |
0 | 108 _processing_is_mt(mt_processing), |
109 _next_id(0) | |
110 { | |
111 _span = span; | |
112 _discovery_is_atomic = atomic_discovery; | |
113 _discovery_is_mt = mt_discovery; | |
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114 _num_q = MAX2(1U, mt_processing_degree); |
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115 _max_num_q = MAX2(_num_q, mt_discovery_degree); |
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116 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, |
6197 | 117 _max_num_q * number_of_subclasses_of_ref(), mtGC); |
118 | |
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119 if (_discovered_refs == NULL) { |
0 | 120 vm_exit_during_initialization("Could not allocated RefProc Array"); |
121 } | |
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122 _discoveredSoftRefs = &_discovered_refs[0]; |
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123 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
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124 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
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125 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
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126 |
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127 // Initialize all entries to NULL |
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128 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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129 _discovered_refs[i].set_head(NULL); |
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130 _discovered_refs[i].set_length(0); |
0 | 131 } |
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132 |
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133 // If we do barriers, cache a copy of the barrier set. |
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134 if (discovered_list_needs_barrier) { |
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135 _bs = Universe::heap()->barrier_set(); |
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136 } |
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137 setup_policy(false /* default soft ref policy */); |
0 | 138 } |
139 | |
140 #ifndef PRODUCT | |
141 void ReferenceProcessor::verify_no_references_recorded() { | |
142 guarantee(!_discovering_refs, "Discovering refs?"); | |
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143 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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144 guarantee(_discovered_refs[i].is_empty(), |
0 | 145 "Found non-empty discovered list"); |
146 } | |
147 } | |
148 #endif | |
149 | |
150 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
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151 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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152 if (UseCompressedOops) { |
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153 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); |
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154 } else { |
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155 f->do_oop((oop*)_discovered_refs[i].adr_head()); |
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156 } |
0 | 157 } |
158 } | |
159 | |
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160 void ReferenceProcessor::update_soft_ref_master_clock() { |
0 | 161 // Update (advance) the soft ref master clock field. This must be done |
162 // after processing the soft ref list. | |
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163 |
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164 // We need a monotonically non-deccreasing time in ms but |
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165 // os::javaTimeMillis() does not guarantee monotonicity. |
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166 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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167 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); |
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168 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); |
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169 |
0 | 170 NOT_PRODUCT( |
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171 if (now < _soft_ref_timestamp_clock) { |
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172 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, |
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173 _soft_ref_timestamp_clock, now); |
0 | 174 } |
175 ) | |
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176 // The values of now and _soft_ref_timestamp_clock are set using |
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177 // javaTimeNanos(), which is guaranteed to be monotonically |
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178 // non-decreasing provided the underlying platform provides such |
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179 // a time source (and it is bug free). |
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180 // In product mode, however, protect ourselves from non-monotonicty. |
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181 if (now > _soft_ref_timestamp_clock) { |
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182 _soft_ref_timestamp_clock = now; |
0 | 183 java_lang_ref_SoftReference::set_clock(now); |
184 } | |
185 // Else leave clock stalled at its old value until time progresses | |
186 // past clock value. | |
187 } | |
188 | |
10405 | 189 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) { |
190 size_t total = 0; | |
191 for (uint i = 0; i < _max_num_q; ++i) { | |
192 total += lists[i].length(); | |
193 } | |
194 return total; | |
195 } | |
196 | |
197 ReferenceProcessorStats ReferenceProcessor::process_discovered_references( | |
0 | 198 BoolObjectClosure* is_alive, |
199 OopClosure* keep_alive, | |
200 VoidClosure* complete_gc, | |
10405 | 201 AbstractRefProcTaskExecutor* task_executor, |
202 GCTimer* gc_timer) { | |
0 | 203 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
204 | |
205 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
206 // Stop treating discovered references specially. | |
207 disable_discovery(); | |
208 | |
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209 // If discovery was concurrent, someone could have modified |
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210 // the value of the static field in the j.l.r.SoftReference |
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211 // class that holds the soft reference timestamp clock using |
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212 // reflection or Unsafe between when discovery was enabled and |
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213 // now. Unconditionally update the static field in ReferenceProcessor |
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214 // here so that we use the new value during processing of the |
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215 // discovered soft refs. |
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216 |
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217 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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218 |
0 | 219 bool trace_time = PrintGCDetails && PrintReferenceGC; |
10405 | 220 |
0 | 221 // Soft references |
10405 | 222 size_t soft_count = 0; |
0 | 223 { |
10405 | 224 GCTraceTime tt("SoftReference", trace_time, false, gc_timer); |
225 soft_count = | |
226 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, | |
227 is_alive, keep_alive, complete_gc, task_executor); | |
0 | 228 } |
229 | |
230 update_soft_ref_master_clock(); | |
231 | |
232 // Weak references | |
10405 | 233 size_t weak_count = 0; |
0 | 234 { |
10405 | 235 GCTraceTime tt("WeakReference", trace_time, false, gc_timer); |
236 weak_count = | |
237 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
238 is_alive, keep_alive, complete_gc, task_executor); | |
0 | 239 } |
240 | |
241 // Final references | |
10405 | 242 size_t final_count = 0; |
0 | 243 { |
10405 | 244 GCTraceTime tt("FinalReference", trace_time, false, gc_timer); |
245 final_count = | |
246 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
247 is_alive, keep_alive, complete_gc, task_executor); | |
0 | 248 } |
249 | |
250 // Phantom references | |
10405 | 251 size_t phantom_count = 0; |
0 | 252 { |
10405 | 253 GCTraceTime tt("PhantomReference", trace_time, false, gc_timer); |
254 phantom_count = | |
255 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
256 is_alive, keep_alive, complete_gc, task_executor); | |
0 | 257 } |
258 | |
259 // Weak global JNI references. It would make more sense (semantically) to | |
260 // traverse these simultaneously with the regular weak references above, but | |
261 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
262 // thus use JNI weak references to circumvent the phantom references and | |
263 // resurrect a "post-mortem" object. | |
264 { | |
10405 | 265 GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer); |
0 | 266 if (task_executor != NULL) { |
267 task_executor->set_single_threaded_mode(); | |
268 } | |
269 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
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270 #ifdef GRAAL |
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271 process_phaseGraalNMethods(keep_alive, complete_gc); |
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272 #endif |
0 | 273 } |
10405 | 274 |
275 return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count); | |
0 | 276 } |
277 | |
278 #ifndef PRODUCT | |
279 // Calculate the number of jni handles. | |
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280 uint ReferenceProcessor::count_jni_refs() { |
0 | 281 class AlwaysAliveClosure: public BoolObjectClosure { |
282 public: | |
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283 virtual bool do_object_b(oop obj) { return true; } |
0 | 284 }; |
285 | |
286 class CountHandleClosure: public OopClosure { | |
287 private: | |
288 int _count; | |
289 public: | |
