1 /* 2 * Copyright (c) 2001, 2011, 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/g1MarkSweep.hpp" 33 #include "memory/gcLocker.hpp" 34 #include "memory/genCollectedHeap.hpp" 35 #include "memory/modRefBarrierSet.hpp" 36 #include "memory/referencePolicy.hpp" 37 #include "memory/space.hpp" 38 #include "oops/instanceRefKlass.hpp" 39 #include "oops/oop.inline.hpp" 40 #include "prims/jvmtiExport.hpp" 41 #include "runtime/aprofiler.hpp" 42 #include "runtime/biasedLocking.hpp" 43 #include "runtime/fprofiler.hpp" 44 #include "runtime/synchronizer.hpp" 45 #include "runtime/thread.hpp" 46 #include "runtime/vmThread.hpp" 47 #include "utilities/copy.hpp" 48 #include "utilities/events.hpp" 49 50 class HeapRegion; 51 52 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, 53 bool clear_all_softrefs) { 54 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 55 56 SharedHeap* sh = SharedHeap::heap(); 57 #ifdef ASSERT 58 if (sh->collector_policy()->should_clear_all_soft_refs()) { 59 assert(clear_all_softrefs, "Policy should have been checked earler"); 60 } 61 #endif 62 // hook up weak ref data so it can be used during Mark-Sweep 63 assert(GenMarkSweep::ref_processor() == NULL, "no stomping"); 64 assert(rp != NULL, "should be non-NULL"); 65 GenMarkSweep::_ref_processor = rp; 66 rp->setup_policy(clear_all_softrefs); 67 68 // When collecting the permanent generation methodOops may be moving, 69 // so we either have to flush all bcp data or convert it into bci. 70 CodeCache::gc_prologue(); 71 Threads::gc_prologue(); 72 73 // Increment the invocation count for the permanent generation, since it is 74 // implicitly collected whenever we do a full mark sweep collection. 75 sh->perm_gen()->stat_record()->invocations++; 76 77 bool marked_for_unloading = false; 78 79 allocate_stacks(); 80 81 // We should save the marks of the currently locked biased monitors. 82 // The marking doesn't preserve the marks of biased objects. 83 BiasedLocking::preserve_marks(); 84 85 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs); 86 87 mark_sweep_phase2(); 88 89 // Don't add any more derived pointers during phase3 90 COMPILER2_PRESENT(DerivedPointerTable::set_active(false)); 91 92 mark_sweep_phase3(); 93 94 mark_sweep_phase4(); 95 96 GenMarkSweep::restore_marks(); 97 BiasedLocking::restore_marks(); 98 GenMarkSweep::deallocate_stacks(); 99 100 // We must invalidate the perm-gen rs, so that it gets rebuilt. 101 GenRemSet* rs = sh->rem_set(); 102 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/); 103 104 // "free at last gc" is calculated from these. 105 // CHF: cheating for now!!! 106 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity()); 107 // Universe::set_heap_used_at_last_gc(Universe::heap()->used()); 108 109 Threads::gc_epilogue(); 110 CodeCache::gc_epilogue(); 111 JvmtiExport::gc_epilogue(); 112 113 // refs processing: clean slate 114 GenMarkSweep::_ref_processor = NULL; 115 } 116 117 118 void G1MarkSweep::allocate_stacks() { 119 GenMarkSweep::_preserved_count_max = 0; 120 GenMarkSweep::_preserved_marks = NULL; 121 GenMarkSweep::_preserved_count = 0; 122 } 123 124 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading, 125 bool clear_all_softrefs) { 126 // Recursively traverse all live objects and mark them 127 EventMark m("1 mark object"); 128 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty); 129 GenMarkSweep::trace(" 1"); 130 131 SharedHeap* sh = SharedHeap::heap(); 132 133 sh->process_strong_roots(true, // activeate StrongRootsScope 134 true, // Collecting permanent generation. 135 SharedHeap::SO_SystemClasses, 136 &GenMarkSweep::follow_root_closure, 137 &GenMarkSweep::follow_code_root_closure, 138 &GenMarkSweep::follow_root_closure); 139 140 // Process reference objects found during marking 141 ReferenceProcessor* rp = GenMarkSweep::ref_processor(); 142 rp->setup_policy(clear_all_softrefs); 143 rp->process_discovered_references(&GenMarkSweep::is_alive, 144 &GenMarkSweep::keep_alive, 145 &GenMarkSweep::follow_stack_closure, 146 NULL); 147 148 // Follow system dictionary roots and unload classes 149 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive); 150 assert(GenMarkSweep::_marking_stack.is_empty(), 151 "stack should be empty by now"); 152 153 // Follow code cache roots (has to be done after system dictionary, 154 // assumes all live klasses are marked) 155 CodeCache::do_unloading(&GenMarkSweep::is_alive, 156 &GenMarkSweep::keep_alive, 157 purged_class); 158 GenMarkSweep::follow_stack(); 159 160 // Update subklass/sibling/implementor links of live klasses 161 GenMarkSweep::follow_weak_klass_links(); 162 assert(GenMarkSweep::_marking_stack.is_empty(), 163 "stack should be empty by now"); 164 165 // Visit memoized MDO's and clear any unmarked weak refs 166 GenMarkSweep::follow_mdo_weak_refs(); 167 assert(GenMarkSweep::_marking_stack.is_empty(), "just drained"); 168 169 170 // Visit interned string tables and delete unmarked oops 171 StringTable::unlink(&GenMarkSweep::is_alive); 172 // Clean up unreferenced symbols in symbol table. 