1 /*
   2  * Copyright (c) 2001, 2012, 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 "memory/gcLocker.hpp"
  35 #include "memory/genCollectedHeap.hpp"
  36 #include "memory/modRefBarrierSet.hpp"
  37 #include "memory/referencePolicy.hpp"
  38 #include "memory/space.hpp"
  39 #include "oops/instanceRefKlass.hpp"
  40 #include "oops/oop.inline.hpp"
  41 #include "prims/jvmtiExport.hpp"
  42 #include "runtime/aprofiler.hpp"
  43 #include "runtime/biasedLocking.hpp"
  44 #include "runtime/fprofiler.hpp"
  45 #include "runtime/synchronizer.hpp"
  46 #include "runtime/thread.hpp"
  47 #include "runtime/vmThread.hpp"
  48 #include "utilities/copy.hpp"
  49 #include "utilities/events.hpp"
  50 
  51 class HeapRegion;
  52 
  53 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
  54                                       bool clear_all_softrefs) {
  55   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  56 
  57   SharedHeap* sh = SharedHeap::heap();
  58 #ifdef ASSERT
  59   if (sh->collector_policy()->should_clear_all_soft_refs()) {
  60     assert(clear_all_softrefs, "Policy should have been checked earler");
  61   }
  62 #endif
  63   // hook up weak ref data so it can be used during Mark-Sweep
  64   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  65   assert(rp != NULL, "should be non-NULL");
  66   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
  67 
  68   GenMarkSweep::_ref_processor = rp;
  69   rp->setup_policy(clear_all_softrefs);
  70 
  71   // When collecting the permanent generation Method*s may be moving,
  72   // so we either have to flush all bcp data or convert it into bci.
  73   CodeCache::gc_prologue();
  74   Threads::gc_prologue();
  75 
  76   bool marked_for_unloading = false;
  77 
  78   allocate_stacks();
  79 
  80   // We should save the marks of the currently locked biased monitors.
  81   // The marking doesn't preserve the marks of biased objects.
  82   BiasedLocking::preserve_marks();
  83 
  84   mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
  85 
  86   mark_sweep_phase2();
  87 
  88   // Don't add any more derived pointers during phase3
  89   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
  90 
  91   mark_sweep_phase3();
  92 
  93   mark_sweep_phase4();
  94 
  95   GenMarkSweep::restore_marks();
  96   BiasedLocking::restore_marks();
  97   GenMarkSweep::deallocate_stacks();
  98 
  99   // "free at last gc" is calculated from these.
 100   // CHF: cheating for now!!!
 101   //  Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
 102   //  Universe::set_heap_used_at_last_gc(Universe::heap()->used());
 103 
 104   Threads::gc_epilogue();
 105   CodeCache::gc_epilogue();
 106   JvmtiExport::gc_epilogue();
 107 
 108   // refs processing: clean slate
 109   GenMarkSweep::_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   TraceTime tm("phase 1", G1Log::fine() && Verbose, true, gclog_or_tty);
 123   GenMarkSweep::trace(" 1");
 124 
 125   SharedHeap* sh = SharedHeap::heap();
 126 
 127   // Need cleared claim bits for the strong roots processing
 128   ClassLoaderDataGraph::clear_claimed_marks();
 129 
 130   sh->process_strong_roots(true,  // activate StrongRootsScope
 131                            false, // not scavenging.
 132                            SharedHeap::SO_SystemClasses,
 133                            &GenMarkSweep::follow_root_closure,
 134                            &GenMarkSweep::follow_code_root_closure,
 135                            &GenMarkSweep::follow_klass_closure);
 136 
 137   // Process reference objects found during marking
 138   ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 139   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity");
 140 
 141   rp->setup_policy(clear_all_softrefs);
 142   rp->process_discovered_references(&GenMarkSweep::is_alive,
 143                                     &GenMarkSweep::keep_alive,
 144                                     &GenMarkSweep::follow_stack_closure,
 145                                     NULL);
 146 
 147 
 148   // This is the point where the entire marking should have completed.
