1 /* 2 * Copyright (c) 2001, 2012, 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/symbolTable.hpp" 28 #include "classfile/systemDictionary.hpp" 29 #include "classfile/vmSymbols.hpp" 30 #include "code/codeCache.hpp" 31 #include "code/icBuffer.hpp" 32 #include "gc_interface/collectedHeap.inline.hpp" 33 #include "memory/genCollectedHeap.hpp" 34 #include "memory/genMarkSweep.hpp" 35 #include "memory/genOopClosures.inline.hpp" 36 #include "memory/generation.inline.hpp" 37 #include "memory/modRefBarrierSet.hpp" 38 #include "memory/referencePolicy.hpp" 39 #include "memory/space.hpp" 40 #include "oops/instanceRefKlass.hpp" 41 #include "oops/oop.inline.hpp" 42 #include "prims/jvmtiExport.hpp" 43 #include "runtime/fprofiler.hpp" 44 #include "runtime/handles.inline.hpp" 45 #include "runtime/synchronizer.hpp" 46 #include "runtime/thread.inline.hpp" 47 #include "runtime/vmThread.hpp" 48 #include "utilities/copy.hpp" 49 #include "utilities/events.hpp" 50 51 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, 52 bool clear_all_softrefs) { 53 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 54 55 GenCollectedHeap* gch = GenCollectedHeap::heap(); 56 #ifdef ASSERT 57 if (gch->collector_policy()->should_clear_all_soft_refs()) { 58 assert(clear_all_softrefs, "Policy should have been checked earlier"); 59 } 60 #endif 61 62 // hook up weak ref data so it can be used during Mark-Sweep 63 assert(ref_processor() == NULL, "no stomping"); 64 assert(rp != NULL, "should be non-NULL"); 65 _ref_processor = rp; 66 rp->setup_policy(clear_all_softrefs); 67 68 TraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, gclog_or_tty); 69 70 // When collecting the permanent generation Method*s may be moving, 71 // so we either have to flush all bcp data or convert it into bci. 72 CodeCache::gc_prologue(); 73 Threads::gc_prologue(); 74 75 // Increment the invocation count 76 _total_invocations++; 77 78 // Capture heap size before collection for printing. 79 size_t gch_prev_used = gch->used(); 80 81 // Some of the card table updates below assume that the perm gen is 82 // also being collected. 83 assert(level == gch->n_gens() - 1, 84 "All generations are being collected, ergo perm gen too."); 85 86 // Capture used regions for each generation that will be 87 // subject to collection, so that card table adjustments can 88 // be made intelligently (see clear / invalidate further below). 89 gch->save_used_regions(level); 90 91 allocate_stacks(); 92 93 mark_sweep_phase1(level, clear_all_softrefs); 94 95 mark_sweep_phase2(); 96 97 // Don't add any more derived pointers during phase3 98 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity")); 99 COMPILER2_PRESENT(DerivedPointerTable::set_active(false)); 100 101 mark_sweep_phase3(level); 102 103 VALIDATE_MARK_SWEEP_ONLY( 104 if (ValidateMarkSweep) { 105 guarantee(_root_refs_stack->length() == 0, "should be empty by now"); 106 } 107 ) 108 109 mark_sweep_phase4(); 110 111 VALIDATE_MARK_SWEEP_ONLY( 112 if (ValidateMarkSweep) { 113 guarantee(_live_oops->length() == _live_oops_moved_to->length(), 114 "should be the same size"); 115 } 116 ) 117 118 restore_marks(); 119 120 // Set saved marks for allocation profiler (and other things? -- dld) 121 // (Should this be in general part?) 122 gch->save_marks(); 123 124 deallocate_stacks(); 125 126 // If compaction completely evacuated all generations younger than this 127 // one, then we can clear the card table. Otherwise, we must invalidate 128 // it (consider all cards dirty). In the future, we might consider doing 129 // compaction within generations only, and doing card-table sliding. 130 bool all_empty = true; 131 for (int i = 0; all_empty && i < level; i++) { 132 Generation* g = gch->get_gen(i); 133 all_empty = all_empty && gch->get_gen(i)->used() == 0; 134 } 135 GenRemSet* rs = gch->rem_set(); 136 // Clear/invalidate below make use of the "prev_used_regions" saved earlier. 137 if (all_empty) { 138 // We've evacuated all generations below us. 139 Generation* g = gch->get_gen(level); 140 rs->clear_into_younger(g); 141 } else { 142 // Invalidate the cards corresponding to the currently used 143 // region and clear those corresponding to the evacuated region 144 // of all generations just collected (i.e. level and younger). 