Mercurial > hg > graal-jvmci-8
annotate src/share/vm/memory/referenceProcessor.cpp @ 10032:4a7dc38ae96b
Checkstyle fixes
author | Christos Kotselidis <christos.kotselidis@oracle.com> |
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date | Wed, 12 Jun 2013 11:36:54 +0200 |
parents | ebb32c4589f3 |
children | 836a62f43af9 |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 2001, 2012, 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" | |
28 #include "gc_interface/collectedHeap.hpp" | |
29 #include "gc_interface/collectedHeap.inline.hpp" | |
30 #include "memory/referencePolicy.hpp" | |
31 #include "memory/referenceProcessor.hpp" | |
32 #include "oops/oop.inline.hpp" | |
33 #include "runtime/java.hpp" | |
34 #include "runtime/jniHandles.hpp" | |
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35 #ifdef GRAAL |
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36 #include "code/codeCache.hpp" |
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37 #include "code/nmethod.hpp" |
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38 #endif |
0 | 39 |
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40 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
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41 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
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42 bool ReferenceProcessor::_pending_list_uses_discovered_field = false; |
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43 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; |
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44 |
0 | 45 void referenceProcessor_init() { |
46 ReferenceProcessor::init_statics(); | |
47 } | |
48 | |
49 void ReferenceProcessor::init_statics() { | |
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50 // We need a monotonically non-deccreasing time in ms but |
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51 // os::javaTimeMillis() does not guarantee monotonicity. |
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52 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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53 |
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54 // Initialize the soft ref timestamp clock. |
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55 _soft_ref_timestamp_clock = now; |
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56 // Also update the soft ref clock in j.l.r.SoftReference |
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57 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); |
0 | 58 |
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59 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
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60 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
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61 NOT_COMPILER2(LRUCurrentHeapPolicy()); |
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62 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
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63 vm_exit_during_initialization("Could not allocate reference policy object"); |
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64 } |
0 | 65 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
66 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
67 "Unrecongnized RefDiscoveryPolicy"); | |
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68 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field(); |
0 | 69 } |
70 | |
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71 void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) { |
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72 #ifdef ASSERT |
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73 // Verify that we're not currently discovering refs |
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74 assert(!verify_disabled || !_discovering_refs, "nested call?"); |
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75 |
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76 if (check_no_refs) { |
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77 // Verify that the discovered lists are empty |
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78 verify_no_references_recorded(); |
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79 } |
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80 #endif // ASSERT |
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81 |
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82 // Someone could have modified the value of the static |
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83 // field in the j.l.r.SoftReference class that holds the |
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84 // soft reference timestamp clock using reflection or |
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85 // Unsafe between GCs. Unconditionally update the static |
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86 // field in ReferenceProcessor here so that we use the new |
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87 // value during reference discovery. |
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88 |
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89 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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90 _discovering_refs = true; |
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91 } |
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92 |
0 | 93 ReferenceProcessor::ReferenceProcessor(MemRegion span, |
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94 bool mt_processing, |
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95 uint mt_processing_degree, |
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96 bool mt_discovery, |
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97 uint mt_discovery_degree, |
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98 bool atomic_discovery, |
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99 BoolObjectClosure* is_alive_non_header, |
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100 bool discovered_list_needs_barrier) : |
0 | 101 _discovering_refs(false), |
102 _enqueuing_is_done(false), | |
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103 _is_alive_non_header(is_alive_non_header), |
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104 _discovered_list_needs_barrier(discovered_list_needs_barrier), |
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105 _bs(NULL), |
0 | 106 _processing_is_mt(mt_processing), |
107 _next_id(0) | |
108 { | |
109 _span = span; | |
110 _discovery_is_atomic = atomic_discovery; | |
111 _discovery_is_mt = mt_discovery; | |
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112 _num_q = MAX2(1U, mt_processing_degree); |
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113 _max_num_q = MAX2(_num_q, mt_discovery_degree); |
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114 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, |
6197 | 115 _max_num_q * number_of_subclasses_of_ref(), mtGC); |
116 | |
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117 if (_discovered_refs == NULL) { |
0 | 118 vm_exit_during_initialization("Could not allocated RefProc Array"); |
119 } | |
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120 _discoveredSoftRefs = &_discovered_refs[0]; |
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121 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
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122 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
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123 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
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124 |
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125 // Initialize all entries to NULL |
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126 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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127 _discovered_refs[i].set_head(NULL); |
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128 _discovered_refs[i].set_length(0); |
0 | 129 } |
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130 |
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131 // If we do barriers, cache a copy of the barrier set. |
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132 if (discovered_list_needs_barrier) { |
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133 _bs = Universe::heap()->barrier_set(); |
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134 } |
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135 setup_policy(false /* default soft ref policy */); |
0 | 136 } |
137 | |
138 #ifndef PRODUCT | |
139 void ReferenceProcessor::verify_no_references_recorded() { | |
140 guarantee(!_discovering_refs, "Discovering refs?"); | |
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141 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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142 guarantee(_discovered_refs[i].is_empty(), |
0 | 143 "Found non-empty discovered list"); |
144 } | |
145 } | |
146 #endif | |
147 | |
148 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
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149 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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150 if (UseCompressedOops) { |
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151 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); |
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152 } else { |
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153 f->do_oop((oop*)_discovered_refs[i].adr_head()); |
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154 } |
0 | 155 } |
156 } | |
157 | |
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158 void ReferenceProcessor::update_soft_ref_master_clock() { |
0 | 159 // Update (advance) the soft ref master clock field. This must be done |
160 // after processing the soft ref list. | |
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161 |
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162 // We need a monotonically non-deccreasing time in ms but |
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163 // os::javaTimeMillis() does not guarantee monotonicity. |
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164 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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165 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); |
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166 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); |
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167 |
0 | 168 NOT_PRODUCT( |
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169 if (now < _soft_ref_timestamp_clock) { |
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170 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, |
