Mercurial > hg > truffle
annotate src/share/vm/memory/referenceProcessor.cpp @ 4005:2ef3386478e6
7096278: Update the VM name to indicate it is an embedded build
Reviewed-by: kvn, never, jcoomes, bobv
author | dholmes |
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date | Mon, 10 Oct 2011 21:01:36 -0400 |
parents | eca1193ca245 |
children | 4dfb2df418f2 |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved. |
0 | 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
0 | 22 * |
23 */ | |
24 | |
1972 | 25 #include "precompiled.hpp" |
26 #include "classfile/javaClasses.hpp" | |
27 #include "classfile/systemDictionary.hpp" | |
28 #include "gc_interface/collectedHeap.hpp" | |
29 #include "gc_interface/collectedHeap.inline.hpp" | |
30 #include "memory/referencePolicy.hpp" | |
31 #include "memory/referenceProcessor.hpp" | |
32 #include "oops/oop.inline.hpp" | |
33 #include "runtime/java.hpp" | |
34 #include "runtime/jniHandles.hpp" | |
0 | 35 |
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36 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
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37 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
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38 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER; |
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39 bool ReferenceProcessor::_pending_list_uses_discovered_field = false; |
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40 |
0 | 41 // List of discovered references. |
42 class DiscoveredList { | |
43 public: | |
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44 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } |
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45 oop head() const { |
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46 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) : |
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47 _oop_head; |
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48 } |
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49 HeapWord* adr_head() { |
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50 return UseCompressedOops ? (HeapWord*)&_compressed_head : |
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51 (HeapWord*)&_oop_head; |
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52 } |
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53 void set_head(oop o) { |
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54 if (UseCompressedOops) { |
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55 // Must compress the head ptr. |
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56 _compressed_head = oopDesc::encode_heap_oop(o); |
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57 } else { |
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58 _oop_head = o; |
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59 } |
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60 } |
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61 bool empty() const { return head() == NULL; } |
0 | 62 size_t length() { return _len; } |
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63 void set_length(size_t len) { _len = len; } |
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64 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } |
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65 void dec_length(size_t dec) { _len -= dec; } |
0 | 66 private: |
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67 // Set value depending on UseCompressedOops. This could be a template class |
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68 // but then we have to fix all the instantiations and declarations that use this class. |
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69 oop _oop_head; |
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70 narrowOop _compressed_head; |
0 | 71 size_t _len; |
72 }; | |
73 | |
74 void referenceProcessor_init() { | |
75 ReferenceProcessor::init_statics(); | |
76 } | |
77 | |
78 void ReferenceProcessor::init_statics() { | |
79 // Initialize the master soft ref clock. | |
80 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis()); | |
81 | |
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82 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
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83 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
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84 NOT_COMPILER2(LRUCurrentHeapPolicy()); |
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85 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
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86 vm_exit_during_initialization("Could not allocate reference policy object"); |
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87 } |
0 | 88 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
89 RefDiscoveryPolicy == ReferentBasedDiscovery, | |
90 "Unrecongnized RefDiscoveryPolicy"); | |
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91 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field(); |
0 | 92 } |
93 | |
94 ReferenceProcessor::ReferenceProcessor(MemRegion span, | |
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95 bool mt_processing, |
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96 int mt_processing_degree, |
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97 bool mt_discovery, |
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98 int mt_discovery_degree, |
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99 bool atomic_discovery, |
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100 BoolObjectClosure* is_alive_non_header, |
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101 bool discovered_list_needs_barrier) : |
0 | 102 _discovering_refs(false), |
103 _enqueuing_is_done(false), | |
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104 _is_alive_non_header(is_alive_non_header), |
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105 _discovered_list_needs_barrier(discovered_list_needs_barrier), |
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106 _bs(NULL), |
0 | 107 _processing_is_mt(mt_processing), |
108 _next_id(0) | |
109 { | |
110 _span = span; | |
111 _discovery_is_atomic = atomic_discovery; | |
112 _discovery_is_mt = mt_discovery; | |
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113 _num_q = MAX2(1, mt_processing_degree); |
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114 _max_num_q = MAX2(_num_q, mt_discovery_degree); |
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115 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _max_num_q * subclasses_of_ref); |
0 | 116 if (_discoveredSoftRefs == NULL) { |
117 vm_exit_during_initialization("Could not allocated RefProc Array"); | |
118 } | |
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119 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
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120 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
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121 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
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122 // Initialized all entries to NULL |
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123 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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124 _discoveredSoftRefs[i].set_head(NULL); |
0 | 125 _discoveredSoftRefs[i].set_length(0); |
126 } | |
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127 // If we do barriers, cache a copy of the barrier set. |
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128 if (discovered_list_needs_barrier) { |
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129 _bs = Universe::heap()->barrier_set(); |
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130 } |
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131 setup_policy(false /* default soft ref policy */); |
0 | 132 } |
133 | |
134 #ifndef PRODUCT | |
135 void ReferenceProcessor::verify_no_references_recorded() { | |
136 guarantee(!_discovering_refs, "Discovering refs?"); | |
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137 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 138 guarantee(_discoveredSoftRefs[i].empty(), |
139 "Found non-empty discovered list"); | |
140 } | |
141 } | |
142 #endif | |
143 | |
144 void ReferenceProcessor::weak_oops_do(OopClosure* f) { | |
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145 // Should this instead be |
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146 // for (int i = 0; i < subclasses_of_ref; i++_ { |
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147 // for (int j = 0; j < _num_q; j++) { |
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148 // int index = i * _max_num_q + j; |
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149 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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150 if (UseCompressedOops) { |
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151 f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head()); |
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152 } else { |
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153 f->do_oop((oop*)_discoveredSoftRefs[i].adr_head()); |
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154 } |
0 | 155 } |
156 } | |
157 | |
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158 void ReferenceProcessor::update_soft_ref_master_clock() { |
0 | 159 // Update (advance) the soft ref master clock field. This must be done |
160 // after processing the soft ref list. | |
161 jlong now = os::javaTimeMillis(); | |
162 jlong clock = java_lang_ref_SoftReference::clock(); | |
163 NOT_PRODUCT( | |
164 if (now < clock) { | |
165 warning("time warp: %d to %d", clock, now); | |
166 } | |
167 ) | |
168 // In product mode, protect ourselves from system time being adjusted | |
169 // externally and going backward; see note in the implementation of | |
170 // GenCollectedHeap::time_since_last_gc() for the right way to fix | |
171 // this uniformly throughout the VM; see bug-id 4741166. XXX | |
172 if (now > clock) { | |
173 java_lang_ref_SoftReference::set_clock(now); | |
174 } | |
175 // Else leave clock stalled at its old value until time progresses | |
176 // past clock value. | |
177 } | |
178 | |
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179 void ReferenceProcessor::process_discovered_references( |
0 | 180 BoolObjectClosure* is_alive, |
181 OopClosure* keep_alive, | |
182 VoidClosure* complete_gc, | |
183 AbstractRefProcTaskExecutor* task_executor) { | |
184 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
185 | |
186 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); | |
187 // Stop treating discovered references specially. | |
188 disable_discovery(); | |
189 | |
190 bool trace_time = PrintGCDetails && PrintReferenceGC; | |
191 // Soft references | |
192 { | |
193 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); | |
