1 /* 2 * Copyright (c) 2001, 2015, 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/systemDictionary.hpp" 29 #include "classfile/vmSymbols.hpp" 30 #include "code/codeCache.hpp" 31 #include "code/icBuffer.hpp" 32 #include "gc/serial/genMarkSweep.hpp" 33 #include "gc/shared/collectedHeap.inline.hpp" 34 #include "gc/shared/gcHeapSummary.hpp" 35 #include "gc/shared/gcTimer.hpp" 36 #include "gc/shared/gcTrace.hpp" 37 #include "gc/shared/gcTraceTime.hpp" 38 #include "gc/shared/genCollectedHeap.hpp" 39 #include "gc/shared/genOopClosures.inline.hpp" 40 #include "gc/shared/modRefBarrierSet.hpp" 41 #include "gc/shared/referencePolicy.hpp" 42 #include "gc/shared/space.hpp" 43 #include "gc/shared/strongRootsScope.hpp" 44 #include "oops/instanceRefKlass.hpp" 45 #include "oops/oop.inline.hpp" 46 #include "prims/jvmtiExport.hpp" 47 #include "runtime/fprofiler.hpp" 48 #include "runtime/handles.inline.hpp" 49 #include "runtime/synchronizer.hpp" 50 #include "runtime/thread.inline.hpp" 51 #include "runtime/vmThread.hpp" 52 #include "utilities/copy.hpp" 53 #include "utilities/events.hpp" 54 #include "utilities/stack.inline.hpp" 55 56 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) { 57 guarantee(level == 1, "We always collect both old and young."); 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 _ref_processor = rp; 71 rp->setup_policy(clear_all_softrefs); 72 73 GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id()); 74 75 gch->trace_heap_before_gc(_gc_tracer); 76 77 // When collecting the permanent generation Method*s may be moving, 78 // so we either have to flush all bcp data or convert it into bci. 79 CodeCache::gc_prologue(); 80 81 // Increment the invocation count 82 _total_invocations++; 83 84 // Capture heap size before collection for printing. 85 size_t gch_prev_used = gch->used(); 86 87 // Capture used regions for each generation that will be 88 // subject to collection, so that card table adjustments can 89 // be made intelligently (see clear / invalidate further below). 90 gch->save_used_regions(level); 91 92 allocate_stacks(); 93 94 mark_sweep_phase1(level, clear_all_softrefs); 95 96 mark_sweep_phase2(); 97 98 // Don't add any more derived pointers during phase3 99 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity")); 100 COMPILER2_PRESENT(DerivedPointerTable::set_active(false)); 101 102 mark_sweep_phase3(level); 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 GenRemSet* 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 if (PrintGC && !PrintGCDetails) { 135 gch->print_heap_change(gch_prev_used); 136 } 137 138 // refs processing: clean slate 139 _ref_processor = NULL; 140 141 // Update heap occupancy information which is used as 142 // input to soft ref clearing policy at the next gc. 143 Universe::update_heap_info_at_gc(); 144 145 // Update time of last gc for all generations we collected 146 // (which currently is all the generations in the heap). 147 // We need to use a monotonically non-decreasing time in ms 148 // or we will see time-warp warnings and os::javaTimeMillis() 149 // does not guarantee monotonicity. 150 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 151 gch->update_time_of_last_gc(now); 152 153 gch->trace_heap_after_gc(_gc_tracer); 154 } 155 156 void GenMarkSweep::allocate_stacks() { 157 GenCollectedHeap* gch = GenCollectedHeap::heap(); 158 // Scratch request on behalf of old generation; will do no allocation. 159 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0); 160 161 // $$$ To cut a corner, we'll only use the first scratch block, and then 162 // revert to malloc. 