1 /* 2 * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/classLoaderDataGraph.hpp" 27 #include "classfile/javaClasses.hpp" 28 #include "classfile/stringTable.hpp" 29 #include "classfile/symbolTable.hpp" 30 #include "classfile/systemDictionary.hpp" 31 #include "classfile/vmSymbols.hpp" 32 #include "code/codeCache.hpp" 33 #include "code/icBuffer.hpp" 34 #include "gc/serial/genMarkSweep.hpp" 35 #include "gc/shared/collectedHeap.inline.hpp" 36 #include "gc/shared/gcHeapSummary.hpp" 37 #include "gc/shared/gcTimer.hpp" 38 #include "gc/shared/gcTrace.hpp" 39 #include "gc/shared/gcTraceTime.inline.hpp" 40 #include "gc/shared/genCollectedHeap.hpp" 41 #include "gc/shared/generation.hpp" 42 #include "gc/shared/genOopClosures.inline.hpp" 43 #include "gc/shared/modRefBarrierSet.hpp" 44 #include "gc/shared/referencePolicy.hpp" 45 #include "gc/shared/referenceProcessorPhaseTimes.hpp" 46 #include "gc/shared/space.hpp" 47 #include "gc/shared/strongRootsScope.hpp" 48 #include "gc/shared/weakProcessor.hpp" 49 #include "oops/instanceRefKlass.hpp" 50 #include "oops/oop.inline.hpp" 51 #include "prims/jvmtiExport.hpp" 52 #include "runtime/handles.inline.hpp" 53 #include "runtime/synchronizer.hpp" 54 #include "runtime/thread.inline.hpp" 55 #include "runtime/vmThread.hpp" 56 #include "utilities/copy.hpp" 57 #include "utilities/events.hpp" 58 #include "utilities/stack.inline.hpp" 59 60 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) { 61 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 62 63 GenCollectedHeap* gch = GenCollectedHeap::heap(); 64 #ifdef ASSERT 65 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) { 66 assert(clear_all_softrefs, "Policy should have been checked earlier"); 67 } 68 #endif 69 70 // hook up weak ref data so it can be used during Mark-Sweep 71 assert(ref_processor() == NULL, "no stomping"); 72 assert(rp != NULL, "should be non-NULL"); 73 set_ref_processor(rp); 74 rp->setup_policy(clear_all_softrefs); 75 76 gch->trace_heap_before_gc(_gc_tracer); 77 78 // When collecting the permanent generation Method*s may be moving, 79 // so we either have to flush all bcp data or convert it into bci. 80 CodeCache::gc_prologue(); 81 82 // Increment the invocation count 83 _total_invocations++; 84 85 // Capture used regions for each generation that will be 86 // subject to collection, so that card table adjustments can 87 // be made intelligently (see clear / invalidate further below). 88 gch->save_used_regions(); 89 90 allocate_stacks(); 91 92 mark_sweep_phase1(clear_all_softrefs); 93 94 mark_sweep_phase2(); 95 96 // Don't add any more derived pointers during phase3 97 #if COMPILER2_OR_JVMCI 98 assert(DerivedPointerTable::is_active(), "Sanity"); 99 DerivedPointerTable::set_active(false); 100 #endif 101 102 mark_sweep_phase3(); 103 104 mark_sweep_phase4(); 105 106 restore_marks(); 107 108 // Set saved marks for allocation profiler (and other things? -- dld) 109 // (Should this be in general part?) 110 gch->save_marks(); 111 112 deallocate_stacks(); 113 114 // If compaction completely evacuated the young generation then we 115 // can clear the card table. Otherwise, we must invalidate 116 // it (consider all cards dirty). In the future, we might consider doing 117 // compaction within generations only, and doing card-table sliding. 118 CardTableRS* rs = gch->rem_set(); 119 Generation* old_gen = gch->old_gen(); 120 121 // Clear/invalidate below make use of the "prev_used_regions" saved earlier. 122 if (gch->young_gen()->used() == 0) { 123 // We've evacuated the young generation. 124 rs->clear_into_younger(old_gen); 125 } else { 126 // Invalidate the cards corresponding to the currently used 127 // region and clear those corresponding to the evacuated region. 128 rs->invalidate_or_clear(old_gen); 129 } 130 131 CodeCache::gc_epilogue(); 132 JvmtiExport::gc_epilogue(); 133 134 // refs processing: clean slate 135 set_ref_processor(NULL); 136 137 // Update heap occupancy information which is used as 138 // input to soft ref clearing policy at the next gc. 139 Universe::update_heap_info_at_gc(); 140 141 // Update time of last gc for all generations we collected 142 // (which currently is all the generations in the heap). 143 // We need to use a monotonically non-decreasing time in ms 144 // or we will see time-warp warnings and os::javaTimeMillis() 145 // does not guarantee monotonicity. 146 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 147 gch->update_time_of_last_gc(now); 148 149 gch->trace_heap_after_gc(_gc_tracer); 150 } 151 152 void GenMarkSweep::allocate_stacks() { 153 GenCollectedHeap* gch = GenCollectedHeap::heap(); 154 // Scratch request on behalf of old generation; will do no allocation. 155 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0); 156 157 // $$$ To cut a corner, we'll only use the first scratch block, and then 158 // revert to malloc. 