1 /*
   2  * Copyright (c) 2001, 2018, 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 "gc_implementation/g1/g1RootProcessor.hpp"
  35 #include "gc_implementation/g1/g1StringDedup.hpp"
  36 #include "gc_implementation/shared/gcHeapSummary.hpp"
  37 #include "gc_implementation/shared/gcTimer.hpp"
  38 #include "gc_implementation/shared/gcTrace.hpp"
  39 #include "gc_implementation/shared/gcTraceTime.hpp"
  40 #include "memory/gcLocker.hpp"
  41 #include "memory/genCollectedHeap.hpp"
  42 #include "memory/modRefBarrierSet.hpp"
  43 #include "memory/referencePolicy.hpp"
  44 #include "memory/space.hpp"
  45 #include "oops/instanceRefKlass.hpp"
  46 #include "oops/oop.inline.hpp"
  47 #include "prims/jvmtiExport.hpp"
  48 #include "runtime/biasedLocking.hpp"
  49 #include "runtime/fprofiler.hpp"
  50 #include "runtime/synchronizer.hpp"
  51 #include "runtime/thread.hpp"
  52 #include "runtime/vmThread.hpp"
  53 #include "utilities/copy.hpp"
  54 #include "utilities/events.hpp"
  55 #if INCLUDE_JFR
  56 #include "jfr/jfr.hpp"
  57 #endif // INCLUDE_JFR
  58 
  59 class HeapRegion;
  60 
  61 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
  62                                       bool clear_all_softrefs) {
  63   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  64 
  65   SharedHeap* sh = SharedHeap::heap();
  66 #ifdef ASSERT
  67   if (sh->collector_policy()->should_clear_all_soft_refs()) {
  68     assert(clear_all_softrefs, "Policy should have been checked earler");
  69   }
  70 #endif
  71   // hook up weak ref data so it can be used during Mark-Sweep
  72   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  73   assert(rp != NULL, "should be non-NULL");
  74   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
  75 
  76   GenMarkSweep::_ref_processor = rp;
  77   rp->setup_policy(clear_all_softrefs);
  78 
  79   // When collecting the permanent generation Method*s may be moving,
  80   // so we either have to flush all bcp data or convert it into bci.
  81   CodeCache::gc_prologue();
  82   Threads::gc_prologue();
  83 
  84   bool marked_for_unloading = false;
  85 
  86   allocate_stacks();
  87 
  88   // We should save the marks of the currently locked biased monitors.
  89   // The marking doesn't preserve the marks of biased objects.
  90   BiasedLocking::preserve_marks();
  91 
  92   mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
  93 
  94   mark_sweep_phase2();
  95 
  96   // Don't add any more derived pointers during phase3
  97   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
  98 
  99   mark_sweep_phase3();
 100 
 101   mark_sweep_phase4();
 102 
 103   GenMarkSweep::restore_marks();
 104   BiasedLocking::restore_marks();
 105   GenMarkSweep::deallocate_stacks();
 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   GCTraceTime tm("phase 1", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 131   GenMarkSweep::trace(" 1");
 132 
 133   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 134 
 135   // Need cleared claim bits for the roots processing
 136   ClassLoaderDataGraph::clear_claimed_marks();
 137 
 138   MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
 139   {
 140     G1RootProcessor root_processor(g1h);
 141     if (ClassUnloading) {
 142       root_processor.process_strong_roots(&GenMarkSweep::follow_root_closure,
 143                                           &GenMarkSweep::follow_cld_closure,
 144                                           &follow_code_closure);
 145     } else {
 146       root_processor.process_all_roots_no_string_table(
 147                                           &GenMarkSweep::follow_root_closure,
 148                                           &GenMarkSweep::follow_cld_closure,
 149                                           &follow_code_closure);
 150     }
 151   }
 152 
 153   // Process reference objects found during marking
 154   ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 155   assert(rp == g1h->ref_processor_stw(), "Sanity");
 156 
 157   rp->setup_policy(clear_all_softrefs);
 158   const ReferenceProcessorStats& stats =
 159     rp->process_discovered_references(&GenMarkSweep::is_alive,
 160                                       &GenMarkSweep::keep_alive,
 161                                       &GenMarkSweep::follow_stack_closure,
 162                                       NULL,
 163                                       gc_timer(),
 164                                       gc_tracer()->gc_id());
 165   gc_tracer()->report_gc_reference_stats(stats);
 166 
 167 
 168   // This is the point where the entire marking should have completed.