290 CountHandleClosure(): _count(0) {} | |
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291 void do_oop(oop* unused) { _count++; } |
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292 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
0 | 293 int count() { return _count; } |
294 }; | |
295 CountHandleClosure global_handle_count; | |
296 AlwaysAliveClosure always_alive; | |
297 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
298 return global_handle_count.count(); | |
299 } | |
300 #endif | |
301 | |
302 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
303 OopClosure* keep_alive, | |
304 VoidClosure* complete_gc) { | |
305 #ifndef PRODUCT | |
306 if (PrintGCDetails && PrintReferenceGC) { | |
307 unsigned int count = count_jni_refs(); | |
308 gclog_or_tty->print(", %u refs", count); | |
309 } | |
310 #endif | |
311 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
312 complete_gc->do_void(); | |
313 } | |
314 | |
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315 #ifdef GRAAL |
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316 void ReferenceProcessor::process_phaseGraalNMethods(OopClosure* keep_alive, |
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317 VoidClosure* complete_gc) { |
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318 CodeCache::alive_nmethods_do_graal_methods(keep_alive); |
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319 complete_gc->do_void(); |
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320 } |
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321 |
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322 #endif |
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323 |
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324 template <class T> |
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325 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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326 AbstractRefProcTaskExecutor* task_executor) { |
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327 |
0 | 328 // Remember old value of pending references list |
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329 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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330 T old_pending_list_value = *pending_list_addr; |
0 | 331 |
332 // Enqueue references that are not made active again, and | |
333 // clear the decks for the next collection (cycle). | |
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334 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
0 | 335 // Do the oop-check on pending_list_addr missed in |
336 // enqueue_discovered_reflist. We should probably | |
337 // do a raw oop_check so that future such idempotent | |
338 // oop_stores relying on the oop-check side-effect | |
339 // may be elided automatically and safely without | |
340 // affecting correctness. | |
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341 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
0 | 342 |
343 // Stop treating discovered references specially. | |
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344 ref->disable_discovery(); |
0 | 345 |
346 // Return true if new pending references were added | |
347 return old_pending_list_value != *pending_list_addr; | |
348 } | |
349 | |
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350 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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351 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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352 if (UseCompressedOops) { |
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353 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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354 } else { |
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355 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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356 } |
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357 } |
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358 |
0 | 359 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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360 HeapWord* pending_list_addr) { |
0 | 361 // Given a list of refs linked through the "discovered" field |
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362 // (java.lang.ref.Reference.discovered), self-loop their "next" field |
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363 // thus distinguishing them from active References, then |
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364 // prepend them to the pending list. |
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365 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777), |
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366 // the "next" field is used to chain the pending list, not the discovered |
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367 // field. |
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368 |
0 | 369 if (TraceReferenceGC && PrintGCDetails) { |
370 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
371 INTPTR_FORMAT, (address)refs_list.head()); | |
372 } | |
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373 |
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374 oop obj = NULL; |
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375 oop next_d = refs_list.head(); |
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376 if (pending_list_uses_discovered_field()) { // New behaviour |
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377 // Walk down the list, self-looping the next field |
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378 // so that the References are not considered active. |
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379 while (obj != next_d) { |
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380 obj = next_d; |
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381 assert(obj->is_instanceRef(), "should be reference object"); |
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382 next_d = java_lang_ref_Reference::discovered(obj); |
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383 if (TraceReferenceGC && PrintGCDetails) { |
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384 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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385 obj, next_d); |
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386 } |
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387 assert(java_lang_ref_Reference::next(obj) == NULL, |
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388 "Reference not active; should not be discovered"); |
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389 // Self-loop next, so as to make Ref not active. |
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390 java_lang_ref_Reference::set_next(obj, obj); |
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391 if (next_d == obj) { // obj is last |
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392 // Swap refs_list into pendling_list_addr and |
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393 // set obj's discovered to what we read from pending_list_addr. |
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394 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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395 // Need oop_check on pending_list_addr above; |
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396 // see special oop-check code at the end of |
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397 // enqueue_discovered_reflists() further below. |
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398 java_lang_ref_Reference::set_discovered(obj, old); // old may be NULL |
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399 } |
0 | 400 } |
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401 } else { // Old behaviour |
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402 // Walk down the list, copying the discovered field into |
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403 // the next field and clearing the discovered field. |
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404 while (obj != next_d) { |
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405 obj = next_d; |
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406 assert(obj->is_instanceRef(), "should be reference object"); |
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407 next_d = java_lang_ref_Reference::discovered(obj); |
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408 if (TraceReferenceGC && PrintGCDetails) { |
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409 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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410 obj, next_d); |
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411 } |
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412 assert(java_lang_ref_Reference::next(obj) == NULL, |
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413 "The reference should not be enqueued"); |
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414 if (next_d == obj) { // obj is last |
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415 // Swap refs_list into pendling_list_addr and |
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416 // set obj's next to what we read from pending_list_addr. |
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417 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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418 // Need oop_check on pending_list_addr above; |
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419 // see special oop-check code at the end of |
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420 // enqueue_discovered_reflists() further below. |
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421 if (old == NULL) { |
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422 // obj should be made to point to itself, since |
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423 // pending list was empty. |
