1 /* 2 * Copyright (c) 2001, 2017, 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/javaClasses.hpp" 27 #include "classfile/stringTable.hpp" 28 #include "classfile/symbolTable.hpp" 29 #include "classfile/systemDictionary.hpp" 30 #include "classfile/vmSymbols.hpp" 31 #include "code/codeCache.hpp" 32 #include "code/icBuffer.hpp" 33 #include "gc/serial/genMarkSweep.hpp" 34 #include "gc/shared/collectedHeap.inline.hpp" 35 #include "gc/shared/gcHeapSummary.hpp" 36 #include "gc/shared/gcTimer.hpp" 37 #include "gc/shared/gcTrace.hpp" 38 #include "gc/shared/gcTraceTime.inline.hpp" 39 #include "gc/shared/genCollectedHeap.hpp" 40 #include "gc/shared/generation.hpp" 41 #include "gc/shared/genOopClosures.inline.hpp" 42 #include "gc/shared/modRefBarrierSet.hpp" 43 #include "gc/shared/referencePolicy.hpp" 44 #include "gc/shared/space.hpp" 45 #include "gc/shared/strongRootsScope.hpp" 46 #include "oops/instanceRefKlass.hpp" 47 #include "oops/oop.inline.hpp" 48 #include "prims/jvmtiExport.hpp" 49 #include "runtime/fprofiler.hpp" 50 #include "runtime/handles.inline.hpp" 51 #include "runtime/synchronizer.hpp" 52 #include "runtime/thread.inline.hpp" 53 #include "runtime/vmThread.hpp" 54 #include "utilities/copy.hpp" 55 #include "utilities/events.hpp" 56 #include "utilities/stack.inline.hpp" 57 58 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) { 59 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 60 61 GenCollectedHeap* gch = GenCollectedHeap::heap(); 62 #ifdef ASSERT 63 if (gch->collector_policy()->should_clear_all_soft_refs()) { 64 assert(clear_all_softrefs, "Policy should have been checked earlier"); 65 } 66 #endif 67 68 // hook up weak ref data so it can be used during Mark-Sweep 69 assert(ref_processor() == NULL, "no stomping"); 70 assert(rp != NULL, "should be non-NULL"); 71 set_ref_processor(rp); 72 rp->setup_policy(clear_all_softrefs); 73 74 gch->trace_heap_before_gc(_gc_tracer); 75 76 // When collecting the permanent generation Method*s may be moving, 77 // so we either have to flush all bcp data or convert it into bci. 78 CodeCache::gc_prologue(); 79 80 // Increment the invocation count 81 _total_invocations++; 82 83 // Capture used regions for each generation that will be 84 // subject to collection, so that card table adjustments can 85 // be made intelligently (see clear / invalidate further below). 86 gch->save_used_regions(); 87 88 allocate_stacks(); 89 90 mark_sweep_phase1(clear_all_softrefs); 91 92 mark_sweep_phase2(); 93 94 // Don't add any more derived pointers during phase3 95 #if defined(COMPILER2) || INCLUDE_JVMCI 96 assert(DerivedPointerTable::is_active(), "Sanity"); 97 DerivedPointerTable::set_active(false); 98 #endif 99 100 mark_sweep_phase3(); 101 102 mark_sweep_phase4(); 103 104 restore_marks(); 105 106 // Set saved marks for allocation profiler (and other things? -- dld) 107 // (Should this be in general part?) 108 gch->save_marks(); 109 110 deallocate_stacks(); 111 112 // If compaction completely evacuated the young generation then we 113 // can clear the card table. Otherwise, we must invalidate 114 // it (consider all cards dirty). In the future, we might consider doing 115 // compaction within generations only, and doing card-table sliding. 116 CardTableRS* rs = gch->rem_set(); 117 Generation* old_gen = gch->old_gen(); 118 119 // Clear/invalidate below make use of the "prev_used_regions" saved earlier. 120 if (gch->young_gen()->used() == 0) { 121 // We've evacuated the young generation. 122 rs->clear_into_younger(old_gen); 123 } else { 124 // Invalidate the cards corresponding to the currently used 125 // region and clear those corresponding to the evacuated region. 126 rs->invalidate_or_clear(old_gen); 127 } 128 129 CodeCache::gc_epilogue(); 130 JvmtiExport::gc_epilogue(); 131 132 // refs processing: clean slate 133 set_ref_processor(NULL); 134 135 // Update heap occupancy information which is used as 136 // input to soft ref clearing policy at the next gc. 137 Universe::update_heap_info_at_gc(); 138 139 // Update time of last gc for all generations we collected 140 // (which currently is all the generations in the heap). 141 // We need to use a monotonically non-decreasing time in ms 142 // or we will see time-warp warnings and os::javaTimeMillis() 143 // does not guarantee monotonicity. 144 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 145 gch->update_time_of_last_gc(now); 146 147 gch->trace_heap_after_gc(_gc_tracer); 148 } 149 150 void GenMarkSweep::allocate_stacks() { 151 GenCollectedHeap* gch = GenCollectedHeap::heap(); 152 // Scratch request on behalf of old generation; will do no allocation. 153 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0); 154 155 // $$$ To cut a corner, we'll only use the first scratch block, and then 156 // revert to malloc. 