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171 _soft_ref_timestamp_clock, now); |
0 | 172 } |
173 ) | |
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174 // The values of now and _soft_ref_timestamp_clock are set using |
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175 // javaTimeNanos(), which is guaranteed to be monotonically |
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176 // non-decreasing provided the underlying platform provides such |
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177 // a time source (and it is bug free). |
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178 // In product mode, however, protect ourselves from non-monotonicty. |
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179 if (now > _soft_ref_timestamp_clock) { |
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180 _soft_ref_timestamp_clock = now; |
0 | 181 java_lang_ref_SoftReference::set_clock(now); |
182 } | |
183 // Else leave clock stalled at its old value until time progresses | |
184 // past clock value. | |
185 } | |
186 | |
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187 void ReferenceProcessor::process_discovered_references( |
0 | 188 BoolObjectClosure* is_alive, |
189 OopClosure* keep_alive, | |
190 VoidClosure* complete_gc, | |
191 AbstractRefProcTaskExecutor* task_executor) { | |
192 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
193 | |
194 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
195 // Stop treating discovered references specially. | |
196 disable_discovery(); | |
197 | |
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198 // If discovery was concurrent, someone could have modified |
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199 // the value of the static field in the j.l.r.SoftReference |
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200 // class that holds the soft reference timestamp clock using |
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201 // reflection or Unsafe between when discovery was enabled and |
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202 // now. Unconditionally update the static field in ReferenceProcessor |
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203 // here so that we use the new value during processing of the |
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204 // discovered soft refs. |
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205 |
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206 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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207 |
0 | 208 bool trace_time = PrintGCDetails && PrintReferenceGC; |
209 // Soft references | |
210 { | |
211 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); | |
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212 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, |
0 | 213 is_alive, keep_alive, complete_gc, task_executor); |
214 } | |
215 | |
216 update_soft_ref_master_clock(); | |
217 | |
218 // Weak references | |
219 { | |
220 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); | |
221 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
222 is_alive, keep_alive, complete_gc, task_executor); | |
223 } | |
224 | |
225 // Final references | |
226 { | |
227 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); | |
228 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
229 is_alive, keep_alive, complete_gc, task_executor); | |
230 } | |
231 | |
232 // Phantom references | |
233 { | |
234 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); | |
235 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
236 is_alive, keep_alive, complete_gc, task_executor); | |
237 } | |
238 | |
239 // Weak global JNI references. It would make more sense (semantically) to | |
240 // traverse these simultaneously with the regular weak references above, but | |
241 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
242 // thus use JNI weak references to circumvent the phantom references and | |
243 // resurrect a "post-mortem" object. | |
244 { | |
245 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); | |
246 if (task_executor != NULL) { | |
247 task_executor->set_single_threaded_mode(); | |
248 } | |
249 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
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250 #ifdef GRAAL |
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251 process_phaseGraalNMethods(keep_alive, complete_gc); |
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252 #endif |
0 | 253 } |
254 } | |
255 | |
256 #ifndef PRODUCT | |
257 // Calculate the number of jni handles. | |
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258 uint ReferenceProcessor::count_jni_refs() { |
0 | 259 class AlwaysAliveClosure: public BoolObjectClosure { |
260 public: | |
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261 virtual bool do_object_b(oop obj) { return true; } |
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262 virtual void do_object(oop obj) { assert(false, "Don't call"); } |
0 | 263 }; |
264 | |
265 class CountHandleClosure: public OopClosure { | |
266 private: | |
267 int _count; | |
268 public: | |
269 CountHandleClosure(): _count(0) {} | |
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270 void do_oop(oop* unused) { _count++; } |
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271 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
0 | 272 int count() { return _count; } |
273 }; | |
274 CountHandleClosure global_handle_count; | |
275 AlwaysAliveClosure always_alive; | |
276 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
277 return global_handle_count.count(); | |
278 } | |
279 #endif | |
280 | |
281 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
282 OopClosure* keep_alive, | |
283 VoidClosure* complete_gc) { | |
284 #ifndef PRODUCT | |
285 if (PrintGCDetails && PrintReferenceGC) { | |
286 unsigned int count = count_jni_refs(); | |
287 gclog_or_tty->print(", %u refs", count); | |
288 } | |
289 #endif | |
290 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
291 complete_gc->do_void(); | |
292 } | |
293 | |
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294 #ifdef GRAAL |
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295 void ReferenceProcessor::process_phaseGraalNMethods(OopClosure* keep_alive, |
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296 VoidClosure* complete_gc) { |
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297 CodeCache::alive_nmethods_do_graal_methods(keep_alive); |
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298 complete_gc->do_void(); |
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299 } |
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300 |
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301 #endif |
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302 |
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303 template <class T> |
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304 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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305 AbstractRefProcTaskExecutor* task_executor) { |
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306 |
0 | 307 // Remember old value of pending references list |
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308 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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309 T old_pending_list_value = *pending_list_addr; |
0 | 310 |
311 // Enqueue references that are not made active again, and | |
312 // clear the decks for the next collection (cycle). | |
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313 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
0 | 314 // Do the oop-check on pending_list_addr missed in |
315 // enqueue_discovered_reflist. We should probably | |
316 // do a raw oop_check so that future such idempotent | |
317 // oop_stores relying on the oop-check side-effect | |
318 // may be elided automatically and safely without | |
319 // affecting correctness. | |
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320 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
0 | 321 |
322 // Stop treating discovered references specially. | |
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323 ref->disable_discovery(); |
0 | 324 |
325 // Return true if new pending references were added | |
326 return old_pending_list_value != *pending_list_addr; | |
327 } | |
328 | |
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329 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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330 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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331 if (UseCompressedOops) { |
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332 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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333 } else { |
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334 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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335 } |
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336 } |
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337 |
0 | 338 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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339 HeapWord* pending_list_addr) { |
0 | 340 // Given a list of refs linked through the "discovered" field |
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341 // (java.lang.ref.Reference.discovered), self-loop their "next" field |
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342 // thus distinguishing them from active References, then |
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343 // prepend them to the pending list. |
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344 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777), |
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345 // the "next" field is used to chain the pending list, not the discovered |
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346 // field. |
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347 |
0 | 348 if (TraceReferenceGC && PrintGCDetails) { |
349 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
350 INTPTR_FORMAT, (address)refs_list.head()); | |
351 } | |
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352 |
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353 oop obj = NULL; |
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354 oop next_d = refs_list.head(); |
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355 if (pending_list_uses_discovered_field()) { // New behaviour |
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356 // Walk down the list, self-looping the next field |