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424 java_lang_ref_Reference::set_next(obj, obj); |
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425 } else { |
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426 java_lang_ref_Reference::set_next(obj, old); |
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427 } |
0 | 428 } else { |
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429 java_lang_ref_Reference::set_next(obj, next_d); |
0 | 430 } |
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431 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); |
0 | 432 } |
433 } | |
434 } | |
435 | |
436 // Parallel enqueue task | |
437 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
438 public: | |
439 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
440 DiscoveredList discovered_refs[], | |
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441 HeapWord* pending_list_addr, |
0 | 442 int n_queues) |
443 : EnqueueTask(ref_processor, discovered_refs, | |
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444 pending_list_addr, n_queues) |
0 | 445 { } |
446 | |
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447 virtual void work(unsigned int work_id) { |
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448 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); |
0 | 449 // Simplest first cut: static partitioning. |
450 int index = work_id; | |
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451 // The increment on "index" must correspond to the maximum number of queues |
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452 // (n_queues) with which that ReferenceProcessor was created. That |
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453 // is because of the "clever" way the discovered references lists were |
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454 // allocated and are indexed into. |
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455 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); |
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456 for (int j = 0; |
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457 j < ReferenceProcessor::number_of_subclasses_of_ref(); |
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458 j++, index += _n_queues) { |
0 | 459 _ref_processor.enqueue_discovered_reflist( |
460 _refs_lists[index], _pending_list_addr); | |
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461 _refs_lists[index].set_head(NULL); |
0 | 462 _refs_lists[index].set_length(0); |
463 } | |
464 } | |
465 }; | |
466 | |
467 // Enqueue references that are not made active again | |
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468 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
0 | 469 AbstractRefProcTaskExecutor* task_executor) { |
470 if (_processing_is_mt && task_executor != NULL) { | |
471 // Parallel code | |
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472 RefProcEnqueueTask tsk(*this, _discovered_refs, |
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473 pending_list_addr, _max_num_q); |
0 | 474 task_executor->execute(tsk); |
475 } else { | |
476 // Serial code: call the parent class's implementation | |
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477 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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478 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr); |
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479 _discovered_refs[i].set_head(NULL); |
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480 _discovered_refs[i].set_length(0); |
0 | 481 } |
482 } | |
483 } | |
484 | |
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485 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
0 | 486 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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487 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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488 assert(_discovered_addr && discovered->is_oop_or_null(), |
0 | 489 "discovered field is bad"); |
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490 _next = discovered; |
0 | 491 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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492 _referent = java_lang_ref_Reference::referent(_ref); |
0 | 493 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
494 "Wrong oop found in java.lang.Reference object"); | |
495 assert(allow_null_referent ? | |
496 _referent->is_oop_or_null() | |
497 : _referent->is_oop(), | |
498 "bad referent"); | |
499 } | |
500 | |
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501 void DiscoveredListIterator::remove() { |
0 | 502 assert(_ref->is_oop(), "Dropping a bad reference"); |
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503 oop_store_raw(_discovered_addr, NULL); |
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504 |
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505 // First _prev_next ref actually points into DiscoveredList (gross). |
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506 oop new_next; |
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507 if (_next == _ref) { |
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508 // At the end of the list, we should make _prev point to itself. |
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509 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, |
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510 // and _prev will be NULL. |
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511 new_next = _prev; |
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512 } else { |
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513 new_next = _next; |
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514 } |
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515 |
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516 if (UseCompressedOops) { |
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517 // Remove Reference object from list. |
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518 oopDesc::encode_store_heap_oop((narrowOop*)_prev_next, new_next); |
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519 } else { |
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520 // Remove Reference object from list. |
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521 oopDesc::store_heap_oop((oop*)_prev_next, new_next); |
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522 } |
0 | 523 NOT_PRODUCT(_removed++); |
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524 _refs_list.dec_length(1); |
0 | 525 } |
526 | |
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527 // Make the Reference object active again. |
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528 void DiscoveredListIterator::make_active() { |
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529 // For G1 we don't want to use set_next - it |
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530 // will dirty the card for the next field of |
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531 // the reference object and will fail |
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532 // CT verification. |
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533 if (UseG1GC) { |
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534 BarrierSet* bs = oopDesc::bs(); |
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535 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref); |
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536 |
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537 if (UseCompressedOops) { |
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538 bs->write_ref_field_pre((narrowOop*)next_addr, NULL); |
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539 } else { |
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540 bs->write_ref_field_pre((oop*)next_addr, NULL); |
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541 } |
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542 java_lang_ref_Reference::set_next_raw(_ref, NULL); |
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543 } else { |
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544 java_lang_ref_Reference::set_next(_ref, NULL); |
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545 } |
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546 } |
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547 |
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548 void DiscoveredListIterator::clear_referent() { |
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549 oop_store_raw(_referent_addr, NULL); |
0 | 550 } |
551 | |
552 // NOTE: process_phase*() are largely similar, and at a high level | |
553 // merely iterate over the extant list applying a predicate to | |
554 // each of its elements and possibly removing that element from the | |
555 // list and applying some further closures to that element. | |
556 // We should consider the possibility of replacing these | |
557 // process_phase*() methods by abstracting them into | |
558 // a single general iterator invocation that receives appropriate | |
559 // closures that accomplish this work. | |
560 | |
561 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
562 // referents are not alive, but that should be kept alive for policy reasons. | |
563 // Keep alive the transitive closure of all such referents. | |
564 void | |
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565 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
0 | 566 ReferencePolicy* policy, |
567 BoolObjectClosure* is_alive, | |
568 OopClosure* keep_alive, | |
569 VoidClosure* complete_gc) { | |
570 assert(policy != NULL, "Must have a non-NULL policy"); | |
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571 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 572 // Decide which softly reachable refs should be kept alive. |
573 while (iter.has_next()) { | |
574 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
575 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
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576 if (referent_is_dead && |
