Mercurial > hg > truffle
annotate src/share/vm/memory/referenceProcessor.cpp @ 113:ba764ed4b6f2
6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
Summary: Compressed oops in instances, arrays, and headers. Code contributors are coleenp, phh, never, swamyv
Reviewed-by: jmasa, kamg, acorn, tbell, kvn, rasbold
| author | coleenp |
|---|---|
| date | Sun, 13 Apr 2008 17:43:42 -0400 |
| parents | f21b879b4c72 |
| children | d1605aabd0a1 37f87013dfd8 |
| rev | line source |
|---|---|
| 0 | 1 /* |
| 2 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved. | |
| 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 * | |
| 19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
| 20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
| 21 * have any questions. | |
| 22 * | |
| 23 */ | |
| 24 | |
| 25 # include "incls/_precompiled.incl" | |
| 26 # include "incls/_referenceProcessor.cpp.incl" | |
| 27 | |
| 28 // List of discovered references. | |
| 29 class DiscoveredList { | |
| 30 public: | |
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31 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } |
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32 oop head() const { |
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33 return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) : |
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34 _oop_head; |
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35 } |
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36 HeapWord* adr_head() { |
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37 return UseCompressedOops ? (HeapWord*)&_compressed_head : |
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38 (HeapWord*)&_oop_head; |
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39 } |
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40 void set_head(oop o) { |
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41 if (UseCompressedOops) { |
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42 // Must compress the head ptr. |
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43 _compressed_head = oopDesc::encode_heap_oop_not_null(o); |
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44 } else { |
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45 _oop_head = o; |
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46 } |
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47 } |
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48 bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); } |
| 0 | 49 size_t length() { return _len; } |
| 50 void set_length(size_t len) { _len = len; } | |
| 51 private: | |
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52 // Set value depending on UseCompressedOops. This could be a template class |
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53 // but then we have to fix all the instantiations and declarations that use this class. |
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54 oop _oop_head; |
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55 narrowOop _compressed_head; |
| 0 | 56 size_t _len; |
| 57 }; | |
| 58 | |
| 59 oop ReferenceProcessor::_sentinelRef = NULL; | |
| 60 | |
| 61 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER; | |
| 62 | |
| 63 void referenceProcessor_init() { | |
| 64 ReferenceProcessor::init_statics(); | |
| 65 } | |
| 66 | |
| 67 void ReferenceProcessor::init_statics() { | |
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68 assert(_sentinelRef == NULL, "should be initialized precisely once"); |
| 0 | 69 EXCEPTION_MARK; |
| 70 _sentinelRef = instanceKlass::cast( | |
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71 SystemDictionary::reference_klass())-> |
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72 allocate_permanent_instance(THREAD); |
| 0 | 73 |
| 74 // Initialize the master soft ref clock. | |
| 75 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis()); | |
| 76 | |
| 77 if (HAS_PENDING_EXCEPTION) { | |
| 78 Handle ex(THREAD, PENDING_EXCEPTION); | |
| 79 vm_exit_during_initialization(ex); | |
| 80 } | |
| 81 assert(_sentinelRef != NULL && _sentinelRef->is_oop(), | |
| 82 "Just constructed it!"); | |
| 83 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || | |
| 84 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
| 85 "Unrecongnized RefDiscoveryPolicy"); | |
| 86 } | |
| 87 | |
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88 ReferenceProcessor* |
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89 ReferenceProcessor::create_ref_processor(MemRegion span, |
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90 bool atomic_discovery, |
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91 bool mt_discovery, |
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92 BoolObjectClosure* is_alive_non_header, |
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93 int parallel_gc_threads, |
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94 bool mt_processing) { |
| 0 | 95 int mt_degree = 1; |
| 96 if (parallel_gc_threads > 1) { | |
| 97 mt_degree = parallel_gc_threads; | |
| 98 } | |
| 99 ReferenceProcessor* rp = | |
| 100 new ReferenceProcessor(span, atomic_discovery, | |
| 101 mt_discovery, mt_degree, | |
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102 mt_processing && (parallel_gc_threads > 0)); |
| 0 | 103 if (rp == NULL) { |
| 104 vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); | |
| 105 } | |
| 106 rp->set_is_alive_non_header(is_alive_non_header); | |
| 107 return rp; | |
| 108 } | |
| 109 | |
| 110 ReferenceProcessor::ReferenceProcessor(MemRegion span, | |
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111 bool atomic_discovery, |
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112 bool mt_discovery, |
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113 int mt_degree, |
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114 bool mt_processing) : |
| 0 | 115 _discovering_refs(false), |
| 116 _enqueuing_is_done(false), | |
| 117 _is_alive_non_header(NULL), | |
| 118 _processing_is_mt(mt_processing), | |
| 119 _next_id(0) | |
| 120 { | |
| 121 _span = span; | |
| 122 _discovery_is_atomic = atomic_discovery; | |
| 123 _discovery_is_mt = mt_discovery; | |
| 124 _num_q = mt_degree; | |
| 125 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref); | |
| 126 if (_discoveredSoftRefs == NULL) { | |
| 127 vm_exit_during_initialization("Could not allocated RefProc Array"); | |
| 128 } | |
| 129 _discoveredWeakRefs = &_discoveredSoftRefs[_num_q]; | |
| 130 _discoveredFinalRefs = &_discoveredWeakRefs[_num_q]; | |
| 131 _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q]; | |
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132 assert(sentinel_ref() != NULL, "_sentinelRef is NULL"); |
| 0 | 133 // Initialized all entries to _sentinelRef |
| 134 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
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135 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
| 0 | 136 _discoveredSoftRefs[i].set_length(0); |
| 137 } | |
| 138 } | |
| 139 | |
| 140 #ifndef PRODUCT | |
| 141 void ReferenceProcessor::verify_no_references_recorded() { | |
| 142 guarantee(!_discovering_refs, "Discovering refs?"); | |
| 143 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
| 144 guarantee(_discoveredSoftRefs[i].empty(), | |
| 145 "Found non-empty discovered list"); | |
| 146 } | |
| 147 } | |
| 148 #endif | |
| 149 | |
| 150 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
| 151 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
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152 if (UseCompressedOops) { |
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153 f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head()); |
