Mercurial > hg > graal-jvmci-8
annotate src/share/vm/memory/referenceProcessor.cpp @ 1953:8d81b4a1d3e1
6998802: ScavengeALot: assert(!gch->incremental_collection_failed()) failed: Twice in a row
Summary: Weaken assert by excluding scavenges resulting from -XX:+ScavengeALot stress-testing option.
Reviewed-by: jmasa, tonyp
author | ysr |
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date | Thu, 11 Nov 2010 10:42:43 -0800 |
parents | 8b10f48633dc |
children | f95d63e2154a |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 2001, 2010, 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 | |
25 # include "incls/_precompiled.incl" | |
26 # include "incls/_referenceProcessor.cpp.incl" | |
27 | |
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28 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
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29 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
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30 oop ReferenceProcessor::_sentinelRef = NULL; |
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31 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER; |
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32 |
0 | 33 // List of discovered references. |
34 class DiscoveredList { | |
35 public: | |
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36 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } |
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37 oop head() const { |
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38 return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) : |
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39 _oop_head; |
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40 } |
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41 HeapWord* adr_head() { |
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42 return UseCompressedOops ? (HeapWord*)&_compressed_head : |
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43 (HeapWord*)&_oop_head; |
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44 } |
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45 void set_head(oop o) { |
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46 if (UseCompressedOops) { |
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47 // Must compress the head ptr. |
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48 _compressed_head = oopDesc::encode_heap_oop_not_null(o); |
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49 } else { |
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50 _oop_head = o; |
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51 } |
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52 } |
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53 bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); } |
0 | 54 size_t length() { return _len; } |
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55 void set_length(size_t len) { _len = len; } |
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56 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } |
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57 void dec_length(size_t dec) { _len -= dec; } |
0 | 58 private: |
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59 // Set value depending on UseCompressedOops. This could be a template class |
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60 // but then we have to fix all the instantiations and declarations that use this class. |
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61 oop _oop_head; |
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62 narrowOop _compressed_head; |
0 | 63 size_t _len; |
64 }; | |
65 | |
66 void referenceProcessor_init() { | |
67 ReferenceProcessor::init_statics(); | |
68 } | |
69 | |
70 void ReferenceProcessor::init_statics() { | |
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71 assert(_sentinelRef == NULL, "should be initialized precisely once"); |
0 | 72 EXCEPTION_MARK; |
73 _sentinelRef = instanceKlass::cast( | |
1142 | 74 SystemDictionary::Reference_klass())-> |
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75 allocate_permanent_instance(THREAD); |
0 | 76 |
77 // Initialize the master soft ref clock. | |
78 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis()); | |
79 | |
80 if (HAS_PENDING_EXCEPTION) { | |
81 Handle ex(THREAD, PENDING_EXCEPTION); | |
82 vm_exit_during_initialization(ex); | |
83 } | |
84 assert(_sentinelRef != NULL && _sentinelRef->is_oop(), | |
85 "Just constructed it!"); | |
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86 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
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87 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
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88 NOT_COMPILER2(LRUCurrentHeapPolicy()); |
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89 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
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90 vm_exit_during_initialization("Could not allocate reference policy object"); |
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91 } |
0 | 92 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
93 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
94 "Unrecongnized RefDiscoveryPolicy"); | |
95 } | |
96 | |
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97 ReferenceProcessor* |
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98 ReferenceProcessor::create_ref_processor(MemRegion span, |
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99 bool atomic_discovery, |
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100 bool mt_discovery, |
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101 BoolObjectClosure* is_alive_non_header, |
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102 int parallel_gc_threads, |
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103 bool mt_processing, |
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104 bool dl_needs_barrier) { |
0 | 105 int mt_degree = 1; |
106 if (parallel_gc_threads > 1) { | |
107 mt_degree = parallel_gc_threads; | |
108 } | |
109 ReferenceProcessor* rp = | |
110 new ReferenceProcessor(span, atomic_discovery, | |
111 mt_discovery, mt_degree, | |
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112 mt_processing && (parallel_gc_threads > 0), |
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113 dl_needs_barrier); |
0 | 114 if (rp == NULL) { |
115 vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); | |
116 } | |
117 rp->set_is_alive_non_header(is_alive_non_header); | |
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118 rp->setup_policy(false /* default soft ref policy */); |
0 | 119 return rp; |
120 } | |
121 | |
122 ReferenceProcessor::ReferenceProcessor(MemRegion span, | |
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123 bool atomic_discovery, |
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124 bool mt_discovery, |
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125 int mt_degree, |
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126 bool mt_processing, |
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127 bool discovered_list_needs_barrier) : |
0 | 128 _discovering_refs(false), |
129 _enqueuing_is_done(false), | |
130 _is_alive_non_header(NULL), | |
342
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131 _discovered_list_needs_barrier(discovered_list_needs_barrier), |
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132 _bs(NULL), |
0 | 133 _processing_is_mt(mt_processing), |
134 _next_id(0) | |
135 { | |
136 _span = span; | |
137 _discovery_is_atomic = atomic_discovery; | |
138 _discovery_is_mt = mt_discovery; | |
139 _num_q = mt_degree; | |
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140 _max_num_q = mt_degree; |
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141 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _max_num_q * subclasses_of_ref); |
0 | 142 if (_discoveredSoftRefs == NULL) { |
143 vm_exit_during_initialization("Could not allocated RefProc Array"); | |
144 } | |
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145 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
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146 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
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147 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
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148 assert(sentinel_ref() != NULL, "_sentinelRef is NULL"); |
0 | 149 // Initialized all entries to _sentinelRef |
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150 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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151 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
0 | 152 _discoveredSoftRefs[i].set_length(0); |
153 } | |
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154 // If we do barreirs, cache a copy of the barrier set. |
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155 if (discovered_list_needs_barrier) { |
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156 _bs = Universe::heap()->barrier_set(); |
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157 } |
0 | 158 } |
159 | |
160 #ifndef PRODUCT | |
161 void ReferenceProcessor::verify_no_references_recorded() { | |
162 guarantee(!_discovering_refs, "Discovering refs?"); | |
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163 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 164 guarantee(_discoveredSoftRefs[i].empty(), |
165 "Found non-empty discovered list"); | |
166 } | |
167 } | |
168 #endif | |
169 | |
170 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
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171 // Should this instead be |
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172 // for (int i = 0; i < subclasses_of_ref; i++_ { |
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173 // for (int j = 0; j < _num_q; j++) { |
