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_implementation/g1/g1Log.hpp" 33 #include "gc_implementation/g1/g1MarkSweep.hpp" 34 #include "memory/gcLocker.hpp" 35 #include "memory/genCollectedHeap.hpp" 36 #include "memory/modRefBarrierSet.hpp" 37 #include "memory/referencePolicy.hpp" 38 #include "memory/space.hpp" 39 #include "oops/instanceRefKlass.hpp" 40 #include "oops/oop.inline.hpp" 41 #include "prims/jvmtiExport.hpp" 42 #include "runtime/aprofiler.hpp" 43 #include "runtime/biasedLocking.hpp" 44 #include "runtime/fprofiler.hpp" 45 #include "runtime/synchronizer.hpp" 46 #include "runtime/thread.hpp" 47 #include "runtime/vmThread.hpp" 48 #include "utilities/copy.hpp" 49 #include "utilities/events.hpp" 50 51 class HeapRegion; 52 53 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, 54 bool clear_all_softrefs) { 55 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 56 57 SharedHeap* sh = SharedHeap::heap(); 58 #ifdef ASSERT 59 if (sh->collector_policy()->should_clear_all_soft_refs()) { 60 assert(clear_all_softrefs, "Policy should have been checked earler"); 61 } 62 #endif 63 // hook up weak ref data so it can be used during Mark-Sweep 64 assert(GenMarkSweep::ref_processor() == NULL, "no stomping"); 65 assert(rp != NULL, "should be non-NULL"); 66 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition"); 67 68 GenMarkSweep::_ref_processor = rp; 69 rp->setup_policy(clear_all_softrefs); 70 71 // When collecting the permanent generation methodOops may be moving, 72 // so we either have to flush all bcp data or convert it into bci. 73 CodeCache::gc_prologue(); 74 Threads::gc_prologue(); 75 76 // Increment the invocation count for the permanent generation, since it is 77 // implicitly collected whenever we do a full mark sweep collection. 78 sh->perm_gen()->stat_record()->invocations++; 79 80 bool marked_for_unloading = false; 81 82 allocate_stacks(); 83 84 // We should save the marks of the currently locked biased monitors. 85 // The marking doesn't preserve the marks of biased objects. 86 BiasedLocking::preserve_marks(); 87 88 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs); 89 90 mark_sweep_phase2(); 91 92 // Don't add any more derived pointers during phase3 93 COMPILER2_PRESENT(DerivedPointerTable::set_active(false)); 94 95 mark_sweep_phase3(); 96 97 mark_sweep_phase4(); 98 99 GenMarkSweep::restore_marks(); 100 BiasedLocking::restore_marks(); 101 GenMarkSweep::deallocate_stacks(); 102 103 // We must invalidate the perm-gen rs, so that it gets rebuilt. 104 GenRemSet* rs = sh->rem_set(); 105 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/); 106 107 // "free at last gc" is calculated from these. 108 // CHF: cheating for now!!! 109 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity()); 110 // Universe::set_heap_used_at_last_gc(Universe::heap()->used()); 111 112 Threads::gc_epilogue(); 113 CodeCache::gc_epilogue(); 114 JvmtiExport::gc_epilogue(); 115 116 // refs processing: clean slate 117 GenMarkSweep::_ref_processor = NULL; 118 } 119 120 121 void G1MarkSweep::allocate_stacks() { 122 GenMarkSweep::_preserved_count_max = 0; 123 GenMarkSweep::_preserved_marks = NULL; 124 GenMarkSweep::_preserved_count = 0; 125 } 126 127 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading, 128 bool clear_all_softrefs) { 129 // Recursively traverse all live objects and mark them 130 TraceTime tm("phase 1", G1Log::fine() && Verbose, true, gclog_or_tty); 131 GenMarkSweep::trace(" 1"); 132 133 SharedHeap* sh = SharedHeap::heap(); 134 135 sh->process_strong_roots(true, // activeate StrongRootsScope 136 true, // Collecting permanent generation. 137 SharedHeap::SO_SystemClasses, 138 &GenMarkSweep::follow_root_closure, 139 &GenMarkSweep::follow_code_root_closure, 140 &GenMarkSweep::follow_root_closure); 141 142 // Process reference objects found during marking 143 ReferenceProcessor* rp = GenMarkSweep::ref_processor(); 144 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity"); 145 146 rp->setup_policy(clear_all_softrefs); 147 rp->process_discovered_references(&GenMarkSweep::is_alive, 148 &GenMarkSweep::keep_alive, 149 &GenMarkSweep::follow_stack_closure, 150 NULL); 151 152 // Follow system dictionary roots and unload classes 153 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive); 154 assert(GenMarkSweep::_marking_stack.is_empty(), 155 "stack should be empty by now"); 156 157 // Follow code cache roots (has to be done after system dictionary, 