Mercurial > hg > truffle
annotate src/share/vm/memory/referenceProcessor.cpp @ 5274:e72dd6533eb9
documented importance of nmethod::_graal_compiled_method wrt code unloading and GC
author | Doug Simon <doug.simon@oracle.com> |
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date | Mon, 23 Apr 2012 15:42:30 +0200 |
parents | 441e946dc1af |
children | d2a62e0f25eb |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 2001, 2011, 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" | |
0 | 35 |
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36 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
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37 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
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38 bool ReferenceProcessor::_pending_list_uses_discovered_field = false; |
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39 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; |
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40 |
0 | 41 void referenceProcessor_init() { |
42 ReferenceProcessor::init_statics(); | |
43 } | |
44 | |
45 void ReferenceProcessor::init_statics() { | |
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46 // We need a monotonically non-deccreasing time in ms but |
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47 // os::javaTimeMillis() does not guarantee monotonicity. |
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48 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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49 |
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50 // Initialize the soft ref timestamp clock. |
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51 _soft_ref_timestamp_clock = now; |
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52 // Also update the soft ref clock in j.l.r.SoftReference |
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53 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); |
0 | 54 |
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55 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
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56 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
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57 NOT_COMPILER2(LRUCurrentHeapPolicy()); |
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58 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
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59 vm_exit_during_initialization("Could not allocate reference policy object"); |
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60 } |
0 | 61 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
62 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
63 "Unrecongnized RefDiscoveryPolicy"); | |
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64 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field(); |
0 | 65 } |
66 | |
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67 void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) { |
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68 #ifdef ASSERT |
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69 // Verify that we're not currently discovering refs |
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70 assert(!verify_disabled || !_discovering_refs, "nested call?"); |
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71 |
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72 if (check_no_refs) { |
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73 // Verify that the discovered lists are empty |
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74 verify_no_references_recorded(); |
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75 } |
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76 #endif // ASSERT |
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77 |
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78 // Someone could have modified the value of the static |
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79 // field in the j.l.r.SoftReference class that holds the |
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80 // soft reference timestamp clock using reflection or |
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81 // Unsafe between GCs. Unconditionally update the static |
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82 // field in ReferenceProcessor here so that we use the new |
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83 // value during reference discovery. |
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84 |
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85 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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86 _discovering_refs = true; |
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87 } |
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88 |
0 | 89 ReferenceProcessor::ReferenceProcessor(MemRegion span, |
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90 bool mt_processing, |
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91 uint mt_processing_degree, |
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92 bool mt_discovery, |
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93 uint mt_discovery_degree, |
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94 bool atomic_discovery, |
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95 BoolObjectClosure* is_alive_non_header, |
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96 bool discovered_list_needs_barrier) : |
0 | 97 _discovering_refs(false), |
98 _enqueuing_is_done(false), | |
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99 _is_alive_non_header(is_alive_non_header), |
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100 _discovered_list_needs_barrier(discovered_list_needs_barrier), |
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101 _bs(NULL), |
0 | 102 _processing_is_mt(mt_processing), |
103 _next_id(0) | |
104 { | |
105 _span = span; | |
106 _discovery_is_atomic = atomic_discovery; | |
107 _discovery_is_mt = mt_discovery; | |
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108 _num_q = MAX2(1U, mt_processing_degree); |
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109 _max_num_q = MAX2(_num_q, mt_discovery_degree); |
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110 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, |
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111 _max_num_q * number_of_subclasses_of_ref()); |
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112 if (_discovered_refs == NULL) { |
0 | 113 vm_exit_during_initialization("Could not allocated RefProc Array"); |
114 } | |
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115 _discoveredSoftRefs = &_discovered_refs[0]; |
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116 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
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117 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
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118 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
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119 |
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120 // Initialize all entries to NULL |
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121 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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122 _discovered_refs[i].set_head(NULL); |
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123 _discovered_refs[i].set_length(0); |
0 | 124 } |
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125 |
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126 // If we do barriers, cache a copy of the barrier set. |
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127 if (discovered_list_needs_barrier) { |
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128 _bs = Universe::heap()->barrier_set(); |
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129 } |
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130 setup_policy(false /* default soft ref policy */); |
0 | 131 } |
132 | |
133 #ifndef PRODUCT | |
134 void ReferenceProcessor::verify_no_references_recorded() { | |
135 guarantee(!_discovering_refs, "Discovering refs?"); | |
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136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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137 guarantee(_discovered_refs[i].is_empty(), |
0 | 138 "Found non-empty discovered list"); |
139 } | |
140 } | |
141 #endif | |
142 | |
143 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
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144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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145 if (UseCompressedOops) { |
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146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); |
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147 } else { |
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148 f->do_oop((oop*)_discovered_refs[i].adr_head()); |
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149 } |
0 | 150 } |
151 } | |
152 | |
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153 void ReferenceProcessor::update_soft_ref_master_clock() { |
0 | 154 // Update (advance) the soft ref master clock field. This must be done |
155 // after processing the soft ref list. | |
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156 |
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157 // We need a monotonically non-deccreasing time in ms but |
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158 // os::javaTimeMillis() does not guarantee monotonicity. |
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159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
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160 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); |
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161 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); |
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162 |
0 | 163 NOT_PRODUCT( |
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164 if (now < _soft_ref_timestamp_clock) { |
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165 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, |
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166 _soft_ref_timestamp_clock, now); |
0 | 167 } |
168 ) | |
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169 // The values of now and _soft_ref_timestamp_clock are set using |
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170 // javaTimeNanos(), which is guaranteed to be monotonically |
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171 // non-decreasing provided the underlying platform provides such |