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194 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, |
0 | 195 is_alive, keep_alive, complete_gc, task_executor); |
196 } | |
197 | |
198 update_soft_ref_master_clock(); | |
199 | |
200 // Weak references | |
201 { | |
202 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); | |
203 process_discovered_reflist(_discoveredWeakRefs, NULL, true, | |
204 is_alive, keep_alive, complete_gc, task_executor); | |
205 } | |
206 | |
207 // Final references | |
208 { | |
209 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); | |
210 process_discovered_reflist(_discoveredFinalRefs, NULL, false, | |
211 is_alive, keep_alive, complete_gc, task_executor); | |
212 } | |
213 | |
214 // Phantom references | |
215 { | |
216 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); | |
217 process_discovered_reflist(_discoveredPhantomRefs, NULL, false, | |
218 is_alive, keep_alive, complete_gc, task_executor); | |
219 } | |
220 | |
221 // Weak global JNI references. It would make more sense (semantically) to | |
222 // traverse these simultaneously with the regular weak references above, but | |
223 // that is not how the JDK1.2 specification is. See #4126360. Native code can | |
224 // thus use JNI weak references to circumvent the phantom references and | |
225 // resurrect a "post-mortem" object. | |
226 { | |
227 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); | |
228 if (task_executor != NULL) { | |
229 task_executor->set_single_threaded_mode(); | |
230 } | |
231 process_phaseJNI(is_alive, keep_alive, complete_gc); | |
232 } | |
233 } | |
234 | |
235 #ifndef PRODUCT | |
236 // Calculate the number of jni handles. | |
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237 uint ReferenceProcessor::count_jni_refs() { |
0 | 238 class AlwaysAliveClosure: public BoolObjectClosure { |
239 public: | |
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240 virtual bool do_object_b(oop obj) { return true; } |
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241 virtual void do_object(oop obj) { assert(false, "Don't call"); } |
0 | 242 }; |
243 | |
244 class CountHandleClosure: public OopClosure { | |
245 private: | |
246 int _count; | |
247 public: | |
248 CountHandleClosure(): _count(0) {} | |
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249 void do_oop(oop* unused) { _count++; } |
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250 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
0 | 251 int count() { return _count; } |
252 }; | |
253 CountHandleClosure global_handle_count; | |
254 AlwaysAliveClosure always_alive; | |
255 JNIHandles::weak_oops_do(&always_alive, &global_handle_count); | |
256 return global_handle_count.count(); | |
257 } | |
258 #endif | |
259 | |
260 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, | |
261 OopClosure* keep_alive, | |
262 VoidClosure* complete_gc) { | |
263 #ifndef PRODUCT | |
264 if (PrintGCDetails && PrintReferenceGC) { | |
265 unsigned int count = count_jni_refs(); | |
266 gclog_or_tty->print(", %u refs", count); | |
267 } | |
268 #endif | |
269 JNIHandles::weak_oops_do(is_alive, keep_alive); | |
270 complete_gc->do_void(); | |
271 } | |
272 | |
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273 |
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274 template <class T> |
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275 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
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276 AbstractRefProcTaskExecutor* task_executor) { |
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277 |
0 | 278 // Remember old value of pending references list |
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279 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
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280 T old_pending_list_value = *pending_list_addr; |
0 | 281 |
282 // Enqueue references that are not made active again, and | |
283 // clear the decks for the next collection (cycle). | |
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284 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
0 | 285 // Do the oop-check on pending_list_addr missed in |
286 // enqueue_discovered_reflist. We should probably | |
287 // do a raw oop_check so that future such idempotent | |
288 // oop_stores relying on the oop-check side-effect | |
289 // may be elided automatically and safely without | |
290 // affecting correctness. | |
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291 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
0 | 292 |
293 // Stop treating discovered references specially. | |
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294 ref->disable_discovery(); |
0 | 295 |
296 // Return true if new pending references were added | |
297 return old_pending_list_value != *pending_list_addr; | |
298 } | |
299 | |
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300 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
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301 NOT_PRODUCT(verify_ok_to_handle_reflists()); |
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302 if (UseCompressedOops) { |
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303 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
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304 } else { |
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305 return enqueue_discovered_ref_helper<oop>(this, task_executor); |
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306 } |
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307 } |
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308 |
0 | 309 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
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310 HeapWord* pending_list_addr) { |
0 | 311 // Given a list of refs linked through the "discovered" field |
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312 // (java.lang.ref.Reference.discovered), self-loop their "next" field |
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313 // thus distinguishing them from active References, then |
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314 // prepend them to the pending list. |
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315 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777), |
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316 // the "next" field is used to chain the pending list, not the discovered |
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317 // field. |
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318 |
0 | 319 if (TraceReferenceGC && PrintGCDetails) { |
320 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " | |
321 INTPTR_FORMAT, (address)refs_list.head()); | |
322 } | |
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323 |
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324 oop obj = NULL; |
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325 oop next_d = refs_list.head(); |
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326 if (pending_list_uses_discovered_field()) { // New behaviour |
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327 // Walk down the list, self-looping the next field |
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328 // so that the References are not considered active. |
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329 while (obj != next_d) { |
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330 obj = next_d; |
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331 assert(obj->is_instanceRef(), "should be reference object"); |
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332 next_d = java_lang_ref_Reference::discovered(obj); |
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333 if (TraceReferenceGC && PrintGCDetails) { |
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334 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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335 obj, next_d); |
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336 } |
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337 assert(java_lang_ref_Reference::next(obj) == NULL, |
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338 "Reference not active; should not be discovered"); |
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339 // Self-loop next, so as to make Ref not active. |
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340 java_lang_ref_Reference::set_next(obj, obj); |
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341 if (next_d == obj) { // obj is last |
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342 // Swap refs_list into pendling_list_addr and |
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343 // set obj's discovered to what we read from pending_list_addr. |
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344 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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345 // Need oop_check on pending_list_addr above; |
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346 // see special oop-check code at the end of |
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347 // enqueue_discovered_reflists() further below. |
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348 java_lang_ref_Reference::set_discovered(obj, old); // old may be NULL |
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349 } |
0 | 350 } |
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351 } else { // Old behaviour |
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352 // Walk down the list, copying the discovered field into |
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353 // the next field and clearing the discovered field. |
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354 while (obj != next_d) { |
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355 obj = next_d; |
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356 assert(obj->is_instanceRef(), "should be reference object"); |
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357 next_d = java_lang_ref_Reference::discovered(obj); |
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358 if (TraceReferenceGC && PrintGCDetails) { |
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359 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
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360 obj, next_d); |
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361 } |
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362 assert(java_lang_ref_Reference::next(obj) == NULL, |
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363 "The reference should not be enqueued"); |
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364 if (next_d == obj) { // obj is last |
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365 // Swap refs_list into pendling_list_addr and |
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366 // set obj's next to what we read from pending_list_addr. |
