1 /*
   2  * Copyright (c) 2001, 2014, 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/atomic.inline.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   SharedHeap* sh = SharedHeap::heap();
  64 #ifdef ASSERT
  65   if (sh->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::_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   // Don't add any more derived pointers during phase3
  94   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
  95 
  96   mark_sweep_phase3();
  97 
  98   mark_sweep_phase4();
  99 
 100   GenMarkSweep::restore_marks();
 101   BiasedLocking::restore_marks();
 102   GenMarkSweep::deallocate_stacks();
 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   CodeCache::gc_epilogue();
 110   JvmtiExport::gc_epilogue();
 111 
 112   // refs processing: clean slate
 113   GenMarkSweep::_ref_processor = NULL;
 114 }
 115 
 116 
 117 void G1MarkSweep::allocate_stacks() {
 118   GenMarkSweep::_preserved_count_max = 0;
 119   GenMarkSweep::_preserved_marks = NULL;
 120   GenMarkSweep::_preserved_count = 0;
 121 }
 122 
 123 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
 124                                     bool clear_all_softrefs) {
 125   // Recursively traverse all live objects and mark them
 126   GCTraceTime tm("phase 1", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 127   GenMarkSweep::trace(" 1");
 128 
 129   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 130 
 131   // Need cleared claim bits for the roots processing
 132   ClassLoaderDataGraph::clear_claimed_marks();
 133 
 134   MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
 135   {
 136     G1RootProcessor root_processor(g1h);
 137     root_processor.process_strong_roots(&GenMarkSweep::follow_root_closure,
 138                                         &GenMarkSweep::follow_cld_closure,
 139                                         &follow_code_closure);
 140   }
 141 
 142   // Process reference objects found during marking
 143   ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 144   assert(rp == g1h->ref_processor_stw(), "Sanity");
 145 
 146   rp->setup_policy(clear_all_softrefs);
 147   const ReferenceProcessorStats& stats =
 148     rp->process_discovered_references(&GenMarkSweep::is_alive,
 149                                       &GenMarkSweep::keep_alive,
 150                                       &GenMarkSweep::follow_stack_closure,
 151                                       NULL,
 152                                       gc_timer(),
 153                                       gc_tracer()->gc_id());
 154   gc_tracer()->report_gc_reference_stats(stats);
 155 
 156 
 157   // This is the point where the entire marking should have completed.
 158   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 159 
 160   // Unload classes and purge the SystemDictionary.
 161   bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 162 
 163   // Unload nmethods.
 164   CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
 165 
 166   // Prune dead klasses from subklass/sibling/implementor lists.
 167   Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
 168 
 169   // Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
 170   G1CollectedHeap::heap()->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
 171 
 172   if (VerifyDuringGC) {
 173     HandleMark hm;  // handle scope
 174     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
 175     Universe::heap()->prepare_for_verify();
 176     // Note: we can verify only the heap here. When an object is
 177     // marked, the previous value of the mark word (including
 178     // identity hash values, ages, etc) is preserved, and the mark
 179     // word is set to markOop::marked_value - effectively removing
 180     // any hash values from the mark word. These hash values are
 181     // used when verifying the dictionaries and so removing them
 182     // from the mark word can make verification of the dictionaries
 183     // fail. At the end of the GC, the original mark word values
 184     // (including hash values) are restored to the appropriate
 185     // objects.
 186     if (!VerifySilently) {
 187       gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
 188     }
 189     Universe::heap()->verify(VerifySilently, VerifyOption_G1UseMarkWord);
 190     if (!VerifySilently) {
 191       gclog_or_tty->print_cr("]");
 192     }
 193   }
 194 
 195   gc_tracer()->report_object_count_after_gc(&GenMarkSweep::is_alive);
 196 }
 197 
 198 
 199 void G1MarkSweep::mark_sweep_phase2() {
 200   // Now all live objects are marked, compute the new object addresses.
 201 
 202   // It is not required that we traverse spaces in the same order in
 203   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 204   // tracking expects us to do so. See comment under phase4.
 205 
 206   GCTraceTime tm("phase 2", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 207   GenMarkSweep::trace("2");
 208 
 209   prepare_compaction();
 210 }
 211 
 212 class G1AdjustPointersClosure: public HeapRegionClosure {
 213  public:
 214   bool doHeapRegion(HeapRegion* r) {
 215     if (r->is_humongous()) {
 216       if (r->is_starts_humongous()) {
 217         // We must adjust the pointers on the single H object.
 218         oop obj = oop(r->bottom());
 219         // point all the oops to the new location
 220         obj->adjust_pointers();
 221       }
 222     } else {
 223       // This really ought to be "as_CompactibleSpace"...