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172 // a time source (and it is bug free). |
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173 // In product mode, however, protect ourselves from non-monotonicty. |
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174 if (now > _soft_ref_timestamp_clock) { |
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175 _soft_ref_timestamp_clock = now; |
0 | 176 java_lang_ref_SoftReference::set_clock(now); |
177 } | |
178 // Else leave clock stalled at its old value until time progresses | |
179 // past clock value. | |
180 } | |
181 | |
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182 void ReferenceProcessor::process_discovered_references( |
0 | 183 BoolObjectClosure* is_alive, |
184 OopClosure* keep_alive, | |
185 VoidClosure* complete_gc, | |
186 AbstractRefProcTaskExecutor* task_executor) { | |
187 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
188 | |
189 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
190 // Stop treating discovered references specially. | |
191 disable_discovery(); | |
192 | |
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193 // If discovery was concurrent, someone could have modified |
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194 // the value of the static field in the j.l.r.SoftReference |
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195 // class that holds the soft reference timestamp clock using |
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196 // reflection or Unsafe between when discovery was enabled and |
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197 // now. Unconditionally update the static field in ReferenceProcessor |
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198 // here so that we use the new value during processing of the |
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199 // discovered soft refs. |
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200 |
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201 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
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202 |
0 | 203 bool trace_time = PrintGCDetails && PrintReferenceGC; |
204 // Soft references | |
205 { | |
206 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); | |
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207 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, |
0 | 208 is_alive, keep_alive, complete_gc, task_executor); |
209 } | |
210 | |
211 update_soft_ref_master_clock(); | |
212 | |
213 // Weak references | |
214 { | |
215 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); | |
216 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
217 is_alive, keep_alive, complete_gc, task_executor); | |
218 } | |
219 | |
220 // Final references | |
221 { | |
222 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); | |
223 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
224 is_alive, keep_alive, complete_gc, task_executor); | |
225 } | |
226 | |
227 // Phantom references | |
228 { | |
229 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); | |
230 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
231 is_alive, keep_alive, complete_gc, task_executor); | |
232 } | |
233 | |
234 // Weak global JNI references. It would make more sense (semantically) to | |
235 // traverse these simultaneously with the regular weak references above, but | |
236 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
237 // thus use JNI weak references to circumvent the phantom references and | |
238 // resurrect a "post-mortem" object. | |
239 { | |
240 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); | |
241 if (task_executor != NULL) { | |
242 task_executor->set_single_threaded_mode(); | |
243 } | |
244 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
245 } | |
246 } | |
247 | |
248 #ifndef PRODUCT | |
249 // Calculate the number of jni handles. | |
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250 uint ReferenceProcessor::count_jni_refs() { |
0 | 251 class AlwaysAliveClosure: public BoolObjectClosure { |
252 public: | |
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253 virtual bool do_object_b(oop obj) { return true; } |
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254 virtual void do_object(oop obj) { assert(false, "Don't call"); } |
0 | 255 }; |
256 | |
257 class CountHandleClosure: public OopClosure { | |
258 private: | |
259 int _count; | |
260 public: | |
261 CountHandleClosure(): _count(0) {} | |
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262 void do_oop(oop* unused) { _count++; } |
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263 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
0 | 264 int count() { return _count; } |
265 }; | |
266 CountHandleClosure global_handle_count; | |
267 AlwaysAliveClosure always_alive; | |
268 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
269 return global_handle_count.count(); | |
270 } | |
271 #endif | |
272 | |
273 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
274 OopClosure* keep_alive, | |
275 VoidClosure* complete_gc) { | |
276 #ifndef PRODUCT | |
277 if (PrintGCDetails && PrintReferenceGC) { | |
278 unsigned int count = count_jni_refs(); | |
279 gclog_or_tty->print(", %u refs", count); | |
280 } | |
281 #endif | |
282 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
283 complete_gc->do_void(); | |
284 } | |
285 | |
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286 |
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287 template <class T> |
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288 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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289 AbstractRefProcTaskExecutor* task_executor) { |
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290 |
0 | 291 // Remember old value of pending references list |
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292 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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293 T old_pending_list_value = *pending_list_addr; |
0 | 294 |
295 // Enqueue references that are not made active again, and | |
296 // clear the decks for the next collection (cycle). | |
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297 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
0 | 298 // Do the oop-check on pending_list_addr missed in |
299 // enqueue_discovered_reflist. We should probably | |
300 // do a raw oop_check so that future such idempotent | |
301 // oop_stores relying on the oop-check side-effect | |
302 // may be elided automatically and safely without | |
303 // affecting correctness. | |
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304 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
0 | 305 |
306 // Stop treating discovered references specially. | |
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307 ref->disable_discovery(); |
0 | 308 |
309 // Return true if new pending references were added | |
310 return old_pending_list_value != *pending_list_addr; | |
311 } | |
312 | |
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313 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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314 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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315 if (UseCompressedOops) { |
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316 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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317 } else { |
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318 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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319 } |
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320 } |
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321 |
0 | 322 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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323 HeapWord* pending_list_addr) { |
0 | 324 // Given a list of refs linked through the "discovered" field |
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325 // (java.lang.ref.Reference.discovered), self-loop their "next" field |
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326 // thus distinguishing them from active References, then |
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327 // prepend them to the pending list. |
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328 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777), |
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329 // the "next" field is used to chain the pending list, not the discovered |
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330 // field. |
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331 |
0 | 332 if (TraceReferenceGC && PrintGCDetails) { |
333 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
334 INTPTR_FORMAT, (address)refs_list.head()); | |
335 } | |
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336 |
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337 oop obj = NULL; |
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338 oop next_d = refs_list.head(); |
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339 if (pending_list_uses_discovered_field()) { // New behaviour |
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340 // Walk down the list, self-looping the next field |
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341 // so that the References are not considered active. |
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342 while (obj != next_d) { |
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343 obj = next_d; |
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344 assert(obj->is_instanceRef(), "should be reference object"); |
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345 next_d = java_lang_ref_Reference::discovered(obj); |
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346 if (TraceReferenceGC && PrintGCDetails) { |
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347 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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348 obj, next_d); |
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349 } |
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350 assert(java_lang_ref_Reference::next(obj) == NULL, |
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351 "Reference not active; should not be discovered"); |
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352 // Self-loop next, so as to make Ref not active. |
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353 java_lang_ref_Reference::set_next(obj, obj); |
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354 if (next_d == obj) { // obj is last |
