1 /*
   2  * Copyright (c) 2001, 2017, 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/g1/g1MarkSweep.hpp"
  33 #include "gc/g1/g1RootProcessor.hpp"
  34 #include "gc/g1/g1StringDedup.hpp"
  35 #include "gc/serial/markSweep.inline.hpp"
  36 #include "gc/shared/gcHeapSummary.hpp"
  37 #include "gc/shared/gcLocker.hpp"
  38 #include "gc/shared/gcTimer.hpp"
  39 #include "gc/shared/gcTrace.hpp"
  40 #include "gc/shared/gcTraceTime.inline.hpp"
  41 #include "gc/shared/genCollectedHeap.hpp"
  42 #include "gc/shared/modRefBarrierSet.hpp"
  43 #include "gc/shared/referencePolicy.hpp"
  44 #include "gc/shared/space.hpp"
  45 #include "oops/instanceRefKlass.hpp"
  46 #include "oops/oop.inline.hpp"
  47 #include "prims/jvmtiExport.hpp"
  48 #include "runtime/atomic.hpp"
  49 #include "runtime/biasedLocking.hpp"
  50 #include "runtime/fprofiler.hpp"
  51 #include "runtime/synchronizer.hpp"
  52 #include "runtime/thread.hpp"
  53 #include "runtime/vmThread.hpp"
  54 #include "utilities/copy.hpp"
  55 #include "utilities/events.hpp"
  56 
  57 class HeapRegion;
  58 
  59 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
  60                                       bool clear_all_softrefs) {
  61   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  62 
  63 #ifdef ASSERT
  64   if (G1CollectedHeap::heap()->collector_policy()->should_clear_all_soft_refs()) {
  65     assert(clear_all_softrefs, "Policy should have been checked earler");
  66   }
  67 #endif
  68   // hook up weak ref data so it can be used during Mark-Sweep
  69   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  70   assert(rp != NULL, "should be non-NULL");
  71   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
  72 
  73   GenMarkSweep::set_ref_processor(rp);
  74   rp->setup_policy(clear_all_softrefs);
  75 
  76   // When collecting the permanent generation Method*s may be moving,
  77   // so we either have to flush all bcp data or convert it into bci.
  78   CodeCache::gc_prologue();
  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 #if defined(COMPILER2) || INCLUDE_JVMCI
  93   // Don't add any more derived pointers during phase3
  94   DerivedPointerTable::set_active(false);
  95 #endif
  96 
  97   mark_sweep_phase3();
  98 
  99   mark_sweep_phase4();
 100 
 101   GenMarkSweep::restore_marks();
 102   BiasedLocking::restore_marks();
 103   GenMarkSweep::deallocate_stacks();
 104 
 105   CodeCache::gc_epilogue();
 106   JvmtiExport::gc_epilogue();
 107 
 108   // refs processing: clean slate
 109   GenMarkSweep::set_ref_processor(NULL);
 110 }
 111 
 112 
 113 void G1MarkSweep::allocate_stacks() {
 114   GenMarkSweep::_preserved_count_max = 0;
 115   GenMarkSweep::_preserved_marks = NULL;
 116   GenMarkSweep::_preserved_count = 0;
 117 }
 118 
 119 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
 120                                     bool clear_all_softrefs) {
 121   // Recursively traverse all live objects and mark them
 122   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", gc_timer());
 123 
 124   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 125 
 126   // Need cleared claim bits for the roots processing
 127   ClassLoaderDataGraph::clear_claimed_marks();
 128 
 129   MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
 130   {
 131     G1RootProcessor root_processor(g1h, 1);
 132     if (ClassUnloading) {
 133       root_processor.process_strong_roots(&GenMarkSweep::follow_root_closure,
 134                                           &GenMarkSweep::follow_cld_closure,
 135                                           &follow_code_closure);
 136     } else {
 137       root_processor.process_all_roots_no_string_table(
 138                                           &GenMarkSweep::follow_root_closure,
 139                                           &GenMarkSweep::follow_cld_closure,
 140                                           &follow_code_closure);
 141     }
 142   }
 143 
 144   {
 145     GCTraceTime(Debug, gc, phases) trace("Reference Processing", gc_timer());
 146 
 147     // Process reference objects found during marking
 148     ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 149     assert(rp == g1h->ref_processor_stw(), "Sanity");
 150 
 151     rp->setup_policy(clear_all_softrefs);
 152     const ReferenceProcessorStats& stats =
 153         rp->process_discovered_references(&GenMarkSweep::is_alive,
 154                                           &GenMarkSweep::keep_alive,
 155                                           &GenMarkSweep::follow_stack_closure,
 156                                           NULL,
 157                                           gc_timer());
 158     gc_tracer()->report_gc_reference_stats(stats);
 159   }
 160 
 161   // This is the point where the entire marking should have completed.