 169   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 170 
 171   if (ClassUnloading) {
 172 
 173      // Unload classes and purge the SystemDictionary.
 174      bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 175 
 176      // Unload nmethods.
 177      CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
 178 
 179      // Prune dead klasses from subklass/sibling/implementor lists.
 180      Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
 181   }
 182   // Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
 183   G1CollectedHeap::heap()->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
 184 
 185   if (VerifyDuringGC) {
 186     HandleMark hm;  // handle scope
 187     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
 188     Universe::heap()->prepare_for_verify();
 189     // Note: we can verify only the heap here. When an object is
 190     // marked, the previous value of the mark word (including
 191     // identity hash values, ages, etc) is preserved, and the mark
 192     // word is set to markOop::marked_value - effectively removing
 193     // any hash values from the mark word. These hash values are
 194     // used when verifying the dictionaries and so removing them
 195     // from the mark word can make verification of the dictionaries
 196     // fail. At the end of the GC, the orginal mark word values
 197     // (including hash values) are restored to the appropriate
 198     // objects.
 199     if (!VerifySilently) {
 200       gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
 201     }
 202     Universe::heap()->verify(VerifySilently, VerifyOption_G1UseMarkWord);
 203     if (!VerifySilently) {
 204       gclog_or_tty->print_cr("]");
 205     }
 206   }
 207 
 208   gc_tracer()->report_object_count_after_gc(&GenMarkSweep::is_alive);
 209 }
 210 
 211 
 212 void G1MarkSweep::mark_sweep_phase2() {
 213   // Now all live objects are marked, compute the new object addresses.
 214 
 215   // It is not required that we traverse spaces in the same order in
 216   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 217   // tracking expects us to do so. See comment under phase4.
 218 
 219   GCTraceTime tm("phase 2", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 220   GenMarkSweep::trace("2");
 221 
 222   prepare_compaction();
 223 }
 224 
 225 class G1AdjustPointersClosure: public HeapRegionClosure {
 226  public:
 227   bool doHeapRegion(HeapRegion* r) {
 228     if (r->isHumongous()) {
 229       if (r->startsHumongous()) {
 230         // We must adjust the pointers on the single H object.
 231         oop obj = oop(r->bottom());
 232         // point all the oops to the new location
 233         obj->adjust_pointers();
 234       }
 235     } else {
 236       // This really ought to be "as_CompactibleSpace"...
 237       r->adjust_pointers();
 238     }
 239     return false;
 240   }
 241 };
 242 
 243 void G1MarkSweep::mark_sweep_phase3() {
 244   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 245 
 246   // Adjust the pointers to reflect the new locations
 247   GCTraceTime tm("phase 3", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 248   GenMarkSweep::trace("3");
 249 
 250   // Need cleared claim bits for the roots processing
 251   ClassLoaderDataGraph::clear_claimed_marks();
 252 
 253   CodeBlobToOopClosure adjust_code_closure(&GenMarkSweep::adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
 254   {
 255     G1RootProcessor root_processor(g1h);
 256     root_processor.process_all_roots(&GenMarkSweep::adjust_pointer_closure,
 257                                      &GenMarkSweep::adjust_cld_closure,
 258                                      &adjust_code_closure);
 259   }
 260 
 261   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 262   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 263 
 264   // Now adjust pointers in remaining weak roots.  (All of which should
 265   // have been cleared if they pointed to non-surviving objects.)