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357 // so that the References are not considered active. |
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358 while (obj != next_d) { |
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359 obj = next_d; |
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360 assert(obj->is_instanceRef(), "should be reference object"); |
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361 next_d = java_lang_ref_Reference::discovered(obj); |
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362 if (TraceReferenceGC && PrintGCDetails) { |
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363 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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364 obj, next_d); |
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365 } |
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366 assert(java_lang_ref_Reference::next(obj) == NULL, |
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367 "Reference not active; should not be discovered"); |
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368 // Self-loop next, so as to make Ref not active. |
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369 java_lang_ref_Reference::set_next(obj, obj); |
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370 if (next_d == obj) { // obj is last |
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371 // Swap refs_list into pendling_list_addr and |
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372 // set obj's discovered to what we read from pending_list_addr. |
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373 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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374 // Need oop_check on pending_list_addr above; |
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375 // see special oop-check code at the end of |
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376 // enqueue_discovered_reflists() further below. |
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377 java_lang_ref_Reference::set_discovered(obj, old); // old may be NULL |
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378 } |
0 | 379 } |
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380 } else { // Old behaviour |
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381 // Walk down the list, copying the discovered field into |
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382 // the next field and clearing the discovered field. |
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383 while (obj != next_d) { |
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384 obj = next_d; |
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385 assert(obj->is_instanceRef(), "should be reference object"); |
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386 next_d = java_lang_ref_Reference::discovered(obj); |
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387 if (TraceReferenceGC && PrintGCDetails) { |
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388 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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389 obj, next_d); |
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390 } |
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391 assert(java_lang_ref_Reference::next(obj) == NULL, |
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392 "The reference should not be enqueued"); |
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393 if (next_d == obj) { // obj is last |
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394 // Swap refs_list into pendling_list_addr and |
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395 // set obj's next to what we read from pending_list_addr. |
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396 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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397 // Need oop_check on pending_list_addr above; |
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398 // see special oop-check code at the end of |
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399 // enqueue_discovered_reflists() further below. |
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400 if (old == NULL) { |
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401 // obj should be made to point to itself, since |
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402 // pending list was empty. |
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403 java_lang_ref_Reference::set_next(obj, obj); |
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404 } else { |
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405 java_lang_ref_Reference::set_next(obj, old); |
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406 } |
0 | 407 } else { |
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408 java_lang_ref_Reference::set_next(obj, next_d); |
0 | 409 } |
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410 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); |
0 | 411 } |
412 } | |
413 } | |
414 | |
415 // Parallel enqueue task | |
416 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
417 public: | |
418 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
419 DiscoveredList discovered_refs[], | |
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420 HeapWord* pending_list_addr, |
0 | 421 int n_queues) |
422 : EnqueueTask(ref_processor, discovered_refs, | |
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423 pending_list_addr, n_queues) |
0 | 424 { } |
425 | |
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426 virtual void work(unsigned int work_id) { |
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427 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); |
0 | 428 // Simplest first cut: static partitioning. |
429 int index = work_id; | |
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430 // The increment on "index" must correspond to the maximum number of queues |
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431 // (n_queues) with which that ReferenceProcessor was created. That |
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432 // is because of the "clever" way the discovered references lists were |
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433 // allocated and are indexed into. |
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434 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); |
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435 for (int j = 0; |
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436 j < ReferenceProcessor::number_of_subclasses_of_ref(); |
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437 j++, index += _n_queues) { |
0 | 438 _ref_processor.enqueue_discovered_reflist( |
439 _refs_lists[index], _pending_list_addr); | |
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440 _refs_lists[index].set_head(NULL); |
0 | 441 _refs_lists[index].set_length(0); |
442 } | |
443 } | |
444 }; | |
445 | |
446 // Enqueue references that are not made active again | |
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447 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
0 | 448 AbstractRefProcTaskExecutor* task_executor) { |
449 if (_processing_is_mt && task_executor != NULL) { | |
450 // Parallel code | |
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451 RefProcEnqueueTask tsk(*this, _discovered_refs, |
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452 pending_list_addr, _max_num_q); |
0 | 453 task_executor->execute(tsk); |
454 } else { | |
455 // Serial code: call the parent class's implementation | |
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456 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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457 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr); |
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458 _discovered_refs[i].set_head(NULL); |
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459 _discovered_refs[i].set_length(0); |
0 | 460 } |
461 } | |
462 } | |
463 | |
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464 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
0 | 465 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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466 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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467 assert(_discovered_addr && discovered->is_oop_or_null(), |
0 | 468 "discovered field is bad"); |
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469 _next = discovered; |
0 | 470 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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471 _referent = java_lang_ref_Reference::referent(_ref); |
0 | 472 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
473 "Wrong oop found in java.lang.Reference object"); | |
474 assert(allow_null_referent ? | |
475 _referent->is_oop_or_null() | |
476 : _referent->is_oop(), | |
477 "bad referent"); | |
478 } | |
479 | |
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480 void DiscoveredListIterator::remove() { |
0 | 481 assert(_ref->is_oop(), "Dropping a bad reference"); |
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482 oop_store_raw(_discovered_addr, NULL); |
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483 |
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484 // First _prev_next ref actually points into DiscoveredList (gross). |
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485 oop new_next; |
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486 if (_next == _ref) { |
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487 // At the end of the list, we should make _prev point to itself. |
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488 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, |
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489 // and _prev will be NULL. |
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490 new_next = _prev; |
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491 } else { |
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492 new_next = _next; |
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493 } |
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494 |
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495 if (UseCompressedOops) { |
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496 // Remove Reference object from list. |
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497 oopDesc::encode_store_heap_oop((narrowOop*)_prev_next, new_next); |
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498 } else { |
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499 // Remove Reference object from list. |
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500 oopDesc::store_heap_oop((oop*)_prev_next, new_next); |