159 if (scratch != NULL) { 160 _preserved_count_max = 161 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 162 } else { 163 _preserved_count_max = 0; 164 } 165 166 _preserved_marks = (PreservedMark*)scratch; 167 _preserved_count = 0; 168 } 169 170 171 void GenMarkSweep::deallocate_stacks() { 172 GenCollectedHeap* gch = GenCollectedHeap::heap(); 173 gch->release_scratch(); 174 175 _preserved_mark_stack.clear(true); 176 _preserved_oop_stack.clear(true); 177 _marking_stack.clear(); 178 _objarray_stack.clear(true); 179 } 180 181 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) { 182 // Recursively traverse all live objects and mark them 183 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer); 184 185 GenCollectedHeap* gch = GenCollectedHeap::heap(); 186 187 // Because follow_root_closure is created statically, cannot 188 // use OopsInGenClosure constructor which takes a generation, 189 // as the Universe has not been created when the static constructors 190 // are run. 191 follow_root_closure.set_orig_generation(gch->old_gen()); 192 193 // Need new claim bits before marking starts. 194 ClassLoaderDataGraph::clear_claimed_marks(); 195 196 { 197 StrongRootsScope srs(1); 198 199 gch->full_process_roots(&srs, 200 false, // not the adjust phase 201 GenCollectedHeap::SO_None, 202 ClassUnloading, // only strong roots if ClassUnloading 203 // is enabled 204 &follow_root_closure, 205 &follow_cld_closure); 206 } 207 208 // Process reference objects found during marking 209 { 210 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer()); 211 212 ref_processor()->setup_policy(clear_all_softrefs); 213 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues()); 214 const ReferenceProcessorStats& stats = 215 ref_processor()->process_discovered_references( 216 &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt); 217 pt.print_all_references(); 218 gc_tracer()->report_gc_reference_stats(stats); 219 } 220 221 // This is the point where the entire marking should have completed. 222 assert(_marking_stack.is_empty(), "Marking should have completed"); 223 224 { 225 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer()); 226 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl); 227 } 228 229 { 230 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer()); 231 232 // Unload classes and purge the SystemDictionary. 233 bool purged_class = SystemDictionary::do_unloading(gc_timer()); 234 235 // Unload nmethods. 236 CodeCache::do_unloading(&is_alive, purged_class); 237 238 // Prune dead klasses from subklass/sibling/implementor lists. 239 Klass::clean_weak_klass_links(purged_class); 240 } 241 242 gc_tracer()->report_object_count_after_gc(&is_alive); 243 } 244 245 246 void GenMarkSweep::mark_sweep_phase2() { 247 // Now all live objects are marked, compute the new object addresses. 248 249 // It is imperative that we traverse perm_gen LAST. If dead space is 250 // allowed a range of dead object may get overwritten by a dead int 251 // array. If perm_gen is not traversed last a Klass* may get 252 // overwritten. This is fine since it is dead, but if the class has dead 253 // instances we have to skip them, and in order to find their size we 254 // need the Klass*! 255 // 256 // It is not required that we traverse spaces in the same order in 257 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 258 // tracking expects us to do so. See comment under phase4. 259 260 GenCollectedHeap* gch = GenCollectedHeap::heap(); 261 262 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer); 263 264 gch->prepare_for_compaction(); 265 } 266 267 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 268 public: 269 void do_generation(Generation* gen) { 270 gen->adjust_pointers(); 271 } 272 }; 273 274 void GenMarkSweep::mark_sweep_phase3() { 275 GenCollectedHeap* gch = GenCollectedHeap::heap(); 276 277 // Adjust the pointers to reflect the new locations 278 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer()); 279 280 // Need new claim bits for the pointer adjustment tracing. 281 ClassLoaderDataGraph::clear_claimed_marks(); 282 283 // Because the closure below is created statically, we cannot 284 // use OopsInGenClosure constructor which takes a generation, 285 // as the Universe has not been created when the static constructors 286 // are run. 287 adjust_pointer_closure.set_orig_generation(gch->old_gen()); 288 289 { 290 StrongRootsScope srs(1); 291 292 gch->full_process_roots(&srs, 293 true, // this is the adjust phase 294 GenCollectedHeap::SO_AllCodeCache, 295 false, // all roots 296 &adjust_pointer_closure, 297 &adjust_cld_closure); 298 } 299 300 gch->gen_process_weak_roots(&adjust_pointer_closure); 301 302 adjust_marks(); 303 GenAdjustPointersClosure blk; 304 gch->generation_iterate(&blk, true); 305 } 306 307 class GenCompactClosure: public GenCollectedHeap::GenClosure { 308 public: 309 void do_generation(Generation* gen) { 310 gen->compact(); 311 } 312 }; 313 314 void GenMarkSweep::mark_sweep_phase4() { 315 // All pointers are now adjusted, move objects accordingly 316 317 // It is imperative that we traverse perm_gen first in phase4. All 318 // classes must be allocated earlier than their instances, and traversing 319 // perm_gen first makes sure that all Klass*s have moved to their new 320 // location before any instance does a dispatch through it's klass! 321 322 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 323 // in the same order in phase2, phase3 and phase4. We don't quite do that 324 // here (perm_gen first rather than last), so we tell the validate code 325 // to use a higher index (saved from phase2) when verifying perm_gen. 326 GenCollectedHeap* gch = GenCollectedHeap::heap(); 327 328 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer); 329 330 GenCompactClosure blk; 331 gch->generation_iterate(&blk, true); 332 }