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