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174 // int index = i * _max_num_q + j; |
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175 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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176 if (UseCompressedOops) { |
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177 f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head()); |
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178 } else { |
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179 f->do_oop((oop*)_discoveredSoftRefs[i].adr_head()); |
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180 } |
0 | 181 } |
182 } | |
183 | |
184 void ReferenceProcessor::oops_do(OopClosure* f) { | |
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185 f->do_oop(adr_sentinel_ref()); |
0 | 186 } |
187 | |
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188 void ReferenceProcessor::update_soft_ref_master_clock() { |
0 | 189 // Update (advance) the soft ref master clock field. This must be done |
190 // after processing the soft ref list. | |
191 jlong now = os::javaTimeMillis(); | |
192 jlong clock = java_lang_ref_SoftReference::clock(); | |
193 NOT_PRODUCT( | |
194 if (now < clock) { | |
195 warning("time warp: %d to %d", clock, now); | |
196 } | |
197 ) | |
198 // In product mode, protect ourselves from system time being adjusted | |
199 // externally and going backward; see note in the implementation of | |
200 // GenCollectedHeap::time_since_last_gc() for the right way to fix | |
201 // this uniformly throughout the VM; see bug-id 4741166. XXX | |
202 if (now > clock) { | |
203 java_lang_ref_SoftReference::set_clock(now); | |
204 } | |
205 // Else leave clock stalled at its old value until time progresses | |
206 // past clock value. | |
207 } | |
208 | |
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209 void ReferenceProcessor::process_discovered_references( |
0 | 210 BoolObjectClosure* is_alive, |
211 OopClosure* keep_alive, | |
212 VoidClosure* complete_gc, | |
213 AbstractRefProcTaskExecutor* task_executor) { | |
214 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
215 | |
216 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
217 // Stop treating discovered references specially. | |
218 disable_discovery(); | |
219 | |
220 bool trace_time = PrintGCDetails && PrintReferenceGC; | |
221 // Soft references | |
222 { | |
223 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); | |
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224 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, |
0 | 225 is_alive, keep_alive, complete_gc, task_executor); |
226 } | |
227 | |
228 update_soft_ref_master_clock(); | |
229 | |
230 // Weak references | |
231 { | |
232 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); | |
233 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
234 is_alive, keep_alive, complete_gc, task_executor); | |
235 } | |
236 | |
237 // Final references | |
238 { | |
239 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); | |
240 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
241 is_alive, keep_alive, complete_gc, task_executor); | |
242 } | |
243 | |
244 // Phantom references | |
245 { | |
246 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); | |
247 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
248 is_alive, keep_alive, complete_gc, task_executor); | |
249 } | |
250 | |
251 // Weak global JNI references. It would make more sense (semantically) to | |
252 // traverse these simultaneously with the regular weak references above, but | |
253 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
254 // thus use JNI weak references to circumvent the phantom references and | |
255 // resurrect a "post-mortem" object. | |
256 { | |
257 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); | |
258 if (task_executor != NULL) { | |
259 task_executor->set_single_threaded_mode(); | |
260 } | |
261 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
262 } | |
263 } | |
264 | |
265 #ifndef PRODUCT | |
266 // Calculate the number of jni handles. | |
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267 uint ReferenceProcessor::count_jni_refs() { |
0 | 268 class AlwaysAliveClosure: public BoolObjectClosure { |
269 public: | |
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270 virtual bool do_object_b(oop obj) { return true; } |
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271 virtual void do_object(oop obj) { assert(false, "Don't call"); } |
0 | 272 }; |
273 | |
274 class CountHandleClosure: public OopClosure { | |
275 private: | |
276 int _count; | |
277 public: | |
278 CountHandleClosure(): _count(0) {} | |
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279 void do_oop(oop* unused) { _count++; } |
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280 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
0 | 281 int count() { return _count; } |
282 }; | |
283 CountHandleClosure global_handle_count; | |
284 AlwaysAliveClosure always_alive; | |
285 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
286 return global_handle_count.count(); | |
287 } | |
288 #endif | |
289 | |
290 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
291 OopClosure* keep_alive, | |
292 VoidClosure* complete_gc) { | |
293 #ifndef PRODUCT | |
294 if (PrintGCDetails && PrintReferenceGC) { | |
295 unsigned int count = count_jni_refs(); | |
296 gclog_or_tty->print(", %u refs", count); | |
297 } | |
298 #endif | |
299 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
300 // Finally remember to keep sentinel around | |
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301 keep_alive->do_oop(adr_sentinel_ref()); |
0 | 302 complete_gc->do_void(); |
303 } | |
304 | |
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305 |
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306 template <class T> |
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307 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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308 AbstractRefProcTaskExecutor* task_executor) { |
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309 |
0 | 310 // Remember old value of pending references list |
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311 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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312 T old_pending_list_value = *pending_list_addr; |
0 | 313 |
314 // Enqueue references that are not made active again, and | |
315 // clear the decks for the next collection (cycle). | |
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316 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
0 | 317 // Do the oop-check on pending_list_addr missed in |
318 // enqueue_discovered_reflist. We should probably | |
319 // do a raw oop_check so that future such idempotent | |
320 // oop_stores relying on the oop-check side-effect | |
321 // may be elided automatically and safely without | |
322 // affecting correctness. | |
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323 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
0 | 324 |
325 // Stop treating discovered references specially. | |
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326 ref->disable_discovery(); |
0 | 327 |
328 // Return true if new pending references were added | |
329 return old_pending_list_value != *pending_list_addr; | |
330 } | |
331 | |
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332 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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333 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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334 if (UseCompressedOops) { |
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335 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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336 } else { |
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337 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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338 } |
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339 } |
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340 |
0 | 341 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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342 HeapWord* pending_list_addr) { |
0 | 343 // Given a list of refs linked through the "discovered" field |
344 // (java.lang.ref.Reference.discovered) chain them through the | |
345 // "next" field (java.lang.ref.Reference.next) and prepend | |
346 // to the pending list. | |
347 if (TraceReferenceGC && PrintGCDetails) { | |
348 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
349 INTPTR_FORMAT, (address)refs_list.head()); | |
350 } | |
351 oop obj = refs_list.head(); | |
352 // Walk down the list, copying the discovered field into | |
353 // the next field and clearing it (except for the last | |
354 // non-sentinel object which is treated specially to avoid | |
355 // confusion with an active reference). | |
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356 while (obj != sentinel_ref()) { |
0 | 357 assert(obj->is_instanceRef(), "should be reference object"); |
358 oop next = java_lang_ref_Reference::discovered(obj); | |
359 if (TraceReferenceGC && PrintGCDetails) { | |
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360 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT, |
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361 obj, next); |
0 | 362 } |
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363 assert(java_lang_ref_Reference::next(obj) == NULL, |
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364 "The reference should not be enqueued"); |
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365 if (next == sentinel_ref()) { // obj is last |
0 | 366 // Swap refs_list into pendling_list_addr and |
367 // set obj's next to what we read from pending_list_addr. | |