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154 } else { |
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155 f->do_oop((oop*)_discoveredSoftRefs[i].adr_head()); |
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156 } |
| 0 | 157 } |
| 158 } | |
| 159 | |
| 160 void ReferenceProcessor::oops_do(OopClosure* f) { | |
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161 f->do_oop(adr_sentinel_ref()); |
| 0 | 162 } |
| 163 | |
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164 void ReferenceProcessor::update_soft_ref_master_clock() { |
| 0 | 165 // Update (advance) the soft ref master clock field. This must be done |
| 166 // after processing the soft ref list. | |
| 167 jlong now = os::javaTimeMillis(); | |
| 168 jlong clock = java_lang_ref_SoftReference::clock(); | |
| 169 NOT_PRODUCT( | |
| 170 if (now < clock) { | |
| 171 warning("time warp: %d to %d", clock, now); | |
| 172 } | |
| 173 ) | |
| 174 // In product mode, protect ourselves from system time being adjusted | |
| 175 // externally and going backward; see note in the implementation of | |
| 176 // GenCollectedHeap::time_since_last_gc() for the right way to fix | |
| 177 // this uniformly throughout the VM; see bug-id 4741166. XXX | |
| 178 if (now > clock) { | |
| 179 java_lang_ref_SoftReference::set_clock(now); | |
| 180 } | |
| 181 // Else leave clock stalled at its old value until time progresses | |
| 182 // past clock value. | |
| 183 } | |
| 184 | |
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185 void ReferenceProcessor::process_discovered_references( |
| 0 | 186 ReferencePolicy* policy, |
| 187 BoolObjectClosure* is_alive, | |
| 188 OopClosure* keep_alive, | |
| 189 VoidClosure* complete_gc, | |
| 190 AbstractRefProcTaskExecutor* task_executor) { | |
| 191 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
| 192 | |
| 193 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
| 194 // Stop treating discovered references specially. | |
| 195 disable_discovery(); | |
| 196 | |
| 197 bool trace_time = PrintGCDetails && PrintReferenceGC; | |
| 198 // Soft references | |
| 199 { | |
| 200 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); | |
| 201 process_discovered_reflist(_discoveredSoftRefs, policy, true, | |
| 202 is_alive, keep_alive, complete_gc, task_executor); | |
| 203 } | |
| 204 | |
| 205 update_soft_ref_master_clock(); | |
| 206 | |
| 207 // Weak references | |
| 208 { | |
| 209 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); | |
| 210 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
| 211 is_alive, keep_alive, complete_gc, task_executor); | |
| 212 } | |
| 213 | |
| 214 // Final references | |
| 215 { | |
| 216 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); | |
| 217 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
| 218 is_alive, keep_alive, complete_gc, task_executor); | |
| 219 } | |
| 220 | |
| 221 // Phantom references | |
| 222 { | |
| 223 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); | |
| 224 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
| 225 is_alive, keep_alive, complete_gc, task_executor); | |
| 226 } | |
| 227 | |
| 228 // Weak global JNI references. It would make more sense (semantically) to | |
| 229 // traverse these simultaneously with the regular weak references above, but | |
| 230 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
| 231 // thus use JNI weak references to circumvent the phantom references and | |
| 232 // resurrect a "post-mortem" object. | |
| 233 { | |
| 234 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); | |
| 235 if (task_executor != NULL) { | |
| 236 task_executor->set_single_threaded_mode(); | |
| 237 } | |
| 238 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
| 239 } | |
| 240 } | |
| 241 | |
| 242 #ifndef PRODUCT | |
| 243 // Calculate the number of jni handles. | |
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244 uint ReferenceProcessor::count_jni_refs() { |
| 0 | 245 class AlwaysAliveClosure: public BoolObjectClosure { |
| 246 public: | |
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247 virtual bool do_object_b(oop obj) { return true; } |
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248 virtual void do_object(oop obj) { assert(false, "Don't call"); } |
| 0 | 249 }; |
| 250 | |
| 251 class CountHandleClosure: public OopClosure { | |
| 252 private: | |
| 253 int _count; | |
| 254 public: | |
| 255 CountHandleClosure(): _count(0) {} | |
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256 void do_oop(oop* unused) { _count++; } |
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257 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
| 0 | 258 int count() { return _count; } |
| 259 }; | |
| 260 CountHandleClosure global_handle_count; | |
| 261 AlwaysAliveClosure always_alive; | |
| 262 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
| 263 return global_handle_count.count(); | |
| 264 } | |
| 265 #endif | |
| 266 | |
| 267 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
| 268 OopClosure* keep_alive, | |
| 269 VoidClosure* complete_gc) { | |
| 270 #ifndef PRODUCT | |
| 271 if (PrintGCDetails && PrintReferenceGC) { | |
| 272 unsigned int count = count_jni_refs(); | |
| 273 gclog_or_tty->print(", %u refs", count); | |
| 274 } | |
| 275 #endif | |
| 276 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
| 277 // Finally remember to keep sentinel around | |
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278 keep_alive->do_oop(adr_sentinel_ref()); |
| 0 | 279 complete_gc->do_void(); |
| 280 } | |
| 281 | |
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282 |
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283 template <class T> |
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284 static bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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285 AbstractRefProcTaskExecutor* task_executor) { |
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286 |
| 0 | 287 // Remember old value of pending references list |
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288 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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289 T old_pending_list_value = *pending_list_addr; |
| 0 | 290 |
| 291 // Enqueue references that are not made active again, and | |
| 292 // clear the decks for the next collection (cycle). | |
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293 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
| 0 | 294 // Do the oop-check on pending_list_addr missed in |
| 295 // enqueue_discovered_reflist. We should probably | |
| 296 // do a raw oop_check so that future such idempotent | |
| 297 // oop_stores relying on the oop-check side-effect | |
| 298 // may be elided automatically and safely without | |
| 299 // affecting correctness. | |
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300 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
| 0 | 301 |
| 302 // Stop treating discovered references specially. | |
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303 ref->disable_discovery(); |
| 0 | 304 |
| 305 // Return true if new pending references were added | |
| 306 return old_pending_list_value != *pending_list_addr; | |
| 307 } | |
| 308 | |
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309 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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310 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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311 if (UseCompressedOops) { |