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367 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
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368 // Need oop_check on pending_list_addr above; |
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369 // see special oop-check code at the end of |
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370 // enqueue_discovered_reflists() further below. |
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371 if (old == NULL) { |
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372 // obj should be made to point to itself, since |
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373 // pending list was empty. |
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374 java_lang_ref_Reference::set_next(obj, obj); |
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375 } else { |
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376 java_lang_ref_Reference::set_next(obj, old); |
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377 } |
0 | 378 } else { |
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379 java_lang_ref_Reference::set_next(obj, next_d); |
0 | 380 } |
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381 java_lang_ref_Reference::set_discovered(obj, (oop) NULL); |
0 | 382 } |
383 } | |
384 } | |
385 | |
386 // Parallel enqueue task | |
387 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { | |
388 public: | |
389 RefProcEnqueueTask(ReferenceProcessor& ref_processor, | |
390 DiscoveredList discovered_refs[], | |
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391 HeapWord* pending_list_addr, |
0 | 392 int n_queues) |
393 : EnqueueTask(ref_processor, discovered_refs, | |
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394 pending_list_addr, n_queues) |
0 | 395 { } |
396 | |
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397 virtual void work(unsigned int work_id) { |
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398 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); |
0 | 399 // Simplest first cut: static partitioning. |
400 int index = work_id; | |
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401 // The increment on "index" must correspond to the maximum number of queues |
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402 // (n_queues) with which that ReferenceProcessor was created. That |
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403 // is because of the "clever" way the discovered references lists were |
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404 // allocated and are indexed into. |
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405 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); |
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406 for (int j = 0; |
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407 j < subclasses_of_ref; |
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408 j++, index += _n_queues) { |
0 | 409 _ref_processor.enqueue_discovered_reflist( |
410 _refs_lists[index], _pending_list_addr); | |
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411 _refs_lists[index].set_head(NULL); |
0 | 412 _refs_lists[index].set_length(0); |
413 } | |
414 } | |
415 }; | |
416 | |
417 // Enqueue references that are not made active again | |
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418 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
0 | 419 AbstractRefProcTaskExecutor* task_executor) { |
420 if (_processing_is_mt && task_executor != NULL) { | |
421 // Parallel code | |
422 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs, | |
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423 pending_list_addr, _max_num_q); |
0 | 424 task_executor->execute(tsk); |
425 } else { | |
426 // Serial code: call the parent class's implementation | |
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427 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
0 | 428 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr); |
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429 _discoveredSoftRefs[i].set_head(NULL); |
0 | 430 _discoveredSoftRefs[i].set_length(0); |
431 } | |
432 } | |
433 } | |
434 | |
435 // Iterator for the list of discovered references. | |
436 class DiscoveredListIterator { | |
437 public: | |
438 inline DiscoveredListIterator(DiscoveredList& refs_list, | |
439 OopClosure* keep_alive, | |
440 BoolObjectClosure* is_alive); | |
441 | |
442 // End Of List. | |
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443 inline bool has_next() const { return _ref != NULL; } |
0 | 444 |
445 // Get oop to the Reference object. | |
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446 inline oop obj() const { return _ref; } |
0 | 447 |
448 // Get oop to the referent object. | |
113
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449 inline oop referent() const { return _referent; } |
0 | 450 |
451 // Returns true if referent is alive. | |
452 inline bool is_referent_alive() const; | |
453 | |
454 // Loads data for the current reference. | |
455 // The "allow_null_referent" argument tells us to allow for the possibility | |
456 // of a NULL referent in the discovered Reference object. This typically | |
457 // happens in the case of concurrent collectors that may have done the | |
452
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458 // discovery concurrently, or interleaved, with mutator execution. |
0 | 459 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); |
460 | |
461 // Move to the next discovered reference. | |
462 inline void next(); | |
463 | |
452
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464 // Remove the current reference from the list |
0 | 465 inline void remove(); |
466 | |
467 // Make the Reference object active again. | |
468 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); } | |
469 | |
470 // Make the referent alive. | |
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471 inline void make_referent_alive() { |
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472 if (UseCompressedOops) { |
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473 _keep_alive->do_oop((narrowOop*)_referent_addr); |
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474 } else { |
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475 _keep_alive->do_oop((oop*)_referent_addr); |
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476 } |
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477 } |
0 | 478 |
479 // Update the discovered field. | |
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480 inline void update_discovered() { |
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481 // First _prev_next ref actually points into DiscoveredList (gross). |
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482 if (UseCompressedOops) { |
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483 if (!oopDesc::is_null(*(narrowOop*)_prev_next)) { |
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484 _keep_alive->do_oop((narrowOop*)_prev_next); |
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485 } |
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486 } else { |
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487 if (!oopDesc::is_null(*(oop*)_prev_next)) { |
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488 _keep_alive->do_oop((oop*)_prev_next); |
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489 } |
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490 } |
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491 } |
0 | 492 |
493 // NULL out referent pointer. | |
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494 inline void clear_referent() { oop_store_raw(_referent_addr, NULL); } |
0 | 495 |
496 // Statistics | |
497 NOT_PRODUCT( | |
498 inline size_t processed() const { return _processed; } | |
499 inline size_t removed() const { return _removed; } | |
500 ) | |
501 | |
502 inline void move_to_next(); | |
503 | |
504 private: | |
505 DiscoveredList& _refs_list; | |
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506 HeapWord* _prev_next; |
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507 oop _prev; |
0 | 508 oop _ref; |
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509 HeapWord* _discovered_addr; |
0 | 510 oop _next; |
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511 HeapWord* _referent_addr; |
0 | 512 oop _referent; |
513 OopClosure* _keep_alive; | |
514 BoolObjectClosure* _is_alive; | |
515 DEBUG_ONLY( | |
516 oop _first_seen; // cyclic linked list check | |
517 ) | |
518 NOT_PRODUCT( | |
519 size_t _processed; | |
520 size_t _removed; | |
521 ) | |
522 }; | |
523 | |
524 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list, | |
525 OopClosure* keep_alive, | |
526 BoolObjectClosure* is_alive) | |
527 : _refs_list(refs_list), | |
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528 _prev_next(refs_list.adr_head()), |
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529 _prev(NULL), |
0 | 530 _ref(refs_list.head()), |
531 #ifdef ASSERT | |
532 _first_seen(refs_list.head()), | |
533 #endif | |
534 #ifndef PRODUCT | |
535 _processed(0), | |
536 _removed(0), | |
537 #endif | |
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538 _next(NULL), |
0 | 539 _keep_alive(keep_alive), |
540 _is_alive(is_alive) | |
541 { } | |
542 | |
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543 inline bool DiscoveredListIterator::is_referent_alive() const { |
0 | 544 return _is_alive->do_object_b(_referent); |
545 } | |
546 | |
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547 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
0 | 548 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
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549 oop discovered = java_lang_ref_Reference::discovered(_ref); |
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550 assert(_discovered_addr && discovered->is_oop_or_null(), |
0 | 551 "discovered field is bad"); |
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552 _next = discovered; |
0 | 553 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
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554 _referent = java_lang_ref_Reference::referent(_ref); |
0 | 555 assert(Universe::heap()->is_in_reserved_or_null(_referent), |
556 "Wrong oop found in java.lang.Reference object"); | |
557 assert(allow_null_referent ? | |
558 _referent->is_oop_or_null() | |
559 : _referent->is_oop(), | |
560 "bad referent"); | |
561 } | |
562 | |
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563 inline void DiscoveredListIterator::next() { |
0 | 564 _prev_next = _discovered_addr; |
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565 _prev = _ref; |
0 | 566 move_to_next(); |
567 } | |
568 | |
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569 inline void DiscoveredListIterator::remove() { |
0 | 570 assert(_ref->is_oop(), "Dropping a bad reference"); |
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571 oop_store_raw(_discovered_addr, NULL); |
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572 |