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368 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
0 | 369 // Need oop_check on pending_list_addr above; |
370 // see special oop-check code at the end of | |
371 // enqueue_discovered_reflists() further below. | |
372 if (old == NULL) { | |
373 // obj should be made to point to itself, since | |
374 // pending list was empty. | |
375 java_lang_ref_Reference::set_next(obj, obj); | |
376 } else { | |
377 java_lang_ref_Reference::set_next(obj, old); | |
378 } | |
379 } else { | |
380 java_lang_ref_Reference::set_next(obj, next); | |
381 } | |
382 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); | |
383 obj = next; | |
384 } | |
385 } | |
386 | |
387 // Parallel enqueue task | |
388 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
389 public: | |
390 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
391 DiscoveredList discovered_refs[], | |
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392 HeapWord* pending_list_addr, |
0 | 393 oop sentinel_ref, |
394 int n_queues) | |
395 : EnqueueTask(ref_processor, discovered_refs, | |
396 pending_list_addr, sentinel_ref, n_queues) | |
397 { } | |
398 | |
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399 virtual void work(unsigned int work_id) { |
0 | 400 assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds"); |
401 // Simplest first cut: static partitioning. | |
402 int index = work_id; | |
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403 // The increment on "index" must correspond to the maximum number of queues |
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404 // (n_queues) with which that ReferenceProcessor was created. That |
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405 // is because of the "clever" way the discovered references lists were |
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406 // allocated and are indexed into. That number is ParallelGCThreads |
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407 // currently. Assert that. |
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408 assert(_n_queues == (int) ParallelGCThreads, "Different number not expected"); |
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409 for (int j = 0; |
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410 j < subclasses_of_ref; |
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411 j++, index += _n_queues) { |
0 | 412 _ref_processor.enqueue_discovered_reflist( |
413 _refs_lists[index], _pending_list_addr); | |
414 _refs_lists[index].set_head(_sentinel_ref); | |
415 _refs_lists[index].set_length(0); | |
416 } | |
417 } | |
418 }; | |
419 | |
420 // Enqueue references that are not made active again | |
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421 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
0 | 422 AbstractRefProcTaskExecutor* task_executor) { |
423 if (_processing_is_mt && task_executor != NULL) { | |
424 // Parallel code | |
425 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs, | |
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426 pending_list_addr, sentinel_ref(), _max_num_q); |
0 | 427 task_executor->execute(tsk); |
428 } else { | |
429 // Serial code: call the parent class's implementation | |
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430 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 431 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr); |
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432 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
0 | 433 _discoveredSoftRefs[i].set_length(0); |
434 } | |
435 } | |
436 } | |
437 | |
438 // Iterator for the list of discovered references. | |
439 class DiscoveredListIterator { | |
440 public: | |
441 inline DiscoveredListIterator(DiscoveredList& refs_list, | |
442 OopClosure* keep_alive, | |
443 BoolObjectClosure* is_alive); | |
444 | |
445 // End Of List. | |
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446 inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); } |
0 | 447 |
448 // Get oop to the Reference object. | |
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449 inline oop obj() const { return _ref; } |
0 | 450 |
451 // Get oop to the referent object. | |
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452 inline oop referent() const { return _referent; } |
0 | 453 |
454 // Returns true if referent is alive. | |
455 inline bool is_referent_alive() const; | |
456 | |
457 // Loads data for the current reference. | |
458 // The "allow_null_referent" argument tells us to allow for the possibility | |
459 // of a NULL referent in the discovered Reference object. This typically | |
460 // happens in the case of concurrent collectors that may have done the | |
452
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461 // discovery concurrently, or interleaved, with mutator execution. |
0 | 462 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); |
463 | |
464 // Move to the next discovered reference. | |
465 inline void next(); | |
466 | |
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467 // Remove the current reference from the list |
0 | 468 inline void remove(); |
469 | |
470 // Make the Reference object active again. | |
471 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); } | |
472 | |
473 // Make the referent alive. | |
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474 inline void make_referent_alive() { |
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475 if (UseCompressedOops) { |
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476 _keep_alive->do_oop((narrowOop*)_referent_addr); |
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477 } else { |
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478 _keep_alive->do_oop((oop*)_referent_addr); |
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479 } |
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480 } |
0 | 481 |
482 // Update the discovered field. | |
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483 inline void update_discovered() { |
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484 // First _prev_next ref actually points into DiscoveredList (gross). |
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485 if (UseCompressedOops) { |
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486 _keep_alive->do_oop((narrowOop*)_prev_next); |
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487 } else { |
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488 _keep_alive->do_oop((oop*)_prev_next); |
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489 } |
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490 } |
0 | 491 |
492 // NULL out referent pointer. | |
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493 inline void clear_referent() { oop_store_raw(_referent_addr, NULL); } |
0 | 494 |
495 // Statistics | |
496 NOT_PRODUCT( | |
497 inline size_t processed() const { return _processed; } | |
498 inline size_t removed() const { return _removed; } | |
499 ) | |
500 | |
501 inline void move_to_next(); | |
502 | |
503 private: | |
504 DiscoveredList& _refs_list; | |
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505 HeapWord* _prev_next; |
0 | 506 oop _ref; |
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507 HeapWord* _discovered_addr; |
0 | 508 oop _next; |
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509 HeapWord* _referent_addr; |
0 | 510 oop _referent; |
511 OopClosure* _keep_alive; | |
512 BoolObjectClosure* _is_alive; | |
513 DEBUG_ONLY( | |
514 oop _first_seen; // cyclic linked list check | |
515 ) | |
516 NOT_PRODUCT( | |
517 size_t _processed; | |
518 size_t _removed; | |
519 ) | |
520 }; | |
521 | |
522 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list, | |
523 OopClosure* keep_alive, | |
524 BoolObjectClosure* is_alive) | |
525 : _refs_list(refs_list), | |
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526 _prev_next(refs_list.adr_head()), |
0 | 527 _ref(refs_list.head()), |
528 #ifdef ASSERT | |
529 _first_seen(refs_list.head()), | |
530 #endif | |
531 #ifndef PRODUCT | |
532 _processed(0), | |
533 _removed(0), | |
534 #endif | |
535 _next(refs_list.head()), | |
536 _keep_alive(keep_alive), | |
537 _is_alive(is_alive) | |
538 { } | |
539 | |
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540 inline bool DiscoveredListIterator::is_referent_alive() const { |
0 | 541 return _is_alive->do_object_b(_referent); |
542 } | |
543 | |
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544 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
0 | 545 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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546 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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547 assert(_discovered_addr && discovered->is_oop_or_null(), |
0 | 548 "discovered field is bad"); |
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549 _next = discovered; |
0 | 550 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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551 _referent = java_lang_ref_Reference::referent(_ref); |
0 | 552 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
553 "Wrong oop found in java.lang.Reference object"); | |
554 assert(allow_null_referent ? | |
555 _referent->is_oop_or_null() | |
556 : _referent->is_oop(), | |
557 "bad referent"); | |
558 } | |
559 | |
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560 inline void DiscoveredListIterator::next() { |
0 | 561 _prev_next = _discovered_addr; |
562 move_to_next(); | |
563 } | |
564 | |
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565 inline void DiscoveredListIterator::remove() { |
0 | 566 assert(_ref->is_oop(), "Dropping a bad reference"); |
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567 oop_store_raw(_discovered_addr, NULL); |
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568 // First _prev_next ref actually points into DiscoveredList (gross). |
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569 if (UseCompressedOops) { |