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312 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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313 } else { |
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314 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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315 } |
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316 } |
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317 |
| 0 | 318 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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319 HeapWord* pending_list_addr) { |
| 0 | 320 // Given a list of refs linked through the "discovered" field |
| 321 // (java.lang.ref.Reference.discovered) chain them through the | |
| 322 // "next" field (java.lang.ref.Reference.next) and prepend | |
| 323 // to the pending list. | |
| 324 if (TraceReferenceGC && PrintGCDetails) { | |
| 325 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
| 326 INTPTR_FORMAT, (address)refs_list.head()); | |
| 327 } | |
| 328 oop obj = refs_list.head(); | |
| 329 // Walk down the list, copying the discovered field into | |
| 330 // the next field and clearing it (except for the last | |
| 331 // non-sentinel object which is treated specially to avoid | |
| 332 // confusion with an active reference). | |
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333 while (obj != sentinel_ref()) { |
| 0 | 334 assert(obj->is_instanceRef(), "should be reference object"); |
| 335 oop next = java_lang_ref_Reference::discovered(obj); | |
| 336 if (TraceReferenceGC && PrintGCDetails) { | |
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337 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT, |
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338 obj, next); |
| 0 | 339 } |
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340 assert(java_lang_ref_Reference::next(obj) == NULL, |
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341 "The reference should not be enqueued"); |
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342 if (next == sentinel_ref()) { // obj is last |
| 0 | 343 // Swap refs_list into pendling_list_addr and |
| 344 // set obj's next to what we read from pending_list_addr. | |
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345 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
| 0 | 346 // Need oop_check on pending_list_addr above; |
| 347 // see special oop-check code at the end of | |
| 348 // enqueue_discovered_reflists() further below. | |
| 349 if (old == NULL) { | |
| 350 // obj should be made to point to itself, since | |
| 351 // pending list was empty. | |
| 352 java_lang_ref_Reference::set_next(obj, obj); | |
| 353 } else { | |
| 354 java_lang_ref_Reference::set_next(obj, old); | |
| 355 } | |
| 356 } else { | |
| 357 java_lang_ref_Reference::set_next(obj, next); | |
| 358 } | |
| 359 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); | |
| 360 obj = next; | |
| 361 } | |
| 362 } | |
| 363 | |
| 364 // Parallel enqueue task | |
| 365 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
| 366 public: | |
| 367 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
| 368 DiscoveredList discovered_refs[], | |
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369 HeapWord* pending_list_addr, |
| 0 | 370 oop sentinel_ref, |
| 371 int n_queues) | |
| 372 : EnqueueTask(ref_processor, discovered_refs, | |
| 373 pending_list_addr, sentinel_ref, n_queues) | |
| 374 { } | |
| 375 | |
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376 virtual void work(unsigned int work_id) { |
| 0 | 377 assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds"); |
| 378 // Simplest first cut: static partitioning. | |
| 379 int index = work_id; | |
| 380 for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) { | |
| 381 _ref_processor.enqueue_discovered_reflist( | |
| 382 _refs_lists[index], _pending_list_addr); | |
| 383 _refs_lists[index].set_head(_sentinel_ref); | |
| 384 _refs_lists[index].set_length(0); | |
| 385 } | |
| 386 } | |
| 387 }; | |
| 388 | |
| 389 // Enqueue references that are not made active again | |
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390 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
| 0 | 391 AbstractRefProcTaskExecutor* task_executor) { |
| 392 if (_processing_is_mt && task_executor != NULL) { | |
| 393 // Parallel code | |
| 394 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs, | |
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395 pending_list_addr, sentinel_ref(), _num_q); |
| 0 | 396 task_executor->execute(tsk); |
| 397 } else { | |
| 398 // Serial code: call the parent class's implementation | |
| 399 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
| 400 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr); | |
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401 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
| 0 | 402 _discoveredSoftRefs[i].set_length(0); |
| 403 } | |
| 404 } | |
| 405 } | |
| 406 | |
| 407 // Iterator for the list of discovered references. | |
| 408 class DiscoveredListIterator { | |
| 409 public: | |
| 410 inline DiscoveredListIterator(DiscoveredList& refs_list, | |
| 411 OopClosure* keep_alive, | |
| 412 BoolObjectClosure* is_alive); | |
| 413 | |
| 414 // End Of List. | |
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415 inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); } |
| 0 | 416 |
| 417 // Get oop to the Reference object. | |
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418 inline oop obj() const { return _ref; } |
| 0 | 419 |
| 420 // Get oop to the referent object. | |
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421 inline oop referent() const { return _referent; } |
| 0 | 422 |
| 423 // Returns true if referent is alive. | |
| 424 inline bool is_referent_alive() const; | |
| 425 | |
| 426 // Loads data for the current reference. | |
| 427 // The "allow_null_referent" argument tells us to allow for the possibility | |
| 428 // of a NULL referent in the discovered Reference object. This typically | |
| 429 // happens in the case of concurrent collectors that may have done the | |
| 430 // discovery concurrently or interleaved with mutator execution. | |
| 431 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); | |
| 432 | |
| 433 // Move to the next discovered reference. | |
| 434 inline void next(); | |
| 435 | |
| 436 // Remove the current reference from the list and move to the next. | |
| 437 inline void remove(); | |
| 438 | |
| 439 // Make the Reference object active again. | |
| 440 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); } | |
| 441 | |
| 442 // Make the referent alive. | |
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443 inline void make_referent_alive() { |
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444 if (UseCompressedOops) { |
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445 _keep_alive->do_oop((narrowOop*)_referent_addr); |
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446 } else { |
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447 _keep_alive->do_oop((oop*)_referent_addr); |
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448 } |
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449 } |
| 0 | 450 |
| 451 // Update the discovered field. | |
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452 inline void update_discovered() { |
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453 // First _prev_next ref actually points into DiscoveredList (gross). |
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454 if (UseCompressedOops) { |
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455 _keep_alive->do_oop((narrowOop*)_prev_next); |
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456 } else { |
