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/heapMonitoring.hpp"
  52 #include "runtime/synchronizer.hpp"
  53 #include "runtime/thread.hpp"
  54 #include "runtime/vmThread.hpp"
  55 #include "utilities/copy.hpp"
  56 #include "utilities/events.hpp"
  57 
  58 class HeapRegion;
  59 
  60 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
  61                                       bool clear_all_softrefs) {
  62   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  63 
  64 #ifdef ASSERT
  65   if (G1CollectedHeap::heap()->collector_policy()->should_clear_all_soft_refs()) {
  66     assert(clear_all_softrefs, "Policy should have been checked earler");
  67   }
  68 #endif
  69   // hook up weak ref data so it can be used during Mark-Sweep
  70   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  71   assert(rp != NULL, "should be non-NULL");
  72   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
  73 
  74   GenMarkSweep::set_ref_processor(rp);
  75   rp->setup_policy(clear_all_softrefs);
  76 
  77   // When collecting the permanent generation Method*s may be moving,
  78   // so we either have to flush all bcp data or convert it into bci.
  79   CodeCache::gc_prologue();
  80 
  81   bool marked_for_unloading = false;
  82 
  83   allocate_stacks();
  84 
  85   // We should save the marks of the currently locked biased monitors.
  86   // The marking doesn't preserve the marks of biased objects.
  87   BiasedLocking::preserve_marks();
  88 
  89   mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
  90 
  91   mark_sweep_phase2();
  92 
  93 #if defined(COMPILER2) || INCLUDE_JVMCI
  94   // Don't add any more derived pointers during phase3
  95   DerivedPointerTable::set_active(false);
  96 #endif
  97 
  98   mark_sweep_phase3();
  99 
 100   mark_sweep_phase4();
 101 
 102   GenMarkSweep::restore_marks();
 103   BiasedLocking::restore_marks();
 104   GenMarkSweep::deallocate_stacks();
 105 
 106   CodeCache::gc_epilogue();
 107   JvmtiExport::gc_epilogue();
 108 
 109   // refs processing: clean slate
 110   GenMarkSweep::set_ref_processor(NULL);
 111 }
 112 
 113 
 114 void G1MarkSweep::allocate_stacks() {
 115   GenMarkSweep::_preserved_count_max = 0;
 116   GenMarkSweep::_preserved_marks = NULL;
 117   GenMarkSweep::_preserved_count = 0;
 118 }
 119 
 120 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
 121                                     bool clear_all_softrefs) {
 122   // Recursively traverse all live objects and mark them
 123   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", gc_timer());
 124 
 125   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 126 
 127   // Need cleared claim bits for the roots processing
 128   ClassLoaderDataGraph::clear_claimed_marks();
 129 
 130   MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
 131   {
 132     G1RootProcessor root_processor(g1h, 1);
 133     if (ClassUnloading) {
 134       root_processor.process_strong_roots(&GenMarkSweep::follow_root_closure,
 135                                           &GenMarkSweep::follow_cld_closure,
 136                                           &follow_code_closure);
 137     } else {
 138       root_processor.process_all_roots_no_string_table(
 139                                           &GenMarkSweep::follow_root_closure,
 140                                           &GenMarkSweep::follow_cld_closure,
 141                                           &follow_code_closure);
 142     }
 143   }
 144 
 145   {
 146     GCTraceTime(Debug, gc, phases) trace("Reference Processing", gc_timer());
 147 
 148     // Process reference objects found during marking
 149     ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 150     assert(rp == g1h->ref_processor_stw(), "Sanity");
 151 
 152     rp->setup_policy(clear_all_softrefs);
 153     const ReferenceProcessorStats& stats =
 154         rp->process_discovered_references(&GenMarkSweep::is_alive,
 155                                           &GenMarkSweep::keep_alive,
 156                                           &GenMarkSweep::follow_stack_closure,
 157                                           NULL,
 158                                           gc_timer());
 159     gc_tracer()->report_gc_reference_stats(stats);
 160   }
 161 
 162   // This is the point where the entire marking should have completed.
 163   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 164 
 165   if (ClassUnloading) {
 166     GCTraceTime(Debug, gc, phases) trace("Class Unloading", gc_timer());
 167 
 168     // Unload classes and purge the SystemDictionary.
 169     bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive, gc_timer());
 170 
 171     g1h->complete_cleaning(&GenMarkSweep::is_alive, purged_class);
 172   } else {
 173     GCTraceTime(Debug, gc, phases) trace("Cleanup", gc_timer());
 174     g1h->partial_cleaning(&GenMarkSweep::is_alive, true, true, G1StringDedup::is_enabled());
 175   }
 176 
 177   if (VerifyDuringGC) {
 178     HandleMark hm;  // handle scope
 179 #if defined(COMPILER2) || INCLUDE_JVMCI
 180     DerivedPointerTableDeactivate dpt_deact;
 181 #endif
 182     g1h->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 original mark word values
 191     // (including hash values) are restored to the appropriate
 192     // objects.
 193     GCTraceTime(Info, gc, verify)("During GC (full)");
 194     g1h->verify(VerifyOption_G1UseMarkWord);
 195   }
 196 
 197   gc_tracer()->report_object_count_after_gc(&GenMarkSweep::is_alive);
 198 }
 199 
 200 
 201 void G1MarkSweep::mark_sweep_phase2() {
 202   // Now all live objects are marked, compute the new object addresses.
 203 
 204   // It is not required that we traverse spaces in the same order in
 205   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 206   // tracking expects us to do so. See comment under phase4.