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573 // First _prev_next ref actually points into DiscoveredList (gross). |
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574 oop new_next; |
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575 if (_next == _ref) { |
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576 // At the end of the list, we should make _prev point to itself. |
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577 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, |
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578 // and _prev will be NULL. |
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579 new_next = _prev; |
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580 } else { |
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581 new_next = _next; |
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582 } |
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583 |
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584 if (UseCompressedOops) { |
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585 // Remove Reference object from list. |
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586 oopDesc::encode_store_heap_oop((narrowOop*)_prev_next, new_next); |
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587 } else { |
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588 // Remove Reference object from list. |
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589 oopDesc::store_heap_oop((oop*)_prev_next, new_next); |
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590 } |
0 | 591 NOT_PRODUCT(_removed++); |
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592 _refs_list.dec_length(1); |
0 | 593 } |
594 | |
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595 inline void DiscoveredListIterator::move_to_next() { |
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596 if (_ref == _next) { |
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597 // End of the list. |
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598 _ref = NULL; |
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599 } else { |
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600 _ref = _next; |
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601 } |
0 | 602 assert(_ref != _first_seen, "cyclic ref_list found"); |
603 NOT_PRODUCT(_processed++); | |
604 } | |
605 | |
606 // NOTE: process_phase*() are largely similar, and at a high level | |
607 // merely iterate over the extant list applying a predicate to | |
608 // each of its elements and possibly removing that element from the | |
609 // list and applying some further closures to that element. | |
610 // We should consider the possibility of replacing these | |
611 // process_phase*() methods by abstracting them into | |
612 // a single general iterator invocation that receives appropriate | |
613 // closures that accomplish this work. | |
614 | |
615 // (SoftReferences only) Traverse the list and remove any SoftReferences whose | |
616 // referents are not alive, but that should be kept alive for policy reasons. | |
617 // Keep alive the transitive closure of all such referents. | |
618 void | |
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619 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
0 | 620 ReferencePolicy* policy, |
621 BoolObjectClosure* is_alive, | |
622 OopClosure* keep_alive, | |
623 VoidClosure* complete_gc) { | |
624 assert(policy != NULL, "Must have a non-NULL policy"); | |
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625 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 626 // Decide which softly reachable refs should be kept alive. |
627 while (iter.has_next()) { | |
628 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); | |
629 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); | |
630 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) { | |
631 if (TraceReferenceGC) { | |
632 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", | |
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633 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 634 } |
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635 // Remove Reference object from list |
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636 iter.remove(); |
0 | 637 // Make the Reference object active again |
638 iter.make_active(); | |
639 // keep the referent around | |
640 iter.make_referent_alive(); | |
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641 iter.move_to_next(); |
0 | 642 } else { |
643 iter.next(); | |
644 } | |
645 } | |
646 // Close the reachable set | |
647 complete_gc->do_void(); | |
648 NOT_PRODUCT( | |
649 if (PrintGCDetails && TraceReferenceGC) { | |
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650 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
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651 "discovered Refs by policy, from list " INTPTR_FORMAT, |
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652 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 653 } |
654 ) | |
655 } | |
656 | |
657 // Traverse the list and remove any Refs that are not active, or | |
658 // whose referents are either alive or NULL. | |
659 void | |
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660 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
0 | 661 BoolObjectClosure* is_alive, |
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662 OopClosure* keep_alive) { |
0 | 663 assert(discovery_is_atomic(), "Error"); |
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664 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 665 while (iter.has_next()) { |
666 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
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667 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
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668 assert(next == NULL, "Should not discover inactive Reference"); |
0 | 669 if (iter.is_referent_alive()) { |
670 if (TraceReferenceGC) { | |
671 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", | |
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672 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 673 } |
674 // The referent is reachable after all. | |
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675 // Remove Reference object from list. |
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676 iter.remove(); |
0 | 677 // Update the referent pointer as necessary: Note that this |
678 // should not entail any recursive marking because the | |
679 // referent must already have been traversed. | |
680 iter.make_referent_alive(); | |
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681 iter.move_to_next(); |
0 | 682 } else { |
683 iter.next(); | |
684 } | |
685 } | |
686 NOT_PRODUCT( | |
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687 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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688 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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689 "Refs in discovered list " INTPTR_FORMAT, |
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690 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 691 } |
692 ) | |
693 } | |
694 | |
695 void | |
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696 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
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697 BoolObjectClosure* is_alive, |
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698 OopClosure* keep_alive, |
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699 VoidClosure* complete_gc) { |
0 | 700 assert(!discovery_is_atomic(), "Error"); |
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701 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 702 while (iter.has_next()) { |
703 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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704 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
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705 oop next = java_lang_ref_Reference::next(iter.obj()); |
0 | 706 if ((iter.referent() == NULL || iter.is_referent_alive() || |
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707 next != NULL)) { |
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708 assert(next->is_oop_or_null(), "bad next field"); |
0 | 709 // Remove Reference object from list |
710 iter.remove(); | |
711 // Trace the cohorts | |
712 iter.make_referent_alive(); | |
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713 if (UseCompressedOops) { |
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714 keep_alive->do_oop((narrowOop*)next_addr); |
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715 } else { |
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716 keep_alive->do_oop((oop*)next_addr); |
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717 } |
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718 iter.move_to_next(); |
0 | 719 } else { |
720 iter.next(); | |
721 } | |
722 } | |
723 // Now close the newly reachable set | |
724 complete_gc->do_void(); | |
725 NOT_PRODUCT( | |
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726 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
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727 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
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728 "Refs in discovered list " INTPTR_FORMAT, |
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729 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 730 } |
731 ) | |
732 } | |
733 | |
734 // Traverse the list and process the referents, by either | |
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735 // clearing them or keeping them (and their reachable |
0 | 736 // closure) alive. |
737 void | |
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738 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
0 | 739 bool clear_referent, |
740 BoolObjectClosure* is_alive, | |
741 OopClosure* keep_alive, | |
742 VoidClosure* complete_gc) { | |
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743 ResourceMark rm; |
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744 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
0 | 745 while (iter.has_next()) { |
746 iter.update_discovered(); | |
747 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); | |
748 if (clear_referent) { | |
749 // NULL out referent pointer | |
750 iter.clear_referent(); | |
751 } else { | |
752 // keep the referent around | |
753 iter.make_referent_alive(); | |
754 } | |
755 if (TraceReferenceGC) { | |
756 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", | |
757 clear_referent ? "cleared " : "", | |
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758 iter.obj(), iter.obj()->blueprint()->internal_name()); |
0 | 759 } |
760 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); | |
761 iter.next(); | |
762 } | |
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763 // Remember to update the next pointer of the last ref. |