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457 _keep_alive->do_oop((oop*)_prev_next); |
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458 } |
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459 } |
| 0 | 460 |
| 461 // NULL out referent pointer. | |
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462 inline void clear_referent() { oop_store_raw(_referent_addr, NULL); } |
| 0 | 463 |
| 464 // Statistics | |
| 465 NOT_PRODUCT( | |
| 466 inline size_t processed() const { return _processed; } | |
| 467 inline size_t removed() const { return _removed; } | |
| 468 ) | |
| 469 | |
| 470 private: | |
| 471 inline void move_to_next(); | |
| 472 | |
| 473 private: | |
| 474 DiscoveredList& _refs_list; | |
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475 HeapWord* _prev_next; |
| 0 | 476 oop _ref; |
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477 HeapWord* _discovered_addr; |
| 0 | 478 oop _next; |
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479 HeapWord* _referent_addr; |
| 0 | 480 oop _referent; |
| 481 OopClosure* _keep_alive; | |
| 482 BoolObjectClosure* _is_alive; | |
| 483 DEBUG_ONLY( | |
| 484 oop _first_seen; // cyclic linked list check | |
| 485 ) | |
| 486 NOT_PRODUCT( | |
| 487 size_t _processed; | |
| 488 size_t _removed; | |
| 489 ) | |
| 490 }; | |
| 491 | |
| 492 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list, | |
| 493 OopClosure* keep_alive, | |
| 494 BoolObjectClosure* is_alive) | |
| 495 : _refs_list(refs_list), | |
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496 _prev_next(refs_list.adr_head()), |
| 0 | 497 _ref(refs_list.head()), |
| 498 #ifdef ASSERT | |
| 499 _first_seen(refs_list.head()), | |
| 500 #endif | |
| 501 #ifndef PRODUCT | |
| 502 _processed(0), | |
| 503 _removed(0), | |
| 504 #endif | |
| 505 _next(refs_list.head()), | |
| 506 _keep_alive(keep_alive), | |
| 507 _is_alive(is_alive) | |
| 508 { } | |
| 509 | |
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510 inline bool DiscoveredListIterator::is_referent_alive() const { |
| 0 | 511 return _is_alive->do_object_b(_referent); |
| 512 } | |
| 513 | |
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514 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
| 0 | 515 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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516 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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517 assert(_discovered_addr && discovered->is_oop_or_null(), |
| 0 | 518 "discovered field is bad"); |
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519 _next = discovered; |
| 0 | 520 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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521 _referent = java_lang_ref_Reference::referent(_ref); |
| 0 | 522 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
| 523 "Wrong oop found in java.lang.Reference object"); | |
| 524 assert(allow_null_referent ? | |
| 525 _referent->is_oop_or_null() | |
| 526 : _referent->is_oop(), | |
| 527 "bad referent"); | |
| 528 } | |
| 529 | |
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530 inline void DiscoveredListIterator::next() { |
| 0 | 531 _prev_next = _discovered_addr; |
| 532 move_to_next(); | |
| 533 } | |
| 534 | |
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535 inline void DiscoveredListIterator::remove() { |
| 0 | 536 assert(_ref->is_oop(), "Dropping a bad reference"); |
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537 oop_store_raw(_discovered_addr, NULL); |
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538 // First _prev_next ref actually points into DiscoveredList (gross). |
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539 if (UseCompressedOops) { |
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540 // Remove Reference object from list. |
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541 oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next); |
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542 } else { |
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543 // Remove Reference object from list. |
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544 oopDesc::store_heap_oop((oop*)_prev_next, _next); |
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545 } |
| 0 | 546 NOT_PRODUCT(_removed++); |
| 547 move_to_next(); | |
| 548 } | |
| 549 | |
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550 inline void DiscoveredListIterator::move_to_next() { |
| 0 | 551 _ref = _next; |
| 552 assert(_ref != _first_seen, "cyclic ref_list found"); | |
| 553 NOT_PRODUCT(_processed++); | |
| 554 } | |
| 555 | |
| 556 // NOTE: process_phase*() are largely similar, and at a high level | |
| 557 // merely iterate over the extant list applying a predicate to | |
| 558 // each of its elements and possibly removing that element from the | |
| 559 // list and applying some further closures to that element. | |
| 560 // We should consider the possibility of replacing these | |
| 561 // process_phase*() methods by abstracting them into | |
| 562 // a single general iterator invocation that receives appropriate | |
| 563 // closures that accomplish this work. | |
| 564 | |
| 565 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
| 566 // referents are not alive, but that should be kept alive for policy reasons. | |
| 567 // Keep alive the transitive closure of all such referents. | |
| 568 void | |
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569 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
| 0 | 570 ReferencePolicy* policy, |
| 571 BoolObjectClosure* is_alive, | |
| 572 OopClosure* keep_alive, | |
| 573 VoidClosure* complete_gc) { | |
| 574 assert(policy != NULL, "Must have a non-NULL policy"); | |
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575 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| 0 | 576 // Decide which softly reachable refs should be kept alive. |
| 577 while (iter.has_next()) { | |
| 578 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
| 579 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
| 580 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) { | |
| 581 if (TraceReferenceGC) { | |
| 582 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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583 iter.obj(), iter.obj()->blueprint()->internal_name()); |
| 0 | 584 } |
| 585 // Make the Reference object active again | |
| 586 iter.make_active(); | |
| 587 // keep the referent around | |
| 588 iter.make_referent_alive(); | |
| 589 // Remove Reference object from list | |
| 590 iter.remove(); | |
| 591 } else { | |
| 592 iter.next(); | |
| 593 } | |
| 594 } | |
| 595 // Close the reachable set | |
| 596 complete_gc->do_void(); | |
| 597 NOT_PRODUCT( | |
| 598 if (PrintGCDetails && TraceReferenceGC) { | |
| 599 gclog_or_tty->print(" Dropped %d dead Refs out of %d " | |
| 600 "discovered Refs by policy ", iter.removed(), iter.processed()); | |
| 601 } | |
| 602 ) | |
| 603 } | |
| 604 | |
| 605 // Traverse the list and remove any Refs that are not active, or | |
| 606 // whose referents are either alive or NULL. | |
| 607 void | |
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608 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
| 0 | 609 BoolObjectClosure* is_alive, |
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610 OopClosure* keep_alive) { |
| 0 | 611 assert(discovery_is_atomic(), "Error"); |
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612 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| 0 | 613 while (iter.has_next()) { |