173 SymbolTable::unlink(); 174 175 assert(GenMarkSweep::_marking_stack.is_empty(), 176 "stack should be empty by now"); 177 178 if (VerifyDuringGC) { 179 HandleMark hm; // handle scope 180 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); 181 gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying "); 182 Universe::heap()->prepare_for_verify(); 183 // Note: we can verify only the heap here. When an object is 184 // marked, the previous value of the mark word (including 185 // identity hash values, ages, etc) is preserved, and the mark 186 // word is set to markOop::marked_value - effectively removing 187 // any hash values from the mark word. These hash values are 188 // used when verifying the dictionaries and so removing them 189 // from the mark word can make verification of the dictionaries 190 // fail. At the end of the GC, the orginal mark word values 191 // (including hash values) are restored to the appropriate 192 // objects. 193 Universe::heap()->verify(/* allow dirty */ true, 194 /* silent */ false, 195 /* option */ VerifyOption_G1UseMarkWord); 196 197 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 198 gclog_or_tty->print_cr("]"); 199 } 200 } 201 202 class G1PrepareCompactClosure: public HeapRegionClosure { 203 G1CollectedHeap* _g1h; 204 ModRefBarrierSet* _mrbs; 205 CompactPoint _cp; 206 HumongousRegionSet _humongous_proxy_set; 207 208 void free_humongous_region(HeapRegion* hr) { 209 HeapWord* end = hr->end(); 210 size_t dummy_pre_used; 211 FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep"); 212 213 assert(hr->startsHumongous(), 214 "Only the start of a humongous region should be freed."); 215 _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list, 216 &_humongous_proxy_set, false /* par */); 217 hr->prepare_for_compaction(&_cp); 218 // Also clear the part of the card table that will be unused after 219 // compaction. 220 _mrbs->clear(MemRegion(hr->compaction_top(), end)); 221 dummy_free_list.remove_all(); 222 } 223 224 public: 225 G1PrepareCompactClosure(CompactibleSpace* cs) 226 : _g1h(G1CollectedHeap::heap()), 227 _mrbs(G1CollectedHeap::heap()->mr_bs()), 228 _cp(NULL, cs, cs->initialize_threshold()), 229 _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { } 230 231 void update_sets() { 232 // We'll recalculate total used bytes and recreate the free list 233 // at the end of the GC, so no point in updating those values here. 234 _g1h->update_sets_after_freeing_regions(0, /* pre_used */ 235 NULL, /* free_list */ 236 &_humongous_proxy_set, 237 false /* par */); 238 } 239 240 bool doHeapRegion(HeapRegion* hr) { 241 if (hr->isHumongous()) { 242 if (hr->startsHumongous()) { 243 oop obj = oop(hr->bottom()); 244 if (obj->is_gc_marked()) { 245 obj->forward_to(obj); 246 } else { 247 free_humongous_region(hr); 248 } 249 } else { 250 assert(hr->continuesHumongous(), "Invalid humongous."); 251 } 252 } else { 253 hr->prepare_for_compaction(&_cp); 254 // Also clear the part of the card table that will be unused after 255 // compaction. 256 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end())); 257 } 258 return false; 259 } 260 }; 261 262 // Finds the first HeapRegion. 263 class FindFirstRegionClosure: public HeapRegionClosure { 264 HeapRegion* _a_region; 265 public: 266 FindFirstRegionClosure() : _a_region(NULL) {} 267 bool doHeapRegion(HeapRegion* r) { 268 _a_region = r; 269 return true; 270 } 271 HeapRegion* result() { return _a_region; } 272 }; 273 274 void G1MarkSweep::mark_sweep_phase2() { 275 // Now all live objects are marked, compute the new object addresses. 276 277 // It is imperative that we traverse perm_gen LAST. If dead space is 278 // allowed a range of dead object may get overwritten by a dead int 279 // array. If perm_gen is not traversed last a klassOop may get 280 // overwritten. This is fine since it is dead, but if the class has dead 281 // instances we have to skip them, and in order to find their size we 282 // need the klassOop! 