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570 // Remove Reference object from list. |
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571 oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next); |
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572 } else { |
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573 // Remove Reference object from list. |
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574 oopDesc::store_heap_oop((oop*)_prev_next, _next); |
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575 } |
0 | 576 NOT_PRODUCT(_removed++); |
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577 _refs_list.dec_length(1); |
0 | 578 } |
579 | |
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580 inline void DiscoveredListIterator::move_to_next() { |
0 | 581 _ref = _next; |
582 assert(_ref != _first_seen, "cyclic ref_list found"); | |
583 NOT_PRODUCT(_processed++); | |
584 } | |
585 | |
586 // NOTE: process_phase*() are largely similar, and at a high level | |
587 // merely iterate over the extant list applying a predicate to | |
588 // each of its elements and possibly removing that element from the | |
589 // list and applying some further closures to that element. | |
590 // We should consider the possibility of replacing these | |
591 // process_phase*() methods by abstracting them into | |
592 // a single general iterator invocation that receives appropriate | |
593 // closures that accomplish this work. | |
594 | |
595 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
596 // referents are not alive, but that should be kept alive for policy reasons. | |
597 // Keep alive the transitive closure of all such referents. | |
598 void | |
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599 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
0 | 600 ReferencePolicy* policy, |
601 BoolObjectClosure* is_alive, | |
602 OopClosure* keep_alive, | |
603 VoidClosure* complete_gc) { | |
604 assert(policy != NULL, "Must have a non-NULL policy"); | |
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605 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 606 // Decide which softly reachable refs should be kept alive. |
607 while (iter.has_next()) { | |
608 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
609 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
610 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) { | |
611 if (TraceReferenceGC) { | |
612 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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613 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 614 } |
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615 // Remove Reference object from list |
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616 iter.remove(); |
0 | 617 // Make the Reference object active again |
618 iter.make_active(); | |
619 // keep the referent around | |
620 iter.make_referent_alive(); | |
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621 iter.move_to_next(); |
0 | 622 } else { |
623 iter.next(); | |
624 } | |
625 } | |
626 // Close the reachable set | |
627 complete_gc->do_void(); | |
628 NOT_PRODUCT( | |
629 if (PrintGCDetails && TraceReferenceGC) { | |
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630 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
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631 "discovered Refs by policy list " INTPTR_FORMAT, |
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632 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 633 } |
634 ) | |
635 } | |
636 | |
637 // Traverse the list and remove any Refs that are not active, or | |
638 // whose referents are either alive or NULL. | |
639 void | |
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640 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
0 | 641 BoolObjectClosure* is_alive, |
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642 OopClosure* keep_alive) { |
0 | 643 assert(discovery_is_atomic(), "Error"); |
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644 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 645 while (iter.has_next()) { |
646 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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647 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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648 assert(next == NULL, "Should not discover inactive Reference"); |
0 | 649 if (iter.is_referent_alive()) { |
650 if (TraceReferenceGC) { | |
651 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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652 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 653 } |
654 // The referent is reachable after all. | |
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655 // Remove Reference object from list. |
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656 iter.remove(); |
0 | 657 // Update the referent pointer as necessary: Note that this |
658 // should not entail any recursive marking because the | |
659 // referent must already have been traversed. | |
660 iter.make_referent_alive(); | |
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661 iter.move_to_next(); |
0 | 662 } else { |
663 iter.next(); | |
664 } | |
665 } | |
666 NOT_PRODUCT( | |
667 if (PrintGCDetails && TraceReferenceGC) { | |
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668 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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669 "Refs in discovered list " INTPTR_FORMAT, |
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670 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 671 } |
672 ) | |
673 } | |
674 | |
675 void | |
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676 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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677 BoolObjectClosure* is_alive, |
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678 OopClosure* keep_alive, |
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679 VoidClosure* complete_gc) { |
0 | 680 assert(!discovery_is_atomic(), "Error"); |
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681 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 682 while (iter.has_next()) { |
683 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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684 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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685 oop next = java_lang_ref_Reference::next(iter.obj()); |
0 | 686 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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687 next != NULL)) { |
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688 assert(next->is_oop_or_null(), "bad next field"); |
0 | 689 // Remove Reference object from list |
690 iter.remove(); | |
691 // Trace the cohorts | |
692 iter.make_referent_alive(); | |
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693 if (UseCompressedOops) { |
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694 keep_alive->do_oop((narrowOop*)next_addr); |
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695 } else { |
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696 keep_alive->do_oop((oop*)next_addr); |
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697 } |
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698 iter.move_to_next(); |
0 | 699 } else { |
700 iter.next(); | |
701 } | |
702 } | |
703 // Now close the newly reachable set | |
704 complete_gc->do_void(); | |
705 NOT_PRODUCT( | |
706 if (PrintGCDetails && TraceReferenceGC) { | |
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707 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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708 "Refs in discovered list " INTPTR_FORMAT, |
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709 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 710 } |
711 ) | |
712 } | |
713 | |
714 // Traverse the list and process the referents, by either | |
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715 // clearing them or keeping them (and their reachable |
0 | 716 // closure) alive. |
717 void | |
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718 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
0 | 719 bool clear_referent, |
720 BoolObjectClosure* is_alive, | |
721 OopClosure* keep_alive, | |
722 VoidClosure* complete_gc) { | |
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723 ResourceMark rm; |
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724 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 725 while (iter.has_next()) { |
726 iter.update_discovered(); | |
727 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
728 if (clear_referent) { | |
729 // NULL out referent pointer | |
730 iter.clear_referent(); | |
731 } else { | |
732 // keep the referent around | |
733 iter.make_referent_alive(); | |
734 } | |
735 if (TraceReferenceGC) { | |
736 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
737 clear_referent ? "cleared " : "", | |
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738 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 739 } |
740 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
741 iter.next(); | |
742 } | |
743 // Remember to keep sentinel pointer around | |
744 iter.update_discovered(); | |
745 // Close the reachable set | |
746 complete_gc->do_void(); | |
747 } | |
748 | |
749 void | |
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750 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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751 oop obj = refs_list.head(); |
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752 while (obj != sentinel_ref()) { |
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753 oop discovered = java_lang_ref_Reference::discovered(obj); |
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754 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