 207 
 208   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", gc_timer());
 209 
 210   prepare_compaction();
 211 }
 212 
 213 class G1AdjustPointersClosure: public HeapRegionClosure {
 214  public:
 215   bool doHeapRegion(HeapRegion* r) {
 216     if (r->is_humongous()) {
 217       if (r->is_starts_humongous()) {
 218         // We must adjust the pointers on the single H object.
 219         oop obj = oop(r->bottom());
 220         // point all the oops to the new location
 221         MarkSweep::adjust_pointers(obj);
 222       }
 223     } else if (!r->is_pinned()) {
 224       // This really ought to be "as_CompactibleSpace"...
 225       r->adjust_pointers();
 226     }
 227     return false;
 228   }
 229 };
 230 
 231 void G1MarkSweep::mark_sweep_phase3() {
 232   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 233 
 234   // Adjust the pointers to reflect the new locations
 235   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
 236 
 237   // Need cleared claim bits for the roots processing
 238   ClassLoaderDataGraph::clear_claimed_marks();
 239 
 240   CodeBlobToOopClosure adjust_code_closure(&GenMarkSweep::adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
 241   {
 242     G1RootProcessor root_processor(g1h, 1);
 243     root_processor.process_all_roots(&GenMarkSweep::adjust_pointer_closure,
 244                                      &GenMarkSweep::adjust_cld_closure,
 245                                      &adjust_code_closure);
 246   }
 247 
 248   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 249   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 250 
 251   // Now adjust pointers in remaining weak roots.  (All of which should
 252   // have been cleared if they pointed to non-surviving objects.)
 253   JNIHandles::weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 254   HeapMonitoring::weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 255 
 256   if (G1StringDedup::is_enabled()) {
 257     G1StringDedup::oops_do(&GenMarkSweep::adjust_pointer_closure);
 258   }
 259 
 260   GenMarkSweep::adjust_marks();
 261 
 262   G1AdjustPointersClosure blk;
 263   g1h->heap_region_iterate(&blk);
 264 }
 265 
 266 class G1SpaceCompactClosure: public HeapRegionClosure {
 267 public:
 268   G1SpaceCompactClosure() {}
 269 
 270   bool doHeapRegion(HeapRegion* hr) {
 271     if (hr->is_humongous()) {
 272       if (hr->is_starts_humongous()) {
 273         oop obj = oop(hr->bottom());
 274         if (obj->is_gc_marked()) {
 275           obj->init_mark();
 276         } else {
 277           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 278         }
 279       }
 280       hr->reset_during_compaction();
 281     } else if (!hr->is_pinned()) {
 282       hr->compact();
 283     }
 284     return false;
 285   }
 286 };
 287 
 288 void G1MarkSweep::mark_sweep_phase4() {
 289   // All pointers are now adjusted, move objects accordingly
 290 
 291   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 292   // in the same order in phase2, phase3 and phase4. We don't quite do that
 293   // here (code and comment not fixed for perm removal), so we tell the validate code
 294   // to use a higher index (saved from phase2) when verifying perm_gen.
 295   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 296 
 297   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", gc_timer());
 298 
 299   G1SpaceCompactClosure blk;
 300   g1h->heap_region_iterate(&blk);
 301 
 302 }
 303 
 304 void G1MarkSweep::prepare_compaction_work(G1PrepareCompactClosure* blk) {
 305   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 306   g1h->heap_region_iterate(blk);
 307   blk->update_sets();
 308 }
 309 
 310 void G1PrepareCompactClosure::free_humongous_region(HeapRegion* hr) {
 311   HeapWord* end = hr->end();
 312   FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 313 
 314   hr->set_containing_set(NULL);
 315   _humongous_regions_removed++;
 316 
 317   _g1h->free_humongous_region(hr, &dummy_free_list, false /* skip_remset */);
 318   prepare_for_compaction(hr, end);
 319   dummy_free_list.remove_all();
 320 }
 321 
 322 void G1PrepareCompactClosure::prepare_for_compaction(HeapRegion* hr, HeapWord* end) {
 323   // If this is the first live region that we came across which we can compact,
 324   // initialize the CompactPoint.
 325   if (!is_cp_initialized()) {
 326     _cp.space = hr;
 327     _cp.threshold = hr->initialize_threshold();
 328   }
 329   prepare_for_compaction_work(&_cp, hr, end);
 330 }
 331 
 332 void G1PrepareCompactClosure::prepare_for_compaction_work(CompactPoint* cp,
 333                                                           HeapRegion* hr,
 334                                                           HeapWord* end) {
 335   hr->prepare_for_compaction(cp);
 336   // Also clear the part of the card table that will be unused after
 337   // compaction.
 338   _mrbs->clear(MemRegion(hr->compaction_top(), end));
 339 }
 340 
 341 void G1PrepareCompactClosure::update_sets() {
 342   // We'll recalculate total used bytes and recreate the free list
 343   // at the end of the GC, so no point in updating those values here.
 344   _g1h->remove_from_old_sets(0, _humongous_regions_removed);
 345 }
 346 
 347 bool G1PrepareCompactClosure::doHeapRegion(HeapRegion* hr) {
 348   if (hr->is_humongous()) {
 349     oop obj = oop(hr->humongous_start_region()->bottom());
 350     if (hr->is_starts_humongous() && obj->is_gc_marked()) {
 351       obj->forward_to(obj);
 352     }
 353     if (!obj->is_gc_marked()) {
 354       free_humongous_region(hr);
 355     }
 356   } else if (!hr->is_pinned()) {
 357     prepare_for_compaction(hr, hr->end());
 358   }
 359   return false;
 360 }