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577 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { |
0 | 578 if (TraceReferenceGC) { |
579 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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580 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 581 } |
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582 // Remove Reference object from list |
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583 iter.remove(); |
0 | 584 // Make the Reference object active again |
585 iter.make_active(); | |
586 // keep the referent around | |
587 iter.make_referent_alive(); | |
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588 iter.move_to_next(); |
0 | 589 } else { |
590 iter.next(); | |
591 } | |
592 } | |
593 // Close the reachable set | |
594 complete_gc->do_void(); | |
595 NOT_PRODUCT( | |
596 if (PrintGCDetails && TraceReferenceGC) { | |
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597 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
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598 "discovered Refs by policy, from list " INTPTR_FORMAT, |
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599 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 600 } |
601 ) | |
602 } | |
603 | |
604 // Traverse the list and remove any Refs that are not active, or | |
605 // whose referents are either alive or NULL. | |
606 void | |
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607 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
0 | 608 BoolObjectClosure* is_alive, |
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609 OopClosure* keep_alive) { |
0 | 610 assert(discovery_is_atomic(), "Error"); |
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611 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 612 while (iter.has_next()) { |
613 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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614 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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615 assert(next == NULL, "Should not discover inactive Reference"); |
0 | 616 if (iter.is_referent_alive()) { |
617 if (TraceReferenceGC) { | |
618 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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619 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 620 } |
621 // The referent is reachable after all. | |
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622 // Remove Reference object from list. |
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623 iter.remove(); |
0 | 624 // Update the referent pointer as necessary: Note that this |
625 // should not entail any recursive marking because the | |
626 // referent must already have been traversed. | |
627 iter.make_referent_alive(); | |
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628 iter.move_to_next(); |
0 | 629 } else { |
630 iter.next(); | |
631 } | |
632 } | |
633 NOT_PRODUCT( | |
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634 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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635 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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636 "Refs in discovered list " INTPTR_FORMAT, |
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637 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 638 } |
639 ) | |
640 } | |
641 | |
642 void | |
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643 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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644 BoolObjectClosure* is_alive, |
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645 OopClosure* keep_alive, |
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646 VoidClosure* complete_gc) { |
0 | 647 assert(!discovery_is_atomic(), "Error"); |
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648 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 649 while (iter.has_next()) { |
650 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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651 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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652 oop next = java_lang_ref_Reference::next(iter.obj()); |
0 | 653 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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654 next != NULL)) { |
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655 assert(next->is_oop_or_null(), "bad next field"); |
0 | 656 // Remove Reference object from list |
657 iter.remove(); | |
658 // Trace the cohorts | |
659 iter.make_referent_alive(); | |
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660 if (UseCompressedOops) { |
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661 keep_alive->do_oop((narrowOop*)next_addr); |
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662 } else { |
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663 keep_alive->do_oop((oop*)next_addr); |
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664 } |
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665 iter.move_to_next(); |
0 | 666 } else { |
667 iter.next(); | |
668 } | |
669 } | |
670 // Now close the newly reachable set | |
671 complete_gc->do_void(); | |
672 NOT_PRODUCT( | |
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673 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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674 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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675 "Refs in discovered list " INTPTR_FORMAT, |
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676 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 677 } |
678 ) | |
679 } | |
680 | |
681 // Traverse the list and process the referents, by either | |
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682 // clearing them or keeping them (and their reachable |
0 | 683 // closure) alive. |
684 void | |
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685 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
0 | 686 bool clear_referent, |
687 BoolObjectClosure* is_alive, | |
688 OopClosure* keep_alive, | |
689 VoidClosure* complete_gc) { | |
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690 ResourceMark rm; |
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691 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 692 while (iter.has_next()) { |
693 iter.update_discovered(); | |
694 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
695 if (clear_referent) { | |
696 // NULL out referent pointer | |
697 iter.clear_referent(); | |
698 } else { | |
699 // keep the referent around | |
700 iter.make_referent_alive(); | |
701 } | |
702 if (TraceReferenceGC) { | |
703 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
704 clear_referent ? "cleared " : "", | |
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705 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 706 } |
707 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
708 iter.next(); | |
709 } | |
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710 // Remember to update the next pointer of the last ref. |
0 | 711 iter.update_discovered(); |
712 // Close the reachable set | |
713 complete_gc->do_void(); | |
714 } | |
715 | |
716 void | |
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717 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { |
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718 oop obj = NULL; |
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719 oop next = refs_list.head(); |
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720 while (next != obj) { |
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721 obj = next; |
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722 next = java_lang_ref_Reference::discovered(obj); |
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723 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
0 | 724 } |
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725 refs_list.set_head(NULL); |
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726 refs_list.set_length(0); |
0 | 727 } |
728 | |
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729 void |
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730 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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731 clear_discovered_references(refs_list); |
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732 } |
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733 |
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734 void ReferenceProcessor::abandon_partial_discovery() { |
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735 // loop over the lists |
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736 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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737 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
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738 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i)); |
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739 } |
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740 abandon_partial_discovered_list(_discovered_refs[i]); |
0 | 741 } |
742 } | |
743 | |
744 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
745 public: | |
746 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
747 DiscoveredList refs_lists[], | |
748 ReferencePolicy* policy, | |
749 bool marks_oops_alive) | |
750 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
751 _policy(policy) | |
752 { } | |
753 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
754 OopClosure& keep_alive, | |
755 VoidClosure& complete_gc) | |
756 { | |
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757 Thread* thr = Thread::current(); |
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758 int refs_list_index = ((WorkerThread*)thr)->id(); |
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759 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
0 | 760 &is_alive, &keep_alive, &complete_gc); |