 149   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 150 
 151   // Unload classes and purge the SystemDictionary.
 152   bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 153 
 154   // Unload nmethods.
 155   CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
 156 
 157   // Prune dead klasses from subklass/sibling/implementor lists.
 158   Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
 159 
 160   // Delete entries for dead interned strings.
 161   StringTable::unlink(&GenMarkSweep::is_alive);
 162 
 163   // Clean up unreferenced symbols in symbol table.
 164   SymbolTable::unlink();
 165 
 166   if (VerifyDuringGC) {
 167     HandleMark hm;  // handle scope
 168     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
 169     Universe::heap()->prepare_for_verify();
 170     // Note: we can verify only the heap here. When an object is
 171     // marked, the previous value of the mark word (including
 172     // identity hash values, ages, etc) is preserved, and the mark
 173     // word is set to markOop::marked_value - effectively removing
 174     // any hash values from the mark word. These hash values are
 175     // used when verifying the dictionaries and so removing them
 176     // from the mark word can make verification of the dictionaries
 177     // fail. At the end of the GC, the orginal mark word values
 178     // (including hash values) are restored to the appropriate
 179     // objects.
 180     if (!VerifySilently) {
 181       gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
 182     }
 183     Universe::heap()->verify(VerifySilently, VerifyOption_G1UseMarkWord);
 184     if (!VerifySilently) {
 185       gclog_or_tty->print_cr("]");
 186     }
 187   }
 188 }
 189 
 190 class G1PrepareCompactClosure: public HeapRegionClosure {
 191   G1CollectedHeap* _g1h;
 192   ModRefBarrierSet* _mrbs;
 193   CompactPoint _cp;
 194   HumongousRegionSet _humongous_proxy_set;
 195 
 196   void free_humongous_region(HeapRegion* hr) {
 197     HeapWord* end = hr->end();
 198     size_t dummy_pre_used;
 199     FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 200 
 201     assert(hr->startsHumongous(),
 202            "Only the start of a humongous region should be freed.");
 203     _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list,
 204                                 &_humongous_proxy_set, false /* par */);
 205     hr->prepare_for_compaction(&_cp);
 206     // Also clear the part of the card table that will be unused after
 207     // compaction.
 208     _mrbs->clear(MemRegion(hr->compaction_top(), end));
 209     dummy_free_list.remove_all();
 210   }
 211 
 212 public:
 213   G1PrepareCompactClosure(CompactibleSpace* cs)
 214   : _g1h(G1CollectedHeap::heap()),
 215     _mrbs(G1CollectedHeap::heap()->mr_bs()),
 216     _cp(NULL, cs, cs->initialize_threshold()),
 217     _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { }
 218 
 219   void update_sets() {
 220     // We'll recalculate total used bytes and recreate the free list
 221     // at the end of the GC, so no point in updating those values here.
 222     _g1h->update_sets_after_freeing_regions(0, /* pre_used */
 223                                             NULL, /* free_list */
 224                                             NULL, /* old_proxy_set */
 225                                             &_humongous_proxy_set,
 226                                             false /* par */);
 227   }
 228 
 229   bool doHeapRegion(HeapRegion* hr) {
 230     if (hr->isHumongous()) {
 231       if (hr->startsHumongous()) {
 232         oop obj = oop(hr->bottom());
 233         if (obj->is_gc_marked()) {
 234           obj->forward_to(obj);
 235         } else  {
 236           free_humongous_region(hr);
 237         }
 238       } else {
 239         assert(hr->continuesHumongous(), "Invalid humongous.");
 240       }
 241     } else {
 242       hr->prepare_for_compaction(&_cp);
 243       // Also clear the part of the card table that will be unused after
 244       // compaction.
 245       _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
 246     }
 247     return false;
 248   }
 249 };
 250 
 251 void G1MarkSweep::mark_sweep_phase2() {
 252   // Now all live objects are marked, compute the new object addresses.