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755 obj = discovered; |
0 | 756 } |
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757 refs_list.set_head(sentinel_ref()); |
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758 refs_list.set_length(0); |
0 | 759 } |
760 | |
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761 void ReferenceProcessor::abandon_partial_discovery() { |
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762 // loop over the lists |
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763 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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764 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
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765 gclog_or_tty->print_cr( |
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766 "\nAbandoning %s discovered list", |
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767 list_name(i)); |
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768 } |
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769 abandon_partial_discovered_list(_discoveredSoftRefs[i]); |
0 | 770 } |
771 } | |
772 | |
773 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
774 public: | |
775 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
776 DiscoveredList refs_lists[], | |
777 ReferencePolicy* policy, | |
778 bool marks_oops_alive) | |
779 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
780 _policy(policy) | |
781 { } | |
782 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
783 OopClosure& keep_alive, | |
784 VoidClosure& complete_gc) | |
785 { | |
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786 Thread* thr = Thread::current(); |
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787 int refs_list_index = ((WorkerThread*)thr)->id(); |
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788 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
0 | 789 &is_alive, &keep_alive, &complete_gc); |
790 } | |
791 private: | |
792 ReferencePolicy* _policy; | |
793 }; | |
794 | |
795 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
796 public: | |
797 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
798 DiscoveredList refs_lists[], | |
799 bool marks_oops_alive) | |
800 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
801 { } | |
802 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
803 OopClosure& keep_alive, | |
804 VoidClosure& complete_gc) | |
805 { | |
806 _ref_processor.process_phase2(_refs_lists[i], | |
807 &is_alive, &keep_alive, &complete_gc); | |
808 } | |
809 }; | |
810 | |
811 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
812 public: | |
813 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
814 DiscoveredList refs_lists[], | |
815 bool clear_referent, | |
816 bool marks_oops_alive) | |
817 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
818 _clear_referent(clear_referent) | |
819 { } | |
820 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
821 OopClosure& keep_alive, | |
822 VoidClosure& complete_gc) | |
823 { | |
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824 // Don't use "refs_list_index" calculated in this way because |
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825 // balance_queues() has moved the Ref's into the first n queues. |
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826 // Thread* thr = Thread::current(); |
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827 // int refs_list_index = ((WorkerThread*)thr)->id(); |
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828 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
0 | 829 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
830 &is_alive, &keep_alive, &complete_gc); | |
831 } | |
832 private: | |
833 bool _clear_referent; | |
834 }; | |
835 | |
836 // Balances reference queues. | |
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837 // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
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838 // queues[0, 1, ..., _num_q-1] because only the first _num_q |
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839 // corresponding to the active workers will be processed. |
0 | 840 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
841 { | |
842 // calculate total length | |
843 size_t total_refs = 0; | |
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844 if (TraceReferenceGC && PrintGCDetails) { |
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845 gclog_or_tty->print_cr("\nBalance ref_lists "); |
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846 } |
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847 |
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848 for (int i = 0; i < _max_num_q; ++i) { |
0 | 849 total_refs += ref_lists[i].length(); |
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850 if (TraceReferenceGC && PrintGCDetails) { |
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851 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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852 } |
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853 } |
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854 if (TraceReferenceGC && PrintGCDetails) { |
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855 gclog_or_tty->print_cr(" = %d", total_refs); |
0 | 856 } |
857 size_t avg_refs = total_refs / _num_q + 1; | |
858 int to_idx = 0; | |
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859 for (int from_idx = 0; from_idx < _max_num_q; from_idx++) { |
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860 bool move_all = false; |
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861 if (from_idx >= _num_q) { |
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862 move_all = ref_lists[from_idx].length() > 0; |
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863 } |
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864 while ((ref_lists[from_idx].length() > avg_refs) || |
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865 move_all) { |
0 | 866 assert(to_idx < _num_q, "Sanity Check!"); |
867 if (ref_lists[to_idx].length() < avg_refs) { | |
868 // move superfluous refs | |
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869 size_t refs_to_move; |
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870 // Move all the Ref's if the from queue will not be processed. |
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871 if (move_all) { |
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872 refs_to_move = MIN2(ref_lists[from_idx].length(), |
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873 avg_refs - ref_lists[to_idx].length()); |
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874 } else { |
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875 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
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876 avg_refs - ref_lists[to_idx].length()); |
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877 } |
0 | 878 oop move_head = ref_lists[from_idx].head(); |
879 oop move_tail = move_head; | |
880 oop new_head = move_head; | |
881 // find an element to split the list on | |
882 for (size_t j = 0; j < refs_to_move; ++j) { | |
883 move_tail = new_head; | |
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884 new_head = java_lang_ref_Reference::discovered(new_head); |
0 | 885 } |
886 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head()); | |
887 ref_lists[to_idx].set_head(move_head); | |
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888 ref_lists[to_idx].inc_length(refs_to_move); |
0 | 889 ref_lists[from_idx].set_head(new_head); |
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890 ref_lists[from_idx].dec_length(refs_to_move); |
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891 if (ref_lists[from_idx].length() == 0) { |
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892 break; |
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893 } |
0 | 894 } else { |
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895 to_idx = (to_idx + 1) % _num_q; |
0 | 896 } |
897 } | |
898 } | |
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899 #ifdef ASSERT |
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900 size_t balanced_total_refs = 0; |
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901 for (int i = 0; i < _max_num_q; ++i) { |
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902 balanced_total_refs += ref_lists[i].length(); |
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903 if (TraceReferenceGC && PrintGCDetails) { |
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904 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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905 } |
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906 } |
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907 if (TraceReferenceGC && PrintGCDetails) { |
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908 gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
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909 gclog_or_tty->flush(); |
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910 } |
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911 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
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912 #endif |
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913 } |
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914 |
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915 void ReferenceProcessor::balance_all_queues() { |
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916 balance_queues(_discoveredSoftRefs); |
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917 balance_queues(_discoveredWeakRefs); |
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918 balance_queues(_discoveredFinalRefs); |
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919 balance_queues(_discoveredPhantomRefs); |