145 rs->invalidate_or_clear(gch->get_gen(level), 146 true /* younger */); 147 } 148 149 Threads::gc_epilogue(); 150 CodeCache::gc_epilogue(); 151 JvmtiExport::gc_epilogue(); 152 153 if (PrintGC && !PrintGCDetails) { 154 gch->print_heap_change(gch_prev_used); 155 } 156 157 // refs processing: clean slate 158 _ref_processor = NULL; 159 160 // Update heap occupancy information which is used as 161 // input to soft ref clearing policy at the next gc. 162 Universe::update_heap_info_at_gc(); 163 164 // Update time of last gc for all generations we collected 165 // (which curently is all the generations in the heap). 166 // We need to use a monotonically non-deccreasing time in ms 167 // or we will see time-warp warnings and os::javaTimeMillis() 168 // does not guarantee monotonicity. 169 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 170 gch->update_time_of_last_gc(now); 171 } 172 173 void GenMarkSweep::allocate_stacks() { 174 GenCollectedHeap* gch = GenCollectedHeap::heap(); 175 // Scratch request on behalf of oldest generation; will do no 176 // allocation. 177 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0); 178 179 // $$$ To cut a corner, we'll only use the first scratch block, and then 180 // revert to malloc. 181 if (scratch != NULL) { 182 _preserved_count_max = 183 scratch->num_words * HeapWordSize / sizeof(PreservedMark); 184 } else { 185 _preserved_count_max = 0; 186 } 187 188 _preserved_marks = (PreservedMark*)scratch; 189 _preserved_count = 0; 190 191 #ifdef VALIDATE_MARK_SWEEP 192 if (ValidateMarkSweep) { 193 _root_refs_stack = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true); 194 _other_refs_stack = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true); 195 _adjusted_pointers = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true); 196 _live_oops = new (ResourceObj::C_HEAP, mtGC) GrowableArray<oop>(100, true); 197 _live_oops_moved_to = new (ResourceObj::C_HEAP, mtGC) GrowableArray<oop>(100, true); 198 _live_oops_size = new (ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true); 199 } 200 if (RecordMarkSweepCompaction) { 201 if (_cur_gc_live_oops == NULL) { 202 _cur_gc_live_oops = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true); 203 _cur_gc_live_oops_moved_to = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true); 204 _cur_gc_live_oops_size = new(ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true); 205 _last_gc_live_oops = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true); 206 _last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true); 207 _last_gc_live_oops_size = new(ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true); 208 } else { 209 _cur_gc_live_oops->clear(); 210 _cur_gc_live_oops_moved_to->clear(); 211 _cur_gc_live_oops_size->clear(); 212 } 213 } 214 #endif 215 } 216 217 218 void GenMarkSweep::deallocate_stacks() { 219 if (!UseG1GC) { 220 GenCollectedHeap* gch = GenCollectedHeap::heap(); 221 gch->release_scratch(); 222 } 223 224 _preserved_mark_stack.clear(true); 225 _preserved_oop_stack.clear(true); 226 _marking_stack.clear(); 227 _objarray_stack.clear(true); 228 229 #ifdef VALIDATE_MARK_SWEEP 230 if (ValidateMarkSweep) { 231 delete _root_refs_stack; 232 delete _other_refs_stack; 233 delete _adjusted_pointers; 234 delete _live_oops; 235 delete _live_oops_size; 236 delete _live_oops_moved_to; 237 _live_oops_index = 0; 238 _live_oops_index_at_perm = 0; 239 } 240 #endif 241 } 242 243 void GenMarkSweep::mark_sweep_phase1(int level, 244 bool clear_all_softrefs) { 245 // Recursively traverse all live objects and mark them 246 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty); 247 trace(" 1"); 248 249 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking()); 250 251 GenCollectedHeap* gch = GenCollectedHeap::heap(); 252 253 // Because follow_root_closure is created statically, cannot 254 // use OopsInGenClosure constructor which takes a generation, 255 // as the Universe has not been created when the static constructors 256 // are run. 257 follow_root_closure.set_orig_generation(gch->get_gen(level)); 258 259 // Need new claim bits before marking starts. 260 ClassLoaderDataGraph::clear_claimed_marks(); 261 262 gch->gen_process_strong_roots(level, 263 false, // Younger gens are not roots. 264 true, // activate StrongRootsScope 265 false, // not scavenging 266 SharedHeap::SO_SystemClasses, 267 &follow_root_closure, 268 true, // walk code active on stacks 269 &follow_root_closure, 270 &follow_klass_closure); 271 272 // Process reference objects found during marking 273 { 274 ref_processor()->setup_policy(clear_all_softrefs); 275 ref_processor()->process_discovered_references( 276 &is_alive, &keep_alive, &follow_stack_closure, NULL); 277 } 278 279 // Follow system dictionary roots and unload classes 280 bool purged_class = SystemDictionary::do_unloading(&is_alive); 281 282 // Follow code cache roots 283 CodeCache::do_unloading(&is_alive, purged_class); 284 follow_stack(); // Flush marking stack 285 286 // Update subklass/sibling/implementor links of live klasses 287 Klass::clean_weak_klass_links(&is_alive); 288 assert(_marking_stack.is_empty(), "just drained"); 289 290 // Visit interned string tables and delete unmarked oops 291 StringTable::unlink(&is_alive); 292 // Clean up unreferenced symbols in symbol table. 