761 } | |
762 private: | |
763 ReferencePolicy* _policy; | |
764 }; | |
765 | |
766 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
767 public: | |
768 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
769 DiscoveredList refs_lists[], | |
770 bool marks_oops_alive) | |
771 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
772 { } | |
773 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
774 OopClosure& keep_alive, | |
775 VoidClosure& complete_gc) | |
776 { | |
777 _ref_processor.process_phase2(_refs_lists[i], | |
778 &is_alive, &keep_alive, &complete_gc); | |
779 } | |
780 }; | |
781 | |
782 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
783 public: | |
784 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
785 DiscoveredList refs_lists[], | |
786 bool clear_referent, | |
787 bool marks_oops_alive) | |
788 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
789 _clear_referent(clear_referent) | |
790 { } | |
791 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
792 OopClosure& keep_alive, | |
793 VoidClosure& complete_gc) | |
794 { | |
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795 // Don't use "refs_list_index" calculated in this way because |
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796 // balance_queues() has moved the Ref's into the first n queues. |
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797 // Thread* thr = Thread::current(); |
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798 // int refs_list_index = ((WorkerThread*)thr)->id(); |
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799 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
0 | 800 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
801 &is_alive, &keep_alive, &complete_gc); | |
802 } | |
803 private: | |
804 bool _clear_referent; | |
805 }; | |
806 | |
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807 void ReferenceProcessor::set_discovered(oop ref, oop value) { |
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808 if (_discovered_list_needs_barrier) { |
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809 java_lang_ref_Reference::set_discovered(ref, value); |
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810 } else { |
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811 java_lang_ref_Reference::set_discovered_raw(ref, value); |
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812 } |
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813 } |
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814 |
0 | 815 // Balances reference queues. |
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816 // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
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817 // queues[0, 1, ..., _num_q-1] because only the first _num_q |
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818 // corresponding to the active workers will be processed. |
0 | 819 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
820 { | |
821 // calculate total length | |
822 size_t total_refs = 0; | |
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823 if (TraceReferenceGC && PrintGCDetails) { |
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824 gclog_or_tty->print_cr("\nBalance ref_lists "); |
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825 } |
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826 |
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827 for (uint i = 0; i < _max_num_q; ++i) { |
0 | 828 total_refs += ref_lists[i].length(); |
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829 if (TraceReferenceGC && PrintGCDetails) { |
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830 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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831 } |
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832 } |
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833 if (TraceReferenceGC && PrintGCDetails) { |
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834 gclog_or_tty->print_cr(" = %d", total_refs); |
0 | 835 } |
836 size_t avg_refs = total_refs / _num_q + 1; | |
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837 uint to_idx = 0; |
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838 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { |
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839 bool move_all = false; |
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840 if (from_idx >= _num_q) { |
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841 move_all = ref_lists[from_idx].length() > 0; |
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842 } |
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843 while ((ref_lists[from_idx].length() > avg_refs) || |
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844 move_all) { |
0 | 845 assert(to_idx < _num_q, "Sanity Check!"); |
846 if (ref_lists[to_idx].length() < avg_refs) { | |
847 // move superfluous refs | |
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848 size_t refs_to_move; |
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849 // Move all the Ref's if the from queue will not be processed. |
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850 if (move_all) { |
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851 refs_to_move = MIN2(ref_lists[from_idx].length(), |
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852 avg_refs - ref_lists[to_idx].length()); |
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853 } else { |
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854 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
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855 avg_refs - ref_lists[to_idx].length()); |
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856 } |
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857 |
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858 assert(refs_to_move > 0, "otherwise the code below will fail"); |
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859 |
0 | 860 oop move_head = ref_lists[from_idx].head(); |
861 oop move_tail = move_head; | |
862 oop new_head = move_head; | |
863 // find an element to split the list on | |
864 for (size_t j = 0; j < refs_to_move; ++j) { | |
865 move_tail = new_head; | |
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866 new_head = java_lang_ref_Reference::discovered(new_head); |
0 | 867 } |
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868 |
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869 // Add the chain to the to list. |
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870 if (ref_lists[to_idx].head() == NULL) { |
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871 // to list is empty. Make a loop at the end. |
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872 set_discovered(move_tail, move_tail); |
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873 } else { |
3979
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874 set_discovered(move_tail, ref_lists[to_idx].head()); |
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875 } |
0 | 876 ref_lists[to_idx].set_head(move_head); |
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877 ref_lists[to_idx].inc_length(refs_to_move); |
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878 |
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879 // Remove the chain from the from list. |
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880 if (move_tail == new_head) { |
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881 // We found the end of the from list. |
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882 ref_lists[from_idx].set_head(NULL); |
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883 } else { |
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884 ref_lists[from_idx].set_head(new_head); |
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885 } |
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886 ref_lists[from_idx].dec_length(refs_to_move); |
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887 if (ref_lists[from_idx].length() == 0) { |
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888 break; |
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889 } |
0 | 890 } else { |
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891 to_idx = (to_idx + 1) % _num_q; |
0 | 892 } |
893 } | |
894 } | |
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895 #ifdef ASSERT |
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896 size_t balanced_total_refs = 0; |
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897 for (uint i = 0; i < _max_num_q; ++i) { |
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898 balanced_total_refs += ref_lists[i].length(); |
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899 if (TraceReferenceGC && PrintGCDetails) { |
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900 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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901 } |
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902 } |
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903 if (TraceReferenceGC && PrintGCDetails) { |
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904 gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
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905 gclog_or_tty->flush(); |
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906 } |
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907 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
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908 #endif |
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909 } |
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910 |
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911 void ReferenceProcessor::balance_all_queues() { |
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912 balance_queues(_discoveredSoftRefs); |
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913 balance_queues(_discoveredWeakRefs); |
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914 balance_queues(_discoveredFinalRefs); |