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355 // Swap refs_list into pendling_list_addr and |
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356 // set obj's discovered to what we read from pending_list_addr. |
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357 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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358 // Need oop_check on pending_list_addr above; |
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359 // see special oop-check code at the end of |
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360 // enqueue_discovered_reflists() further below. |
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361 java_lang_ref_Reference::set_discovered(obj, old); // old may be NULL |
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362 } |
0 | 363 } |
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364 } else { // Old behaviour |
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365 // Walk down the list, copying the discovered field into |
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366 // the next field and clearing the discovered field. |
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367 while (obj != next_d) { |
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368 obj = next_d; |
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369 assert(obj->is_instanceRef(), "should be reference object"); |
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370 next_d = java_lang_ref_Reference::discovered(obj); |
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371 if (TraceReferenceGC && PrintGCDetails) { |
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372 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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373 obj, next_d); |
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374 } |
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375 assert(java_lang_ref_Reference::next(obj) == NULL, |
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376 "The reference should not be enqueued"); |
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377 if (next_d == obj) { // obj is last |
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378 // Swap refs_list into pendling_list_addr and |
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379 // set obj's next to what we read from pending_list_addr. |
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380 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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381 // Need oop_check on pending_list_addr above; |
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382 // see special oop-check code at the end of |
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383 // enqueue_discovered_reflists() further below. |
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384 if (old == NULL) { |
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385 // obj should be made to point to itself, since |
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386 // pending list was empty. |
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387 java_lang_ref_Reference::set_next(obj, obj); |
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388 } else { |
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389 java_lang_ref_Reference::set_next(obj, old); |
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390 } |
0 | 391 } else { |
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392 java_lang_ref_Reference::set_next(obj, next_d); |
0 | 393 } |
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394 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); |
0 | 395 } |
396 } | |
397 } | |
398 | |
399 // Parallel enqueue task | |
400 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
401 public: | |
402 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
403 DiscoveredList discovered_refs[], | |
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404 HeapWord* pending_list_addr, |
0 | 405 int n_queues) |
406 : EnqueueTask(ref_processor, discovered_refs, | |
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407 pending_list_addr, n_queues) |
0 | 408 { } |
409 | |
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410 virtual void work(unsigned int work_id) { |
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411 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); |
0 | 412 // Simplest first cut: static partitioning. |
413 int index = work_id; | |
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414 // The increment on "index" must correspond to the maximum number of queues |
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415 // (n_queues) with which that ReferenceProcessor was created. That |
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416 // is because of the "clever" way the discovered references lists were |
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417 // allocated and are indexed into. |
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418 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); |
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419 for (int j = 0; |
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420 j < ReferenceProcessor::number_of_subclasses_of_ref(); |
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421 j++, index += _n_queues) { |
0 | 422 _ref_processor.enqueue_discovered_reflist( |
423 _refs_lists[index], _pending_list_addr); | |
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424 _refs_lists[index].set_head(NULL); |
0 | 425 _refs_lists[index].set_length(0); |
426 } | |
427 } | |
428 }; | |
429 | |
430 // Enqueue references that are not made active again | |
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431 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
0 | 432 AbstractRefProcTaskExecutor* task_executor) { |
433 if (_processing_is_mt && task_executor != NULL) { | |
434 // Parallel code | |
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435 RefProcEnqueueTask tsk(*this, _discovered_refs, |
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436 pending_list_addr, _max_num_q); |
0 | 437 task_executor->execute(tsk); |
438 } else { | |
439 // Serial code: call the parent class's implementation | |
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440 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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441 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr); |
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442 _discovered_refs[i].set_head(NULL); |
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443 _discovered_refs[i].set_length(0); |
0 | 444 } |
445 } | |
446 } | |
447 | |
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448 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
0 | 449 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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450 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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451 assert(_discovered_addr && discovered->is_oop_or_null(), |
0 | 452 "discovered field is bad"); |
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453 _next = discovered; |
0 | 454 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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455 _referent = java_lang_ref_Reference::referent(_ref); |
0 | 456 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
457 "Wrong oop found in java.lang.Reference object"); | |
458 assert(allow_null_referent ? | |
459 _referent->is_oop_or_null() | |
460 : _referent->is_oop(), | |
461 "bad referent"); | |
462 } | |
463 | |
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464 void DiscoveredListIterator::remove() { |
0 | 465 assert(_ref->is_oop(), "Dropping a bad reference"); |
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466 oop_store_raw(_discovered_addr, NULL); |
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467 |
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468 // First _prev_next ref actually points into DiscoveredList (gross). |
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469 oop new_next; |
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470 if (_next == _ref) { |
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471 // At the end of the list, we should make _prev point to itself. |
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472 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, |
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473 // and _prev will be NULL. |
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474 new_next = _prev; |
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475 } else { |
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476 new_next = _next; |
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477 } |
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478 |
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479 if (UseCompressedOops) { |
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480 // Remove Reference object from list. |
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481 oopDesc::encode_store_heap_oop((narrowOop*)_prev_next, new_next); |
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482 } else { |
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483 // Remove Reference object from list. |
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484 oopDesc::store_heap_oop((oop*)_prev_next, new_next); |
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485 } |
0 | 486 NOT_PRODUCT(_removed++); |
452
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487 _refs_list.dec_length(1); |
0 | 488 } |
489 | |
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490 // Make the Reference object active again. |
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491 void DiscoveredListIterator::make_active() { |
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492 // For G1 we don't want to use set_next - it |
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493 // will dirty the card for the next field of |
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494 // the reference object and will fail |
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495 // CT verification. |
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496 if (UseG1GC) { |
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497 BarrierSet* bs = oopDesc::bs(); |
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498 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref); |
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499 |
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500 if (UseCompressedOops) { |
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501 bs->write_ref_field_pre((narrowOop*)next_addr, NULL); |
