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/handles.inline.hpp" 50 #include "runtime/synchronizer.hpp" 51 #include "runtime/thread.inline.hpp" 52 #include "runtime/vmThread.hpp" 53 #include "utilities/copy.hpp" 54 #include "utilities/events.hpp" 55 #include "utilities/stack.inline.hpp" 56 57 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) { 58 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 59 60 GenCollectedHeap* gch = GenCollectedHeap::heap(); 61 #ifdef ASSERT 62 if (gch->collector_policy()->should_clear_all_soft_refs()) { 63 assert(clear_all_softrefs, "Policy should have been checked earlier"); 64 } 65 #endif 66 67 // hook up weak ref data so it can be used during Mark-Sweep 68 assert(ref_processor() == NULL, "no stomping"); 69 assert(rp != NULL, "should be non-NULL"); 70 set_ref_processor(rp); 71 rp->setup_policy(clear_all_softrefs); 72 73 gch->trace_heap_before_gc(_gc_tracer); 74 75 // When collecting the permanent generation Method*s may be moving, 76 // so we either have to flush all bcp data or convert it into bci. 77 CodeCache::gc_prologue(); 78 79 // Increment the invocation count 80 _total_invocations++; 81 82 // Capture used regions for each generation that will be 83 // subject to collection, so that card table adjustments can 84 // be made intelligently (see clear / invalidate further below). 85 gch->save_used_regions(); 86 87 allocate_stacks(); 88 89 mark_sweep_phase1(clear_all_softrefs); 90 91 mark_sweep_phase2(); 92 93 // Don't add any more derived pointers during phase3 94 #if defined(COMPILER2) || INCLUDE_JVMCI 95 assert(DerivedPointerTable::is_active(), "Sanity"); 96 DerivedPointerTable::set_active(false); 97 #endif 98 99 mark_sweep_phase3(); 100 101 mark_sweep_phase4(); 102 103 restore_marks(); 104 105 // Set saved marks for allocation profiler (and other things? -- dld) 106 // (Should this be in general part?) 107 gch->save_marks(); 108 109 deallocate_stacks(); 110 111 // If compaction completely evacuated the young generation then we 112 // can clear the card table. Otherwise, we must invalidate 113 // it (consider all cards dirty). In the future, we might consider doing 114 // compaction within generations only, and doing card-table sliding. 115 CardTableRS* rs = gch->rem_set(); 116 Generation* old_gen = gch->old_gen(); 117 118 // Clear/invalidate below make use of the "prev_used_regions" saved earlier. 119 if (gch->young_gen()->used() == 0) { 120 // We've evacuated the young generation. 121 rs->clear_into_younger(old_gen); 122 } else { 123 // Invalidate the cards corresponding to the currently used 124 // region and clear those corresponding to the evacuated region. 125 rs->invalidate_or_clear(old_gen); 126 } 127 128 CodeCache::gc_epilogue(); 129 JvmtiExport::gc_epilogue(); 130 131 // refs processing: clean slate 132 set_ref_processor(NULL); 133 134 // Update heap occupancy information which is used as 135 // input to soft ref clearing policy at the next gc. 136 Universe::update_heap_info_at_gc(); 137 138 // Update time of last gc for all generations we collected 139 // (which currently is all the generations in the heap). 140 // We need to use a monotonically non-decreasing time in ms 141 // or we will see time-warp warnings and os::javaTimeMillis() 142 // does not guarantee monotonicity. 143 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 144 gch->update_time_of_last_gc(now); 145 146 gch->trace_heap_after_gc(_gc_tracer); 147 } 148 149 void GenMarkSweep::allocate_stacks() { 150 GenCollectedHeap* gch = GenCollectedHeap::heap(); 151 // Scratch request on behalf of old generation; will do no allocation. 152 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0); 153 154 // $$$ To cut a corner, we'll only use the first scratch block, and then 155 // revert to malloc. 156 if (scratch != NULL) { 157 _preserved_count_max = 158 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 159 } else { 160 _preserved_count_max = 0; 161 } 162 163 _preserved_marks = (PreservedMark*)scratch; 164 _preserved_count = 0; 165 } 166 167 168 void GenMarkSweep::deallocate_stacks() { 169 if (!UseG1GC) { 170 GenCollectedHeap* gch = GenCollectedHeap::heap(); 171 gch->release_scratch(); 172 } 173 174 _preserved_mark_stack.clear(true); 175 _preserved_oop_stack.clear(true); 176 _marking_stack.clear(); 177 _objarray_stack.clear(true); 178 } 179 180 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) { 181 // Recursively traverse all live objects and mark them 182 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer); 183 184 GenCollectedHeap* gch = GenCollectedHeap::heap(); 185 186 // Because follow_root_closure is created statically, cannot 187 // use OopsInGenClosure constructor which takes a generation, 188 // as the Universe has not been created when the static constructors 189 // are run. 190 follow_root_closure.set_orig_generation(gch->old_gen()); 191 192 // Need new claim bits before marking starts. 