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915 balance_queues(_discoveredPhantomRefs); |
0 | 916 } |
917 | |
10405 | 918 size_t |
0 | 919 ReferenceProcessor::process_discovered_reflist( |
920 DiscoveredList refs_lists[], | |
921 ReferencePolicy* policy, | |
922 bool clear_referent, | |
923 BoolObjectClosure* is_alive, | |
924 OopClosure* keep_alive, | |
925 VoidClosure* complete_gc, | |
926 AbstractRefProcTaskExecutor* task_executor) | |
927 { | |
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928 bool mt_processing = task_executor != NULL && _processing_is_mt; |
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929 // If discovery used MT and a dynamic number of GC threads, then |
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930 // the queues must be balanced for correctness if fewer than the |
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931 // maximum number of queues were used. The number of queue used |
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932 // during discovery may be different than the number to be used |
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933 // for processing so don't depend of _num_q < _max_num_q as part |
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934 // of the test. |
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935 bool must_balance = _discovery_is_mt; |
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936 |
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937 if ((mt_processing && ParallelRefProcBalancingEnabled) || |
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938 must_balance) { |
0 | 939 balance_queues(refs_lists); |
940 } | |
10405 | 941 |
942 size_t total_list_count = total_count(refs_lists); | |
943 | |
0 | 944 if (PrintReferenceGC && PrintGCDetails) { |
10405 | 945 gclog_or_tty->print(", %u refs", total_list_count); |
0 | 946 } |
947 | |
948 // Phase 1 (soft refs only): | |
949 // . Traverse the list and remove any SoftReferences whose | |
950 // referents are not alive, but that should be kept alive for | |
951 // policy reasons. Keep alive the transitive closure of all | |
952 // such referents. | |
953 if (policy != NULL) { | |
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954 if (mt_processing) { |
0 | 955 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
956 task_executor->execute(phase1); | |
957 } else { | |
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958 for (uint i = 0; i < _max_num_q; i++) { |
0 | 959 process_phase1(refs_lists[i], policy, |
960 is_alive, keep_alive, complete_gc); | |
961 } | |
962 } | |
963 } else { // policy == NULL | |
964 assert(refs_lists != _discoveredSoftRefs, | |
965 "Policy must be specified for soft references."); | |
966 } | |
967 | |
968 // Phase 2: | |
969 // . Traverse the list and remove any refs whose referents are alive. | |
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970 if (mt_processing) { |
0 | 971 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
972 task_executor->execute(phase2); | |
973 } else { | |
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974 for (uint i = 0; i < _max_num_q; i++) { |
0 | 975 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); |
976 } | |
977 } | |
978 | |
979 // Phase 3: | |
980 // . Traverse the list and process referents as appropriate. | |
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981 if (mt_processing) { |
0 | 982 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
983 task_executor->execute(phase3); | |
984 } else { | |
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985 for (uint i = 0; i < _max_num_q; i++) { |
0 | 986 process_phase3(refs_lists[i], clear_referent, |
987 is_alive, keep_alive, complete_gc); | |
988 } | |
989 } | |
10405 | 990 |
991 return total_list_count; | |
0 | 992 } |
993 | |
994 void ReferenceProcessor::clean_up_discovered_references() { | |
995 // loop over the lists | |
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996 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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997 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
0 | 998 gclog_or_tty->print_cr( |
999 "\nScrubbing %s discovered list of Null referents", | |
1000 list_name(i)); | |
1001 } | |
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1002 clean_up_discovered_reflist(_discovered_refs[i]); |
0 | 1003 } |
1004 } | |
1005 | |
1006 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
1007 assert(!discovery_is_atomic(), "Else why call this method?"); | |
1008 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
1009 while (iter.has_next()) { | |
1010 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1011 oop next = java_lang_ref_Reference::next(iter.obj()); |
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1012 assert(next->is_oop_or_null(), "bad next field"); |
0 | 1013 // If referent has been cleared or Reference is not active, |
1014 // drop it. | |
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1015 if (iter.referent() == NULL || next != NULL) { |
0 | 1016 debug_only( |
1017 if (PrintGCDetails && TraceReferenceGC) { | |
1018 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
1019 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
1020 " and referent: " INTPTR_FORMAT, | |
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1021 iter.obj(), next, iter.referent()); |
0 | 1022 } |
1023 ) | |
1024 // Remove Reference object from list | |
1025 iter.remove(); | |
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1026 iter.move_to_next(); |
0 | 1027 } else { |
1028 iter.next(); | |
1029 } | |
1030 } | |
1031 NOT_PRODUCT( | |
1032 if (PrintGCDetails && TraceReferenceGC) { | |
1033 gclog_or_tty->print( | |
1034 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
1035 iter.removed(), iter.processed()); | |
1036 } | |
1037 ) | |
1038 } | |
1039 | |
1040 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
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1041 uint id = 0; |
0 | 1042 // Determine the queue index to use for this object. |
1043 if (_discovery_is_mt) { | |
1044 // During a multi-threaded discovery phase, | |
1045 // each thread saves to its "own" list. | |
1046 Thread* thr = Thread::current(); | |
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1047 id = thr->as_Worker_thread()->id(); |
0 | 1048 } else { |
1049 // single-threaded discovery, we save in round-robin | |
1050 // fashion to each of the lists. | |
1051 if (_processing_is_mt) { | |
1052 id = next_id(); | |
1053 } | |
1054 } | |
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1055 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
0 | 1056 |
1057 // Get the discovered queue to which we will add | |
1058 DiscoveredList* list = NULL; | |
1059 switch (rt) { | |
1060 case REF_OTHER: | |
1061 // Unknown reference type, no special treatment | |
1062 break; | |
1063 case REF_SOFT: | |
1064 list = &_discoveredSoftRefs[id]; | |
1065 break; | |
1066 case REF_WEAK: | |
1067 list = &_discoveredWeakRefs[id]; | |
1068 break; | |
1069 case REF_FINAL: | |
1070 list = &_discoveredFinalRefs[id]; | |
1071 break; | |
1072 case REF_PHANTOM: | |
1073 list = &_discoveredPhantomRefs[id]; | |
1074 break; | |
1075 case REF_NONE: | |
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1076 // we should not reach here if we are an InstanceRefKlass |
0 | 1077 default: |
1078 ShouldNotReachHere(); | |
1079 } | |
1833
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1080 if (TraceReferenceGC && PrintGCDetails) { |
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1081 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); |
1833
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1082 } |
0 | 1083 return list; |
1084 } | |
1085 | |
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1086 inline void |
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1087 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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1088 oop obj, |
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1089 HeapWord* discovered_addr) { |
0 | 1090 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
1091 // First we must make sure this object is only enqueued once. CAS in a non null | |
1092 // discovered_addr. | |
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1093 oop current_head = refs_list.head(); |
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1094 // The last ref must have its discovered field pointing to itself. |
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1095 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1096 |
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1097 // Note: In the case of G1, this specific pre-barrier is strictly |
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1098 // not necessary because the only case we are interested in |
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1099 // here is when *discovered_addr is NULL (see the CAS further below), |
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1100 // so this will expand to nothing. As a result, we have manually |
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1101 // elided this out for G1, but left in the test for some future |
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1102 // collector that might have need for a pre-barrier here, e.g.:- |
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1103 // _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1104 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1105 "Need to check non-G1 collector: " |
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1106 "may need a pre-write-barrier for CAS from NULL below"); |
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1107 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, |
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1108 NULL); |
0 | 1109 if (retest == NULL) { |
1110 // This thread just won the right to enqueue the object. | |
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1111 // We have separate lists for enqueueing, so no synchronization |
0 | 1112 // is necessary. |