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501 } |
0 | 502 NOT_PRODUCT(_removed++); |
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503 _refs_list.dec_length(1); |
0 | 504 } |
505 | |
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506 // Make the Reference object active again. |
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507 void DiscoveredListIterator::make_active() { |
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508 // For G1 we don't want to use set_next - it |
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509 // will dirty the card for the next field of |
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510 // the reference object and will fail |
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511 // CT verification. |
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512 if (UseG1GC) { |
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513 BarrierSet* bs = oopDesc::bs(); |
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514 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref); |
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515 |
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516 if (UseCompressedOops) { |
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517 bs->write_ref_field_pre((narrowOop*)next_addr, NULL); |
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518 } else { |
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519 bs->write_ref_field_pre((oop*)next_addr, NULL); |
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520 } |
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521 java_lang_ref_Reference::set_next_raw(_ref, NULL); |
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522 } else { |
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523 java_lang_ref_Reference::set_next(_ref, NULL); |
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524 } |
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525 } |
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526 |
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527 void DiscoveredListIterator::clear_referent() { |
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528 oop_store_raw(_referent_addr, NULL); |
0 | 529 } |
530 | |
531 // NOTE: process_phase*() are largely similar, and at a high level | |
532 // merely iterate over the extant list applying a predicate to | |
533 // each of its elements and possibly removing that element from the | |
534 // list and applying some further closures to that element. | |
535 // We should consider the possibility of replacing these | |
536 // process_phase*() methods by abstracting them into | |
537 // a single general iterator invocation that receives appropriate | |
538 // closures that accomplish this work. | |
539 | |
540 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
541 // referents are not alive, but that should be kept alive for policy reasons. | |
542 // Keep alive the transitive closure of all such referents. | |
543 void | |
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544 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
0 | 545 ReferencePolicy* policy, |
546 BoolObjectClosure* is_alive, | |
547 OopClosure* keep_alive, | |
548 VoidClosure* complete_gc) { | |
549 assert(policy != NULL, "Must have a non-NULL policy"); | |
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550 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 551 // Decide which softly reachable refs should be kept alive. |
552 while (iter.has_next()) { | |
553 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
554 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
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555 if (referent_is_dead && |
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556 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { |
0 | 557 if (TraceReferenceGC) { |
558 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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559 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 560 } |
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561 // Remove Reference object from list |
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562 iter.remove(); |
0 | 563 // Make the Reference object active again |
564 iter.make_active(); | |
565 // keep the referent around | |
566 iter.make_referent_alive(); | |
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567 iter.move_to_next(); |
0 | 568 } else { |
569 iter.next(); | |
570 } | |
571 } | |
572 // Close the reachable set | |
573 complete_gc->do_void(); | |
574 NOT_PRODUCT( | |
575 if (PrintGCDetails && TraceReferenceGC) { | |
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576 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
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577 "discovered Refs by policy, from list " INTPTR_FORMAT, |
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578 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 579 } |
580 ) | |
581 } | |
582 | |
583 // Traverse the list and remove any Refs that are not active, or | |
584 // whose referents are either alive or NULL. | |
585 void | |
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586 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
0 | 587 BoolObjectClosure* is_alive, |
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588 OopClosure* keep_alive) { |
0 | 589 assert(discovery_is_atomic(), "Error"); |
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590 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 591 while (iter.has_next()) { |
592 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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593 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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594 assert(next == NULL, "Should not discover inactive Reference"); |
0 | 595 if (iter.is_referent_alive()) { |
596 if (TraceReferenceGC) { | |
597 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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598 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 599 } |
600 // The referent is reachable after all. | |
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601 // Remove Reference object from list. |
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602 iter.remove(); |
0 | 603 // Update the referent pointer as necessary: Note that this |
604 // should not entail any recursive marking because the | |
605 // referent must already have been traversed. | |
606 iter.make_referent_alive(); | |
452
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607 iter.move_to_next(); |
0 | 608 } else { |
609 iter.next(); | |
610 } | |
611 } | |
612 NOT_PRODUCT( | |
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613 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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614 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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615 "Refs in discovered list " INTPTR_FORMAT, |
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616 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 617 } |
618 ) | |
619 } | |
620 | |
621 void | |
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622 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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623 BoolObjectClosure* is_alive, |
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624 OopClosure* keep_alive, |
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625 VoidClosure* complete_gc) { |
0 | 626 assert(!discovery_is_atomic(), "Error"); |
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627 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 628 while (iter.has_next()) { |
629 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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630 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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631 oop next = java_lang_ref_Reference::next(iter.obj()); |
0 | 632 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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633 next != NULL)) { |
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634 assert(next->is_oop_or_null(), "bad next field"); |
0 | 635 // Remove Reference object from list |
636 iter.remove(); | |
637 // Trace the cohorts | |
638 iter.make_referent_alive(); | |
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639 if (UseCompressedOops) { |
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640 keep_alive->do_oop((narrowOop*)next_addr); |
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641 } else { |
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642 keep_alive->do_oop((oop*)next_addr); |
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643 } |
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644 iter.move_to_next(); |
0 | 645 } else { |
646 iter.next(); | |
647 } | |
648 } | |
649 // Now close the newly reachable set | |
650 complete_gc->do_void(); | |
651 NOT_PRODUCT( | |
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652 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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653 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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654 "Refs in discovered list " INTPTR_FORMAT, |
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655 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 656 } |
657 ) | |
658 } | |
659 | |
660 // Traverse the list and process the referents, by either | |
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661 // clearing them or keeping them (and their reachable |
0 | 662 // closure) alive. |
663 void | |
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664 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
0 | 665 bool clear_referent, |
666 BoolObjectClosure* is_alive, | |
667 OopClosure* keep_alive, | |
668 VoidClosure* complete_gc) { | |
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669 ResourceMark rm; |
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670 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 671 while (iter.has_next()) { |
672 iter.update_discovered(); | |
673 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
674 if (clear_referent) { | |
675 // NULL out referent pointer | |
676 iter.clear_referent(); | |
677 } else { | |
678 // keep the referent around | |
679 iter.make_referent_alive(); | |
680 } | |
681 if (TraceReferenceGC) { | |
682 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
683 clear_referent ? "cleared " : "", | |
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684 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 685 } |
686 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
687 iter.next(); | |
688 } | |
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689 // Remember to update the next pointer of the last ref. |