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502 } else { |
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503 bs->write_ref_field_pre((oop*)next_addr, NULL); |
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504 } |
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505 java_lang_ref_Reference::set_next_raw(_ref, NULL); |
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506 } else { |
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507 java_lang_ref_Reference::set_next(_ref, NULL); |
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508 } |
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509 } |
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510 |
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511 void DiscoveredListIterator::clear_referent() { |
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512 oop_store_raw(_referent_addr, NULL); |
0 | 513 } |
514 | |
515 // NOTE: process_phase*() are largely similar, and at a high level | |
516 // merely iterate over the extant list applying a predicate to | |
517 // each of its elements and possibly removing that element from the | |
518 // list and applying some further closures to that element. | |
519 // We should consider the possibility of replacing these | |
520 // process_phase*() methods by abstracting them into | |
521 // a single general iterator invocation that receives appropriate | |
522 // closures that accomplish this work. | |
523 | |
524 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
525 // referents are not alive, but that should be kept alive for policy reasons. | |
526 // Keep alive the transitive closure of all such referents. | |
527 void | |
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528 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
0 | 529 ReferencePolicy* policy, |
530 BoolObjectClosure* is_alive, | |
531 OopClosure* keep_alive, | |
532 VoidClosure* complete_gc) { | |
533 assert(policy != NULL, "Must have a non-NULL policy"); | |
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534 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 535 // Decide which softly reachable refs should be kept alive. |
536 while (iter.has_next()) { | |
537 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
538 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
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539 if (referent_is_dead && |
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540 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { |
0 | 541 if (TraceReferenceGC) { |
542 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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543 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 544 } |
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545 // Remove Reference object from list |
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546 iter.remove(); |
0 | 547 // Make the Reference object active again |
548 iter.make_active(); | |
549 // keep the referent around | |
550 iter.make_referent_alive(); | |
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551 iter.move_to_next(); |
0 | 552 } else { |
553 iter.next(); | |
554 } | |
555 } | |
556 // Close the reachable set | |
557 complete_gc->do_void(); | |
558 NOT_PRODUCT( | |
559 if (PrintGCDetails && TraceReferenceGC) { | |
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560 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
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561 "discovered Refs by policy, from list " INTPTR_FORMAT, |
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562 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 563 } |
564 ) | |
565 } | |
566 | |
567 // Traverse the list and remove any Refs that are not active, or | |
568 // whose referents are either alive or NULL. | |
569 void | |
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570 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
0 | 571 BoolObjectClosure* is_alive, |
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572 OopClosure* keep_alive) { |
0 | 573 assert(discovery_is_atomic(), "Error"); |
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574 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 575 while (iter.has_next()) { |
576 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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577 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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578 assert(next == NULL, "Should not discover inactive Reference"); |
0 | 579 if (iter.is_referent_alive()) { |
580 if (TraceReferenceGC) { | |
581 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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582 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 583 } |
584 // The referent is reachable after all. | |
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585 // Remove Reference object from list. |
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586 iter.remove(); |
0 | 587 // Update the referent pointer as necessary: Note that this |
588 // should not entail any recursive marking because the | |
589 // referent must already have been traversed. | |
590 iter.make_referent_alive(); | |
452
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591 iter.move_to_next(); |
0 | 592 } else { |
593 iter.next(); | |
594 } | |
595 } | |
596 NOT_PRODUCT( | |
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597 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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598 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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599 "Refs in discovered list " INTPTR_FORMAT, |
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600 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 601 } |
602 ) | |
603 } | |
604 | |
605 void | |
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606 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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607 BoolObjectClosure* is_alive, |
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608 OopClosure* keep_alive, |
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609 VoidClosure* complete_gc) { |
0 | 610 assert(!discovery_is_atomic(), "Error"); |
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611 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 612 while (iter.has_next()) { |
613 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
113
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614 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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615 oop next = java_lang_ref_Reference::next(iter.obj()); |
0 | 616 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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617 next != NULL)) { |
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618 assert(next->is_oop_or_null(), "bad next field"); |
0 | 619 // Remove Reference object from list |
620 iter.remove(); | |
621 // Trace the cohorts | |
622 iter.make_referent_alive(); | |
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623 if (UseCompressedOops) { |
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624 keep_alive->do_oop((narrowOop*)next_addr); |
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625 } else { |
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626 keep_alive->do_oop((oop*)next_addr); |
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627 } |
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628 iter.move_to_next(); |
0 | 629 } else { |
630 iter.next(); | |
631 } | |
632 } | |
633 // Now close the newly reachable set | |
634 complete_gc->do_void(); | |
635 NOT_PRODUCT( | |
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636 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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637 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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638 "Refs in discovered list " INTPTR_FORMAT, |
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639 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 640 } |
641 ) | |
642 } | |
643 | |
644 // Traverse the list and process the referents, by either | |
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645 // clearing them or keeping them (and their reachable |
0 | 646 // closure) alive. |
647 void | |
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648 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
0 | 649 bool clear_referent, |
650 BoolObjectClosure* is_alive, | |
651 OopClosure* keep_alive, | |
652 VoidClosure* complete_gc) { | |
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653 ResourceMark rm; |
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654 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 655 while (iter.has_next()) { |
656 iter.update_discovered(); | |
657 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
658 if (clear_referent) { | |
659 // NULL out referent pointer | |
660 iter.clear_referent(); | |
661 } else { | |
662 // keep the referent around | |
663 iter.make_referent_alive(); | |
664 } | |
665 if (TraceReferenceGC) { | |
666 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
667 clear_referent ? "cleared " : "", | |
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668 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 669 } |
670 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
671 iter.next(); | |
672 } | |
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673 // Remember to update the next pointer of the last ref. |
0 | 674 iter.update_discovered(); |
675 // Close the reachable set | |
676 complete_gc->do_void(); | |
677 } | |
678 | |
679 void | |
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680 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { |
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681 oop obj = NULL; |
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682 oop next = refs_list.head(); |
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683 while (next != obj) { |
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684 obj = next; |
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685 next = java_lang_ref_Reference::discovered(obj); |
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686 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
0 | 687 } |
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688 refs_list.set_head(NULL); |
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689 refs_list.set_length(0); |
0 | 690 } |
691 | |
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692 void |
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693 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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694 clear_discovered_references(refs_list); |