| 614 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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615 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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616 assert(next == NULL, "Should not discover inactive Reference"); |
| 0 | 617 if (iter.is_referent_alive()) { |
| 618 if (TraceReferenceGC) { | |
| 619 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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620 iter.obj(), iter.obj()->blueprint()->internal_name()); |
| 0 | 621 } |
| 622 // The referent is reachable after all. | |
| 623 // Update the referent pointer as necessary: Note that this | |
| 624 // should not entail any recursive marking because the | |
| 625 // referent must already have been traversed. | |
| 626 iter.make_referent_alive(); | |
| 627 // Remove Reference object from list | |
| 628 iter.remove(); | |
| 629 } else { | |
| 630 iter.next(); | |
| 631 } | |
| 632 } | |
| 633 NOT_PRODUCT( | |
| 634 if (PrintGCDetails && TraceReferenceGC) { | |
| 635 gclog_or_tty->print(" Dropped %d active Refs out of %d " | |
| 636 "Refs in discovered list ", iter.removed(), iter.processed()); | |
| 637 } | |
| 638 ) | |
| 639 } | |
| 640 | |
| 641 void | |
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642 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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643 BoolObjectClosure* is_alive, |
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644 OopClosure* keep_alive, |
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645 VoidClosure* complete_gc) { |
| 0 | 646 assert(!discovery_is_atomic(), "Error"); |
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647 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| 0 | 648 while (iter.has_next()) { |
| 649 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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650 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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651 oop next = java_lang_ref_Reference::next(iter.obj()); |
| 0 | 652 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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653 next != NULL)) { |
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654 assert(next->is_oop_or_null(), "bad next field"); |
| 0 | 655 // Remove Reference object from list |
| 656 iter.remove(); | |
| 657 // Trace the cohorts | |
| 658 iter.make_referent_alive(); | |
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659 if (UseCompressedOops) { |
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660 keep_alive->do_oop((narrowOop*)next_addr); |
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661 } else { |
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662 keep_alive->do_oop((oop*)next_addr); |
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663 } |
| 0 | 664 } else { |
| 665 iter.next(); | |
| 666 } | |
| 667 } | |
| 668 // Now close the newly reachable set | |
| 669 complete_gc->do_void(); | |
| 670 NOT_PRODUCT( | |
| 671 if (PrintGCDetails && TraceReferenceGC) { | |
| 672 gclog_or_tty->print(" Dropped %d active Refs out of %d " | |
| 673 "Refs in discovered list ", iter.removed(), iter.processed()); | |
| 674 } | |
| 675 ) | |
| 676 } | |
| 677 | |
| 678 // Traverse the list and process the referents, by either | |
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679 // clearing them or keeping them (and their reachable |
| 0 | 680 // closure) alive. |
| 681 void | |
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682 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
| 0 | 683 bool clear_referent, |
| 684 BoolObjectClosure* is_alive, | |
| 685 OopClosure* keep_alive, | |
| 686 VoidClosure* complete_gc) { | |
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687 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| 0 | 688 while (iter.has_next()) { |
| 689 iter.update_discovered(); | |
| 690 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
| 691 if (clear_referent) { | |
| 692 // NULL out referent pointer | |
| 693 iter.clear_referent(); | |
| 694 } else { | |
| 695 // keep the referent around | |
| 696 iter.make_referent_alive(); | |
| 697 } | |
| 698 if (TraceReferenceGC) { | |
| 699 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
| 700 clear_referent ? "cleared " : "", | |
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701 iter.obj(), iter.obj()->blueprint()->internal_name()); |
| 0 | 702 } |
| 703 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
| 704 // If discovery is concurrent, we may have objects with null referents, | |
| 705 // being those that were concurrently cleared after they were discovered | |
| 706 // (and not subsequently precleaned). | |
| 707 assert( (discovery_is_atomic() && iter.referent()->is_oop()) | |
| 708 || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)), | |
| 709 "Adding a bad referent"); | |
| 710 iter.next(); | |
| 711 } | |
| 712 // Remember to keep sentinel pointer around | |
| 713 iter.update_discovered(); | |
| 714 // Close the reachable set | |
| 715 complete_gc->do_void(); | |
| 716 } | |
| 717 | |
| 718 void | |
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719 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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720 oop obj = refs_list.head(); |
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721 while (obj != sentinel_ref()) { |
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722 oop discovered = java_lang_ref_Reference::discovered(obj); |
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723 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
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724 obj = discovered; |
| 0 | 725 } |
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726 refs_list.set_head(sentinel_ref()); |
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727 refs_list.set_length(0); |
| 0 | 728 } |
| 729 | |
| 730 void | |
| 731 ReferenceProcessor::abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]) { | |
| 732 for (int i = 0; i < _num_q; i++) { | |
| 733 abandon_partial_discovered_list(refs_lists[i]); | |
| 734 } | |
| 735 } | |
| 736 | |
| 737 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
| 738 public: | |
| 739 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
| 740 DiscoveredList refs_lists[], | |
| 741 ReferencePolicy* policy, | |
| 742 bool marks_oops_alive) | |
| 743 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
| 744 _policy(policy) | |
| 745 { } | |
| 746 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
| 747 OopClosure& keep_alive, | |
| 748 VoidClosure& complete_gc) | |
| 749 { | |
| 750 _ref_processor.process_phase1(_refs_lists[i], _policy, | |
| 751 &is_alive, &keep_alive, &complete_gc); | |
| 752 } | |
| 753 private: | |
| 754 ReferencePolicy* _policy; | |
| 755 }; | |
| 756 | |
| 757 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
| 758 public: | |
| 759 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
| 760 DiscoveredList refs_lists[], | |
| 761 bool marks_oops_alive) | |
| 762 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
| 763 { } | |
| 764 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
| 765 OopClosure& keep_alive, | |
| 766 VoidClosure& complete_gc) | |
| 767 { | |
| 768 _ref_processor.process_phase2(_refs_lists[i], | |
| 769 &is_alive, &keep_alive, &complete_gc); | |
| 770 } | |
| 771 }; | |
| 772 | |
| 773 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
| 774 public: | |
| 775 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
| 776 DiscoveredList refs_lists[], | |
| 777 bool clear_referent, | |
| 778 bool marks_oops_alive) | |
| 779 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