0 | 690 iter.update_discovered(); |
691 // Close the reachable set | |
692 complete_gc->do_void(); | |
693 } | |
694 | |
695 void | |
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696 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { |
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697 oop obj = NULL; |
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698 oop next = refs_list.head(); |
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699 while (next != obj) { |
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700 obj = next; |
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701 next = java_lang_ref_Reference::discovered(obj); |
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702 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
0 | 703 } |
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704 refs_list.set_head(NULL); |
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705 refs_list.set_length(0); |
0 | 706 } |
707 | |
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708 void |
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709 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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710 clear_discovered_references(refs_list); |
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711 } |
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712 |
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713 void ReferenceProcessor::abandon_partial_discovery() { |
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714 // loop over the lists |
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715 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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716 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
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717 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i)); |
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718 } |
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719 abandon_partial_discovered_list(_discovered_refs[i]); |
0 | 720 } |
721 } | |
722 | |
723 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
724 public: | |
725 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
726 DiscoveredList refs_lists[], | |
727 ReferencePolicy* policy, | |
728 bool marks_oops_alive) | |
729 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
730 _policy(policy) | |
731 { } | |
732 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
733 OopClosure& keep_alive, | |
734 VoidClosure& complete_gc) | |
735 { | |
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736 Thread* thr = Thread::current(); |
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737 int refs_list_index = ((WorkerThread*)thr)->id(); |
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738 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
0 | 739 &is_alive, &keep_alive, &complete_gc); |
740 } | |
741 private: | |
742 ReferencePolicy* _policy; | |
743 }; | |
744 | |
745 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
746 public: | |
747 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
748 DiscoveredList refs_lists[], | |
749 bool marks_oops_alive) | |
750 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
751 { } | |
752 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
753 OopClosure& keep_alive, | |
754 VoidClosure& complete_gc) | |
755 { | |
756 _ref_processor.process_phase2(_refs_lists[i], | |
757 &is_alive, &keep_alive, &complete_gc); | |
758 } | |
759 }; | |
760 | |
761 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
762 public: | |
763 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
764 DiscoveredList refs_lists[], | |
765 bool clear_referent, | |
766 bool marks_oops_alive) | |
767 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
768 _clear_referent(clear_referent) | |
769 { } | |
770 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
771 OopClosure& keep_alive, | |
772 VoidClosure& complete_gc) | |
773 { | |
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774 // Don't use "refs_list_index" calculated in this way because |
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775 // balance_queues() has moved the Ref's into the first n queues. |
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776 // Thread* thr = Thread::current(); |
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777 // int refs_list_index = ((WorkerThread*)thr)->id(); |
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778 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
0 | 779 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
780 &is_alive, &keep_alive, &complete_gc); | |
781 } | |
782 private: | |
783 bool _clear_referent; | |
784 }; | |
785 | |
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786 void ReferenceProcessor::set_discovered(oop ref, oop value) { |
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787 if (_discovered_list_needs_barrier) { |
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788 java_lang_ref_Reference::set_discovered(ref, value); |
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789 } else { |
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790 java_lang_ref_Reference::set_discovered_raw(ref, value); |
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791 } |
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792 } |
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793 |
0 | 794 // Balances reference queues. |
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795 // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
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796 // queues[0, 1, ..., _num_q-1] because only the first _num_q |
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797 // corresponding to the active workers will be processed. |
0 | 798 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
799 { | |
800 // calculate total length | |
801 size_t total_refs = 0; | |
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802 if (TraceReferenceGC && PrintGCDetails) { |
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803 gclog_or_tty->print_cr("\nBalance ref_lists "); |
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804 } |
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805 |
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806 for (uint i = 0; i < _max_num_q; ++i) { |
0 | 807 total_refs += ref_lists[i].length(); |
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808 if (TraceReferenceGC && PrintGCDetails) { |
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809 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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810 } |
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811 } |
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812 if (TraceReferenceGC && PrintGCDetails) { |
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813 gclog_or_tty->print_cr(" = %d", total_refs); |
0 | 814 } |
815 size_t avg_refs = total_refs / _num_q + 1; | |
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816 uint to_idx = 0; |
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817 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { |
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818 bool move_all = false; |
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819 if (from_idx >= _num_q) { |
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820 move_all = ref_lists[from_idx].length() > 0; |
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821 } |
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822 while ((ref_lists[from_idx].length() > avg_refs) || |
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823 move_all) { |
0 | 824 assert(to_idx < _num_q, "Sanity Check!"); |
825 if (ref_lists[to_idx].length() < avg_refs) { | |
826 // move superfluous refs | |
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827 size_t refs_to_move; |
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828 // Move all the Ref's if the from queue will not be processed. |
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829 if (move_all) { |
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830 refs_to_move = MIN2(ref_lists[from_idx].length(), |
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831 avg_refs - ref_lists[to_idx].length()); |
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832 } else { |
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833 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
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834 avg_refs - ref_lists[to_idx].length()); |
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835 } |
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836 |
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837 assert(refs_to_move > 0, "otherwise the code below will fail"); |
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838 |
0 | 839 oop move_head = ref_lists[from_idx].head(); |
840 oop move_tail = move_head; | |
841 oop new_head = move_head; | |
842 // find an element to split the list on | |
843 for (size_t j = 0; j < refs_to_move; ++j) { | |
844 move_tail = new_head; | |
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845 new_head = java_lang_ref_Reference::discovered(new_head); |
0 | 846 } |
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847 |
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848 // Add the chain to the to list. |
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849 if (ref_lists[to_idx].head() == NULL) { |
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850 // to list is empty. Make a loop at the end. |
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851 set_discovered(move_tail, move_tail); |
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852 } else { |
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853 set_discovered(move_tail, ref_lists[to_idx].head()); |
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854 } |
0 | 855 ref_lists[to_idx].set_head(move_head); |
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856 ref_lists[to_idx].inc_length(refs_to_move); |
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857 |
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858 // Remove the chain from the from list. |
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859 if (move_tail == new_head) { |
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860 // We found the end of the from list. |
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861 ref_lists[from_idx].set_head(NULL); |
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862 } else { |
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863 ref_lists[from_idx].set_head(new_head); |
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864 } |