 224       r->adjust_pointers();
 225     }
 226     return false;
 227   }
 228 };
 229 
 230 class G1AlwaysTrueClosure: public BoolObjectClosure {
 231 public:
 232   bool do_object_b(oop p) { return true; }
 233 };
 234 static G1AlwaysTrueClosure always_true;
 235 
 236 void G1MarkSweep::mark_sweep_phase3() {
 237   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 238 
 239   // Adjust the pointers to reflect the new locations
 240   GCTraceTime tm("phase 3", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 241   GenMarkSweep::trace("3");
 242 
 243   // Need cleared claim bits for the roots processing
 244   ClassLoaderDataGraph::clear_claimed_marks();
 245 
 246   CodeBlobToOopClosure adjust_code_closure(&GenMarkSweep::adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
 247   {
 248     G1RootProcessor root_processor(g1h);
 249     root_processor.process_all_roots(&GenMarkSweep::adjust_pointer_closure,
 250                                      &GenMarkSweep::adjust_cld_closure,
 251                                      &adjust_code_closure);
 252   }
 253 
 254   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 255   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 256 
 257   // Now adjust pointers in remaining weak roots.  (All of which should
 258   // have been cleared if they pointed to non-surviving objects.)
 259   JNIHandles::weak_oops_do(&always_true, &GenMarkSweep::adjust_pointer_closure);
 260 
 261   if (G1StringDedup::is_enabled()) {
 262     G1StringDedup::oops_do(&GenMarkSweep::adjust_pointer_closure);
 263   }
 264 
 265   GenMarkSweep::adjust_marks();
 266 
 267   G1AdjustPointersClosure blk;
 268   g1h->heap_region_iterate(&blk);
 269 }
 270 
 271 class G1SpaceCompactClosure: public HeapRegionClosure {
 272 public:
 273   G1SpaceCompactClosure() {}
 274 
 275   bool doHeapRegion(HeapRegion* hr) {
 276     if (hr->is_humongous()) {
 277       if (hr->is_starts_humongous()) {
 278         oop obj = oop(hr->bottom());
 279         if (obj->is_gc_marked()) {
 280           obj->init_mark();
 281         } else {
 282           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 283         }
 284         hr->reset_during_compaction();
 285       }
 286     } else {
 287       hr->compact();
 288     }
 289     return false;
 290   }
 291 };
 292 
 293 void G1MarkSweep::mark_sweep_phase4() {
 294   // All pointers are now adjusted, move objects accordingly
 295 
 296   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 297   // in the same order in phase2, phase3 and phase4. We don't quite do that
 298   // here (code and comment not fixed for perm removal), so we tell the validate code
 299   // to use a higher index (saved from phase2) when verifying perm_gen.
 300   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 301 
 302   GCTraceTime tm("phase 4", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
 303   GenMarkSweep::trace("4");
 304 
 305   G1SpaceCompactClosure blk;
 306   g1h->heap_region_iterate(&blk);
 307 
 308 }
 309 
 310 void G1MarkSweep::prepare_compaction_work(G1PrepareCompactClosure* blk) {
 311   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 312   g1h->heap_region_iterate(blk);
 313   blk->update_sets();
 314 }
 315 
 316 void G1PrepareCompactClosure::free_humongous_region(HeapRegion* hr) {
 317   HeapWord* end = hr->end();
 318   FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 319 
 320   assert(hr->is_starts_humongous(),
 321          "Only the start of a humongous region should be freed.");
 322 
 323   hr->set_containing_set(NULL);
 324   _humongous_regions_removed.increment(1u, hr->capacity());
 325 
 326   _g1h->free_humongous_region(hr, &dummy_free_list, false /* par */);
 327   prepare_for_compaction(hr, end);
 328   dummy_free_list.remove_all();
 329 }
 330 
 331 void G1PrepareCompactClosure::prepare_for_compaction(HeapRegion* hr, HeapWord* end) {
 332   // If this is the first live region that we came across which we can compact,
 333   // initialize the CompactPoint.
 334   if (!is_cp_initialized()) {
 335     _cp.space = hr;
 336     _cp.threshold = hr->initialize_threshold();
 337   }
 338   prepare_for_compaction_work(&_cp, hr, end);
 339 }
 340 
 341 void G1PrepareCompactClosure::prepare_for_compaction_work(CompactPoint* cp,
 342                                                           HeapRegion* hr,
 343                                                           HeapWord* end) {
 344   hr->prepare_for_compaction(cp);
 345   // Also clear the part of the card table that will be unused after
 346   // compaction.
 347   _mrbs->clear(MemRegion(hr->compaction_top(), end));
 348 }
 349 
 350 void G1PrepareCompactClosure::update_sets() {
 351   // We'll recalculate total used bytes and recreate the free list
 352   // at the end of the GC, so no point in updating those values here.
 353   HeapRegionSetCount empty_set;
 354   _g1h->remove_from_old_sets(empty_set, _humongous_regions_removed);
 355 }
 356 
 357 bool G1PrepareCompactClosure::doHeapRegion(HeapRegion* hr) {
 358   if (hr->is_humongous()) {
 359     if (hr->is_starts_humongous()) {
 360       oop obj = oop(hr->bottom());
 361       if (obj->is_gc_marked()) {
 362         obj->forward_to(obj);
 363       } else  {
 364         free_humongous_region(hr);
 365       }
 366     } else {
 367       assert(hr->is_continues_humongous(), "Invalid humongous.");
 368     }
 369   } else {
 370     prepare_for_compaction(hr, hr->end());
 371   }
 372   return false;
 373 }