158 // assumes all live klasses are marked) 159 CodeCache::do_unloading(&GenMarkSweep::is_alive, 160 &GenMarkSweep::keep_alive, 161 purged_class); 162 GenMarkSweep::follow_stack(); 163 164 // Update subklass/sibling/implementor links of live klasses 165 GenMarkSweep::follow_weak_klass_links(); 166 assert(GenMarkSweep::_marking_stack.is_empty(), 167 "stack should be empty by now"); 168 169 // Visit memoized MDO's and clear any unmarked weak refs 170 GenMarkSweep::follow_mdo_weak_refs(); 171 assert(GenMarkSweep::_marking_stack.is_empty(), "just drained"); 172 173 // Visit interned string tables and delete unmarked oops 174 StringTable::unlink(&GenMarkSweep::is_alive); 175 // Clean up unreferenced symbols in symbol table. 176 SymbolTable::unlink(); 177 178 assert(GenMarkSweep::_marking_stack.is_empty(), 179 "stack should be empty by now"); 180 181 if (VerifyDuringGC) { 182 HandleMark hm; // handle scope 183 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); 184 gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying "); 185 Universe::heap()->prepare_for_verify(); 186 // Note: we can verify only the heap here. When an object is 187 // marked, the previous value of the mark word (including 188 // identity hash values, ages, etc) is preserved, and the mark 189 // word is set to markOop::marked_value - effectively removing 190 // any hash values from the mark word. These hash values are 191 // used when verifying the dictionaries and so removing them 192 // from the mark word can make verification of the dictionaries 193 // fail. At the end of the GC, the orginal mark word values 194 // (including hash values) are restored to the appropriate 195 // objects. 196 Universe::heap()->verify(/* silent */ false, 197 /* option */ VerifyOption_G1UseMarkWord); 198 199 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 200 gclog_or_tty->print_cr("]"); 201 } 202 } 203 204 class G1PrepareCompactClosure: public HeapRegionClosure { 205 G1CollectedHeap* _g1h; 206 ModRefBarrierSet* _mrbs; 207 CompactPoint _cp; 208 HumongousRegionSet _humongous_proxy_set; 209 210 void free_humongous_region(HeapRegion* hr) { 211 HeapWord* end = hr->end(); 212 size_t dummy_pre_used; 213 FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep"); 214 215 assert(hr->startsHumongous(), 216 "Only the start of a humongous region should be freed."); 217 _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list, 218 &_humongous_proxy_set, false /* par */); 219 hr->prepare_for_compaction(&_cp); 220 // Also clear the part of the card table that will be unused after 221 // compaction. 222 _mrbs->clear(MemRegion(hr->compaction_top(), end)); 223 dummy_free_list.remove_all(); 224 } 225 226 public: 227 G1PrepareCompactClosure(CompactibleSpace* cs) 228 : _g1h(G1CollectedHeap::heap()), 229 _mrbs(G1CollectedHeap::heap()->mr_bs()), 230 _cp(NULL, cs, cs->initialize_threshold()), 231 _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { } 232 233 void update_sets() { 234 // We'll recalculate total used bytes and recreate the free list 235 // at the end of the GC, so no point in updating those values here. 236 _g1h->update_sets_after_freeing_regions(0, /* pre_used */ 237 NULL, /* free_list */ 238 NULL, /* old_proxy_set */ 239 &_humongous_proxy_set, 240 false /* par */); 241 } 242 243 bool doHeapRegion(HeapRegion* hr) { 244 if (hr->isHumongous()) { 245 if (hr->startsHumongous()) { 246 oop obj = oop(hr->bottom()); 247 if (obj->is_gc_marked()) { 248 obj->forward_to(obj); 249 } else { 250 free_humongous_region(hr); 251 } 252 } else { 253 assert(hr->continuesHumongous(), "Invalid humongous."); 254 } 255 } else { 256 hr->prepare_for_compaction(&_cp); 257 // Also clear the part of the card table that will be unused after 258 // compaction. 259 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end())); 260 } 261 return false; 262 } 263 }; 264 265 // Finds the first HeapRegion. 266 class FindFirstRegionClosure: public HeapRegionClosure { 267 HeapRegion* _a_region; 268 public: 269 FindFirstRegionClosure() : _a_region(NULL) {} 270 bool doHeapRegion(HeapRegion* r) { 271 _a_region = r; 272 return true; 273 } 274 HeapRegion* result() { return _a_region; } 275 }; 276 277 void G1MarkSweep::mark_sweep_phase2() { 278 // Now all live objects are marked, compute the new object addresses. 