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695 } |
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696 |
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697 void ReferenceProcessor::abandon_partial_discovery() { |
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698 // loop over the lists |
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699 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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700 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
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701 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i)); |
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702 } |
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703 abandon_partial_discovered_list(_discovered_refs[i]); |
0 | 704 } |
705 } | |
706 | |
707 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
708 public: | |
709 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
710 DiscoveredList refs_lists[], | |
711 ReferencePolicy* policy, | |
712 bool marks_oops_alive) | |
713 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
714 _policy(policy) | |
715 { } | |
716 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
717 OopClosure& keep_alive, | |
718 VoidClosure& complete_gc) | |
719 { | |
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720 Thread* thr = Thread::current(); |
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721 int refs_list_index = ((WorkerThread*)thr)->id(); |
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722 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
0 | 723 &is_alive, &keep_alive, &complete_gc); |
724 } | |
725 private: | |
726 ReferencePolicy* _policy; | |
727 }; | |
728 | |
729 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
730 public: | |
731 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
732 DiscoveredList refs_lists[], | |
733 bool marks_oops_alive) | |
734 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
735 { } | |
736 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
737 OopClosure& keep_alive, | |
738 VoidClosure& complete_gc) | |
739 { | |
740 _ref_processor.process_phase2(_refs_lists[i], | |
741 &is_alive, &keep_alive, &complete_gc); | |
742 } | |
743 }; | |
744 | |
745 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
746 public: | |
747 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
748 DiscoveredList refs_lists[], | |
749 bool clear_referent, | |
750 bool marks_oops_alive) | |
751 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
752 _clear_referent(clear_referent) | |
753 { } | |
754 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
755 OopClosure& keep_alive, | |
756 VoidClosure& complete_gc) | |
757 { | |
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758 // Don't use "refs_list_index" calculated in this way because |
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759 // balance_queues() has moved the Ref's into the first n queues. |
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760 // Thread* thr = Thread::current(); |
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761 // int refs_list_index = ((WorkerThread*)thr)->id(); |
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762 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
0 | 763 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
764 &is_alive, &keep_alive, &complete_gc); | |
765 } | |
766 private: | |
767 bool _clear_referent; | |
768 }; | |
769 | |
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770 void ReferenceProcessor::set_discovered(oop ref, oop value) { |
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771 if (_discovered_list_needs_barrier) { |
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772 java_lang_ref_Reference::set_discovered(ref, value); |
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773 } else { |
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774 java_lang_ref_Reference::set_discovered_raw(ref, value); |
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775 } |
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776 } |
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777 |
0 | 778 // Balances reference queues. |
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779 // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
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780 // queues[0, 1, ..., _num_q-1] because only the first _num_q |
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781 // corresponding to the active workers will be processed. |
0 | 782 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
783 { | |
784 // calculate total length | |
785 size_t total_refs = 0; | |
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786 if (TraceReferenceGC && PrintGCDetails) { |
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787 gclog_or_tty->print_cr("\nBalance ref_lists "); |
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788 } |
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789 |
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790 for (uint i = 0; i < _max_num_q; ++i) { |
0 | 791 total_refs += ref_lists[i].length(); |
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792 if (TraceReferenceGC && PrintGCDetails) { |
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793 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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794 } |
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795 } |
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796 if (TraceReferenceGC && PrintGCDetails) { |
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797 gclog_or_tty->print_cr(" = %d", total_refs); |
0 | 798 } |
799 size_t avg_refs = total_refs / _num_q + 1; | |
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800 uint to_idx = 0; |
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801 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { |
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802 bool move_all = false; |
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803 if (from_idx >= _num_q) { |
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804 move_all = ref_lists[from_idx].length() > 0; |
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805 } |
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806 while ((ref_lists[from_idx].length() > avg_refs) || |
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807 move_all) { |
0 | 808 assert(to_idx < _num_q, "Sanity Check!"); |
809 if (ref_lists[to_idx].length() < avg_refs) { | |
810 // move superfluous refs | |
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811 size_t refs_to_move; |
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812 // Move all the Ref's if the from queue will not be processed. |
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813 if (move_all) { |
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814 refs_to_move = MIN2(ref_lists[from_idx].length(), |
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815 avg_refs - ref_lists[to_idx].length()); |
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816 } else { |
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817 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
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818 avg_refs - ref_lists[to_idx].length()); |
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819 } |
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820 |
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821 assert(refs_to_move > 0, "otherwise the code below will fail"); |
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822 |
0 | 823 oop move_head = ref_lists[from_idx].head(); |
824 oop move_tail = move_head; | |
825 oop new_head = move_head; | |
826 // find an element to split the list on | |
827 for (size_t j = 0; j < refs_to_move; ++j) { | |
828 move_tail = new_head; | |
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829 new_head = java_lang_ref_Reference::discovered(new_head); |
0 | 830 } |
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831 |
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832 // Add the chain to the to list. |
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833 if (ref_lists[to_idx].head() == NULL) { |
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834 // to list is empty. Make a loop at the end. |
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835 set_discovered(move_tail, move_tail); |
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836 } else { |
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837 set_discovered(move_tail, ref_lists[to_idx].head()); |
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838 } |
0 | 839 ref_lists[to_idx].set_head(move_head); |
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840 ref_lists[to_idx].inc_length(refs_to_move); |
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841 |
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842 // Remove the chain from the from list. |
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843 if (move_tail == new_head) { |
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844 // We found the end of the from list. |
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845 ref_lists[from_idx].set_head(NULL); |
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846 } else { |
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847 ref_lists[from_idx].set_head(new_head); |
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848 } |
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849 ref_lists[from_idx].dec_length(refs_to_move); |
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850 if (ref_lists[from_idx].length() == 0) { |
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851 break; |
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852 } |
0 | 853 } else { |
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854 to_idx = (to_idx + 1) % _num_q; |
0 | 855 } |
856 } | |
857 } | |
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858 #ifdef ASSERT |
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859 size_t balanced_total_refs = 0; |
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860 for (uint i = 0; i < _max_num_q; ++i) { |
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861 balanced_total_refs += ref_lists[i].length(); |
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862 if (TraceReferenceGC && PrintGCDetails) { |
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863 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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864 } |
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865 } |