0 | 920 } |
921 | |
922 void | |
923 ReferenceProcessor::process_discovered_reflist( | |
924 DiscoveredList refs_lists[], | |
925 ReferencePolicy* policy, | |
926 bool clear_referent, | |
927 BoolObjectClosure* is_alive, | |
928 OopClosure* keep_alive, | |
929 VoidClosure* complete_gc, | |
930 AbstractRefProcTaskExecutor* task_executor) | |
931 { | |
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932 bool mt_processing = task_executor != NULL && _processing_is_mt; |
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933 // If discovery used MT and a dynamic number of GC threads, then |
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934 // the queues must be balanced for correctness if fewer than the |
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935 // maximum number of queues were used. The number of queue used |
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936 // during discovery may be different than the number to be used |
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937 // for processing so don't depend of _num_q < _max_num_q as part |
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938 // of the test. |
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939 bool must_balance = _discovery_is_mt; |
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940 |
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941 if ((mt_processing && ParallelRefProcBalancingEnabled) || |
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942 must_balance) { |
0 | 943 balance_queues(refs_lists); |
944 } | |
945 if (PrintReferenceGC && PrintGCDetails) { | |
946 size_t total = 0; | |
947 for (int i = 0; i < _num_q; ++i) { | |
948 total += refs_lists[i].length(); | |
949 } | |
950 gclog_or_tty->print(", %u refs", total); | |
951 } | |
952 | |
953 // Phase 1 (soft refs only): | |
954 // . Traverse the list and remove any SoftReferences whose | |
955 // referents are not alive, but that should be kept alive for | |
956 // policy reasons. Keep alive the transitive closure of all | |
957 // such referents. | |
958 if (policy != NULL) { | |
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959 if (mt_processing) { |
0 | 960 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
961 task_executor->execute(phase1); | |
962 } else { | |
963 for (int i = 0; i < _num_q; i++) { | |
964 process_phase1(refs_lists[i], policy, | |
965 is_alive, keep_alive, complete_gc); | |
966 } | |
967 } | |
968 } else { // policy == NULL | |
969 assert(refs_lists != _discoveredSoftRefs, | |
970 "Policy must be specified for soft references."); | |
971 } | |
972 | |
973 // Phase 2: | |
974 // . Traverse the list and remove any refs whose referents are alive. | |
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975 if (mt_processing) { |
0 | 976 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
977 task_executor->execute(phase2); | |
978 } else { | |
979 for (int i = 0; i < _num_q; i++) { | |
980 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); | |
981 } | |
982 } | |
983 | |
984 // Phase 3: | |
985 // . Traverse the list and process referents as appropriate. | |
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986 if (mt_processing) { |
0 | 987 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
988 task_executor->execute(phase3); | |
989 } else { | |
990 for (int i = 0; i < _num_q; i++) { | |
991 process_phase3(refs_lists[i], clear_referent, | |
992 is_alive, keep_alive, complete_gc); | |
993 } | |
994 } | |
995 } | |
996 | |
997 void ReferenceProcessor::clean_up_discovered_references() { | |
998 // loop over the lists | |
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999 // Should this instead be |
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1000 // for (int i = 0; i < subclasses_of_ref; i++_ { |
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1001 // for (int j = 0; j < _num_q; j++) { |
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1002 // int index = i * _max_num_q + j; |
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1003 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 1004 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) { |
1005 gclog_or_tty->print_cr( | |
1006 "\nScrubbing %s discovered list of Null referents", | |
1007 list_name(i)); | |
1008 } | |
1009 clean_up_discovered_reflist(_discoveredSoftRefs[i]); | |
1010 } | |
1011 } | |
1012 | |
1013 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
1014 assert(!discovery_is_atomic(), "Else why call this method?"); | |
1015 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
1016 while (iter.has_next()) { | |
1017 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1018 oop next = java_lang_ref_Reference::next(iter.obj()); |
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1019 assert(next->is_oop_or_null(), "bad next field"); |
0 | 1020 // If referent has been cleared or Reference is not active, |
1021 // drop it. | |
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1022 if (iter.referent() == NULL || next != NULL) { |
0 | 1023 debug_only( |
1024 if (PrintGCDetails && TraceReferenceGC) { | |
1025 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
1026 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
1027 " and referent: " INTPTR_FORMAT, | |
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1028 iter.obj(), next, iter.referent()); |
0 | 1029 } |
1030 ) | |
1031 // Remove Reference object from list | |
1032 iter.remove(); | |
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1033 iter.move_to_next(); |
0 | 1034 } else { |
1035 iter.next(); | |
1036 } | |
1037 } | |
1038 NOT_PRODUCT( | |
1039 if (PrintGCDetails && TraceReferenceGC) { | |
1040 gclog_or_tty->print( | |
1041 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
1042 iter.removed(), iter.processed()); | |
1043 } | |
1044 ) | |
1045 } | |
1046 | |
1047 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
1048 int id = 0; | |
1049 // Determine the queue index to use for this object. | |
1050 if (_discovery_is_mt) { | |
1051 // During a multi-threaded discovery phase, | |
1052 // each thread saves to its "own" list. | |
1053 Thread* thr = Thread::current(); | |
1054 assert(thr->is_GC_task_thread(), | |
1055 "Dubious cast from Thread* to WorkerThread*?"); | |
1056 id = ((WorkerThread*)thr)->id(); | |
1057 } else { | |
1058 // single-threaded discovery, we save in round-robin | |
1059 // fashion to each of the lists. | |
1060 if (_processing_is_mt) { | |
1061 id = next_id(); | |
1062 } | |
1063 } | |
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1064 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
0 | 1065 |
1066 // Get the discovered queue to which we will add | |
1067 DiscoveredList* list = NULL; | |
1068 switch (rt) { | |
1069 case REF_OTHER: | |
1070 // Unknown reference type, no special treatment | |
1071 break; | |
1072 case REF_SOFT: | |
1073 list = &_discoveredSoftRefs[id]; | |
1074 break; | |
1075 case REF_WEAK: | |
1076 list = &_discoveredWeakRefs[id]; | |
1077 break; | |
1078 case REF_FINAL: | |
1079 list = &_discoveredFinalRefs[id]; | |
1080 break; | |
1081 case REF_PHANTOM: | |
1082 list = &_discoveredPhantomRefs[id]; | |
1083 break; | |
1084 case REF_NONE: | |
1085 // we should not reach here if we are an instanceRefKlass | |
1086 default: | |
1087 ShouldNotReachHere(); | |
1088 } | |
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1089 if (TraceReferenceGC && PrintGCDetails) { |
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1090 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, |
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1091 id, list); |
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1092 } |
0 | 1093 return list; |
1094 } | |
1095 | |
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1096 inline void |
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1097 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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1098 oop obj, |
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1099 HeapWord* discovered_addr) { |
0 | 1100 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
1101 // First we must make sure this object is only enqueued once. CAS in a non null | |
1102 // discovered_addr. | |
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1103 oop current_head = refs_list.head(); |
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1104 |
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1105 // Note: In the case of G1, this specific pre-barrier is strictly |
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1106 // not necessary because the only case we are interested in |
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1107 // here is when *discovered_addr is NULL (see the CAS further below), |
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1108 // so this will expand to nothing. As a result, we have manually |
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1109 // elided this out for G1, but left in the test for some future |
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1110 // collector that might have need for a pre-barrier here. |
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1111 if (_discovered_list_needs_barrier && !UseG1GC) { |
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1112 if (UseCompressedOops) { |
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1113 _bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head); |
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1114 } else { |
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1115 _bs->write_ref_field_pre((oop*)discovered_addr, current_head); |
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1116 } |
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1117 guarantee(false, "Need to check non-G1 collector"); |
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1118 } |
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1119 oop retest = oopDesc::atomic_compare_exchange_oop(current_head, discovered_addr, |