0 | 764 iter.update_discovered(); |
765 // Close the reachable set | |
766 complete_gc->do_void(); | |
767 } | |
768 | |
769 void | |
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770 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { |
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771 oop obj = NULL; |
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772 oop next = refs_list.head(); |
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773 while (next != obj) { |
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774 obj = next; |
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775 next = java_lang_ref_Reference::discovered(obj); |
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776 java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
0 | 777 } |
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778 refs_list.set_head(NULL); |
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779 refs_list.set_length(0); |
0 | 780 } |
781 | |
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782 void |
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783 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
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784 clear_discovered_references(refs_list); |
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785 } |
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786 |
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787 void ReferenceProcessor::abandon_partial_discovery() { |
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788 // loop over the lists |
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789 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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790 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
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791 gclog_or_tty->print_cr("\nAbandoning %s discovered list", |
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792 list_name(i)); |
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793 } |
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794 abandon_partial_discovered_list(_discoveredSoftRefs[i]); |
0 | 795 } |
796 } | |
797 | |
798 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
799 public: | |
800 RefProcPhase1Task(ReferenceProcessor& ref_processor, | |
801 DiscoveredList refs_lists[], | |
802 ReferencePolicy* policy, | |
803 bool marks_oops_alive) | |
804 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
805 _policy(policy) | |
806 { } | |
807 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
808 OopClosure& keep_alive, | |
809 VoidClosure& complete_gc) | |
810 { | |
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811 Thread* thr = Thread::current(); |
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812 int refs_list_index = ((WorkerThread*)thr)->id(); |
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813 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
0 | 814 &is_alive, &keep_alive, &complete_gc); |
815 } | |
816 private: | |
817 ReferencePolicy* _policy; | |
818 }; | |
819 | |
820 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
821 public: | |
822 RefProcPhase2Task(ReferenceProcessor& ref_processor, | |
823 DiscoveredList refs_lists[], | |
824 bool marks_oops_alive) | |
825 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) | |
826 { } | |
827 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
828 OopClosure& keep_alive, | |
829 VoidClosure& complete_gc) | |
830 { | |
831 _ref_processor.process_phase2(_refs_lists[i], | |
832 &is_alive, &keep_alive, &complete_gc); | |
833 } | |
834 }; | |
835 | |
836 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { | |
837 public: | |
838 RefProcPhase3Task(ReferenceProcessor& ref_processor, | |
839 DiscoveredList refs_lists[], | |
840 bool clear_referent, | |
841 bool marks_oops_alive) | |
842 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), | |
843 _clear_referent(clear_referent) | |
844 { } | |
845 virtual void work(unsigned int i, BoolObjectClosure& is_alive, | |
846 OopClosure& keep_alive, | |
847 VoidClosure& complete_gc) | |
848 { | |
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849 // Don't use "refs_list_index" calculated in this way because |
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850 // balance_queues() has moved the Ref's into the first n queues. |
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851 // Thread* thr = Thread::current(); |
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852 // int refs_list_index = ((WorkerThread*)thr)->id(); |
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853 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
0 | 854 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
855 &is_alive, &keep_alive, &complete_gc); | |
856 } | |
857 private: | |
858 bool _clear_referent; | |
859 }; | |
860 | |
861 // Balances reference queues. | |
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862 // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
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863 // queues[0, 1, ..., _num_q-1] because only the first _num_q |
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864 // corresponding to the active workers will be processed. |
0 | 865 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
866 { | |
867 // calculate total length | |
868 size_t total_refs = 0; | |
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869 if (TraceReferenceGC && PrintGCDetails) { |
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870 gclog_or_tty->print_cr("\nBalance ref_lists "); |
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871 } |
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872 |
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873 for (int i = 0; i < _max_num_q; ++i) { |
0 | 874 total_refs += ref_lists[i].length(); |
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875 if (TraceReferenceGC && PrintGCDetails) { |
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876 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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877 } |
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878 } |
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879 if (TraceReferenceGC && PrintGCDetails) { |
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880 gclog_or_tty->print_cr(" = %d", total_refs); |
0 | 881 } |
882 size_t avg_refs = total_refs / _num_q + 1; | |
883 int to_idx = 0; | |
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884 for (int from_idx = 0; from_idx < _max_num_q; from_idx++) { |
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885 bool move_all = false; |
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886 if (from_idx >= _num_q) { |
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887 move_all = ref_lists[from_idx].length() > 0; |
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888 } |
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889 while ((ref_lists[from_idx].length() > avg_refs) || |
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890 move_all) { |
0 | 891 assert(to_idx < _num_q, "Sanity Check!"); |
892 if (ref_lists[to_idx].length() < avg_refs) { | |
893 // move superfluous refs | |
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894 size_t refs_to_move; |
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895 // Move all the Ref's if the from queue will not be processed. |
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896 if (move_all) { |
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897 refs_to_move = MIN2(ref_lists[from_idx].length(), |
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898 avg_refs - ref_lists[to_idx].length()); |
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899 } else { |
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900 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
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901 avg_refs - ref_lists[to_idx].length()); |
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902 } |
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903 |
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904 assert(refs_to_move > 0, "otherwise the code below will fail"); |
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905 |
0 | 906 oop move_head = ref_lists[from_idx].head(); |
907 oop move_tail = move_head; | |
908 oop new_head = move_head; | |
909 // find an element to split the list on | |
910 for (size_t j = 0; j < refs_to_move; ++j) { | |
911 move_tail = new_head; | |
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912 new_head = java_lang_ref_Reference::discovered(new_head); |
0 | 913 } |
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914 |
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915 // Add the chain to the to list. |
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916 if (ref_lists[to_idx].head() == NULL) { |
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917 // to list is empty. Make a loop at the end. |
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918 java_lang_ref_Reference::set_discovered(move_tail, move_tail); |
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919 } else { |
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920 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head()); |
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921 } |
0 | 922 ref_lists[to_idx].set_head(move_head); |
452
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923 ref_lists[to_idx].inc_length(refs_to_move); |
3915
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924 |
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925 // Remove the chain from the from list. |
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926 if (move_tail == new_head) { |
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927 // We found the end of the from list. |
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928 ref_lists[from_idx].set_head(NULL); |
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929 } else { |
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930 ref_lists[from_idx].set_head(new_head); |
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931 } |
452
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932 ref_lists[from_idx].dec_length(refs_to_move); |
1833
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933 if (ref_lists[from_idx].length() == 0) { |
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934 break; |
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935 } |
0 | 936 } else { |
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937 to_idx = (to_idx + 1) % _num_q; |
0 | 938 } |
939 } | |
940 } | |
1833
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941 #ifdef ASSERT |
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942 size_t balanced_total_refs = 0; |
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943 for (int i = 0; i < _max_num_q; ++i) { |