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866 if (TraceReferenceGC && PrintGCDetails) { |
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867 gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
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868 gclog_or_tty->flush(); |
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869 } |
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870 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
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871 #endif |
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872 } |
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873 |
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874 void ReferenceProcessor::balance_all_queues() { |
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875 balance_queues(_discoveredSoftRefs); |
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876 balance_queues(_discoveredWeakRefs); |
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877 balance_queues(_discoveredFinalRefs); |
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878 balance_queues(_discoveredPhantomRefs); |
0 | 879 } |
880 | |
881 void | |
882 ReferenceProcessor::process_discovered_reflist( | |
883 DiscoveredList refs_lists[], | |
884 ReferencePolicy* policy, | |
885 bool clear_referent, | |
886 BoolObjectClosure* is_alive, | |
887 OopClosure* keep_alive, | |
888 VoidClosure* complete_gc, | |
889 AbstractRefProcTaskExecutor* task_executor) | |
890 { | |
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891 bool mt_processing = task_executor != NULL && _processing_is_mt; |
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892 // If discovery used MT and a dynamic number of GC threads, then |
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893 // the queues must be balanced for correctness if fewer than the |
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894 // maximum number of queues were used. The number of queue used |
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895 // during discovery may be different than the number to be used |
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896 // for processing so don't depend of _num_q < _max_num_q as part |
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897 // of the test. |
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898 bool must_balance = _discovery_is_mt; |
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899 |
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900 if ((mt_processing && ParallelRefProcBalancingEnabled) || |
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901 must_balance) { |
0 | 902 balance_queues(refs_lists); |
903 } | |
904 if (PrintReferenceGC && PrintGCDetails) { | |
905 size_t total = 0; | |
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906 for (uint i = 0; i < _max_num_q; ++i) { |
0 | 907 total += refs_lists[i].length(); |
908 } | |
909 gclog_or_tty->print(", %u refs", total); | |
910 } | |
911 | |
912 // Phase 1 (soft refs only): | |
913 // . Traverse the list and remove any SoftReferences whose | |
914 // referents are not alive, but that should be kept alive for | |
915 // policy reasons. Keep alive the transitive closure of all | |
916 // such referents. | |
917 if (policy != NULL) { | |
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918 if (mt_processing) { |
0 | 919 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
920 task_executor->execute(phase1); | |
921 } else { | |
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922 for (uint i = 0; i < _max_num_q; i++) { |
0 | 923 process_phase1(refs_lists[i], policy, |
924 is_alive, keep_alive, complete_gc); | |
925 } | |
926 } | |
927 } else { // policy == NULL | |
928 assert(refs_lists != _discoveredSoftRefs, | |
929 "Policy must be specified for soft references."); | |
930 } | |
931 | |
932 // Phase 2: | |
933 // . Traverse the list and remove any refs whose referents are alive. | |
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934 if (mt_processing) { |
0 | 935 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
936 task_executor->execute(phase2); | |
937 } else { | |
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938 for (uint i = 0; i < _max_num_q; i++) { |
0 | 939 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); |
940 } | |
941 } | |
942 | |
943 // Phase 3: | |
944 // . Traverse the list and process referents as appropriate. | |
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945 if (mt_processing) { |
0 | 946 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
947 task_executor->execute(phase3); | |
948 } else { | |
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949 for (uint i = 0; i < _max_num_q; i++) { |
0 | 950 process_phase3(refs_lists[i], clear_referent, |
951 is_alive, keep_alive, complete_gc); | |
952 } | |
953 } | |
954 } | |
955 | |
956 void ReferenceProcessor::clean_up_discovered_references() { | |
957 // loop over the lists | |
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958 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
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959 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
0 | 960 gclog_or_tty->print_cr( |
961 "\nScrubbing %s discovered list of Null referents", | |
962 list_name(i)); | |
963 } | |
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964 clean_up_discovered_reflist(_discovered_refs[i]); |
0 | 965 } |
966 } | |
967 | |
968 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
969 assert(!discovery_is_atomic(), "Else why call this method?"); | |
970 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
971 while (iter.has_next()) { | |
972 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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973 oop next = java_lang_ref_Reference::next(iter.obj()); |
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974 assert(next->is_oop_or_null(), "bad next field"); |
0 | 975 // If referent has been cleared or Reference is not active, |
976 // drop it. | |
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977 if (iter.referent() == NULL || next != NULL) { |
0 | 978 debug_only( |
979 if (PrintGCDetails && TraceReferenceGC) { | |
980 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
981 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
982 " and referent: " INTPTR_FORMAT, | |
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983 iter.obj(), next, iter.referent()); |
0 | 984 } |
985 ) | |
986 // Remove Reference object from list | |
987 iter.remove(); | |
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988 iter.move_to_next(); |
0 | 989 } else { |
990 iter.next(); | |
991 } | |
992 } | |
993 NOT_PRODUCT( | |
994 if (PrintGCDetails && TraceReferenceGC) { | |
995 gclog_or_tty->print( | |
996 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
997 iter.removed(), iter.processed()); | |
998 } | |
999 ) | |
1000 } | |
1001 | |
1002 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
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1003 uint id = 0; |
0 | 1004 // Determine the queue index to use for this object. |
1005 if (_discovery_is_mt) { | |
1006 // During a multi-threaded discovery phase, | |
1007 // each thread saves to its "own" list. | |
1008 Thread* thr = Thread::current(); | |
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1009 id = thr->as_Worker_thread()->id(); |
0 | 1010 } else { |
1011 // single-threaded discovery, we save in round-robin | |
1012 // fashion to each of the lists. | |
1013 if (_processing_is_mt) { | |
1014 id = next_id(); | |
1015 } | |
1016 } | |
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1017 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
0 | 1018 |
1019 // Get the discovered queue to which we will add | |
1020 DiscoveredList* list = NULL; | |
1021 switch (rt) { | |
1022 case REF_OTHER: | |
1023 // Unknown reference type, no special treatment | |
1024 break; | |
1025 case REF_SOFT: | |
1026 list = &_discoveredSoftRefs[id]; | |
1027 break; | |
1028 case REF_WEAK: | |
1029 list = &_discoveredWeakRefs[id]; | |
1030 break; | |
1031 case REF_FINAL: | |
1032 list = &_discoveredFinalRefs[id]; | |
1033 break; | |
1034 case REF_PHANTOM: | |
1035 list = &_discoveredPhantomRefs[id]; | |
1036 break; | |
1037 case REF_NONE: | |
1038 // we should not reach here if we are an instanceRefKlass | |
1039 default: | |
1040 ShouldNotReachHere(); | |
1041 } | |
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1042 if (TraceReferenceGC && PrintGCDetails) { |
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1043 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); |
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1044 } |
0 | 1045 return list; |
1046 } | |
1047 | |
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1048 inline void |
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1049 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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1050 oop obj, |
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1051 HeapWord* discovered_addr) { |
0 | 1052 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
1053 // First we must make sure this object is only enqueued once. CAS in a non null | |
1054 // discovered_addr. | |
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1055 oop current_head = refs_list.head(); |
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1056 // The last ref must have its discovered field pointing to itself. |
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1057 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1058 |
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1059 // Note: In the case of G1, this specific pre-barrier is strictly |
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1060 // not necessary because the only case we are interested in |
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1061 // here is when *discovered_addr is NULL (see the CAS further below), |
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1062 // so this will expand to nothing. As a result, we have manually |
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1063 // elided this out for G1, but left in the test for some future |
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1064 // collector that might have need for a pre-barrier here, e.g.:- |
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1065 // _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1066 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1067 "Need to check non-G1 collector: " |
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1068 "may need a pre-write-barrier for CAS from NULL below"); |
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1069 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, |