| 780 _clear_referent(clear_referent) | |
| 781 { } | |
| 782 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
| 783 OopClosure& keep_alive, | |
| 784 VoidClosure& complete_gc) | |
| 785 { | |
| 786 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, | |
| 787 &is_alive, &keep_alive, &complete_gc); | |
| 788 } | |
| 789 private: | |
| 790 bool _clear_referent; | |
| 791 }; | |
| 792 | |
| 793 // Balances reference queues. | |
| 794 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) | |
| 795 { | |
| 796 // calculate total length | |
| 797 size_t total_refs = 0; | |
| 798 for (int i = 0; i < _num_q; ++i) { | |
| 799 total_refs += ref_lists[i].length(); | |
| 800 } | |
| 801 size_t avg_refs = total_refs / _num_q + 1; | |
| 802 int to_idx = 0; | |
| 803 for (int from_idx = 0; from_idx < _num_q; from_idx++) { | |
| 804 while (ref_lists[from_idx].length() > avg_refs) { | |
| 805 assert(to_idx < _num_q, "Sanity Check!"); | |
| 806 if (ref_lists[to_idx].length() < avg_refs) { | |
| 807 // move superfluous refs | |
| 808 size_t refs_to_move = | |
| 809 MIN2(ref_lists[from_idx].length() - avg_refs, | |
| 810 avg_refs - ref_lists[to_idx].length()); | |
| 811 oop move_head = ref_lists[from_idx].head(); | |
| 812 oop move_tail = move_head; | |
| 813 oop new_head = move_head; | |
| 814 // find an element to split the list on | |
| 815 for (size_t j = 0; j < refs_to_move; ++j) { | |
| 816 move_tail = new_head; | |
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817 new_head = java_lang_ref_Reference::discovered(new_head); |
| 0 | 818 } |
| 819 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head()); | |
| 820 ref_lists[to_idx].set_head(move_head); | |
| 821 ref_lists[to_idx].set_length(ref_lists[to_idx].length() + refs_to_move); | |
| 822 ref_lists[from_idx].set_head(new_head); | |
| 823 ref_lists[from_idx].set_length(ref_lists[from_idx].length() - refs_to_move); | |
| 824 } else { | |
| 825 ++to_idx; | |
| 826 } | |
| 827 } | |
| 828 } | |
| 829 } | |
| 830 | |
| 831 void | |
| 832 ReferenceProcessor::process_discovered_reflist( | |
| 833 DiscoveredList refs_lists[], | |
| 834 ReferencePolicy* policy, | |
| 835 bool clear_referent, | |
| 836 BoolObjectClosure* is_alive, | |
| 837 OopClosure* keep_alive, | |
| 838 VoidClosure* complete_gc, | |
| 839 AbstractRefProcTaskExecutor* task_executor) | |
| 840 { | |
| 841 bool mt = task_executor != NULL && _processing_is_mt; | |
| 842 if (mt && ParallelRefProcBalancingEnabled) { | |
| 843 balance_queues(refs_lists); | |
| 844 } | |
| 845 if (PrintReferenceGC && PrintGCDetails) { | |
| 846 size_t total = 0; | |
| 847 for (int i = 0; i < _num_q; ++i) { | |
| 848 total += refs_lists[i].length(); | |
| 849 } | |
| 850 gclog_or_tty->print(", %u refs", total); | |
| 851 } | |
| 852 | |
| 853 // Phase 1 (soft refs only): | |
| 854 // . Traverse the list and remove any SoftReferences whose | |
| 855 // referents are not alive, but that should be kept alive for | |
| 856 // policy reasons. Keep alive the transitive closure of all | |
| 857 // such referents. | |
| 858 if (policy != NULL) { | |
| 859 if (mt) { | |
| 860 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); | |
| 861 task_executor->execute(phase1); | |
| 862 } else { | |
| 863 for (int i = 0; i < _num_q; i++) { | |
| 864 process_phase1(refs_lists[i], policy, | |
| 865 is_alive, keep_alive, complete_gc); | |
| 866 } | |
| 867 } | |
| 868 } else { // policy == NULL | |
| 869 assert(refs_lists != _discoveredSoftRefs, | |
| 870 "Policy must be specified for soft references."); | |
| 871 } | |
| 872 | |
| 873 // Phase 2: | |
| 874 // . Traverse the list and remove any refs whose referents are alive. | |
| 875 if (mt) { | |
| 876 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); | |
| 877 task_executor->execute(phase2); | |
| 878 } else { | |
| 879 for (int i = 0; i < _num_q; i++) { | |
| 880 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); | |
| 881 } | |
| 882 } | |
| 883 | |
| 884 // Phase 3: | |
| 885 // . Traverse the list and process referents as appropriate. | |
| 886 if (mt) { | |
| 887 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); | |
| 888 task_executor->execute(phase3); | |
| 889 } else { | |
| 890 for (int i = 0; i < _num_q; i++) { | |
| 891 process_phase3(refs_lists[i], clear_referent, | |
| 892 is_alive, keep_alive, complete_gc); | |
| 893 } | |
| 894 } | |
| 895 } | |
| 896 | |
| 897 void ReferenceProcessor::clean_up_discovered_references() { | |
| 898 // loop over the lists | |
| 899 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
| 900 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) { | |
| 901 gclog_or_tty->print_cr( | |
| 902 "\nScrubbing %s discovered list of Null referents", | |
| 903 list_name(i)); | |
| 904 } | |
| 905 clean_up_discovered_reflist(_discoveredSoftRefs[i]); | |
| 906 } | |
| 907 } | |
| 908 | |
| 909 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
| 910 assert(!discovery_is_atomic(), "Else why call this method?"); | |
| 911 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
| 912 size_t length = refs_list.length(); | |
| 913 while (iter.has_next()) { | |
| 914 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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915 oop next = java_lang_ref_Reference::next(iter.obj()); |
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916 assert(next->is_oop_or_null(), "bad next field"); |
| 0 | 917 // If referent has been cleared or Reference is not active, |
| 918 // drop it. | |
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919 if (iter.referent() == NULL || next != NULL) { |
| 0 | 920 debug_only( |
| 921 if (PrintGCDetails && TraceReferenceGC) { | |
| 922 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
| 923 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
| 924 " and referent: " INTPTR_FORMAT, | |
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925 iter.obj(), next, iter.referent()); |
| 0 | 926 } |
| 927 ) | |
| 928 // Remove Reference object from list | |
| 929 iter.remove(); | |
| 930 --length; | |
| 931 } else { | |
| 932 iter.next(); | |
| 933 } | |
| 934 } | |
| 935 refs_list.set_length(length); | |
| 936 NOT_PRODUCT( | |
| 937 if (PrintGCDetails && TraceReferenceGC) { | |
| 938 gclog_or_tty->print( | |
| 939 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
| 940 iter.removed(), iter.processed()); | |
| 941 } | |
| 942 ) | |
| 943 } | |
| 944 | |
| 945 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
| 946 int id = 0; | |
| 947 // Determine the queue index to use for this object. | |
| 948 if (_discovery_is_mt) { | |
| 949 // During a multi-threaded discovery phase, | |
| 950 // each thread saves to its "own" list. | |
| 951 Thread* thr = Thread::current(); | |
| 952 assert(thr->is_GC_task_thread(), | |
| 953 "Dubious cast from Thread* to WorkerThread*?"); | |
| 954 id = ((WorkerThread*)thr)->id(); | |
| 955 } else { | |
| 956 // single-threaded discovery, we save in round-robin | |
| 957 // fashion to each of the lists. | |
| 958 if (_processing_is_mt) { | |
| 959 id = next_id(); | |
| 960 } | |
| 961 } | |
| 962 assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)"); | |
| 963 | |
| 964 // Get the discovered queue to which we will add | |
| 965 DiscoveredList* list = NULL; | |
| 966 switch (rt) { | |
| 967 case REF_OTHER: | |
| 968 // Unknown reference type, no special treatment | |
| 969 break; | |
| 970 case REF_SOFT: | |
| 971 list = &_discoveredSoftRefs[id]; | |
| 972 break; | |
| 973 case REF_WEAK: | |
| 974 list = &_discoveredWeakRefs[id]; | |
| 975 break; | |
| 976 case REF_FINAL: | |
| 977 list = &_discoveredFinalRefs[id]; | |
| 978 break; | |
| 979 case REF_PHANTOM: | |
| 980 list = &_discoveredPhantomRefs[id]; | |