193 ClassLoaderDataGraph::clear_claimed_marks(); 194 195 { 196 StrongRootsScope srs(1); 197 198 gch->full_process_roots(&srs, 199 false, // not the adjust phase 200 GenCollectedHeap::SO_None, 201 ClassUnloading, // only strong roots if ClassUnloading 202 // is enabled 203 &follow_root_closure, 204 &follow_cld_closure); 205 } 206 207 // Process reference objects found during marking 208 { 209 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer()); 210 211 ref_processor()->setup_policy(clear_all_softrefs); 212 const ReferenceProcessorStats& stats = 213 ref_processor()->process_discovered_references( 214 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer); 215 gc_tracer()->report_gc_reference_stats(stats); 216 } 217 218 // This is the point where the entire marking should have completed. 219 assert(_marking_stack.is_empty(), "Marking should have completed"); 220 221 { 222 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer()); 223 224 // Unload classes and purge the SystemDictionary. 225 bool purged_class = SystemDictionary::do_unloading(&is_alive, gc_timer()); 226 227 // Unload nmethods. 228 CodeCache::do_unloading(&is_alive, purged_class); 229 230 // Prune dead klasses from subklass/sibling/implementor lists. 231 Klass::clean_weak_klass_links(&is_alive); 232 } 233 234 { 235 GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer()); 236 // Delete entries for dead interned strings. 237 StringTable::unlink(&is_alive); 238 } 239 240 { 241 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer()); 242 // Clean up unreferenced symbols in symbol table. 243 SymbolTable::unlink(); 244 } 245 246 gc_tracer()->report_object_count_after_gc(&is_alive); 247 } 248 249 250 void GenMarkSweep::mark_sweep_phase2() { 251 // Now all live objects are marked, compute the new object addresses. 252 253 // It is imperative that we traverse perm_gen LAST. If dead space is 254 // allowed a range of dead object may get overwritten by a dead int 255 // array. If perm_gen is not traversed last a Klass* may get 256 // overwritten. This is fine since it is dead, but if the class has dead 257 // instances we have to skip them, and in order to find their size we 258 // need the Klass*! 259 // 260 // It is not required that we traverse spaces in the same order in 261 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 262 // tracking expects us to do so. See comment under phase4. 263 264 GenCollectedHeap* gch = GenCollectedHeap::heap(); 265 266 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer); 267 268 gch->prepare_for_compaction(); 269 } 270 271 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 272 public: 273 void do_generation(Generation* gen) { 274 gen->adjust_pointers(); 275 } 276 }; 277 278 void GenMarkSweep::mark_sweep_phase3() { 279 GenCollectedHeap* gch = GenCollectedHeap::heap(); 280 281 // Adjust the pointers to reflect the new locations 282 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer()); 283 284 // Need new claim bits for the pointer adjustment tracing. 285 ClassLoaderDataGraph::clear_claimed_marks(); 286 287 // Because the closure below is created statically, we cannot 288 // use OopsInGenClosure constructor which takes a generation, 289 // as the Universe has not been created when the static constructors 290 // are run. 291 adjust_pointer_closure.set_orig_generation(gch->old_gen()); 292 293 { 294 StrongRootsScope srs(1); 295 296 gch->full_process_roots(&srs, 297 true, // this is the adjust phase 298 GenCollectedHeap::SO_AllCodeCache, 299 false, // all roots 300 &adjust_pointer_closure, 301 &adjust_cld_closure); 302 } 303 304 gch->gen_process_weak_roots(&adjust_pointer_closure); 305 306 adjust_marks(); 307 GenAdjustPointersClosure blk; 308 gch->generation_iterate(&blk, true); 309 } 310 311 class GenCompactClosure: public GenCollectedHeap::GenClosure { 312 public: 313 void do_generation(Generation* gen) { 314 gen->compact(); 315 } 316 }; 317 318 void GenMarkSweep::mark_sweep_phase4() { 319 // All pointers are now adjusted, move objects accordingly 320 321 // It is imperative that we traverse perm_gen first in phase4. All 322 // classes must be allocated earlier than their instances, and traversing 323 // perm_gen first makes sure that all Klass*s have moved to their new 324 // location before any instance does a dispatch through it's klass! 325 326 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 327 // in the same order in phase2, phase3 and phase4. We don't quite do that 328 // here (perm_gen first rather than last), so we tell the validate code 329 // to use a higher index (saved from phase2) when verifying perm_gen. 330 GenCollectedHeap* gch = GenCollectedHeap::heap(); 331 332 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer); 333 334 GenCompactClosure blk; 335 gch->generation_iterate(&blk, true); 336 }