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1120 NULL); |
0 | 1121 if (retest == NULL) { |
1122 // This thread just won the right to enqueue the object. | |
1123 // We have separate lists for enqueueing so no synchronization | |
1124 // is necessary. | |
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1125 refs_list.set_head(obj); |
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1126 refs_list.inc_length(1); |
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1127 if (_discovered_list_needs_barrier) { |
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1128 _bs->write_ref_field((void*)discovered_addr, current_head); |
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1129 } |
0 | 1130 } else { |
1131 // If retest was non NULL, another thread beat us to it: | |
1132 // The reference has already been discovered... | |
1133 if (TraceReferenceGC) { | |
1134 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", | |
1135 obj, obj->blueprint()->internal_name()); | |
1136 } | |
1137 } | |
1138 } | |
1139 | |
1140 // We mention two of several possible choices here: | |
1141 // #0: if the reference object is not in the "originating generation" | |
1142 // (or part of the heap being collected, indicated by our "span" | |
1143 // we don't treat it specially (i.e. we scan it as we would | |
1144 // a normal oop, treating its references as strong references). | |
1145 // This means that references can't be enqueued unless their | |
1146 // referent is also in the same span. This is the simplest, | |
1147 // most "local" and most conservative approach, albeit one | |
1148 // that may cause weak references to be enqueued least promptly. | |
1149 // We call this choice the "ReferenceBasedDiscovery" policy. | |
1150 // #1: the reference object may be in any generation (span), but if | |
1151 // the referent is in the generation (span) being currently collected | |
1152 // then we can discover the reference object, provided | |
1153 // the object has not already been discovered by | |
1154 // a different concurrently running collector (as may be the | |
1155 // case, for instance, if the reference object is in CMS and | |
1156 // the referent in DefNewGeneration), and provided the processing | |
1157 // of this reference object by the current collector will | |
1158 // appear atomic to every other collector in the system. | |
1159 // (Thus, for instance, a concurrent collector may not | |
1160 // discover references in other generations even if the | |
1161 // referent is in its own generation). This policy may, | |
1162 // in certain cases, enqueue references somewhat sooner than | |
1163 // might Policy #0 above, but at marginally increased cost | |
1164 // and complexity in processing these references. | |
1165 // We call this choice the "RefeferentBasedDiscovery" policy. | |
1166 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
1167 // We enqueue references only if we are discovering refs | |
1168 // (rather than processing discovered refs). | |
1169 if (!_discovering_refs || !RegisterReferences) { | |
1170 return false; | |
1171 } | |
1172 // We only enqueue active references. | |
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1173 oop next = java_lang_ref_Reference::next(obj); |
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1174 if (next != NULL) { |
0 | 1175 return false; |
1176 } | |
1177 | |
1178 HeapWord* obj_addr = (HeapWord*)obj; | |
1179 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1180 !_span.contains(obj_addr)) { | |
1181 // Reference is not in the originating generation; | |
1182 // don't treat it specially (i.e. we want to scan it as a normal | |
1183 // object with strong references). | |
1184 return false; | |
1185 } | |
1186 | |
1187 // We only enqueue references whose referents are not (yet) strongly | |
1188 // reachable. | |
1189 if (is_alive_non_header() != NULL) { | |
1190 oop referent = java_lang_ref_Reference::referent(obj); | |
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1191 // In the case of non-concurrent discovery, the last |
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1192 // disjunct below should hold. It may not hold in the |
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1193 // case of concurrent discovery because mutators may |
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1194 // concurrently clear() a Reference. |
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1195 assert(UseConcMarkSweepGC || UseG1GC || referent != NULL, |
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1196 "Refs with null referents already filtered"); |
0 | 1197 if (is_alive_non_header()->do_object_b(referent)) { |
1198 return false; // referent is reachable | |
1199 } | |
1200 } | |
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1201 if (rt == REF_SOFT) { |
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1202 // For soft refs we can decide now if these are not |
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1203 // current candidates for clearing, in which case we |
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1204 // can mark through them now, rather than delaying that |
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1205 // to the reference-processing phase. Since all current |
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1206 // time-stamp policies advance the soft-ref clock only |
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1207 // at a major collection cycle, this is always currently |
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1208 // accurate. |
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1209 if (!_current_soft_ref_policy->should_clear_reference(obj)) { |
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1210 return false; |
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1211 } |
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1212 } |
0 | 1213 |
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1214 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1215 const oop discovered = java_lang_ref_Reference::discovered(obj); |
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1216 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1217 if (discovered != NULL) { |
0 | 1218 // The reference has already been discovered... |
1219 if (TraceReferenceGC) { | |
1220 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", | |
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1221 obj, obj->blueprint()->internal_name()); |
0 | 1222 } |
1223 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1224 // assumes that an object is not processed twice; | |
1225 // if it's been already discovered it must be on another | |
1226 // generation's discovered list; so we won't discover it. | |
1227 return false; | |
1228 } else { | |
1229 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
1230 "Unrecognized policy"); | |
1231 // Check assumption that an object is not potentially | |
1232 // discovered twice except by concurrent collectors that potentially | |
1233 // trace the same Reference object twice. | |
1234 assert(UseConcMarkSweepGC, | |
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1235 "Only possible with an incremental-update concurrent collector"); |
0 | 1236 return true; |
1237 } | |
1238 } | |
1239 | |
1240 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1241 oop referent = java_lang_ref_Reference::referent(obj); | |
1242 assert(referent->is_oop(), "bad referent"); | |
1243 // enqueue if and only if either: | |
1244 // reference is in our span or | |
1245 // we are an atomic collector and referent is in our span | |
1246 if (_span.contains(obj_addr) || | |
1247 (discovery_is_atomic() && _span.contains(referent))) { | |
1248 // should_enqueue = true; | |
1249 } else { | |
1250 return false; | |
1251 } | |
1252 } else { | |
1253 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1254 _span.contains(obj_addr), "code inconsistency"); | |
1255 } | |
1256 | |
1257 // Get the right type of discovered queue head. | |
1258 DiscoveredList* list = get_discovered_list(rt); | |
1259 if (list == NULL) { | |
1260 return false; // nothing special needs to be done | |
1261 } | |
1262 | |
1263 if (_discovery_is_mt) { | |
1264 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
1265 } else { | |
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1266 // If "_discovered_list_needs_barrier", we do write barriers when |
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1267 // updating the discovered reference list. Otherwise, we do a raw store |
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1268 // here: the field will be visited later when processing the discovered |
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1269 // references. |
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1270 oop current_head = list->head(); |
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1271 // As in the case further above, since we are over-writing a NULL |
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1272 // pre-value, we can safely elide the pre-barrier here for the case of G1. |
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1273 assert(discovered == NULL, "control point invariant"); |
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1274 if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1 |
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1275 if (UseCompressedOops) { |
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1276 _bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head); |
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1277 } else { |
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1278 _bs->write_ref_field_pre((oop*)discovered_addr, current_head); |
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1279 } |
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1280 guarantee(false, "Need to check non-G1 collector"); |