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1070 NULL); |
0 | 1071 if (retest == NULL) { |
1072 // This thread just won the right to enqueue the object. | |
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1073 // We have separate lists for enqueueing, so no synchronization |
0 | 1074 // is necessary. |
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1075 refs_list.set_head(obj); |
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1076 refs_list.inc_length(1); |
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1077 if (_discovered_list_needs_barrier) { |
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1078 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1079 } |
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1080 |
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1081 if (TraceReferenceGC) { |
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1082 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", |
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1083 obj, obj->blueprint()->internal_name()); |
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1084 } |
0 | 1085 } else { |
1086 // If retest was non NULL, another thread beat us to it: | |
1087 // The reference has already been discovered... | |
1088 if (TraceReferenceGC) { | |
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1089 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
0 | 1090 obj, obj->blueprint()->internal_name()); |
1091 } | |
1092 } | |
1093 } | |
1094 | |
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1095 #ifndef PRODUCT |
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1096 // Non-atomic (i.e. concurrent) discovery might allow us |
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1097 // to observe j.l.References with NULL referents, being those |
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1098 // cleared concurrently by mutators during (or after) discovery. |
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1099 void ReferenceProcessor::verify_referent(oop obj) { |
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1100 bool da = discovery_is_atomic(); |
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1101 oop referent = java_lang_ref_Reference::referent(obj); |
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1102 assert(da ? referent->is_oop() : referent->is_oop_or_null(), |
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1103 err_msg("Bad referent " INTPTR_FORMAT " found in Reference " |
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1104 INTPTR_FORMAT " during %satomic discovery ", |
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1105 (intptr_t)referent, (intptr_t)obj, da ? "" : "non-")); |
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1106 } |
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1107 #endif |
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1108 |
0 | 1109 // We mention two of several possible choices here: |
1110 // #0: if the reference object is not in the "originating generation" | |
1111 // (or part of the heap being collected, indicated by our "span" | |
1112 // we don't treat it specially (i.e. we scan it as we would | |
1113 // a normal oop, treating its references as strong references). | |
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1114 // This means that references can't be discovered unless their |
0 | 1115 // referent is also in the same span. This is the simplest, |
1116 // most "local" and most conservative approach, albeit one | |
1117 // that may cause weak references to be enqueued least promptly. | |
1118 // We call this choice the "ReferenceBasedDiscovery" policy. | |
1119 // #1: the reference object may be in any generation (span), but if | |
1120 // the referent is in the generation (span) being currently collected | |
1121 // then we can discover the reference object, provided | |
1122 // the object has not already been discovered by | |
1123 // a different concurrently running collector (as may be the | |
1124 // case, for instance, if the reference object is in CMS and | |
1125 // the referent in DefNewGeneration), and provided the processing | |
1126 // of this reference object by the current collector will | |
1127 // appear atomic to every other collector in the system. | |
1128 // (Thus, for instance, a concurrent collector may not | |
1129 // discover references in other generations even if the | |
1130 // referent is in its own generation). This policy may, | |
1131 // in certain cases, enqueue references somewhat sooner than | |
1132 // might Policy #0 above, but at marginally increased cost | |
1133 // and complexity in processing these references. | |
1134 // We call this choice the "RefeferentBasedDiscovery" policy. | |
1135 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
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1136 // Make sure we are discovering refs (rather than processing discovered refs). |
0 | 1137 if (!_discovering_refs || !RegisterReferences) { |
1138 return false; | |
1139 } | |
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1140 // We only discover active references. |
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1141 oop next = java_lang_ref_Reference::next(obj); |
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1142 if (next != NULL) { // Ref is no longer active |
0 | 1143 return false; |
1144 } | |
1145 | |
1146 HeapWord* obj_addr = (HeapWord*)obj; | |
1147 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1148 !_span.contains(obj_addr)) { | |
1149 // Reference is not in the originating generation; | |
1150 // don't treat it specially (i.e. we want to scan it as a normal | |
1151 // object with strong references). | |
1152 return false; | |
1153 } | |
1154 | |
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1155 // We only discover references whose referents are not (yet) |
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1156 // known to be strongly reachable. |
0 | 1157 if (is_alive_non_header() != NULL) { |
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1158 verify_referent(obj); |
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1159 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { |
0 | 1160 return false; // referent is reachable |
1161 } | |
1162 } | |
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1163 if (rt == REF_SOFT) { |
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1164 // For soft refs we can decide now if these are not |
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1165 // current candidates for clearing, in which case we |
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1166 // can mark through them now, rather than delaying that |
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1167 // to the reference-processing phase. Since all current |
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1168 // time-stamp policies advance the soft-ref clock only |
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1169 // at a major collection cycle, this is always currently |
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1170 // accurate. |
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1171 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { |
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1172 return false; |
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1173 } |
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1174 } |
0 | 1175 |
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1176 ResourceMark rm; // Needed for tracing. |
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1177 |
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1178 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1179 const oop discovered = java_lang_ref_Reference::discovered(obj); |
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1180 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1181 if (discovered != NULL) { |
0 | 1182 // The reference has already been discovered... |
1183 if (TraceReferenceGC) { | |
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1184 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1185 obj, obj->blueprint()->internal_name()); |
0 | 1186 } |
1187 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1188 // assumes that an object is not processed twice; | |
1189 // if it's been already discovered it must be on another | |
1190 // generation's discovered list; so we won't discover it. | |
1191 return false; | |
1192 } else { | |
1193 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
1194 "Unrecognized policy"); | |
1195 // Check assumption that an object is not potentially | |
1196 // discovered twice except by concurrent collectors that potentially | |
1197 // trace the same Reference object twice. | |
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1198 assert(UseConcMarkSweepGC || UseG1GC, |
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1199 "Only possible with a concurrent marking collector"); |
0 | 1200 return true; |
1201 } | |
1202 } | |
1203 | |
1204 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
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1205 verify_referent(obj); |
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1206 // Discover if and only if EITHER: |
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1207 // .. reference is in our span, OR |
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1208 // .. we are an atomic collector and referent is in our span |
0 | 1209 if (_span.contains(obj_addr) || |
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1210 (discovery_is_atomic() && |
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1211 _span.contains(java_lang_ref_Reference::referent(obj)))) { |
0 | 1212 // should_enqueue = true; |
1213 } else { | |
1214 return false; | |
1215 } | |
1216 } else { | |
1217 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1218 _span.contains(obj_addr), "code inconsistency"); | |
1219 } | |
1220 | |
1221 // Get the right type of discovered queue head. | |
1222 DiscoveredList* list = get_discovered_list(rt); | |
1223 if (list == NULL) { | |
1224 return false; // nothing special needs to be done | |
1225 } | |
1226 | |
1227 if (_discovery_is_mt) { | |
1228 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
1229 } else { | |
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1230 // If "_discovered_list_needs_barrier", we do write barriers when |
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1231 // updating the discovered reference list. Otherwise, we do a raw store |
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1232 // here: the field will be visited later when processing the discovered |
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1233 // references. |
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1234 oop current_head = list->head(); |