157 if (scratch != NULL) { 158 _preserved_count_max = 159 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 160 } else { 161 _preserved_count_max = 0; 162 } 163 164 _preserved_marks = (PreservedMark*)scratch; 165 _preserved_count = 0; 166 } 167 168 169 void GenMarkSweep::deallocate_stacks() { 170 if (!UseG1GC) { 171 GenCollectedHeap* gch = GenCollectedHeap::heap(); 172 gch->release_scratch(); 173 } 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 const ReferenceProcessorStats& stats = 214 ref_processor()->process_discovered_references( 215 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer); 216 gc_tracer()->report_gc_reference_stats(stats); 217 } 218 219 // This is the point where the entire marking should have completed. 220 assert(_marking_stack.is_empty(), "Marking should have completed"); 221 222 { 223 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer()); 224 225 // Unload classes and purge the SystemDictionary. 226 bool purged_class = SystemDictionary::do_unloading(&is_alive, gc_timer()); 227 228 // Unload nmethods. 229 CodeCache::do_unloading(&is_alive, purged_class); 230 231 // Prune dead klasses from subklass/sibling/implementor lists. 232 Klass::clean_weak_klass_links(&is_alive); 233 } 234 235 { 236 GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer()); 237 // Delete entries for dead interned strings. 238 StringTable::unlink(&is_alive); 239 } 240 241 { 242 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer()); 243 // Clean up unreferenced symbols in symbol table. 244 SymbolTable::unlink(); 245 } 246 247 gc_tracer()->report_object_count_after_gc(&is_alive); 248 } 249 250 251 void GenMarkSweep::mark_sweep_phase2() { 252 // Now all live objects are marked, compute the new object addresses. 253 254 // It is imperative that we traverse perm_gen LAST. If dead space is 255 // allowed a range of dead object may get overwritten by a dead int 256 // array. If perm_gen is not traversed last a Klass* may get 257 // overwritten. This is fine since it is dead, but if the class has dead 258 // instances we have to skip them, and in order to find their size we 259 // need the Klass*! 260 // 261 // It is not required that we traverse spaces in the same order in 262 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 263 // tracking expects us to do so. See comment under phase4. 264 265 GenCollectedHeap* gch = GenCollectedHeap::heap(); 266 267 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer); 268 269 gch->prepare_for_compaction(); 270 } 271 272 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 273 public: 274 void do_generation(Generation* gen) { 275 gen->adjust_pointers(); 276 } 277 }; 278 279 void GenMarkSweep::mark_sweep_phase3() { 280 GenCollectedHeap* gch = GenCollectedHeap::heap(); 281 282 // Adjust the pointers to reflect the new locations 283 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer()); 284 285 // Need new claim bits for the pointer adjustment tracing. 286 ClassLoaderDataGraph::clear_claimed_marks(); 287 288 // Because the closure below is created statically, we cannot 289 // use OopsInGenClosure constructor which takes a generation, 290 // as the Universe has not been created when the static constructors 291 // are run. 292 adjust_pointer_closure.set_orig_generation(gch->old_gen()); 293 294 { 295 StrongRootsScope srs(1); 296 297 gch->full_process_roots(&srs, 298 true, // this is the adjust phase 299 GenCollectedHeap::SO_AllCodeCache, 300 false, // all roots 301 &adjust_pointer_closure, 302 &adjust_cld_closure); 303 } 304 305 gch->gen_process_weak_roots(&adjust_pointer_closure); 306 307 adjust_marks(); 308 GenAdjustPointersClosure blk; 309 gch->generation_iterate(&blk, true); 310 } 311 312 class GenCompactClosure: public GenCollectedHeap::GenClosure { 313 public: 314 void do_generation(Generation* gen) { 315 gen->compact(); 316 } 317 }; 318 319 void GenMarkSweep::mark_sweep_phase4() { 320 // All pointers are now adjusted, move objects accordingly 321 322 // It is imperative that we traverse perm_gen first in phase4. All 323 // classes must be allocated earlier than their instances, and traversing 324 // perm_gen first makes sure that all Klass*s have moved to their new 325 // location before any instance does a dispatch through it's klass! 326 327 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 328 // in the same order in phase2, phase3 and phase4. We don't quite do that 329 // here (perm_gen first rather than last), so we tell the validate code 330 // to use a higher index (saved from phase2) when verifying perm_gen. 331 GenCollectedHeap* gch = GenCollectedHeap::heap(); 332 333 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer); 334 335 GenCompactClosure blk; 336 gch->generation_iterate(&blk, true); 337 }