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944 balanced_total_refs += ref_lists[i].length(); |
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945 if (TraceReferenceGC && PrintGCDetails) { |
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946 gclog_or_tty->print("%d ", ref_lists[i].length()); |
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947 } |
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948 } |
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949 if (TraceReferenceGC && PrintGCDetails) { |
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950 gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
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951 gclog_or_tty->flush(); |
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952 } |
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953 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
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954 #endif |
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955 } |
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956 |
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957 void ReferenceProcessor::balance_all_queues() { |
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958 balance_queues(_discoveredSoftRefs); |
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959 balance_queues(_discoveredWeakRefs); |
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960 balance_queues(_discoveredFinalRefs); |
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961 balance_queues(_discoveredPhantomRefs); |
0 | 962 } |
963 | |
964 void | |
965 ReferenceProcessor::process_discovered_reflist( | |
966 DiscoveredList refs_lists[], | |
967 ReferencePolicy* policy, | |
968 bool clear_referent, | |
969 BoolObjectClosure* is_alive, | |
970 OopClosure* keep_alive, | |
971 VoidClosure* complete_gc, | |
972 AbstractRefProcTaskExecutor* task_executor) | |
973 { | |
1833
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974 bool mt_processing = task_executor != NULL && _processing_is_mt; |
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975 // If discovery used MT and a dynamic number of GC threads, then |
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976 // the queues must be balanced for correctness if fewer than the |
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977 // maximum number of queues were used. The number of queue used |
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978 // during discovery may be different than the number to be used |
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979 // for processing so don't depend of _num_q < _max_num_q as part |
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980 // of the test. |
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981 bool must_balance = _discovery_is_mt; |
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|
982 |
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983 if ((mt_processing && ParallelRefProcBalancingEnabled) || |
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984 must_balance) { |
0 | 985 balance_queues(refs_lists); |
986 } | |
987 if (PrintReferenceGC && PrintGCDetails) { | |
988 size_t total = 0; | |
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989 for (int i = 0; i < _max_num_q; ++i) { |
0 | 990 total += refs_lists[i].length(); |
991 } | |
992 gclog_or_tty->print(", %u refs", total); | |
993 } | |
994 | |
995 // Phase 1 (soft refs only): | |
996 // . Traverse the list and remove any SoftReferences whose | |
997 // referents are not alive, but that should be kept alive for | |
998 // policy reasons. Keep alive the transitive closure of all | |
999 // such referents. | |
1000 if (policy != NULL) { | |
1833
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1001 if (mt_processing) { |
0 | 1002 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
1003 task_executor->execute(phase1); | |
1004 } else { | |
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1005 for (int i = 0; i < _max_num_q; i++) { |
0 | 1006 process_phase1(refs_lists[i], policy, |
1007 is_alive, keep_alive, complete_gc); | |
1008 } | |
1009 } | |
1010 } else { // policy == NULL | |
1011 assert(refs_lists != _discoveredSoftRefs, | |
1012 "Policy must be specified for soft references."); | |
1013 } | |
1014 | |
1015 // Phase 2: | |
1016 // . Traverse the list and remove any refs whose referents are alive. | |
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1017 if (mt_processing) { |
0 | 1018 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
1019 task_executor->execute(phase2); | |
1020 } else { | |
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1021 for (int i = 0; i < _max_num_q; i++) { |
0 | 1022 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); |
1023 } | |
1024 } | |
1025 | |
1026 // Phase 3: | |
1027 // . Traverse the list and process referents as appropriate. | |
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1028 if (mt_processing) { |
0 | 1029 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
1030 task_executor->execute(phase3); | |
1031 } else { | |
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1032 for (int i = 0; i < _max_num_q; i++) { |
0 | 1033 process_phase3(refs_lists[i], clear_referent, |
1034 is_alive, keep_alive, complete_gc); | |
1035 } | |
1036 } | |
1037 } | |
1038 | |
1039 void ReferenceProcessor::clean_up_discovered_references() { | |
1040 // loop over the lists | |
1833
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1041 // Should this instead be |
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1042 // for (int i = 0; i < subclasses_of_ref; i++_ { |
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1043 // for (int j = 0; j < _num_q; j++) { |
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1044 // int index = i * _max_num_q + j; |
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1045 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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1046 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
0 | 1047 gclog_or_tty->print_cr( |
1048 "\nScrubbing %s discovered list of Null referents", | |
1049 list_name(i)); | |
1050 } | |
1051 clean_up_discovered_reflist(_discoveredSoftRefs[i]); | |
1052 } | |
1053 } | |
1054 | |
1055 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { | |
1056 assert(!discovery_is_atomic(), "Else why call this method?"); | |
1057 DiscoveredListIterator iter(refs_list, NULL, NULL); | |
1058 while (iter.has_next()) { | |
1059 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1060 oop next = java_lang_ref_Reference::next(iter.obj()); |
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1061 assert(next->is_oop_or_null(), "bad next field"); |
0 | 1062 // If referent has been cleared or Reference is not active, |
1063 // drop it. | |
113
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1064 if (iter.referent() == NULL || next != NULL) { |
0 | 1065 debug_only( |
1066 if (PrintGCDetails && TraceReferenceGC) { | |
1067 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " | |
1068 INTPTR_FORMAT " with next field: " INTPTR_FORMAT | |
1069 " and referent: " INTPTR_FORMAT, | |
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1070 iter.obj(), next, iter.referent()); |
0 | 1071 } |
1072 ) | |
1073 // Remove Reference object from list | |
1074 iter.remove(); | |
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1075 iter.move_to_next(); |
0 | 1076 } else { |
1077 iter.next(); | |
1078 } | |
1079 } | |
1080 NOT_PRODUCT( | |
1081 if (PrintGCDetails && TraceReferenceGC) { | |
1082 gclog_or_tty->print( | |
1083 " Removed %d Refs with NULL referents out of %d discovered Refs", | |
1084 iter.removed(), iter.processed()); | |
1085 } | |
1086 ) | |
1087 } | |
1088 | |
1089 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { | |
1090 int id = 0; | |
1091 // Determine the queue index to use for this object. | |
1092 if (_discovery_is_mt) { | |
1093 // During a multi-threaded discovery phase, | |
1094 // each thread saves to its "own" list. | |
1095 Thread* thr = Thread::current(); | |
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1096 id = thr->as_Worker_thread()->id(); |
0 | 1097 } else { |
1098 // single-threaded discovery, we save in round-robin | |
1099 // fashion to each of the lists. | |
1100 if (_processing_is_mt) { | |
1101 id = next_id(); | |
1102 } | |
1103 } | |
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1104 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
0 | 1105 |
1106 // Get the discovered queue to which we will add | |
1107 DiscoveredList* list = NULL; | |
1108 switch (rt) { | |
1109 case REF_OTHER: | |
1110 // Unknown reference type, no special treatment | |
1111 break; | |
1112 case REF_SOFT: | |
1113 list = &_discoveredSoftRefs[id]; | |
1114 break; | |
1115 case REF_WEAK: | |
1116 list = &_discoveredWeakRefs[id]; | |
1117 break; | |
1118 case REF_FINAL: | |
1119 list = &_discoveredFinalRefs[id]; | |
1120 break; | |
1121 case REF_PHANTOM: | |
1122 list = &_discoveredPhantomRefs[id]; | |
1123 break; | |
1124 case REF_NONE: | |
1125 // we should not reach here if we are an instanceRefKlass | |
1126 default: | |
1127 ShouldNotReachHere(); | |
1128 } | |
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1129 if (TraceReferenceGC && PrintGCDetails) { |
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1130 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); |
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1131 } |
0 | 1132 return list; |
1133 } | |
1134 | |
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1135 inline void |
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1136 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
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1137 oop obj, |
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1138 HeapWord* discovered_addr) { |
0 | 1139 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
1140 // First we must make sure this object is only enqueued once. CAS in a non null | |
1141 // discovered_addr. | |
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1142 oop current_head = refs_list.head(); |
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1143 // The last ref must have its discovered field pointing to itself. |
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1144 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1145 |
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1146 // Note: In the case of G1, this specific pre-barrier is strictly |
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1147 // not necessary because the only case we are interested in |
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1148 // here is when *discovered_addr is NULL (see the CAS further below), |
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1149 // so this will expand to nothing. As a result, we have manually |
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1150 // elided this out for G1, but left in the test for some future |