| 981 break; | |
| 982 case REF_NONE: | |
| 983 // we should not reach here if we are an instanceRefKlass | |
| 984 default: | |
| 985 ShouldNotReachHere(); | |
| 986 } | |
| 987 return list; | |
| 988 } | |
| 989 | |
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990 inline void |
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991 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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992 oop obj, |
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993 HeapWord* discovered_addr) { |
| 0 | 994 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
| 995 // First we must make sure this object is only enqueued once. CAS in a non null | |
| 996 // discovered_addr. | |
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997 oop retest = oopDesc::atomic_compare_exchange_oop(refs_list.head(), discovered_addr, |
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998 NULL); |
| 0 | 999 if (retest == NULL) { |
| 1000 // This thread just won the right to enqueue the object. | |
| 1001 // We have separate lists for enqueueing so no synchronization | |
| 1002 // is necessary. | |
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1003 refs_list.set_head(obj); |
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1004 refs_list.set_length(refs_list.length() + 1); |
| 0 | 1005 } else { |
| 1006 // If retest was non NULL, another thread beat us to it: | |
| 1007 // The reference has already been discovered... | |
| 1008 if (TraceReferenceGC) { | |
| 1009 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", | |
| 1010 obj, obj->blueprint()->internal_name()); | |
| 1011 } | |
| 1012 } | |
| 1013 } | |
| 1014 | |
| 1015 // We mention two of several possible choices here: | |
| 1016 // #0: if the reference object is not in the "originating generation" | |
| 1017 // (or part of the heap being collected, indicated by our "span" | |
| 1018 // we don't treat it specially (i.e. we scan it as we would | |
| 1019 // a normal oop, treating its references as strong references). | |
| 1020 // This means that references can't be enqueued unless their | |
| 1021 // referent is also in the same span. This is the simplest, | |
| 1022 // most "local" and most conservative approach, albeit one | |
| 1023 // that may cause weak references to be enqueued least promptly. | |
| 1024 // We call this choice the "ReferenceBasedDiscovery" policy. | |
| 1025 // #1: the reference object may be in any generation (span), but if | |
| 1026 // the referent is in the generation (span) being currently collected | |
| 1027 // then we can discover the reference object, provided | |
| 1028 // the object has not already been discovered by | |
| 1029 // a different concurrently running collector (as may be the | |
| 1030 // case, for instance, if the reference object is in CMS and | |
| 1031 // the referent in DefNewGeneration), and provided the processing | |
| 1032 // of this reference object by the current collector will | |
| 1033 // appear atomic to every other collector in the system. | |
| 1034 // (Thus, for instance, a concurrent collector may not | |
| 1035 // discover references in other generations even if the | |
| 1036 // referent is in its own generation). This policy may, | |
| 1037 // in certain cases, enqueue references somewhat sooner than | |
| 1038 // might Policy #0 above, but at marginally increased cost | |
| 1039 // and complexity in processing these references. | |
| 1040 // We call this choice the "RefeferentBasedDiscovery" policy. | |
| 1041 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
| 1042 // We enqueue references only if we are discovering refs | |
| 1043 // (rather than processing discovered refs). | |
| 1044 if (!_discovering_refs || !RegisterReferences) { | |
| 1045 return false; | |
| 1046 } | |
| 1047 // We only enqueue active references. | |
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1048 oop next = java_lang_ref_Reference::next(obj); |
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1049 if (next != NULL) { |
| 0 | 1050 return false; |
| 1051 } | |
| 1052 | |
| 1053 HeapWord* obj_addr = (HeapWord*)obj; | |
| 1054 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
| 1055 !_span.contains(obj_addr)) { | |
| 1056 // Reference is not in the originating generation; | |
| 1057 // don't treat it specially (i.e. we want to scan it as a normal | |
| 1058 // object with strong references). | |
| 1059 return false; | |
| 1060 } | |
| 1061 | |
| 1062 // We only enqueue references whose referents are not (yet) strongly | |
| 1063 // reachable. | |
| 1064 if (is_alive_non_header() != NULL) { | |
| 1065 oop referent = java_lang_ref_Reference::referent(obj); | |
| 1066 // We'd like to assert the following: | |
| 1067 // assert(referent != NULL, "Refs with null referents already filtered"); | |
| 1068 // However, since this code may be executed concurrently with | |
| 1069 // mutators, which can clear() the referent, it is not | |
| 1070 // guaranteed that the referent is non-NULL. | |
| 1071 if (is_alive_non_header()->do_object_b(referent)) { | |
| 1072 return false; // referent is reachable | |
| 1073 } | |
| 1074 } | |
| 1075 | |
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1076 HeapWord* discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1077 oop discovered = java_lang_ref_Reference::discovered(obj); |
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1078 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1079 if (discovered != NULL) { |
| 0 | 1080 // The reference has already been discovered... |
| 1081 if (TraceReferenceGC) { | |
| 1082 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", | |
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1083 obj, obj->blueprint()->internal_name()); |
| 0 | 1084 } |
| 1085 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
| 1086 // assumes that an object is not processed twice; | |
| 1087 // if it's been already discovered it must be on another | |
| 1088 // generation's discovered list; so we won't discover it. | |
| 1089 return false; | |
| 1090 } else { | |
| 1091 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
| 1092 "Unrecognized policy"); | |
| 1093 // Check assumption that an object is not potentially | |
| 1094 // discovered twice except by concurrent collectors that potentially | |
| 1095 // trace the same Reference object twice. | |
| 1096 assert(UseConcMarkSweepGC, | |
| 1097 "Only possible with a concurrent collector"); | |
| 1098 return true; | |
| 1099 } | |
| 1100 } | |
| 1101 | |
| 1102 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
| 1103 oop referent = java_lang_ref_Reference::referent(obj); | |
| 1104 assert(referent->is_oop(), "bad referent"); | |
| 1105 // enqueue if and only if either: | |
| 1106 // reference is in our span or | |
| 1107 // we are an atomic collector and referent is in our span | |
| 1108 if (_span.contains(obj_addr) || | |
| 1109 (discovery_is_atomic() && _span.contains(referent))) { | |
| 1110 // should_enqueue = true; | |
| 1111 } else { | |
| 1112 return false; | |
| 1113 } | |
| 1114 } else { | |
| 1115 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
| 1116 _span.contains(obj_addr), "code inconsistency"); | |
| 1117 } | |
| 1118 | |
| 1119 // Get the right type of discovered queue head. | |
| 1120 DiscoveredList* list = get_discovered_list(rt); | |
| 1121 if (list == NULL) { | |
| 1122 return false; // nothing special needs to be done | |
| 1123 } | |
| 1124 | |
| 1125 // We do a raw store here, the field will be visited later when | |
| 1126 // processing the discovered references. | |
| 1127 if (_discovery_is_mt) { | |
| 1128 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