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865 ref_lists[from_idx].dec_length(refs_to_move); |
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866 if (ref_lists[from_idx].length() == 0) { |
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867 break; |
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868 } |
0 | 869 } else { |
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870 to_idx = (to_idx + 1) % _num_q; |
0 | 871 } |
872 } | |
873 } | |
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874 #ifdef ASSERT |
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875 size_t balanced_total_refs = 0; |
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876 for (uint i = 0; i < _max_num_q; ++i) { |
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877 balanced_total_refs += ref_lists[i].length(); |
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878 if (TraceReferenceGC && PrintGCDetails) { |
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879 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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880 } |
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881 } |
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882 if (TraceReferenceGC && PrintGCDetails) { |
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883 gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
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884 gclog_or_tty->flush(); |
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885 } |
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886 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
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887 #endif |
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888 } |
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889 |
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890 void ReferenceProcessor::balance_all_queues() { |
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891 balance_queues(_discoveredSoftRefs); |
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892 balance_queues(_discoveredWeakRefs); |
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893 balance_queues(_discoveredFinalRefs); |
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894 balance_queues(_discoveredPhantomRefs); |
0 | 895 } |
896 | |
897 void | |
898 ReferenceProcessor::process_discovered_reflist( | |
899 DiscoveredList refs_lists[], | |
900 ReferencePolicy* policy, | |
901 bool clear_referent, | |
902 BoolObjectClosure* is_alive, | |
903 OopClosure* keep_alive, | |
904 VoidClosure* complete_gc, | |
905 AbstractRefProcTaskExecutor* task_executor) | |
906 { | |
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907 bool mt_processing = task_executor != NULL && _processing_is_mt; |
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908 // If discovery used MT and a dynamic number of GC threads, then |
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909 // the queues must be balanced for correctness if fewer than the |
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910 // maximum number of queues were used. The number of queue used |
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911 // during discovery may be different than the number to be used |
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912 // for processing so don't depend of _num_q < _max_num_q as part |
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913 // of the test. |
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914 bool must_balance = _discovery_is_mt; |
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915 |
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916 if ((mt_processing && ParallelRefProcBalancingEnabled) || |
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917 must_balance) { |
0 | 918 balance_queues(refs_lists); |
919 } | |
920 if (PrintReferenceGC && PrintGCDetails) { | |
921 size_t total = 0; | |
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922 for (uint i = 0; i < _max_num_q; ++i) { |
0 | 923 total += refs_lists[i].length(); |
924 } | |
925 gclog_or_tty->print(", %u refs", total); | |
926 } | |
927 | |
928 // Phase 1 (soft refs only): | |
929 // . Traverse the list and remove any SoftReferences whose | |
930 // referents are not alive, but that should be kept alive for | |
931 // policy reasons. Keep alive the transitive closure of all | |
932 // such referents. | |
933 if (policy != NULL) { | |
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934 if (mt_processing) { |
0 | 935 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
936 task_executor->execute(phase1); | |
937 } else { | |
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938 for (uint i = 0; i < _max_num_q; i++) { |
0 | 939 process_phase1(refs_lists[i], policy, |
940 is_alive, keep_alive, complete_gc); | |
941 } | |
942 } | |
943 } else { // policy == NULL | |
944 assert(refs_lists != _discoveredSoftRefs, | |
945 "Policy must be specified for soft references."); | |
946 } | |
947 | |
948 // Phase 2: | |
949 // . Traverse the list and remove any refs whose referents are alive. | |
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950 if (mt_processing) { |
0 | 951 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
952 task_executor->execute(phase2); | |
953 } else { | |
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954 for (uint i = 0; i < _max_num_q; i++) { |
0 | 955 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); |
956 } | |
957 } | |
958 | |
959 // Phase 3: | |
960 // . Traverse the list and process referents as appropriate. | |
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961 if (mt_processing) { |
0 | 962 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
963 task_executor->execute(phase3); | |
964 } else { | |
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965 for (uint i = 0; i < _max_num_q; i++) { |
0 | 966 process_phase3(refs_lists[i], clear_referent, |
967 is_alive, keep_alive, complete_gc); | |
968 } | |
969 } | |
970 } | |
971 | |
972 void ReferenceProcessor::clean_up_discovered_references() { | |
973 // loop over the lists | |
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974 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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975 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
0 | 976 gclog_or_tty->print_cr( |
977 "\nScrubbing %s discovered list of Null referents", | |
978 list_name(i)); | |
979 } | |
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980 clean_up_discovered_reflist(_discovered_refs[i]); |
0 | 981 } |
982 } | |
983 | |
984 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
985 assert(!discovery_is_atomic(), "Else why call this method?"); | |
986 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
987 while (iter.has_next()) { | |
988 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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989 oop next = java_lang_ref_Reference::next(iter.obj()); |
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990 assert(next->is_oop_or_null(), "bad next field"); |
0 | 991 // If referent has been cleared or Reference is not active, |
992 // drop it. | |
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993 if (iter.referent() == NULL || next != NULL) { |
0 | 994 debug_only( |
995 if (PrintGCDetails && TraceReferenceGC) { | |
996 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
997 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
998 " and referent: " INTPTR_FORMAT, | |
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999 iter.obj(), next, iter.referent()); |
0 | 1000 } |
1001 ) | |
1002 // Remove Reference object from list | |
1003 iter.remove(); | |
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1004 iter.move_to_next(); |
0 | 1005 } else { |
1006 iter.next(); | |
1007 } | |
1008 } | |
1009 NOT_PRODUCT( | |
1010 if (PrintGCDetails && TraceReferenceGC) { | |
1011 gclog_or_tty->print( | |
1012 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
1013 iter.removed(), iter.processed()); | |
1014 } | |
1015 ) | |
1016 } | |
1017 | |
1018 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
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1019 uint id = 0; |
0 | 1020 // Determine the queue index to use for this object. |
1021 if (_discovery_is_mt) { | |
1022 // During a multi-threaded discovery phase, | |
1023 // each thread saves to its "own" list. | |
1024 Thread* thr = Thread::current(); | |
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1025 id = thr->as_Worker_thread()->id(); |
0 | 1026 } else { |
1027 // single-threaded discovery, we save in round-robin | |
1028 // fashion to each of the lists. | |
1029 if (_processing_is_mt) { | |
1030 id = next_id(); | |
1031 } | |
1032 } | |
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1033 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
0 | 1034 |
1035 // Get the discovered queue to which we will add | |
1036 DiscoveredList* list = NULL; | |
1037 switch (rt) { | |
1038 case REF_OTHER: | |
1039 // Unknown reference type, no special treatment | |
1040 break; | |
1041 case REF_SOFT: | |
1042 list = &_discoveredSoftRefs[id]; | |
1043 break; | |
1044 case REF_WEAK: | |
1045 list = &_discoveredWeakRefs[id]; | |
1046 break; | |
1047 case REF_FINAL: | |
1048 list = &_discoveredFinalRefs[id]; | |
1049 break; | |
1050 case REF_PHANTOM: | |
1051 list = &_discoveredPhantomRefs[id]; | |
1052 break; | |
1053 case REF_NONE: | |
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1054 // we should not reach here if we are an InstanceRefKlass |
0 | 1055 default: |
1056 ShouldNotReachHere(); | |
1057 } | |
1833
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1058 if (TraceReferenceGC && PrintGCDetails) { |
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1059 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); |
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1060 } |
0 | 1061 return list; |
1062 } | |
1063 | |
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1064 inline void |
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1065 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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1066 oop obj, |
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1067 HeapWord* discovered_addr) { |
0 | 1068 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
1069 // First we must make sure this object is only enqueued once. CAS in a non null | |
1070 // discovered_addr. | |
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1071 oop current_head = refs_list.head(); |
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1072 // The last ref must have its discovered field pointing to itself. |
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1073 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1074 |
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1075 // Note: In the case of G1, this specific pre-barrier is strictly |