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1151 // collector that might have need for a pre-barrier here, e.g.:- |
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1152 // _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1153 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1154 "Need to check non-G1 collector: " |
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1155 "may need a pre-write-barrier for CAS from NULL below"); |
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1156 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, |
113
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1157 NULL); |
0 | 1158 if (retest == NULL) { |
1159 // This thread just won the right to enqueue the object. | |
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1160 // We have separate lists for enqueueing, so no synchronization |
0 | 1161 // is necessary. |
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1162 refs_list.set_head(obj); |
452
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1163 refs_list.inc_length(1); |
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1164 if (_discovered_list_needs_barrier) { |
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1165 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1166 } |
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1167 |
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1168 if (TraceReferenceGC) { |
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1169 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", |
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1170 obj, obj->blueprint()->internal_name()); |
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1171 } |
0 | 1172 } else { |
1173 // If retest was non NULL, another thread beat us to it: | |
1174 // The reference has already been discovered... | |
1175 if (TraceReferenceGC) { | |
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1176 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
0 | 1177 obj, obj->blueprint()->internal_name()); |
1178 } | |
1179 } | |
1180 } | |
1181 | |
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1182 #ifndef PRODUCT |
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1183 // Non-atomic (i.e. concurrent) discovery might allow us |
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1184 // to observe j.l.References with NULL referents, being those |
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1185 // cleared concurrently by mutators during (or after) discovery. |
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1186 void ReferenceProcessor::verify_referent(oop obj) { |
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1187 bool da = discovery_is_atomic(); |
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1188 oop referent = java_lang_ref_Reference::referent(obj); |
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1189 assert(da ? referent->is_oop() : referent->is_oop_or_null(), |
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1190 err_msg("Bad referent " INTPTR_FORMAT " found in Reference " |
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1191 INTPTR_FORMAT " during %satomic discovery ", |
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1192 (intptr_t)referent, (intptr_t)obj, da ? "" : "non-")); |
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1193 } |
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1194 #endif |
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1195 |
0 | 1196 // We mention two of several possible choices here: |
1197 // #0: if the reference object is not in the "originating generation" | |
1198 // (or part of the heap being collected, indicated by our "span" | |
1199 // we don't treat it specially (i.e. we scan it as we would | |
1200 // a normal oop, treating its references as strong references). | |
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1201 // This means that references can't be discovered unless their |
0 | 1202 // referent is also in the same span. This is the simplest, |
1203 // most "local" and most conservative approach, albeit one | |
1204 // that may cause weak references to be enqueued least promptly. | |
1205 // We call this choice the "ReferenceBasedDiscovery" policy. | |
1206 // #1: the reference object may be in any generation (span), but if | |
1207 // the referent is in the generation (span) being currently collected | |
1208 // then we can discover the reference object, provided | |
1209 // the object has not already been discovered by | |
1210 // a different concurrently running collector (as may be the | |
1211 // case, for instance, if the reference object is in CMS and | |
1212 // the referent in DefNewGeneration), and provided the processing | |
1213 // of this reference object by the current collector will | |
1214 // appear atomic to every other collector in the system. | |
1215 // (Thus, for instance, a concurrent collector may not | |
1216 // discover references in other generations even if the | |
1217 // referent is in its own generation). This policy may, | |
1218 // in certain cases, enqueue references somewhat sooner than | |
1219 // might Policy #0 above, but at marginally increased cost | |
1220 // and complexity in processing these references. | |
1221 // We call this choice the "RefeferentBasedDiscovery" policy. | |
1222 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { | |
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1223 // Make sure we are discovering refs (rather than processing discovered refs). |
0 | 1224 if (!_discovering_refs || !RegisterReferences) { |
1225 return false; | |
1226 } | |
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1227 // We only discover active references. |
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1228 oop next = java_lang_ref_Reference::next(obj); |
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1229 if (next != NULL) { // Ref is no longer active |
0 | 1230 return false; |
1231 } | |
1232 | |
1233 HeapWord* obj_addr = (HeapWord*)obj; | |
1234 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1235 !_span.contains(obj_addr)) { | |
1236 // Reference is not in the originating generation; | |
1237 // don't treat it specially (i.e. we want to scan it as a normal | |
1238 // object with strong references). | |
1239 return false; | |
1240 } | |
1241 | |
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1242 // We only discover references whose referents are not (yet) |
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1243 // known to be strongly reachable. |
0 | 1244 if (is_alive_non_header() != NULL) { |
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1245 verify_referent(obj); |
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1246 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { |
0 | 1247 return false; // referent is reachable |
1248 } | |
1249 } | |
453
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1250 if (rt == REF_SOFT) { |
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1251 // For soft refs we can decide now if these are not |
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1252 // current candidates for clearing, in which case we |
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1253 // can mark through them now, rather than delaying that |
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1254 // to the reference-processing phase. Since all current |
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1255 // time-stamp policies advance the soft-ref clock only |
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1256 // at a major collection cycle, this is always currently |
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1257 // accurate. |
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1258 if (!_current_soft_ref_policy->should_clear_reference(obj)) { |
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1259 return false; |
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1260 } |
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1261 } |
0 | 1262 |
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1263 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
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1264 const oop discovered = java_lang_ref_Reference::discovered(obj); |
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1265 assert(discovered->is_oop_or_null(), "bad discovered field"); |
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1266 if (discovered != NULL) { |
0 | 1267 // The reference has already been discovered... |
1268 if (TraceReferenceGC) { | |
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1269 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
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1270 obj, obj->blueprint()->internal_name()); |
0 | 1271 } |
1272 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
1273 // assumes that an object is not processed twice; | |
1274 // if it's been already discovered it must be on another | |
1275 // generation's discovered list; so we won't discover it. | |
1276 return false; | |
1277 } else { | |
1278 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, | |
1279 "Unrecognized policy"); | |
1280 // Check assumption that an object is not potentially | |
1281 // discovered twice except by concurrent collectors that potentially | |
1282 // trace the same Reference object twice. | |
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1283 assert(UseConcMarkSweepGC || UseG1GC, |
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1284 "Only possible with a concurrent marking collector"); |
0 | 1285 return true; |
1286 } | |
1287 } | |
1288 | |
1289 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { | |
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1290 verify_referent(obj); |
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1291 // Discover if and only if EITHER: |
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1292 // .. reference is in our span, OR |
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1293 // .. we are an atomic collector and referent is in our span |
0 | 1294 if (_span.contains(obj_addr) || |
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1295 (discovery_is_atomic() && |
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1296 _span.contains(java_lang_ref_Reference::referent(obj)))) { |
0 | 1297 // should_enqueue = true; |
1298 } else { | |
1299 return false; | |
1300 } | |
1301 } else { | |
1302 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && | |
1303 _span.contains(obj_addr), "code inconsistency"); | |
1304 } | |
1305 | |
1306 // Get the right type of discovered queue head. | |
1307 DiscoveredList* list = get_discovered_list(rt); | |
1308 if (list == NULL) { | |
1309 return false; // nothing special needs to be done | |
1310 } | |
1311 | |
1312 if (_discovery_is_mt) { | |
1313 add_to_discovered_list_mt(*list, obj, discovered_addr); | |
1314 } else { | |
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1315 // If "_discovered_list_needs_barrier", we do write barriers when |