279 280 // It is imperative that we traverse perm_gen LAST. If dead space is 281 // allowed a range of dead object may get overwritten by a dead int 282 // array. If perm_gen is not traversed last a klassOop may get 283 // overwritten. This is fine since it is dead, but if the class has dead 284 // instances we have to skip them, and in order to find their size we 285 // need the klassOop! 286 // 287 // It is not required that we traverse spaces in the same order in 288 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 289 // tracking expects us to do so. See comment under phase4. 290 291 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 292 Generation* pg = g1h->perm_gen(); 293 294 TraceTime tm("phase 2", G1Log::fine() && Verbose, true, gclog_or_tty); 295 GenMarkSweep::trace("2"); 296 297 FindFirstRegionClosure cl; 298 g1h->heap_region_iterate(&cl); 299 HeapRegion *r = cl.result(); 300 CompactibleSpace* sp = r; 301 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) { 302 sp = r->next_compaction_space(); 303 } 304 305 G1PrepareCompactClosure blk(sp); 306 g1h->heap_region_iterate(&blk); 307 blk.update_sets(); 308 309 CompactPoint perm_cp(pg, NULL, NULL); 310 pg->prepare_for_compaction(&perm_cp); 311 } 312 313 class G1AdjustPointersClosure: public HeapRegionClosure { 314 public: 315 bool doHeapRegion(HeapRegion* r) { 316 if (r->isHumongous()) { 317 if (r->startsHumongous()) { 318 // We must adjust the pointers on the single H object. 319 oop obj = oop(r->bottom()); 320 debug_only(GenMarkSweep::track_interior_pointers(obj)); 321 // point all the oops to the new location 322 obj->adjust_pointers(); 323 debug_only(GenMarkSweep::check_interior_pointers()); 324 } 325 } else { 326 // This really ought to be "as_CompactibleSpace"... 327 r->adjust_pointers(); 328 } 329 return false; 330 } 331 }; 332 333 void G1MarkSweep::mark_sweep_phase3() { 334 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 335 Generation* pg = g1h->perm_gen(); 336 337 // Adjust the pointers to reflect the new locations 338 TraceTime tm("phase 3", G1Log::fine() && Verbose, true, gclog_or_tty); 339 GenMarkSweep::trace("3"); 340 341 SharedHeap* sh = SharedHeap::heap(); 342 343 sh->process_strong_roots(true, // activate StrongRootsScope 344 true, // Collecting permanent generation. 345 SharedHeap::SO_AllClasses, 346 &GenMarkSweep::adjust_root_pointer_closure, 347 NULL, // do not touch code cache here 348 &GenMarkSweep::adjust_pointer_closure); 349 350 assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity"); 351 g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure); 352 353 // Now adjust pointers in remaining weak roots. (All of which should 354 // have been cleared if they pointed to non-surviving objects.) 355 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure, 356 &GenMarkSweep::adjust_pointer_closure); 357 358 GenMarkSweep::adjust_marks(); 359 360 G1AdjustPointersClosure blk; 361 g1h->heap_region_iterate(&blk); 362 pg->adjust_pointers(); 363 } 364 365 class G1SpaceCompactClosure: public HeapRegionClosure { 366 public: 367 G1SpaceCompactClosure() {} 368 369 bool doHeapRegion(HeapRegion* hr) { 370 if (hr->isHumongous()) { 371 if (hr->startsHumongous()) { 372 oop obj = oop(hr->bottom()); 373 if (obj->is_gc_marked()) { 374 obj->init_mark(); 375 } else { 376 assert(hr->is_empty(), "Should have been cleared in phase 2."); 377 } 378 hr->reset_during_compaction(); 379 } 380 } else { 381 hr->compact(); 382 } 383 return false; 384 } 385 }; 386 387 void G1MarkSweep::mark_sweep_phase4() { 388 // All pointers are now adjusted, move objects accordingly 389 390 // It is imperative that we traverse perm_gen first in phase4. All 391 // classes must be allocated earlier than their instances, and traversing 392 // perm_gen first makes sure that all klassOops have moved to their new 393 // location before any instance does a dispatch through it's klass! 394 395 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 396 // in the same order in phase2, phase3 and phase4. We don't quite do that 397 // here (perm_gen first rather than last), so we tell the validate code 398 // to use a higher index (saved from phase2) when verifying perm_gen. 399 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 400 Generation* pg = g1h->perm_gen(); 401 402 TraceTime tm("phase 4", G1Log::fine() && Verbose, true, gclog_or_tty); 403 GenMarkSweep::trace("4"); 404 405 pg->compact(); 406 407 G1SpaceCompactClosure blk; 408 g1h->heap_region_iterate(&blk); 409 410 } 411 412 // Local Variables: *** 413 // c-indentation-style: gnu *** 414 // End: ***