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1076 // not necessary because the only case we are interested in |
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1077 // here is when *discovered_addr is NULL (see the CAS further below), |
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1078 // so this will expand to nothing. As a result, we have manually |
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1079 // elided this out for G1, but left in the test for some future |
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1080 // collector that might have need for a pre-barrier here, e.g.:- |
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1081 // _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1082 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1083 "Need to check non-G1 collector: " |
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1084 "may need a pre-write-barrier for CAS from NULL below"); |
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1085 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, |
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1086 NULL); |
0 | 1087 if (retest == NULL) { |
1088 // This thread just won the right to enqueue the object. | |
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1089 // We have separate lists for enqueueing, so no synchronization |
0 | 1090 // is necessary. |
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1091 refs_list.set_head(obj); |
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1092 refs_list.inc_length(1); |
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1093 if (_discovered_list_needs_barrier) { |
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1094 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1095 } |
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1096 |
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1097 if (TraceReferenceGC) { |
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1098 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", |
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1099 obj, obj->klass()->internal_name()); |
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1100 } |
0 | 1101 } else { |
1102 // If retest was non NULL, another thread beat us to it: | |
1103 // The reference has already been discovered... | |
1104 if (TraceReferenceGC) { | |
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1105 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1106 obj, obj->klass()->internal_name()); |
0 | 1107 } |
1108 } | |
1109 } | |
1110 | |
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1111 #ifndef PRODUCT |
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1112 // Non-atomic (i.e. concurrent) discovery might allow us |
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1113 // to observe j.l.References with NULL referents, being those |
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1114 // cleared concurrently by mutators during (or after) discovery. |
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1115 void ReferenceProcessor::verify_referent(oop obj) { |
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1116 bool da = discovery_is_atomic(); |
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1117 oop referent = java_lang_ref_Reference::referent(obj); |
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1118 assert(da ? referent->is_oop() : referent->is_oop_or_null(), |
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1119 err_msg("Bad referent " INTPTR_FORMAT " found in Reference " |
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1120 INTPTR_FORMAT " during %satomic discovery ", |
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1121 (intptr_t)referent, (intptr_t)obj, da ? "" : "non-")); |
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1122 } |
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1123 #endif |
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1124 |
0 | 1125 // We mention two of several possible choices here: |
1126 // #0: if the reference object is not in the "originating generation" | |
1127 // (or part of the heap being collected, indicated by our "span" | |
1128 // we don't treat it specially (i.e. we scan it as we would | |
1129 // a normal oop, treating its references as strong references). | |
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1130 // This means that references can't be discovered unless their |
0 | 1131 // referent is also in the same span. This is the simplest, |
1132 // most "local" and most conservative approach, albeit one | |
1133 // that may cause weak references to be enqueued least promptly. | |
1134 // We call this choice the "ReferenceBasedDiscovery" policy. | |
1135 // #1: the reference object may be in any generation (span), but if | |
1136 // the referent is in the generation (span) being currently collected | |
1137 // then we can discover the reference object, provided | |
1138 // the object has not already been discovered by | |
1139 // a different concurrently running collector (as may be the | |
1140 // case, for instance, if the reference object is in CMS and | |
1141 // the referent in DefNewGeneration), and provided the processing | |
1142 // of this reference object by the current collector will | |
1143 // appear atomic to every other collector in the system. | |
1144 // (Thus, for instance, a concurrent collector may not | |
1145 // discover references in other generations even if the | |
1146 // referent is in its own generation). This policy may, | |
1147 // in certain cases, enqueue references somewhat sooner than | |
1148 // might Policy #0 above, but at marginally increased cost | |
1149 // and complexity in processing these references. | |
1150 // We call this choice the "RefeferentBasedDiscovery" policy. | |
1151 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
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1152 // Make sure we are discovering refs (rather than processing discovered refs). |
0 | 1153 if (!_discovering_refs || !RegisterReferences) { |
1154 return false; | |
1155 } | |
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1156 // We only discover active references. |
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1157 oop next = java_lang_ref_Reference::next(obj); |
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1158 if (next != NULL) { // Ref is no longer active |
0 | 1159 return false; |
1160 } | |
1161 | |
1162 HeapWord* obj_addr = (HeapWord*)obj; | |
1163 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1164 !_span.contains(obj_addr)) { | |
1165 // Reference is not in the originating generation; | |
1166 // don't treat it specially (i.e. we want to scan it as a normal | |
1167 // object with strong references). | |
1168 return false; | |
1169 } | |
1170 | |
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1171 // We only discover references whose referents are not (yet) |
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1172 // known to be strongly reachable. |
0 | 1173 if (is_alive_non_header() != NULL) { |
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1174 verify_referent(obj); |
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1175 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { |
0 | 1176 return false; // referent is reachable |
1177 } | |
1178 } | |
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1179 if (rt == REF_SOFT) { |
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1180 // For soft refs we can decide now if these are not |
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1181 // current candidates for clearing, in which case we |
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1182 // can mark through them now, rather than delaying that |
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1183 // to the reference-processing phase. Since all current |
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1184 // time-stamp policies advance the soft-ref clock only |
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1185 // at a major collection cycle, this is always currently |
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1186 // accurate. |
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1187 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { |
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1188 return false; |
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1189 } |
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1190 } |
0 | 1191 |
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1192 ResourceMark rm; // Needed for tracing. |
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1193 |
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1194 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1195 const oop discovered = java_lang_ref_Reference::discovered(obj); |
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1196 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1197 if (discovered != NULL) { |
0 | 1198 // The reference has already been discovered... |
1199 if (TraceReferenceGC) { | |
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1200 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1201 obj, obj->klass()->internal_name()); |
0 | 1202 } |
1203 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1204 // assumes that an object is not processed twice; | |
1205 // if it's been already discovered it must be on another | |
1206 // generation's discovered list; so we won't discover it. | |
1207 return false; | |
1208 } else { | |
1209 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
1210 "Unrecognized policy"); | |
1211 // Check assumption that an object is not potentially | |
1212 // discovered twice except by concurrent collectors that potentially | |
1213 // trace the same Reference object twice. | |
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1214 assert(UseConcMarkSweepGC || UseG1GC, |
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1215 "Only possible with a concurrent marking collector"); |
0 | 1216 return true; |
1217 } | |
1218 } | |
1219 | |
1220 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
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1221 verify_referent(obj); |
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1222 // Discover if and only if EITHER: |
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1223 // .. reference is in our span, OR |
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1224 // .. we are an atomic collector and referent is in our span |
0 | 1225 if (_span.contains(obj_addr) || |
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1226 (discovery_is_atomic() && |
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1227 _span.contains(java_lang_ref_Reference::referent(obj)))) { |
0 | 1228 // should_enqueue = true; |