283 // 284 // It is not required that we traverse spaces in the same order in 285 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops 286 // tracking expects us to do so. See comment under phase4. 287 288 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 289 Generation* pg = g1h->perm_gen(); 290 291 EventMark m("2 compute new addresses"); 292 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty); 293 GenMarkSweep::trace("2"); 294 295 FindFirstRegionClosure cl; 296 g1h->heap_region_iterate(&cl); 297 HeapRegion *r = cl.result(); 298 CompactibleSpace* sp = r; 299 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) { 300 sp = r->next_compaction_space(); 301 } 302 303 G1PrepareCompactClosure blk(sp); 304 g1h->heap_region_iterate(&blk); 305 blk.update_sets(); 306 307 CompactPoint perm_cp(pg, NULL, NULL); 308 pg->prepare_for_compaction(&perm_cp); 309 } 310 311 class G1AdjustPointersClosure: public HeapRegionClosure { 312 public: 313 bool doHeapRegion(HeapRegion* r) { 314 if (r->isHumongous()) { 315 if (r->startsHumongous()) { 316 // We must adjust the pointers on the single H object. 317 oop obj = oop(r->bottom()); 318 debug_only(GenMarkSweep::track_interior_pointers(obj)); 319 // point all the oops to the new location 320 obj->adjust_pointers(); 321 debug_only(GenMarkSweep::check_interior_pointers()); 322 } 323 } else { 324 // This really ought to be "as_CompactibleSpace"... 325 r->adjust_pointers(); 326 } 327 return false; 328 } 329 }; 330 331 void G1MarkSweep::mark_sweep_phase3() { 332 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 333 Generation* pg = g1h->perm_gen(); 334 335 // Adjust the pointers to reflect the new locations 336 EventMark m("3 adjust pointers"); 337 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty); 338 GenMarkSweep::trace("3"); 339 340 SharedHeap* sh = SharedHeap::heap(); 341 342 sh->process_strong_roots(true, // activate StrongRootsScope 343 true, // Collecting permanent generation. 344 SharedHeap::SO_AllClasses, 345 &GenMarkSweep::adjust_root_pointer_closure, 346 NULL, // do not touch code cache here 347 &GenMarkSweep::adjust_pointer_closure); 348 349 g1h->ref_processor()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure); 350 351 // Now adjust pointers in remaining weak roots. (All of which should 352 // have been cleared if they pointed to non-surviving objects.) 353 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure, 354 &GenMarkSweep::adjust_pointer_closure); 355 356 GenMarkSweep::adjust_marks(); 357 358 G1AdjustPointersClosure blk; 359 g1h->heap_region_iterate(&blk); 360 pg->adjust_pointers(); 361 } 362 363 class G1SpaceCompactClosure: public HeapRegionClosure { 364 public: 365 G1SpaceCompactClosure() {} 366 367 bool doHeapRegion(HeapRegion* hr) { 368 if (hr->isHumongous()) { 369 if (hr->startsHumongous()) { 370 oop obj = oop(hr->bottom()); 371 if (obj->is_gc_marked()) { 372 obj->init_mark(); 373 } else { 374 assert(hr->is_empty(), "Should have been cleared in phase 2."); 375 } 376 hr->reset_during_compaction(); 377 } 378 } else { 379 hr->compact(); 380 } 381 return false; 382 } 383 }; 384 385 void G1MarkSweep::mark_sweep_phase4() { 386 // All pointers are now adjusted, move objects accordingly 387 388 // It is imperative that we traverse perm_gen first in phase4. All 389 // classes must be allocated earlier than their instances, and traversing 390 // perm_gen first makes sure that all klassOops have moved to their new 391 // location before any instance does a dispatch through it's klass! 392 393 // The ValidateMarkSweep live oops tracking expects us to traverse spaces 394 // in the same order in phase2, phase3 and phase4. We don't quite do that 395 // here (perm_gen first rather than last), so we tell the validate code 396 // to use a higher index (saved from phase2) when verifying perm_gen. 397 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 398 Generation* pg = g1h->perm_gen(); 399 400 EventMark m("4 compact heap"); 401 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty); 402 GenMarkSweep::trace("4"); 403 404 pg->compact(); 405 406 G1SpaceCompactClosure blk; 407 g1h->heap_region_iterate(&blk); 408 409 } 410 411 // Local Variables: *** 412 // c-indentation-style: gnu *** 413 // End: ***