1 /*
   2  * Copyright (c) 2001, 2011, 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/g1MarkSweep.hpp"
  33 #include "memory/gcLocker.hpp"
  34 #include "memory/genCollectedHeap.hpp"
  35 #include "memory/modRefBarrierSet.hpp"
  36 #include "memory/referencePolicy.hpp"
  37 #include "memory/space.hpp"
  38 #include "oops/instanceRefKlass.hpp"
  39 #include "oops/oop.inline.hpp"
  40 #include "prims/jvmtiExport.hpp"
  41 #include "runtime/aprofiler.hpp"
  42 #include "runtime/biasedLocking.hpp"
  43 #include "runtime/fprofiler.hpp"
  44 #include "runtime/synchronizer.hpp"
  45 #include "runtime/thread.hpp"
  46 #include "runtime/vmThread.hpp"
  47 #include "utilities/copy.hpp"
  48 #include "utilities/events.hpp"
  49 
  50 class HeapRegion;
  51 
  52 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
  53                                       bool clear_all_softrefs) {
  54   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  55 
  56   SharedHeap* sh = SharedHeap::heap();
  57 #ifdef ASSERT
  58   if (sh->collector_policy()->should_clear_all_soft_refs()) {
  59     assert(clear_all_softrefs, "Policy should have been checked earler");
  60   }
  61 #endif
  62   // hook up weak ref data so it can be used during Mark-Sweep
  63   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  64   assert(rp != NULL, "should be non-NULL");
  65   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
  66 
  67   GenMarkSweep::_ref_processor = rp;
  68   rp->setup_policy(clear_all_softrefs);
  69 
  70   // When collecting the permanent generation methodOops may be moving,
  71   // so we either have to flush all bcp data or convert it into bci.
  72   CodeCache::gc_prologue();
  73   Threads::gc_prologue();
  74 
  75   // Increment the invocation count for the permanent generation, since it is
  76   // implicitly collected whenever we do a full mark sweep collection.
  77   sh->perm_gen()->stat_record()->invocations++;
  78 
  79   bool marked_for_unloading = false;
  80 
  81   allocate_stacks();
  82 
  83   // We should save the marks of the currently locked biased monitors.
  84   // The marking doesn't preserve the marks of biased objects.
  85   BiasedLocking::preserve_marks();
  86 
  87   mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
  88 
  89   mark_sweep_phase2();
  90 
  91   // Don't add any more derived pointers during phase3
  92   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
  93 
  94   mark_sweep_phase3();
  95 
  96   mark_sweep_phase4();
  97 
  98   GenMarkSweep::restore_marks();
  99   BiasedLocking::restore_marks();
 100   GenMarkSweep::deallocate_stacks();
 101 
 102   // We must invalidate the perm-gen rs, so that it gets rebuilt.
 103   GenRemSet* rs = sh->rem_set();
 104   rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
 105 
 106   // "free at last gc" is calculated from these.
 107   // CHF: cheating for now!!!
 108   //  Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
 109   //  Universe::set_heap_used_at_last_gc(Universe::heap()->used());
 110 
 111   Threads::gc_epilogue();
 112   CodeCache::gc_epilogue();
 113   JvmtiExport::gc_epilogue();
 114 
 115   // refs processing: clean slate
 116   GenMarkSweep::_ref_processor = NULL;
 117 }
 118 
 119 
 120 void G1MarkSweep::allocate_stacks() {
 121   GenMarkSweep::_preserved_count_max = 0;
 122   GenMarkSweep::_preserved_marks = NULL;
 123   GenMarkSweep::_preserved_count = 0;
 124 }
 125 
 126 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
 127                                     bool clear_all_softrefs) {
 128   // Recursively traverse all live objects and mark them
 129   EventMark m("1 mark object");
 130   TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
 131   GenMarkSweep::trace(" 1");
 132 
 133   SharedHeap* sh = SharedHeap::heap();
 134 
 135   sh->process_strong_roots(true,  // activeate StrongRootsScope
 136                            true,  // Collecting permanent generation.
 137                            SharedHeap::SO_SystemClasses,
 138                            &GenMarkSweep::follow_root_closure,
 139                            &GenMarkSweep::follow_code_root_closure,
 140                            &GenMarkSweep::follow_root_closure);
 141 
 142   // Process reference objects found during marking
 143   ReferenceProcessor* rp = GenMarkSweep::ref_processor();
 144   assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity");
 145 
 146   rp->setup_policy(clear_all_softrefs);
 147   rp->process_discovered_references(&GenMarkSweep::is_alive,
 148                                     &GenMarkSweep::keep_alive,
 149                                     &GenMarkSweep::follow_stack_closure,
 150                                     NULL);
 151 
 152   // Follow system dictionary roots and unload classes
 153   bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 154   assert(GenMarkSweep::_marking_stack.is_empty(),
 155          "stack should be empty by now");
 156 
 157   // Follow code cache roots (has to be done after system dictionary,
 158   // assumes all live klasses are marked)
 159   CodeCache::do_unloading(&GenMarkSweep::is_alive,
 160                                    &GenMarkSweep::keep_alive,
 161                                    purged_class);
 162   GenMarkSweep::follow_stack();
 163 
 164   // Update subklass/sibling/implementor links of live klasses
 165   GenMarkSweep::follow_weak_klass_links();
 166   assert(GenMarkSweep::_marking_stack.is_empty(),
 167          "stack should be empty by now");
 168 
 169   // Visit memoized MDO's and clear any unmarked weak refs
 170   GenMarkSweep::follow_mdo_weak_refs();
 171   assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");
 172 
 173   // Visit interned string tables and delete unmarked oops
 174   StringTable::unlink(&GenMarkSweep::is_alive);
 175   // Clean up unreferenced symbols in symbol table.