 162   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 163 
 164   if (ClassUnloading) {
 165     GCTraceTime(Debug, gc, phases) trace("Class Unloading", gc_timer());
 166 
 167     // Unload classes and purge the SystemDictionary.
 168     bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 169 
 170     // Unload nmethods.
 171     CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
 172 
 173     // Prune dead klasses from subklass/sibling/implementor lists.
 174     Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
 175   }
 176 
 177   {
 178     GCTraceTime(Debug, gc, phases) trace("Scrub String and Symbol Tables", gc_timer());
 179     // Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
 180     g1h->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
 181   }
 182 
 183   if (G1StringDedup::is_enabled()) {
 184     GCTraceTime(Debug, gc, phases) trace("String Deduplication Unlink", gc_timer());
 185     G1StringDedup::unlink(&GenMarkSweep::is_alive);
 186   }
 187 
 188   if (VerifyDuringGC) {
 189     HandleMark hm;  // handle scope
 190 #if defined(COMPILER2) || INCLUDE_JVMCI
 191     DerivedPointerTableDeactivate dpt_deact;
 192 #endif
 193     g1h->prepare_for_verify();
 194     // Note: we can verify only the heap here. When an object is
 195     // marked, the previous value of the mark word (including
 196     // identity hash values, ages, etc) is preserved, and the mark
 197     // word is set to markOop::marked_value - effectively removing
 198     // any hash values from the mark word. These hash values are
 199     // used when verifying the dictionaries and so removing them
 200     // from the mark word can make verification of the dictionaries
 201     // fail. At the end of the GC, the original mark word values
 202     // (including hash values) are restored to the appropriate
 203     // objects.
 204     GCTraceTime(Info, gc, verify)("During GC (full)");
 205     g1h->verify(VerifyOption_G1UseMarkWord);
 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(Info, gc, phases) tm("Phase 2: Compute new object addresses", gc_timer());
 220 
 221   prepare_compaction();
 222 }
 223 
 224 class G1AdjustPointersClosure: public HeapRegionClosure {
 225  public:
 226   bool doHeapRegion(HeapRegion* r) {
 227     if (r->is_humongous()) {
 228       if (r->is_starts_humongous()) {
 229         // We must adjust the pointers on the single H object.
 230         oop obj = oop(r->bottom());
 231         // point all the oops to the new location
 232         MarkSweep::adjust_pointers(obj);
 233       }
 234     } else if (!r->is_pinned()) {
 235       // This really ought to be "as_CompactibleSpace"...
 236       r->adjust_pointers();
 237     }
 238     return false;
 239   }
 240 };
 241 
 242 void G1MarkSweep::mark_sweep_phase3() {
 243   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 244 
 245   // Adjust the pointers to reflect the new locations
 246   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
 247 
 248   // Need cleared claim bits for the roots processing
 249   ClassLoaderDataGraph::clear_claimed_marks();
 250 
 251   CodeBlobToOopClosure adjust_code_closure(&GenMarkSweep::adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
 252   {
 253     G1RootProcessor root_processor(g1h, 1);
 254     root_processor.process_all_roots(&GenMarkSweep::adjust_pointer_closure,
 255                                      &GenMarkSweep::adjust_cld_closure,
 256                                      &adjust_code_closure);
 257   }
 258 
 259   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 260   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 261 
 262   // Now adjust pointers in remaining weak roots.  (All of which should
 263   // have been cleared if they pointed to non-surviving objects.)