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1235 // The last ref must have its discovered field pointing to itself. |
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1236 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1237 |
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1238 // As in the case further above, since we are over-writing a NULL |
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1239 // pre-value, we can safely elide the pre-barrier here for the case of G1. |
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1240 // e.g.:- _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1241 assert(discovered == NULL, "control point invariant"); |
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1242 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1243 "For non-G1 collector, may need a pre-write-barrier for CAS from NULL below"); |
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1244 oop_store_raw(discovered_addr, next_discovered); |
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1245 if (_discovered_list_needs_barrier) { |
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1246 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1247 } |
0 | 1248 list->set_head(obj); |
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1249 list->inc_length(1); |
0 | 1250 |
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1251 if (TraceReferenceGC) { |
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1252 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)", |
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1253 obj, obj->blueprint()->internal_name()); |
0 | 1254 } |
1255 } | |
3917
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4965777: GC changes to support use of discovered field for pending references
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1256 assert(obj->is_oop(), "Discovered a bad reference"); |
1995
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1257 verify_referent(obj); |
0 | 1258 return true; |
1259 } | |
1260 | |
1261 // Preclean the discovered references by removing those | |
1262 // whose referents are alive, and by marking from those that | |
1263 // are not active. These lists can be handled here | |
1264 // in any order and, indeed, concurrently. | |
1265 void ReferenceProcessor::preclean_discovered_references( | |
1266 BoolObjectClosure* is_alive, | |
1267 OopClosure* keep_alive, | |
1268 VoidClosure* complete_gc, | |
1190
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1269 YieldClosure* yield, |
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1270 bool should_unload_classes) { |
0 | 1271 |
1272 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
1273 | |
935 | 1274 #ifdef ASSERT |
1275 bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC || | |
1190
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1276 CMSClassUnloadingEnabled && UseConcMarkSweepGC || |
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1277 ExplicitGCInvokesConcurrentAndUnloadsClasses && |
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1278 UseConcMarkSweepGC && should_unload_classes; |
935 | 1279 RememberKlassesChecker mx(must_remember_klasses); |
1280 #endif | |
0 | 1281 // Soft references |
1282 { | |
1283 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, | |
1284 false, gclog_or_tty); | |
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1285 for (uint i = 0; i < _max_num_q; i++) { |
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1286 if (yield->should_return()) { |
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1287 return; |
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1288 } |
0 | 1289 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
1290 keep_alive, complete_gc, yield); | |
1291 } | |
1292 } | |
1293 | |
1294 // Weak references | |
1295 { | |
1296 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, | |
1297 false, gclog_or_tty); | |
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1298 for (uint i = 0; i < _max_num_q; i++) { |
452
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1299 if (yield->should_return()) { |
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1300 return; |
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1301 } |
0 | 1302 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
1303 keep_alive, complete_gc, yield); | |
1304 } | |
1305 } | |
1306 | |
1307 // Final references | |
1308 { | |
1309 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, | |
1310 false, gclog_or_tty); | |
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1311 for (uint i = 0; i < _max_num_q; i++) { |
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1312 if (yield->should_return()) { |
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1313 return; |
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1314 } |
0 | 1315 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
1316 keep_alive, complete_gc, yield); | |
1317 } | |
1318 } | |
1319 | |
1320 // Phantom references | |
1321 { | |
1322 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, | |
1323 false, gclog_or_tty); | |
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1324 for (uint i = 0; i < _max_num_q; i++) { |
452
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1325 if (yield->should_return()) { |
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1326 return; |
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1327 } |
0 | 1328 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
1329 keep_alive, complete_gc, yield); | |
1330 } | |
1331 } | |
1332 } | |
1333 | |
1334 // Walk the given discovered ref list, and remove all reference objects | |
1335 // whose referents are still alive, whose referents are NULL or which | |
452
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1336 // are not active (have a non-NULL next field). NOTE: When we are |
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1337 // thus precleaning the ref lists (which happens single-threaded today), |
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1338 // we do not disable refs discovery to honour the correct semantics of |
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1339 // java.lang.Reference. As a result, we need to be careful below |
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1340 // that ref removal steps interleave safely with ref discovery steps |
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1341 // (in this thread). |
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1342 void |
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1343 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1344 BoolObjectClosure* is_alive, |
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1345 OopClosure* keep_alive, |
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1346 VoidClosure* complete_gc, |
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1347 YieldClosure* yield) { |
0 | 1348 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
1349 while (iter.has_next()) { | |
1350 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1351 oop obj = iter.obj(); |
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1352 oop next = java_lang_ref_Reference::next(obj); |
0 | 1353 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1354 next != NULL) { |
0 | 1355 // The referent has been cleared, or is alive, or the Reference is not |
1356 // active; we need to trace and mark its cohort. | |
1357 if (TraceReferenceGC) { | |
1358 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
1359 iter.obj(), iter.obj()->blueprint()->internal_name()); | |
1360 } | |
1361 // Remove Reference object from list | |
1362 iter.remove(); | |
1363 // Keep alive its cohort. | |
1364 iter.make_referent_alive(); | |
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1365 if (UseCompressedOops) { |
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1366 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1367 keep_alive->do_oop(next_addr); |
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1368 } else { |
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1369 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1370 keep_alive->do_oop(next_addr); |
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1371 } |
452
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1372 iter.move_to_next(); |
0 | 1373 } else { |
1374 iter.next(); | |
1375 } | |
1376 } | |
1377 // Close the reachable set | |
1378 complete_gc->do_void(); | |
1379 | |
1380 NOT_PRODUCT( | |
2369
92da084fefc9
6668573: CMS: reference processing crash if ParallelCMSThreads > ParallelGCThreads
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1381 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) { |
1833
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6984287: Regularize how GC parallel workers are specified.
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1382 gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
8b10f48633dc
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1383 "Refs in discovered list " INTPTR_FORMAT, |
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1384 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 1385 } |
1386 ) | |
1387 } | |
1388 | |
4728
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1389 const char* ReferenceProcessor::list_name(uint i) { |
3979
4dfb2df418f2
6484982: G1: process references during evacuation pauses
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1390 assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(), |
4dfb2df418f2
6484982: G1: process references during evacuation pauses
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1391 "Out of bounds index"); |
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|
1392 |
1833
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1393 int j = i / _max_num_q; |
0 | 1394 switch (j) { |
1395 case 0: return "SoftRef"; | |
1396 case 1: return "WeakRef"; | |
1397 case 2: return "FinalRef"; | |
1398 case 3: return "PhantomRef"; | |
1399 } | |
1400 ShouldNotReachHere(); | |
1401 return NULL; | |
1402 } | |
1403 | |
1404 #ifndef PRODUCT | |
1405 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
1406 // empty for now | |
1407 } | |
1408 #endif | |
1409 | |
1410 #ifndef PRODUCT | |
1411 void ReferenceProcessor::clear_discovered_references() { | |
1412 guarantee(!_discovering_refs, "Discovering refs?"); | |
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1413 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
4014
bf2d2b8b1726
7095243: Disambiguate ReferenceProcessor::_discoveredSoftRefs
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1414 clear_discovered_references(_discovered_refs[i]); |
0 | 1415 } |
1416 } | |
3915
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1417 |
0 | 1418 #endif // PRODUCT |