1229 } else { | |
1230 return false; | |
1231 } | |
1232 } else { | |
1233 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1234 _span.contains(obj_addr), "code inconsistency"); | |
1235 } | |
1236 | |
1237 // Get the right type of discovered queue head. | |
1238 DiscoveredList* list = get_discovered_list(rt); | |
1239 if (list == NULL) { | |
1240 return false; // nothing special needs to be done | |
1241 } | |
1242 | |
1243 if (_discovery_is_mt) { | |
1244 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
1245 } else { | |
342
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1246 // If "_discovered_list_needs_barrier", we do write barriers when |
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1247 // updating the discovered reference list. Otherwise, we do a raw store |
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1248 // here: the field will be visited later when processing the discovered |
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1249 // references. |
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1250 oop current_head = list->head(); |
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1251 // The last ref must have its discovered field pointing to itself. |
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1252 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1253 |
342
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1254 // As in the case further above, since we are over-writing a NULL |
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1255 // pre-value, we can safely elide the pre-barrier here for the case of G1. |
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1256 // e.g.:- _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
342
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1257 assert(discovered == NULL, "control point invariant"); |
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1258 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1259 "For non-G1 collector, may need a pre-write-barrier for CAS from NULL below"); |
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1260 oop_store_raw(discovered_addr, next_discovered); |
342
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1261 if (_discovered_list_needs_barrier) { |
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1262 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
342
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1263 } |
0 | 1264 list->set_head(obj); |
452
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1265 list->inc_length(1); |
0 | 1266 |
1974
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1267 if (TraceReferenceGC) { |
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1268 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)", |
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1269 obj, obj->klass()->internal_name()); |
0 | 1270 } |
1271 } | |
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1272 assert(obj->is_oop(), "Discovered a bad reference"); |
1995
8df09fb45352
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1273 verify_referent(obj); |
0 | 1274 return true; |
1275 } | |
1276 | |
1277 // Preclean the discovered references by removing those | |
1278 // whose referents are alive, and by marking from those that | |
1279 // are not active. These lists can be handled here | |
1280 // in any order and, indeed, concurrently. | |
1281 void ReferenceProcessor::preclean_discovered_references( | |
1282 BoolObjectClosure* is_alive, | |
1283 OopClosure* keep_alive, | |
1284 VoidClosure* complete_gc, | |
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1285 YieldClosure* yield) { |
0 | 1286 |
1287 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
1288 | |
1289 // Soft references | |
1290 { | |
1291 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, | |
1292 false, gclog_or_tty); | |
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1293 for (uint i = 0; i < _max_num_q; i++) { |
452
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1294 if (yield->should_return()) { |
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1295 return; |
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1296 } |
0 | 1297 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
1298 keep_alive, complete_gc, yield); | |
1299 } | |
1300 } | |
1301 | |
1302 // Weak references | |
1303 { | |
1304 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, | |
1305 false, gclog_or_tty); | |
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1306 for (uint i = 0; i < _max_num_q; i++) { |
452
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1307 if (yield->should_return()) { |
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1308 return; |
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1309 } |
0 | 1310 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
1311 keep_alive, complete_gc, yield); | |
1312 } | |
1313 } | |
1314 | |
1315 // Final references | |
1316 { | |
1317 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, | |
1318 false, gclog_or_tty); | |
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1319 for (uint i = 0; i < _max_num_q; i++) { |
452
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1320 if (yield->should_return()) { |
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1321 return; |
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1322 } |
0 | 1323 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
1324 keep_alive, complete_gc, yield); | |
1325 } | |
1326 } | |
1327 | |
1328 // Phantom references | |
1329 { | |
1330 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, | |
1331 false, gclog_or_tty); | |
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1332 for (uint i = 0; i < _max_num_q; i++) { |
452
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1333 if (yield->should_return()) { |
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1334 return; |
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|
1335 } |
0 | 1336 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
1337 keep_alive, complete_gc, yield); | |
1338 } | |
1339 } | |
1340 } | |
1341 | |
1342 // Walk the given discovered ref list, and remove all reference objects | |
1343 // whose referents are still alive, whose referents are NULL or which | |
452
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1344 // are not active (have a non-NULL next field). NOTE: When we are |
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1345 // thus precleaning the ref lists (which happens single-threaded today), |
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1346 // we do not disable refs discovery to honour the correct semantics of |
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1347 // java.lang.Reference. As a result, we need to be careful below |
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1348 // that ref removal steps interleave safely with ref discovery steps |
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1349 // (in this thread). |
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1350 void |
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1351 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1352 BoolObjectClosure* is_alive, |
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1353 OopClosure* keep_alive, |
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1354 VoidClosure* complete_gc, |
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1355 YieldClosure* yield) { |
0 | 1356 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
1357 while (iter.has_next()) { | |
1358 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1359 oop obj = iter.obj(); |
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1360 oop next = java_lang_ref_Reference::next(obj); |
0 | 1361 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1362 next != NULL) { |
0 | 1363 // The referent has been cleared, or is alive, or the Reference is not |
1364 // active; we need to trace and mark its cohort. | |
1365 if (TraceReferenceGC) { | |
1366 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
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1367 iter.obj(), iter.obj()->klass()->internal_name()); |
0 | 1368 } |
1369 // Remove Reference object from list | |
1370 iter.remove(); | |
1371 // Keep alive its cohort. | |
1372 iter.make_referent_alive(); | |
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1373 if (UseCompressedOops) { |
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1374 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1375 keep_alive->do_oop(next_addr); |
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1376 } else { |
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1377 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1378 keep_alive->do_oop(next_addr); |
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1379 } |
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1380 iter.move_to_next(); |
0 | 1381 } else { |
1382 iter.next(); | |
1383 } | |
1384 } | |
1385 // Close the reachable set | |
1386 complete_gc->do_void(); | |
1387 | |
1388 NOT_PRODUCT( | |
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|
1389 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) { |
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1390 gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
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1391 "Refs in discovered list " INTPTR_FORMAT, |
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1392 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 1393 } |
1394 ) | |
1395 } | |
1396 | |
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1397 const char* ReferenceProcessor::list_name(uint i) { |
3979
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|
1398 assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(), |
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1399 "Out of bounds index"); |
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|
1400 |
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1401 int j = i / _max_num_q; |
0 | 1402 switch (j) { |
1403 case 0: return "SoftRef"; | |
1404 case 1: return "WeakRef"; | |
1405 case 2: return "FinalRef"; | |
1406 case 3: return "PhantomRef"; | |
1407 } | |
1408 ShouldNotReachHere(); | |
1409 return NULL; | |
1410 } | |
1411 | |
1412 #ifndef PRODUCT | |
1413 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
1414 // empty for now | |
1415 } | |
1416 #endif | |
1417 | |
1418 #ifndef PRODUCT | |
1419 void ReferenceProcessor::clear_discovered_references() { | |
1420 guarantee(!_discovering_refs, "Discovering refs?"); | |
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1421 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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1422 clear_discovered_references(_discovered_refs[i]); |
0 | 1423 } |
1424 } | |
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1425 |
0 | 1426 #endif // PRODUCT |