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1113 refs_list.set_head(obj); |
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1114 refs_list.inc_length(1); |
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1115 if (_discovered_list_needs_barrier) { |
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1116 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1117 } |
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1118 |
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1119 if (TraceReferenceGC) { |
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1120 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", |
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1121 obj, obj->klass()->internal_name()); |
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1122 } |
0 | 1123 } else { |
1124 // If retest was non NULL, another thread beat us to it: | |
1125 // The reference has already been discovered... | |
1126 if (TraceReferenceGC) { | |
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1127 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1128 obj, obj->klass()->internal_name()); |
0 | 1129 } |
1130 } | |
1131 } | |
1132 | |
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1133 #ifndef PRODUCT |
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1134 // Non-atomic (i.e. concurrent) discovery might allow us |
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1135 // to observe j.l.References with NULL referents, being those |
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1136 // cleared concurrently by mutators during (or after) discovery. |
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1137 void ReferenceProcessor::verify_referent(oop obj) { |
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1138 bool da = discovery_is_atomic(); |
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1139 oop referent = java_lang_ref_Reference::referent(obj); |
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1140 assert(da ? referent->is_oop() : referent->is_oop_or_null(), |
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1141 err_msg("Bad referent " INTPTR_FORMAT " found in Reference " |
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1142 INTPTR_FORMAT " during %satomic discovery ", |
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1143 (intptr_t)referent, (intptr_t)obj, da ? "" : "non-")); |
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1144 } |
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1145 #endif |
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1146 |
0 | 1147 // We mention two of several possible choices here: |
1148 // #0: if the reference object is not in the "originating generation" | |
1149 // (or part of the heap being collected, indicated by our "span" | |
1150 // we don't treat it specially (i.e. we scan it as we would | |
1151 // a normal oop, treating its references as strong references). | |
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1152 // This means that references can't be discovered unless their |
0 | 1153 // referent is also in the same span. This is the simplest, |
1154 // most "local" and most conservative approach, albeit one | |
1155 // that may cause weak references to be enqueued least promptly. | |
1156 // We call this choice the "ReferenceBasedDiscovery" policy. | |
1157 // #1: the reference object may be in any generation (span), but if | |
1158 // the referent is in the generation (span) being currently collected | |
1159 // then we can discover the reference object, provided | |
1160 // the object has not already been discovered by | |
1161 // a different concurrently running collector (as may be the | |
1162 // case, for instance, if the reference object is in CMS and | |
1163 // the referent in DefNewGeneration), and provided the processing | |
1164 // of this reference object by the current collector will | |
1165 // appear atomic to every other collector in the system. | |
1166 // (Thus, for instance, a concurrent collector may not | |
1167 // discover references in other generations even if the | |
1168 // referent is in its own generation). This policy may, | |
1169 // in certain cases, enqueue references somewhat sooner than | |
1170 // might Policy #0 above, but at marginally increased cost | |
1171 // and complexity in processing these references. | |
1172 // We call this choice the "RefeferentBasedDiscovery" policy. | |
1173 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
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1174 // Make sure we are discovering refs (rather than processing discovered refs). |
0 | 1175 if (!_discovering_refs || !RegisterReferences) { |
1176 return false; | |
1177 } | |
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1178 // We only discover active references. |
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1179 oop next = java_lang_ref_Reference::next(obj); |
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1180 if (next != NULL) { // Ref is no longer active |
0 | 1181 return false; |
1182 } | |
1183 | |
1184 HeapWord* obj_addr = (HeapWord*)obj; | |
1185 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1186 !_span.contains(obj_addr)) { | |
1187 // Reference is not in the originating generation; | |
1188 // don't treat it specially (i.e. we want to scan it as a normal | |
1189 // object with strong references). | |
1190 return false; | |
1191 } | |
1192 | |
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1193 // We only discover references whose referents are not (yet) |
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1194 // known to be strongly reachable. |
0 | 1195 if (is_alive_non_header() != NULL) { |
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1196 verify_referent(obj); |
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1197 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { |
0 | 1198 return false; // referent is reachable |
1199 } | |
1200 } | |
453
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1201 if (rt == REF_SOFT) { |
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1202 // For soft refs we can decide now if these are not |
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1203 // current candidates for clearing, in which case we |
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1204 // can mark through them now, rather than delaying that |
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1205 // to the reference-processing phase. Since all current |
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1206 // time-stamp policies advance the soft-ref clock only |
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1207 // at a major collection cycle, this is always currently |
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1208 // accurate. |
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1209 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { |
453
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1210 return false; |
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1211 } |
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1212 } |
0 | 1213 |
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1214 ResourceMark rm; // Needed for tracing. |
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1215 |
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1216 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1217 const oop discovered = java_lang_ref_Reference::discovered(obj); |
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1218 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1219 if (discovered != NULL) { |
0 | 1220 // The reference has already been discovered... |
1221 if (TraceReferenceGC) { | |
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1222 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1223 obj, obj->klass()->internal_name()); |
0 | 1224 } |
1225 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1226 // assumes that an object is not processed twice; | |
1227 // if it's been already discovered it must be on another | |
1228 // generation's discovered list; so we won't discover it. | |
1229 return false; | |
1230 } else { | |
1231 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
1232 "Unrecognized policy"); | |
1233 // Check assumption that an object is not potentially | |
1234 // discovered twice except by concurrent collectors that potentially | |
1235 // trace the same Reference object twice. | |
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1236 assert(UseConcMarkSweepGC || UseG1GC, |
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1237 "Only possible with a concurrent marking collector"); |
0 | 1238 return true; |
1239 } | |
1240 } | |
1241 | |
1242 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
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1243 verify_referent(obj); |
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1244 // Discover if and only if EITHER: |
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1245 // .. reference is in our span, OR |
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1246 // .. we are an atomic collector and referent is in our span |
0 | 1247 if (_span.contains(obj_addr) || |
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1248 (discovery_is_atomic() && |
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1249 _span.contains(java_lang_ref_Reference::referent(obj)))) { |
0 | 1250 // should_enqueue = true; |
1251 } else { | |
1252 return false; | |
1253 } | |
1254 } else { | |
1255 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1256 _span.contains(obj_addr), "code inconsistency"); | |
1257 } | |
1258 | |
1259 // Get the right type of discovered queue head. | |
1260 DiscoveredList* list = get_discovered_list(rt); | |
1261 if (list == NULL) { | |
1262 return false; // nothing special needs to be done | |
1263 } | |
1264 | |
1265 if (_discovery_is_mt) { | |
1266 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
1267 } else { | |
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1268 // If "_discovered_list_needs_barrier", we do write barriers when |