 253 
 254   // It is not required that we traverse spaces in the same order in
 255   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 256   // tracking expects us to do so. See comment under phase4.
 257 
 258   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 259 
 260   TraceTime tm("phase 2", G1Log::fine() && Verbose, true, gclog_or_tty);
 261   GenMarkSweep::trace("2");
 262 
 263   // find the first region
 264   HeapRegion* r = g1h->region_at(0);
 265   CompactibleSpace* sp = r;
 266   if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
 267     sp = r->next_compaction_space();
 268   }
 269 
 270   G1PrepareCompactClosure blk(sp);
 271   g1h->heap_region_iterate(&blk);
 272   blk.update_sets();
 273 }
 274 
 275 class G1AdjustPointersClosure: public HeapRegionClosure {
 276  public:
 277   bool doHeapRegion(HeapRegion* r) {
 278     if (r->isHumongous()) {
 279       if (r->startsHumongous()) {
 280         // We must adjust the pointers on the single H object.
 281         oop obj = oop(r->bottom());
 282         // point all the oops to the new location
 283         obj->adjust_pointers();
 284       }
 285     } else {
 286       // This really ought to be "as_CompactibleSpace"...
 287       r->adjust_pointers();
 288     }
 289     return false;
 290   }
 291 };
 292 
 293 void G1MarkSweep::mark_sweep_phase3() {
 294   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 295 
 296   // Adjust the pointers to reflect the new locations
 297   TraceTime tm("phase 3", G1Log::fine() && Verbose, true, gclog_or_tty);
 298   GenMarkSweep::trace("3");
 299 
 300   SharedHeap* sh = SharedHeap::heap();
 301 
 302   // Need cleared claim bits for the strong roots processing
 303   ClassLoaderDataGraph::clear_claimed_marks();
 304 
 305   sh->process_strong_roots(true,  // activate StrongRootsScope
 306                            false, // not scavenging.
 307                            SharedHeap::SO_AllClasses,
 308                            &GenMarkSweep::adjust_pointer_closure,
 309                            NULL,  // do not touch code cache here
 310                            &GenMarkSweep::adjust_klass_closure);
 311 
 312   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 313   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
 314 
 315   // Now adjust pointers in remaining weak roots.  (All of which should
 316   // have been cleared if they pointed to non-surviving objects.)
 317   g1h->g1_process_weak_roots(&GenMarkSweep::adjust_pointer_closure);
 318 
 319   GenMarkSweep::adjust_marks();
 320 
 321   G1AdjustPointersClosure blk;
 322   g1h->heap_region_iterate(&blk);
 323 }
 324 
 325 class G1SpaceCompactClosure: public HeapRegionClosure {
 326 public:
 327   G1SpaceCompactClosure() {}
 328 
 329   bool doHeapRegion(HeapRegion* hr) {
 330     if (hr->isHumongous()) {
 331       if (hr->startsHumongous()) {
 332         oop obj = oop(hr->bottom());
 333         if (obj->is_gc_marked()) {
 334           obj->init_mark();
 335         } else {
 336           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 337         }
 338         hr->reset_during_compaction();
 339       }
 340     } else {
 341       hr->compact();
 342     }
 343     return false;
 344   }
 345 };
 346 
 347 void G1MarkSweep::mark_sweep_phase4() {
 348   // All pointers are now adjusted, move objects accordingly
 349 
 350   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 351   // in the same order in phase2, phase3 and phase4. We don't quite do that
 352   // here (code and comment not fixed for perm removal), so we tell the validate code
 353   // to use a higher index (saved from phase2) when verifying perm_gen.
 354   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 355 
 356   TraceTime tm("phase 4", G1Log::fine() && Verbose, true, gclog_or_tty);
 357   GenMarkSweep::trace("4");
 358 
 359   G1SpaceCompactClosure blk;
 360   g1h->heap_region_iterate(&blk);
 361 
 362 }