163 if (scratch != NULL) { 164 _preserved_count_max = 165 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 166 } else { 167 _preserved_count_max = 0; 168 } 169 170 _preserved_marks = (PreservedMark*)scratch; 171 _preserved_count = 0; 172 } 173 174 175 void GenMarkSweep::deallocate_stacks() { 176 if (!UseG1GC) { 177 GenCollectedHeap* gch = GenCollectedHeap::heap(); 178 gch->release_scratch(); 179 } 180 181 _preserved_mark_stack.clear(true); 182 _preserved_oop_stack.clear(true); 183 _marking_stack.clear(); 184 _objarray_stack.clear(true); 185 } 186 187 void GenMarkSweep::mark_sweep_phase1(int level, 188 bool clear_all_softrefs) { 189 // Recursively traverse all live objects and mark them 190 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 191 192 GenCollectedHeap* gch = GenCollectedHeap::heap(); 193 194 // Because follow_root_closure is created statically, cannot 195 // use OopsInGenClosure constructor which takes a generation, 196 // as the Universe has not been created when the static constructors 197 // are run. 198 assert(level == 1, "We don't use mark-sweep on young generations"); 199 follow_root_closure.set_orig_generation(gch->old_gen()); 200 201 // Need new claim bits before marking starts. 202 ClassLoaderDataGraph::clear_claimed_marks(); 203 204 { 205 StrongRootsScope srs(1); 206 207 gch->gen_process_roots(&srs, 208 level, 209 false, // Younger gens are not roots. 210 GenCollectedHeap::SO_None, 211 GenCollectedHeap::StrongRootsOnly, 212 &follow_root_closure, 213 &follow_root_closure, 214 &follow_cld_closure); 215 } 216 217 // Process reference objects found during marking 218 { 219 ref_processor()->setup_policy(clear_all_softrefs); 220 const ReferenceProcessorStats& stats = 221 ref_processor()->process_discovered_references( 222 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id()); 223 gc_tracer()->report_gc_reference_stats(stats); 224 } 225 226 // This is the point where the entire marking should have completed. 227 assert(_marking_stack.is_empty(), "Marking should have completed"); 228 229 // Unload classes and purge the SystemDictionary. 230 bool purged_class = SystemDictionary::do_unloading(&is_alive); 231 232 // Unload nmethods. 233 CodeCache::do_unloading(&is_alive, purged_class); 234 235 // Prune dead klasses from subklass/sibling/implementor lists. 236 Klass::clean_weak_klass_links(&is_alive); 237 238 // Delete entries for dead interned strings. 239 StringTable::unlink(&is_alive); 240 241 // Clean up unreferenced symbols in symbol table. 242 SymbolTable::unlink(); 243 244 gc_tracer()->report_object_count_after_gc(&is_alive); 245 } 246 247 248 void GenMarkSweep::mark_sweep_phase2() { 249 // Now all live objects are marked, compute the new object addresses. 250 251 // It is imperative that we traverse perm_gen LAST. If dead space is 252 // allowed a range of dead object may get overwritten by a dead int 253 // array. If perm_gen is not traversed last a Klass* may get 254 // overwritten. This is fine since it is dead, but if the class has dead 255 // instances we have to skip them, and in order to find their size we 256 // need the Klass*! 257 // 258 // It is not required that we traverse spaces in the same order in 259 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 260 // tracking expects us to do so. See comment under phase4. 261 262 GenCollectedHeap* gch = GenCollectedHeap::heap(); 263 264 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 265 266 gch->prepare_for_compaction(); 267 } 268 269 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 270 public: 271 void do_generation(Generation* gen) { 272 gen->adjust_pointers(); 273 } 274 }; 275 276 void GenMarkSweep::mark_sweep_phase3(int level) { 277 GenCollectedHeap* gch = GenCollectedHeap::heap(); 278 279 // Adjust the pointers to reflect the new locations 280 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 281 282 // Need new claim bits for the pointer adjustment tracing. 283 ClassLoaderDataGraph::clear_claimed_marks(); 284 285 // Because the closure below is created statically, we cannot 286 // use OopsInGenClosure constructor which takes a generation, 287 // as the Universe has not been created when the static constructors 288 // are run. 289 assert(level == 1, "We don't use mark-sweep on young generations."); 290 adjust_pointer_closure.set_orig_generation(gch->old_gen()); 291 292 { 293 StrongRootsScope srs(1); 294 295 gch->gen_process_roots(&srs, 296 level, 297 false, // Younger gens are not roots. 298 GenCollectedHeap::SO_AllCodeCache, 299 GenCollectedHeap::StrongAndWeakRoots, 300 &adjust_pointer_closure, 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 tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id()); 334 335 GenCompactClosure blk; 336 gch->generation_iterate(&blk, true); 337 }