 264   JNIHandles::weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 265 
 266   if (G1StringDedup::is_enabled()) {
 267     G1StringDedup::oops_do(&GenMarkSweep::adjust_pointer_closure);
 268   }
 269 
 270   GenMarkSweep::adjust_marks();
 271 
 272   G1AdjustPointersClosure blk;
 273   g1h->heap_region_iterate(&blk);
 274 }
 275 
 276 class G1SpaceCompactClosure: public HeapRegionClosure {
 277 public:
 278   G1SpaceCompactClosure() {}
 279 
 280   bool doHeapRegion(HeapRegion* hr) {
 281     if (hr->is_humongous()) {
 282       if (hr->is_starts_humongous()) {
 283         oop obj = oop(hr->bottom());
 284         if (obj->is_gc_marked()) {
 285           obj->init_mark();
 286         } else {
 287           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 288         }
 289       }
 290       hr->reset_during_compaction();
 291     } else if (!hr->is_pinned()) {
 292       hr->compact();
 293     }
 294     return false;
 295   }
 296 };
 297 
 298 void G1MarkSweep::mark_sweep_phase4() {
 299   // All pointers are now adjusted, move objects accordingly
 300 
 301   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 302   // in the same order in phase2, phase3 and phase4. We don't quite do that
 303   // here (code and comment not fixed for perm removal), so we tell the validate code
 304   // to use a higher index (saved from phase2) when verifying perm_gen.
 305   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 306 
 307   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", gc_timer());
 308 
 309   G1SpaceCompactClosure blk;
 310   g1h->heap_region_iterate(&blk);
 311 
 312 }
 313 
 314 void G1MarkSweep::prepare_compaction_work(G1PrepareCompactClosure* blk) {
 315   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 316   g1h->heap_region_iterate(blk);
 317   blk->update_sets();
 318 }
 319 
 320 void G1PrepareCompactClosure::free_humongous_region(HeapRegion* hr) {
 321   HeapWord* end = hr->end();
 322   FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 323 
 324   hr->set_containing_set(NULL);
 325   _humongous_regions_removed++;
 326 
 327   _g1h->free_humongous_region(hr, &dummy_free_list, false /* skip_remset */);
 328   prepare_for_compaction(hr, end);
 329   dummy_free_list.remove_all();
 330 }
 331 
 332 void G1PrepareCompactClosure::prepare_for_compaction(HeapRegion* hr, HeapWord* end) {
 333   // If this is the first live region that we came across which we can compact,
 334   // initialize the CompactPoint.
 335   if (!is_cp_initialized()) {
 336     _cp.space = hr;
 337     _cp.threshold = hr->initialize_threshold();
 338   }
 339   prepare_for_compaction_work(&_cp, hr, end);
 340 }
 341 
 342 void G1PrepareCompactClosure::prepare_for_compaction_work(CompactPoint* cp,
 343                                                           HeapRegion* hr,
 344                                                           HeapWord* end) {
 345   hr->prepare_for_compaction(cp);
 346   // Also clear the part of the card table that will be unused after
 347   // compaction.
 348   _mrbs->clear(MemRegion(hr->compaction_top(), end));
 349 }
 350 
 351 void G1PrepareCompactClosure::update_sets() {
 352   // We'll recalculate total used bytes and recreate the free list
 353   // at the end of the GC, so no point in updating those values here.
 354   _g1h->remove_from_old_sets(0, _humongous_regions_removed);
 355 }
 356 
 357 bool G1PrepareCompactClosure::doHeapRegion(HeapRegion* hr) {
 358   if (hr->is_humongous()) {
 359     oop obj = oop(hr->humongous_start_region()->bottom());
 360     if (hr->is_starts_humongous() && obj->is_gc_marked()) {
 361       obj->forward_to(obj);
 362     }
 363     if (!obj->is_gc_marked()) {
 364       free_humongous_region(hr);
 365     }
 366   } else if (!hr->is_pinned()) {
 367     prepare_for_compaction(hr, hr->end());
 368   }
 369   return false;
 370 }