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1269 // updating the discovered reference list. Otherwise, we do a raw store |
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1270 // here: the field will be visited later when processing the discovered |
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1271 // references. |
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1272 oop current_head = list->head(); |
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1273 // The last ref must have its discovered field pointing to itself. |
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1274 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1275 |
342
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1276 // As in the case further above, since we are over-writing a NULL |
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1277 // pre-value, we can safely elide the pre-barrier here for the case of G1. |
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1278 // e.g.:- _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
342
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1279 assert(discovered == NULL, "control point invariant"); |
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1280 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1281 "For non-G1 collector, may need a pre-write-barrier for CAS from NULL below"); |
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1282 oop_store_raw(discovered_addr, next_discovered); |
342
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1283 if (_discovered_list_needs_barrier) { |
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1284 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
342
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1285 } |
0 | 1286 list->set_head(obj); |
452
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1287 list->inc_length(1); |
0 | 1288 |
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1289 if (TraceReferenceGC) { |
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1290 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)", |
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1291 obj, obj->klass()->internal_name()); |
0 | 1292 } |
1293 } | |
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1294 assert(obj->is_oop(), "Discovered a bad reference"); |
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1295 verify_referent(obj); |
0 | 1296 return true; |
1297 } | |
1298 | |
1299 // Preclean the discovered references by removing those | |
1300 // whose referents are alive, and by marking from those that | |
1301 // are not active. These lists can be handled here | |
1302 // in any order and, indeed, concurrently. | |
1303 void ReferenceProcessor::preclean_discovered_references( | |
1304 BoolObjectClosure* is_alive, | |
1305 OopClosure* keep_alive, | |
1306 VoidClosure* complete_gc, | |
10405 | 1307 YieldClosure* yield, |
1308 GCTimer* gc_timer) { | |
0 | 1309 |
1310 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
1311 | |
1312 // Soft references | |
1313 { | |
10405 | 1314 GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, |
1315 false, gc_timer); | |
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1316 for (uint i = 0; i < _max_num_q; i++) { |
452
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1317 if (yield->should_return()) { |
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1318 return; |
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1319 } |
0 | 1320 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
1321 keep_alive, complete_gc, yield); | |
1322 } | |
1323 } | |
1324 | |
1325 // Weak references | |
1326 { | |
10405 | 1327 GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, |
1328 false, gc_timer); | |
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1329 for (uint i = 0; i < _max_num_q; i++) { |
452
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1330 if (yield->should_return()) { |
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1331 return; |
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1332 } |
0 | 1333 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
1334 keep_alive, complete_gc, yield); | |
1335 } | |
1336 } | |
1337 | |
1338 // Final references | |
1339 { | |
10405 | 1340 GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, |
1341 false, gc_timer); | |
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1342 for (uint i = 0; i < _max_num_q; i++) { |
452
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1343 if (yield->should_return()) { |
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1344 return; |
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1345 } |
0 | 1346 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
1347 keep_alive, complete_gc, yield); | |
1348 } | |
1349 } | |
1350 | |
1351 // Phantom references | |
1352 { | |
10405 | 1353 GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, |
1354 false, gc_timer); | |
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1355 for (uint i = 0; i < _max_num_q; i++) { |
452
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1356 if (yield->should_return()) { |
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1357 return; |
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1358 } |
0 | 1359 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
1360 keep_alive, complete_gc, yield); | |
1361 } | |
1362 } | |
1363 } | |
1364 | |
1365 // Walk the given discovered ref list, and remove all reference objects | |
1366 // whose referents are still alive, whose referents are NULL or which | |
452
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1367 // are not active (have a non-NULL next field). NOTE: When we are |
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1368 // thus precleaning the ref lists (which happens single-threaded today), |
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1369 // we do not disable refs discovery to honour the correct semantics of |
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1370 // java.lang.Reference. As a result, we need to be careful below |
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1371 // that ref removal steps interleave safely with ref discovery steps |
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1372 // (in this thread). |
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1373 void |
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1374 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1375 BoolObjectClosure* is_alive, |
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1376 OopClosure* keep_alive, |
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1377 VoidClosure* complete_gc, |
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1378 YieldClosure* yield) { |
0 | 1379 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
1380 while (iter.has_next()) { | |
1381 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1382 oop obj = iter.obj(); |
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1383 oop next = java_lang_ref_Reference::next(obj); |
0 | 1384 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1385 next != NULL) { |
0 | 1386 // The referent has been cleared, or is alive, or the Reference is not |
1387 // active; we need to trace and mark its cohort. | |
1388 if (TraceReferenceGC) { | |
1389 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
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1390 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 1391 } |
1392 // Remove Reference object from list | |
1393 iter.remove(); | |
1394 // Keep alive its cohort. | |
1395 iter.make_referent_alive(); | |
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1396 if (UseCompressedOops) { |
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1397 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1398 keep_alive->do_oop(next_addr); |
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1399 } else { |
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1400 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1401 keep_alive->do_oop(next_addr); |
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1402 } |
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1403 iter.move_to_next(); |
0 | 1404 } else { |
1405 iter.next(); | |
1406 } | |
1407 } | |
1408 // Close the reachable set | |
1409 complete_gc->do_void(); | |
1410 | |
1411 NOT_PRODUCT( | |
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1412 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) { |
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1413 gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
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1414 "Refs in discovered list " INTPTR_FORMAT, |
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1415 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 1416 } |
1417 ) | |
1418 } | |
1419 | |
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1420 const char* ReferenceProcessor::list_name(uint i) { |
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1421 assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(), |
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1422 "Out of bounds index"); |
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1423 |
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1424 int j = i / _max_num_q; |
0 | 1425 switch (j) { |
1426 case 0: return "SoftRef"; | |
1427 case 1: return "WeakRef"; | |
1428 case 2: return "FinalRef"; | |
1429 case 3: return "PhantomRef"; | |
1430 } | |
1431 ShouldNotReachHere(); | |
1432 return NULL; | |
1433 } | |
1434 | |
1435 #ifndef PRODUCT | |
1436 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
1437 // empty for now | |
1438 } | |
1439 #endif | |
1440 | |
1441 #ifndef PRODUCT | |
1442 void ReferenceProcessor::clear_discovered_references() { | |
1443 guarantee(!_discovering_refs, "Discovering refs?"); | |
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1444 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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1445 clear_discovered_references(_discovered_refs[i]); |
0 | 1446 } |
1447 } | |
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1448 |
0 | 1449 #endif // PRODUCT |