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1316 // updating the discovered reference list. Otherwise, we do a raw store |
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1317 // here: the field will be visited later when processing the discovered |
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1318 // references. |
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1319 oop current_head = list->head(); |
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1320 // The last ref must have its discovered field pointing to itself. |
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1321 oop next_discovered = (current_head != NULL) ? current_head : obj; |
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1322 |
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1323 // As in the case further above, since we are over-writing a NULL |
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1324 // pre-value, we can safely elide the pre-barrier here for the case of G1. |
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1325 // e.g.:- _bs->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered); |
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1326 assert(discovered == NULL, "control point invariant"); |
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1327 assert(!_discovered_list_needs_barrier || UseG1GC, |
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1328 "For non-G1 collector, may need a pre-write-barrier for CAS from NULL below"); |
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1329 oop_store_raw(discovered_addr, next_discovered); |
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1330 if (_discovered_list_needs_barrier) { |
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1331 _bs->write_ref_field((void*)discovered_addr, next_discovered); |
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1332 } |
0 | 1333 list->set_head(obj); |
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1334 list->inc_length(1); |
0 | 1335 |
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1336 if (TraceReferenceGC) { |
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1337 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)", |
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1338 obj, obj->blueprint()->internal_name()); |
0 | 1339 } |
1340 } | |
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1341 assert(obj->is_oop(), "Discovered a bad reference"); |
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1342 verify_referent(obj); |
0 | 1343 return true; |
1344 } | |
1345 | |
1346 // Preclean the discovered references by removing those | |
1347 // whose referents are alive, and by marking from those that | |
1348 // are not active. These lists can be handled here | |
1349 // in any order and, indeed, concurrently. | |
1350 void ReferenceProcessor::preclean_discovered_references( | |
1351 BoolObjectClosure* is_alive, | |
1352 OopClosure* keep_alive, | |
1353 VoidClosure* complete_gc, | |
1190
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1354 YieldClosure* yield, |
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1355 bool should_unload_classes) { |
0 | 1356 |
1357 NOT_PRODUCT(verify_ok_to_handle_reflists()); | |
1358 | |
935 | 1359 #ifdef ASSERT |
1360 bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC || | |
1190
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1361 CMSClassUnloadingEnabled && UseConcMarkSweepGC || |
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1362 ExplicitGCInvokesConcurrentAndUnloadsClasses && |
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1363 UseConcMarkSweepGC && should_unload_classes; |
935 | 1364 RememberKlassesChecker mx(must_remember_klasses); |
1365 #endif | |
0 | 1366 // Soft references |
1367 { | |
1368 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, | |
1369 false, gclog_or_tty); | |
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1370 for (int i = 0; i < _max_num_q; i++) { |
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1371 if (yield->should_return()) { |
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1372 return; |
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1373 } |
0 | 1374 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
1375 keep_alive, complete_gc, yield); | |
1376 } | |
1377 } | |
1378 | |
1379 // Weak references | |
1380 { | |
1381 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, | |
1382 false, gclog_or_tty); | |
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1383 for (int i = 0; i < _max_num_q; i++) { |
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1384 if (yield->should_return()) { |
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1385 return; |
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1386 } |
0 | 1387 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
1388 keep_alive, complete_gc, yield); | |
1389 } | |
1390 } | |
1391 | |
1392 // Final references | |
1393 { | |
1394 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, | |
1395 false, gclog_or_tty); | |
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1396 for (int i = 0; i < _max_num_q; i++) { |
452
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1397 if (yield->should_return()) { |
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1398 return; |
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1399 } |
0 | 1400 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
1401 keep_alive, complete_gc, yield); | |
1402 } | |
1403 } | |
1404 | |
1405 // Phantom references | |
1406 { | |
1407 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, | |
1408 false, gclog_or_tty); | |
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1409 for (int i = 0; i < _max_num_q; i++) { |
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1410 if (yield->should_return()) { |
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1411 return; |
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1412 } |
0 | 1413 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
1414 keep_alive, complete_gc, yield); | |
1415 } | |
1416 } | |
1417 } | |
1418 | |
1419 // Walk the given discovered ref list, and remove all reference objects | |
1420 // whose referents are still alive, whose referents are NULL or which | |
452
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1421 // are not active (have a non-NULL next field). NOTE: When we are |
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1422 // thus precleaning the ref lists (which happens single-threaded today), |
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1423 // we do not disable refs discovery to honour the correct semantics of |
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1424 // java.lang.Reference. As a result, we need to be careful below |
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1425 // that ref removal steps interleave safely with ref discovery steps |
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1426 // (in this thread). |
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1427 void |
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1428 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
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1429 BoolObjectClosure* is_alive, |
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1430 OopClosure* keep_alive, |
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1431 VoidClosure* complete_gc, |
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1432 YieldClosure* yield) { |
0 | 1433 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
1434 while (iter.has_next()) { | |
1435 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); | |
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1436 oop obj = iter.obj(); |
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1437 oop next = java_lang_ref_Reference::next(obj); |
0 | 1438 if (iter.referent() == NULL || iter.is_referent_alive() || |
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1439 next != NULL) { |
0 | 1440 // The referent has been cleared, or is alive, or the Reference is not |
1441 // active; we need to trace and mark its cohort. | |
1442 if (TraceReferenceGC) { | |
1443 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", | |
1444 iter.obj(), iter.obj()->blueprint()->internal_name()); | |
1445 } | |
1446 // Remove Reference object from list | |
1447 iter.remove(); | |
1448 // Keep alive its cohort. | |
1449 iter.make_referent_alive(); | |
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1450 if (UseCompressedOops) { |
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1451 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
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1452 keep_alive->do_oop(next_addr); |
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1453 } else { |
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1454 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
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1455 keep_alive->do_oop(next_addr); |
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1456 } |
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1457 iter.move_to_next(); |
0 | 1458 } else { |
1459 iter.next(); | |
1460 } | |
1461 } | |
1462 // Close the reachable set | |
1463 complete_gc->do_void(); | |
1464 | |
1465 NOT_PRODUCT( | |
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1466 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) { |
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1467 gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
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1468 "Refs in discovered list " INTPTR_FORMAT, |
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1469 iter.removed(), iter.processed(), (address)refs_list.head()); |
0 | 1470 } |
1471 ) | |
1472 } | |
1473 | |
1474 const char* ReferenceProcessor::list_name(int i) { | |
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1475 assert(i >= 0 && i <= _max_num_q * subclasses_of_ref, "Out of bounds index"); |
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1476 int j = i / _max_num_q; |
0 | 1477 switch (j) { |
1478 case 0: return "SoftRef"; | |
1479 case 1: return "WeakRef"; | |
1480 case 2: return "FinalRef"; | |
1481 case 3: return "PhantomRef"; | |
1482 } | |
1483 ShouldNotReachHere(); | |
1484 return NULL; | |
1485 } | |
1486 | |
1487 #ifndef PRODUCT | |
1488 void ReferenceProcessor::verify_ok_to_handle_reflists() { | |
1489 // empty for now | |
1490 } | |
1491 #endif | |
1492 | |
1493 #ifndef PRODUCT | |
1494 void ReferenceProcessor::clear_discovered_references() { | |
1495 guarantee(!_discovering_refs, "Discovering refs?"); | |
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1496 for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { |
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1497 clear_discovered_references(_discoveredSoftRefs[i]); |
0 | 1498 } |
1499 } | |
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1500 |
0 | 1501 #endif // PRODUCT |