 266   JNIHandles::weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 267   JFR_ONLY(Jfr::weak_oops_do(&GenMarkSweep::adjust_pointer_closure));
 268 
 269   if (G1StringDedup::is_enabled()) {
 270     G1StringDedup::oops_do(&GenMarkSweep::adjust_pointer_closure);
 271   }
 272 
 273   GenMarkSweep::adjust_marks();
 274 
 275   G1AdjustPointersClosure blk;
 276   g1h->heap_region_iterate(&blk);
 277 }
 278 
 279 class G1SpaceCompactClosure: public HeapRegionClosure {
 280 public:
 281   G1SpaceCompactClosure() {}
 282 
 283   bool doHeapRegion(HeapRegion* hr) {
 284     if (hr->isHumongous()) {
 285       if (hr->startsHumongous()) {
 286         oop obj = oop(hr->bottom());
 287         if (obj->is_gc_marked()) {
 288           obj->init_mark();
 289         } else {
 290           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 291         }
 292         hr->reset_during_compaction();
 293       }
 294     } else {
 295       hr->compact();
 296     }
 297     return false;
 298   }
 299 };
 300 
 301 void G1MarkSweep::mark_sweep_phase4() {
 302   // All pointers are now adjusted, move objects accordingly
 303 
 304   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 305   // in the same order in phase2, phase3 and phase4. We don't quite do that
 306   // here (code and comment not fixed for perm removal), so we tell the validate code
 307   // to use a higher index (saved from phase2) when verifying perm_gen.
 308   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 309 
 310   GCTraceTime tm("phase 4", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 311   GenMarkSweep::trace("4");
 312 
 313   G1SpaceCompactClosure blk;
 314   g1h->heap_region_iterate(&blk);
 315 
 316 }
 317 
 318 void G1MarkSweep::prepare_compaction_work(G1PrepareCompactClosure* blk) {
 319   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 320   g1h->heap_region_iterate(blk);
 321   blk->update_sets();
 322 }
 323 
 324 void G1PrepareCompactClosure::free_humongous_region(HeapRegion* hr) {
 325   HeapWord* end = hr->end();
 326   FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 327 
 328   assert(hr->startsHumongous(),
 329          "Only the start of a humongous region should be freed.");
 330 
 331   hr->set_containing_set(NULL);
 332   _humongous_regions_removed.increment(1u, hr->capacity());
 333 
 334   _g1h->free_humongous_region(hr, &dummy_free_list, false /* par */);
 335   prepare_for_compaction(hr, end);
 336   dummy_free_list.remove_all();
 337 }
 338 
 339 void G1PrepareCompactClosure::prepare_for_compaction(HeapRegion* hr, HeapWord* end) {
 340   // If this is the first live region that we came across which we can compact,
 341   // initialize the CompactPoint.
 342   if (!is_cp_initialized()) {
 343     _cp.space = hr;
 344     _cp.threshold = hr->initialize_threshold();
 345   }
 346   prepare_for_compaction_work(&_cp, hr, end);
 347 }
 348 
 349 void G1PrepareCompactClosure::prepare_for_compaction_work(CompactPoint* cp,
 350                                                           HeapRegion* hr,
 351                                                           HeapWord* end) {
 352   hr->prepare_for_compaction(cp);
 353   // Also clear the part of the card table that will be unused after
 354   // compaction.
 355   _mrbs->clear(MemRegion(hr->compaction_top(), end));
 356 }
 357 
 358 void G1PrepareCompactClosure::update_sets() {
 359   // We'll recalculate total used bytes and recreate the free list
 360   // at the end of the GC, so no point in updating those values here.
 361   HeapRegionSetCount empty_set;
 362   _g1h->remove_from_old_sets(empty_set, _humongous_regions_removed);
 363 }
 364 
 365 bool G1PrepareCompactClosure::doHeapRegion(HeapRegion* hr) {
 366   if (hr->isHumongous()) {
 367     if (hr->startsHumongous()) {
 368       oop obj = oop(hr->bottom());
 369       if (obj->is_gc_marked()) {
 370         obj->forward_to(obj);
 371       } else  {
 372         free_humongous_region(hr);
 373       }
 374     } else {
 375       assert(hr->continuesHumongous(), "Invalid humongous.");
 376     }
 377   } else {
 378     prepare_for_compaction(hr, hr->end());
 379   }
 380   return false;
 381 }