| 1129 } else { | |
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1130 oop_store_raw(discovered_addr, list->head()); |
| 0 | 1131 list->set_head(obj); |
| 1132 list->set_length(list->length() + 1); | |
| 1133 } | |
| 1134 | |
| 1135 // In the MT discovery case, it is currently possible to see | |
| 1136 // the following message multiple times if several threads | |
| 1137 // discover a reference about the same time. Only one will | |
| 1138 // however have actually added it to the disocvered queue. | |
| 1139 // One could let add_to_discovered_list_mt() return an | |
| 1140 // indication for success in queueing (by 1 thread) or | |
| 1141 // failure (by all other threads), but I decided the extra | |
| 1142 // code was not worth the effort for something that is | |
| 1143 // only used for debugging support. | |
| 1144 if (TraceReferenceGC) { | |
| 1145 oop referent = java_lang_ref_Reference::referent(obj); | |
| 1146 if (PrintGCDetails) { | |
| 1147 gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)", | |
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1148 obj, obj->blueprint()->internal_name()); |
| 0 | 1149 } |
| 1150 assert(referent->is_oop(), "Enqueued a bad referent"); | |
| 1151 } | |
| 1152 assert(obj->is_oop(), "Enqueued a bad reference"); | |
| 1153 return true; | |
| 1154 } | |
| 1155 | |
| 1156 // Preclean the discovered references by removing those | |
| 1157 // whose referents are alive, and by marking from those that | |
| 1158 // are not active. These lists can be handled here | |
| 1159 // in any order and, indeed, concurrently. | |
| 1160 void ReferenceProcessor::preclean_discovered_references( | |
| 1161 BoolObjectClosure* is_alive, | |
| 1162 OopClosure* keep_alive, | |
| 1163 VoidClosure* complete_gc, | |
| 1164 YieldClosure* yield) { | |
| 1165 | |
| 1166 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
| 1167 | |
| 1168 // Soft references | |
| 1169 { | |
| 1170 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, | |
| 1171 false, gclog_or_tty); | |
| 1172 for (int i = 0; i < _num_q; i++) { | |
| 1173 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, | |
| 1174 keep_alive, complete_gc, yield); | |
| 1175 } | |
| 1176 } | |
| 1177 if (yield->should_return()) { | |
| 1178 return; | |
| 1179 } | |
| 1180 | |
| 1181 // Weak references | |
| 1182 { | |
| 1183 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, | |
| 1184 false, gclog_or_tty); | |
| 1185 for (int i = 0; i < _num_q; i++) { | |
| 1186 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, | |
| 1187 keep_alive, complete_gc, yield); | |
| 1188 } | |
| 1189 } | |
| 1190 if (yield->should_return()) { | |
| 1191 return; | |
| 1192 } | |
| 1193 | |
| 1194 // Final references | |
| 1195 { | |
| 1196 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, | |
| 1197 false, gclog_or_tty); | |
| 1198 for (int i = 0; i < _num_q; i++) { | |
| 1199 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, | |
| 1200 keep_alive, complete_gc, yield); | |
| 1201 } | |
| 1202 } | |
| 1203 if (yield->should_return()) { | |
| 1204 return; | |
| 1205 } | |
| 1206 | |
| 1207 // Phantom references | |
| 1208 { | |
| 1209 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, | |
| 1210 false, gclog_or_tty); | |
| 1211 for (int i = 0; i < _num_q; i++) { | |
| 1212 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, | |
| 1213 keep_alive, complete_gc, yield); | |
| 1214 } | |
| 1215 } | |
| 1216 } | |
| 1217 | |
| 1218 // Walk the given discovered ref list, and remove all reference objects | |
| 1219 // whose referents are still alive, whose referents are NULL or which | |
| 1220 // are not active (have a non-NULL next field). NOTE: For this to work | |
| 1221 // correctly, refs discovery can not be happening concurrently with this | |
| 1222 // step. | |
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1223 void |
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1224 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1225 BoolObjectClosure* is_alive, |
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1226 OopClosure* keep_alive, |
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1227 VoidClosure* complete_gc, |
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1228 YieldClosure* yield) { |
| 0 | 1229 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| 1230 size_t length = refs_list.length(); | |
| 1231 while (iter.has_next()) { | |
| 1232 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1233 oop obj = iter.obj(); |
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1234 oop next = java_lang_ref_Reference::next(obj); |
| 0 | 1235 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1236 next != NULL) { |
| 0 | 1237 // The referent has been cleared, or is alive, or the Reference is not |
| 1238 // active; we need to trace and mark its cohort. | |
| 1239 if (TraceReferenceGC) { | |
| 1240 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
| 1241 iter.obj(), iter.obj()->blueprint()->internal_name()); | |
| 1242 } | |
| 1243 // Remove Reference object from list | |
| 1244 iter.remove(); | |
| 1245 --length; | |
| 1246 // Keep alive its cohort. | |
| 1247 iter.make_referent_alive(); | |
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1248 if (UseCompressedOops) { |
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1249 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1250 keep_alive->do_oop(next_addr); |
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1251 } else { |
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1252 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1253 keep_alive->do_oop(next_addr); |
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1254 } |
| 0 | 1255 } else { |
| 1256 iter.next(); | |
| 1257 } | |
| 1258 } | |
| 1259 refs_list.set_length(length); | |
| 1260 | |
| 1261 // Close the reachable set | |
| 1262 complete_gc->do_void(); | |
| 1263 | |
| 1264 NOT_PRODUCT( | |
| 1265 if (PrintGCDetails && PrintReferenceGC) { | |
| 1266 gclog_or_tty->print(" Dropped %d Refs out of %d " | |
| 1267 "Refs in discovered list ", iter.removed(), iter.processed()); | |
| 1268 } | |
| 1269 ) | |
| 1270 } | |
| 1271 | |
| 1272 const char* ReferenceProcessor::list_name(int i) { | |
| 1273 assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index"); | |
| 1274 int j = i / _num_q; | |
| 1275 switch (j) { | |
| 1276 case 0: return "SoftRef"; | |
| 1277 case 1: return "WeakRef"; | |
| 1278 case 2: return "FinalRef"; | |
| 1279 case 3: return "PhantomRef"; | |
| 1280 } | |
| 1281 ShouldNotReachHere(); | |
| 1282 return NULL; | |
| 1283 } | |
| 1284 | |
| 1285 #ifndef PRODUCT | |
| 1286 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
| 1287 // empty for now | |
| 1288 } | |
| 1289 #endif | |
| 1290 | |
| 1291 void ReferenceProcessor::verify() { | |
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1292 guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef"); |
| 0 | 1293 } |
| 1294 | |
| 1295 #ifndef PRODUCT | |
| 1296 void ReferenceProcessor::clear_discovered_references() { | |
| 1297 guarantee(!_discovering_refs, "Discovering refs?"); | |
| 1298 for (int i = 0; i < _num_q * subclasses_of_ref; i++) { | |
| 1299 oop obj = _discoveredSoftRefs[i].head(); | |
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1300 while (obj != sentinel_ref()) { |
| 0 | 1301 oop next = java_lang_ref_Reference::discovered(obj); |
| 1302 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); | |
| 1303 obj = next; | |
| 1304 } | |
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diff
changeset
|
1305 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
| 0 | 1306 _discoveredSoftRefs[i].set_length(0); |
| 1307 } | |
| 1308 } | |
| 1309 #endif // PRODUCT |