293 SymbolTable::unlink(); 294 295 assert(_marking_stack.is_empty(), "stack should be empty by now"); 296 } 297 298 299 void GenMarkSweep::mark_sweep_phase2() { 300 // Now all live objects are marked, compute the new object addresses. 301 302 // It is imperative that we traverse perm_gen LAST. If dead space is 303 // allowed a range of dead object may get overwritten by a dead int 304 // array. If perm_gen is not traversed last a Klass* may get 305 // overwritten. This is fine since it is dead, but if the class has dead 306 // instances we have to skip them, and in order to find their size we 307 // need the Klass*! 308 // 309 // It is not required that we traverse spaces in the same order in 310 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 311 // tracking expects us to do so. See comment under phase4. 312 313 GenCollectedHeap* gch = GenCollectedHeap::heap(); 314 315 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty); 316 trace("2"); 317 318 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking()); 319 320 gch->prepare_for_compaction(); 321 } 322 323 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure { 324 public: 325 void do_generation(Generation* gen) { 326 gen->adjust_pointers(); 327 } 328 }; 329 330 void GenMarkSweep::mark_sweep_phase3(int level) { 331 GenCollectedHeap* gch = GenCollectedHeap::heap(); 332 333 // Adjust the pointers to reflect the new locations 334 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty); 335 trace("3"); 336 337 // Need new claim bits for the pointer adjustment tracing. 338 ClassLoaderDataGraph::clear_claimed_marks(); 339 340 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking()); 341 342 // Because the two closures below are created statically, cannot 343 // use OopsInGenClosure constructor which takes a generation, 344 // as the Universe has not been created when the static constructors 345 // are run. 346 adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level)); 347 adjust_pointer_closure.set_orig_generation(gch->get_gen(level)); 348 349 gch->gen_process_strong_roots(level, 350 false, // Younger gens are not roots. 351 true, // activate StrongRootsScope 352 false, // not scavenging 353 SharedHeap::SO_AllClasses, 354 &adjust_root_pointer_closure, 355 false, // do not walk code 356 &adjust_root_pointer_closure, 357 &adjust_klass_closure); 358 359 // Now adjust pointers in remaining weak roots. (All of which should 360 // have been cleared if they pointed to non-surviving objects.) 361 CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure, 362 /*do_marking=*/ false); 363 gch->gen_process_weak_roots(&adjust_root_pointer_closure, 364 &adjust_code_pointer_closure, 365 &adjust_pointer_closure); 366 367 adjust_marks(); 368 GenAdjustPointersClosure blk; 369 gch->generation_iterate(&blk, true); 370 } 371 372 class GenCompactClosure: public GenCollectedHeap::GenClosure { 373 public: 374 void do_generation(Generation* gen) { 375 gen->compact(); 376 } 377 }; 378 379 void GenMarkSweep::mark_sweep_phase4() { 380 // All pointers are now adjusted, move objects accordingly 381 382 // It is imperative that we traverse perm_gen first in phase4. All 383 // classes must be allocated earlier than their instances, and traversing 384 // perm_gen first makes sure that all Klass*s have moved to their new 385 // location before any instance does a dispatch through it's klass! 386 387 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 388 // in the same order in phase2, phase3 and phase4. We don't quite do that 389 // here (perm_gen first rather than last), so we tell the validate code 390 // to use a higher index (saved from phase2) when verifying perm_gen. 391 GenCollectedHeap* gch = GenCollectedHeap::heap(); 392 393 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty); 394 trace("4"); 395 396 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking()); 397 398 GenCompactClosure blk; 399 gch->generation_iterate(&blk, true); 400 401 VALIDATE_MARK_SWEEP_ONLY(compaction_complete()); 402 }