 176   SymbolTable::unlink();
 177 
 178   assert(GenMarkSweep::_marking_stack.is_empty(),
 179          "stack should be empty by now");
 180 
 181   if (VerifyDuringGC) {
 182     HandleMark hm;  // handle scope
 183     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
 184     gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
 185     Universe::heap()->prepare_for_verify();
 186     // Note: we can verify only the heap here. When an object is
 187     // marked, the previous value of the mark word (including
 188     // identity hash values, ages, etc) is preserved, and the mark
 189     // word is set to markOop::marked_value - effectively removing
 190     // any hash values from the mark word. These hash values are
 191     // used when verifying the dictionaries and so removing them
 192     // from the mark word can make verification of the dictionaries
 193     // fail. At the end of the GC, the orginal mark word values
 194     // (including hash values) are restored to the appropriate
 195     // objects.
 196     Universe::heap()->verify(/* allow dirty */ true,
 197                              /* silent      */ false,
 198                              /* option      */ VerifyOption_G1UseMarkWord);
 199 
 200     G1CollectedHeap* g1h = G1CollectedHeap::heap();
 201     gclog_or_tty->print_cr("]");
 202   }
 203 }
 204 
 205 class G1PrepareCompactClosure: public HeapRegionClosure {
 206   G1CollectedHeap* _g1h;
 207   ModRefBarrierSet* _mrbs;
 208   CompactPoint _cp;
 209   HumongousRegionSet _humongous_proxy_set;
 210 
 211   void free_humongous_region(HeapRegion* hr) {
 212     HeapWord* end = hr->end();
 213     size_t dummy_pre_used;
 214     FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 215 
 216     assert(hr->startsHumongous(),
 217            "Only the start of a humongous region should be freed.");
 218     _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list,
 219                                 &_humongous_proxy_set, false /* par */);
 220     hr->prepare_for_compaction(&_cp);
 221     // Also clear the part of the card table that will be unused after
 222     // compaction.
 223     _mrbs->clear(MemRegion(hr->compaction_top(), end));
 224     dummy_free_list.remove_all();
 225   }
 226 
 227 public:
 228   G1PrepareCompactClosure(CompactibleSpace* cs)
 229   : _g1h(G1CollectedHeap::heap()),
 230     _mrbs(G1CollectedHeap::heap()->mr_bs()),
 231     _cp(NULL, cs, cs->initialize_threshold()),
 232     _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { }
 233 
 234   void update_sets() {
 235     // We'll recalculate total used bytes and recreate the free list
 236     // at the end of the GC, so no point in updating those values here.
 237     _g1h->update_sets_after_freeing_regions(0, /* pre_used */
 238                                             NULL, /* free_list */
 239                                             &_humongous_proxy_set,
 240                                             false /* par */);
 241   }
 242 
 243   bool doHeapRegion(HeapRegion* hr) {
 244     if (hr->isHumongous()) {
 245       if (hr->startsHumongous()) {
 246         oop obj = oop(hr->bottom());
 247         if (obj->is_gc_marked()) {
 248           obj->forward_to(obj);
 249         } else  {
 250           free_humongous_region(hr);
 251         }
 252       } else {
 253         assert(hr->continuesHumongous(), "Invalid humongous.");
 254       }
 255     } else {
 256       hr->prepare_for_compaction(&_cp);
 257       // Also clear the part of the card table that will be unused after
 258       // compaction.
 259       _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
 260     }
 261     return false;
 262   }
 263 };
 264 
 265 // Finds the first HeapRegion.
 266 class FindFirstRegionClosure: public HeapRegionClosure {
 267   HeapRegion* _a_region;
 268 public:
 269   FindFirstRegionClosure() : _a_region(NULL) {}
 270   bool doHeapRegion(HeapRegion* r) {
 271     _a_region = r;
 272     return true;
 273   }
 274   HeapRegion* result() { return _a_region; }
 275 };
 276 
 277 void G1MarkSweep::mark_sweep_phase2() {
 278   // Now all live objects are marked, compute the new object addresses.
 279 
 280   // It is imperative that we traverse perm_gen LAST. If dead space is
 281   // allowed a range of dead object may get overwritten by a dead int
 282   // array. If perm_gen is not traversed last a klassOop may get
 283   // overwritten. This is fine since it is dead, but if the class has dead
 284   // instances we have to skip them, and in order to find their size we
 285   // need the klassOop!