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1281 } |
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1282 oop_store_raw(discovered_addr, current_head); |
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1283 if (_discovered_list_needs_barrier) { |
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1284 _bs->write_ref_field((void*)discovered_addr, current_head); |
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1285 } |
0 | 1286 list->set_head(obj); |
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1287 list->inc_length(1); |
0 | 1288 } |
1289 | |
1290 // In the MT discovery case, it is currently possible to see | |
1291 // the following message multiple times if several threads | |
1292 // discover a reference about the same time. Only one will | |
1293 // however have actually added it to the disocvered queue. | |
1294 // One could let add_to_discovered_list_mt() return an | |
1295 // indication for success in queueing (by 1 thread) or | |
1296 // failure (by all other threads), but I decided the extra | |
1297 // code was not worth the effort for something that is | |
1298 // only used for debugging support. | |
1299 if (TraceReferenceGC) { | |
1300 oop referent = java_lang_ref_Reference::referent(obj); | |
1301 if (PrintGCDetails) { | |
1302 gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)", | |
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1303 obj, obj->blueprint()->internal_name()); |
0 | 1304 } |
1305 assert(referent->is_oop(), "Enqueued a bad referent"); | |
1306 } | |
1307 assert(obj->is_oop(), "Enqueued a bad reference"); | |
1308 return true; | |
1309 } | |
1310 | |
1311 // Preclean the discovered references by removing those | |
1312 // whose referents are alive, and by marking from those that | |
1313 // are not active. These lists can be handled here | |
1314 // in any order and, indeed, concurrently. | |
1315 void ReferenceProcessor::preclean_discovered_references( | |
1316 BoolObjectClosure* is_alive, | |
1317 OopClosure* keep_alive, | |
1318 VoidClosure* complete_gc, | |
1190
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1319 YieldClosure* yield, |
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1320 bool should_unload_classes) { |
0 | 1321 |
1322 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
1323 | |
935 | 1324 #ifdef ASSERT |
1325 bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC || | |
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1326 CMSClassUnloadingEnabled && UseConcMarkSweepGC || |
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1327 ExplicitGCInvokesConcurrentAndUnloadsClasses && |
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1328 UseConcMarkSweepGC && should_unload_classes; |
935 | 1329 RememberKlassesChecker mx(must_remember_klasses); |
1330 #endif | |
0 | 1331 // Soft references |
1332 { | |
1333 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, | |
1334 false, gclog_or_tty); | |
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1335 for (int i = 0; i < _max_num_q; i++) { |
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1336 if (yield->should_return()) { |
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1337 return; |
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1338 } |
0 | 1339 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
1340 keep_alive, complete_gc, yield); | |
1341 } | |
1342 } | |
1343 | |
1344 // Weak references | |
1345 { | |
1346 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, | |
1347 false, gclog_or_tty); | |
1348 for (int i = 0; i < _num_q; i++) { | |
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1349 if (yield->should_return()) { |
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1350 return; |
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1351 } |
0 | 1352 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
1353 keep_alive, complete_gc, yield); | |
1354 } | |
1355 } | |
1356 | |
1357 // Final references | |
1358 { | |
1359 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, | |
1360 false, gclog_or_tty); | |
1361 for (int i = 0; i < _num_q; i++) { | |
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1362 if (yield->should_return()) { |
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1363 return; |
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1364 } |
0 | 1365 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
1366 keep_alive, complete_gc, yield); | |
1367 } | |
1368 } | |
1369 | |
1370 // Phantom references | |
1371 { | |
1372 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, | |
1373 false, gclog_or_tty); | |
1374 for (int i = 0; i < _num_q; i++) { | |
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1375 if (yield->should_return()) { |
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1376 return; |
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1377 } |
0 | 1378 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
1379 keep_alive, complete_gc, yield); | |
1380 } | |
1381 } | |
1382 } | |
1383 | |
1384 // Walk the given discovered ref list, and remove all reference objects | |
1385 // whose referents are still alive, whose referents are NULL or which | |
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1386 // are not active (have a non-NULL next field). NOTE: When we are |
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1387 // thus precleaning the ref lists (which happens single-threaded today), |
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1388 // we do not disable refs discovery to honour the correct semantics of |
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1389 // java.lang.Reference. As a result, we need to be careful below |
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1390 // that ref removal steps interleave safely with ref discovery steps |
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1391 // (in this thread). |
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1392 void |
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1393 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1394 BoolObjectClosure* is_alive, |
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1395 OopClosure* keep_alive, |
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1396 VoidClosure* complete_gc, |
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1397 YieldClosure* yield) { |
0 | 1398 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
1399 while (iter.has_next()) { | |
1400 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1401 oop obj = iter.obj(); |
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1402 oop next = java_lang_ref_Reference::next(obj); |
0 | 1403 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1404 next != NULL) { |
0 | 1405 // The referent has been cleared, or is alive, or the Reference is not |
1406 // active; we need to trace and mark its cohort. | |
1407 if (TraceReferenceGC) { | |
1408 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
1409 iter.obj(), iter.obj()->blueprint()->internal_name()); | |
1410 } | |
1411 // Remove Reference object from list | |
1412 iter.remove(); | |
1413 // Keep alive its cohort. | |
1414 iter.make_referent_alive(); | |
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1415 if (UseCompressedOops) { |
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1416 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1417 keep_alive->do_oop(next_addr); |
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1418 } else { |
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1419 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1420 keep_alive->do_oop(next_addr); |
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1421 } |
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1422 iter.move_to_next(); |
0 | 1423 } else { |
1424 iter.next(); | |
1425 } | |
1426 } | |
1427 // Close the reachable set | |
1428 complete_gc->do_void(); | |
1429 | |
1430 NOT_PRODUCT( | |
1431 if (PrintGCDetails && PrintReferenceGC) { | |
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1432 gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
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1433 "Refs in discovered list " INTPTR_FORMAT, |
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1434 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 1435 } |
1436 ) | |
1437 } | |
1438 | |
1439 const char* ReferenceProcessor::list_name(int i) { | |
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1440 assert(i >= 0 && i <= _max_num_q * subclasses_of_ref, "Out of bounds index"); |
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1441 int j = i / _max_num_q; |
0 | 1442 switch (j) { |
1443 case 0: return "SoftRef"; | |
1444 case 1: return "WeakRef"; | |
1445 case 2: return "FinalRef"; | |
1446 case 3: return "PhantomRef"; | |
1447 } | |
1448 ShouldNotReachHere(); | |
1449 return NULL; | |
1450 } | |
1451 | |
1452 #ifndef PRODUCT | |
1453 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
1454 // empty for now | |
1455 } | |
1456 #endif | |
1457 | |
1458 void ReferenceProcessor::verify() { | |
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1459 guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef"); |
0 | 1460 } |
1461 | |
1462 #ifndef PRODUCT | |
1463 void ReferenceProcessor::clear_discovered_references() { | |
1464 guarantee(!_discovering_refs, "Discovering refs?"); | |
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1465 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 1466 oop obj = _discoveredSoftRefs[i].head(); |
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1467 while (obj != sentinel_ref()) { |
0 | 1468 oop next = java_lang_ref_Reference::discovered(obj); |
1469 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); | |
1470 obj = next; | |
1471 } | |
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1472 _discoveredSoftRefs[i].set_head(sentinel_ref()); |
0 | 1473 _discoveredSoftRefs[i].set_length(0); |
1474 } | |
1475 } | |
1476 #endif // PRODUCT |