 286   //
 287   // It is not required that we traverse spaces in the same order in
 288   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 289   // tracking expects us to do so. See comment under phase4.
 290 
 291   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 292   Generation* pg = g1h->perm_gen();
 293 
 294   EventMark m("2 compute new addresses");
 295   TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
 296   GenMarkSweep::trace("2");
 297 
 298   FindFirstRegionClosure cl;
 299   g1h->heap_region_iterate(&cl);
 300   HeapRegion *r = cl.result();
 301   CompactibleSpace* sp = r;
 302   if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
 303     sp = r->next_compaction_space();
 304   }
 305 
 306   G1PrepareCompactClosure blk(sp);
 307   g1h->heap_region_iterate(&blk);
 308   blk.update_sets();
 309 
 310   CompactPoint perm_cp(pg, NULL, NULL);
 311   pg->prepare_for_compaction(&perm_cp);
 312 }
 313 
 314 class G1AdjustPointersClosure: public HeapRegionClosure {
 315  public:
 316   bool doHeapRegion(HeapRegion* r) {
 317     if (r->isHumongous()) {
 318       if (r->startsHumongous()) {
 319         // We must adjust the pointers on the single H object.
 320         oop obj = oop(r->bottom());
 321         debug_only(GenMarkSweep::track_interior_pointers(obj));
 322         // point all the oops to the new location
 323         obj->adjust_pointers();
 324         debug_only(GenMarkSweep::check_interior_pointers());
 325       }
 326     } else {
 327       // This really ought to be "as_CompactibleSpace"...
 328       r->adjust_pointers();
 329     }
 330     return false;
 331   }
 332 };
 333 
 334 void G1MarkSweep::mark_sweep_phase3() {
 335   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 336   Generation* pg = g1h->perm_gen();
 337 
 338   // Adjust the pointers to reflect the new locations
 339   EventMark m("3 adjust pointers");
 340   TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
 341   GenMarkSweep::trace("3");
 342 
 343   SharedHeap* sh = SharedHeap::heap();
 344 
 345   sh->process_strong_roots(true,  // activate StrongRootsScope
 346                            true,  // Collecting permanent generation.
 347                            SharedHeap::SO_AllClasses,
 348                            &GenMarkSweep::adjust_root_pointer_closure,
 349                            NULL,  // do not touch code cache here
 350                            &GenMarkSweep::adjust_pointer_closure);
 351 
 352   assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
 353   g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
 354 
 355   // The discovered lists of the CM reference processor were emptied
 356   // at the start of the Full GC but if the sentinel ref was moved
 357   // as part of this Full GC then they need to be adjusted to point
 358   // to the sentinel ref's new location.
 359   g1h->ref_processor_cm()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
 360 
 361   // Now adjust pointers in remaining weak roots.  (All of which should
 362   // have been cleared if they pointed to non-surviving objects.)
 363   g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
 364                              &GenMarkSweep::adjust_pointer_closure);
 365 
 366   GenMarkSweep::adjust_marks();
 367 
 368   G1AdjustPointersClosure blk;
 369   g1h->heap_region_iterate(&blk);
 370   pg->adjust_pointers();
 371 }
 372 
 373 class G1SpaceCompactClosure: public HeapRegionClosure {
 374 public:
 375   G1SpaceCompactClosure() {}
 376 
 377   bool doHeapRegion(HeapRegion* hr) {
 378     if (hr->isHumongous()) {
 379       if (hr->startsHumongous()) {
 380         oop obj = oop(hr->bottom());
 381         if (obj->is_gc_marked()) {
 382           obj->init_mark();
 383         } else {
 384           assert(hr->is_empty(), "Should have been cleared in phase 2.");
 385         }
 386         hr->reset_during_compaction();
 387       }
 388     } else {
 389       hr->compact();
 390     }
 391     return false;
 392   }
 393 };
 394 
 395 void G1MarkSweep::mark_sweep_phase4() {
 396   // All pointers are now adjusted, move objects accordingly
 397 
 398   // It is imperative that we traverse perm_gen first in phase4. All
 399   // classes must be allocated earlier than their instances, and traversing
 400   // perm_gen first makes sure that all klassOops have moved to their new
 401   // location before any instance does a dispatch through it's klass!
 402 
 403   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 404   // in the same order in phase2, phase3 and phase4. We don't quite do that
 405   // here (perm_gen first rather than last), so we tell the validate code
 406   // to use a higher index (saved from phase2) when verifying perm_gen.
 407   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 408   Generation* pg = g1h->perm_gen();
 409 
 410   EventMark m("4 compact heap");
 411   TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
 412   GenMarkSweep::trace("4");
 413 
 414   pg->compact();
 415 
 416   G1SpaceCompactClosure blk;
 417   g1h->heap_region_iterate(&blk);
 418 
 419 }
 420 
 421 // Local Variables: ***
 422 // c-indentation-style: gnu ***
 423 // End: ***