1 /*
   2  * Copyright (c) 2000, 2015, 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/symbolTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "classfile/vmSymbols.hpp"
  29 #include "code/icBuffer.hpp"
  30 #include "gc_implementation/shared/collectorCounters.hpp"
  31 #include "gc_implementation/shared/gcTrace.hpp"
  32 #include "gc_implementation/shared/gcTraceTime.hpp"
  33 #include "gc_implementation/shared/vmGCOperations.hpp"
  34 #include "gc_interface/collectedHeap.inline.hpp"
  35 #include "memory/filemap.hpp"
  36 #include "memory/gcLocker.inline.hpp"
  37 #include "memory/genCollectedHeap.hpp"
  38 #include "memory/genOopClosures.inline.hpp"
  39 #include "memory/generationSpec.hpp"
  40 #include "memory/resourceArea.hpp"
  41 #include "memory/sharedHeap.hpp"
  42 #include "memory/space.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "runtime/biasedLocking.hpp"
  45 #include "runtime/fprofiler.hpp"
  46 #include "runtime/handles.hpp"
  47 #include "runtime/handles.inline.hpp"
  48 #include "runtime/java.hpp"
  49 #include "runtime/vmThread.hpp"
  50 #include "services/memoryService.hpp"
  51 #include "utilities/vmError.hpp"
  52 #include "utilities/workgroup.hpp"
  53 #include "utilities/macros.hpp"
  54 #if INCLUDE_ALL_GCS
  55 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  56 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  57 #endif // INCLUDE_ALL_GCS
  58 
  59 GenCollectedHeap* GenCollectedHeap::_gch;
  60 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;)
  61 
  62 // The set of potentially parallel tasks in root scanning.
  63 enum GCH_strong_roots_tasks {
  64   // We probably want to parallelize both of these internally, but for now...
  65   GCH_PS_younger_gens,
  66   // Leave this one last.
  67   GCH_PS_NumElements
  68 };
  69 
  70 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) :
  71   SharedHeap(policy),
  72   _rem_set(NULL),
  73   _gen_policy(policy),
  74   _gen_process_roots_tasks(new SubTasksDone(GCH_PS_NumElements)),
  75   _full_collections_completed(0)
  76 {
  77   if (_gen_process_roots_tasks == NULL ||
  78       !_gen_process_roots_tasks->valid()) {
  79     vm_exit_during_initialization("Failed necessary allocation.");
  80   }
  81   assert(policy != NULL, "Sanity check");
  82 }
  83 
  84 jint GenCollectedHeap::initialize() {
  85   CollectedHeap::pre_initialize();
  86 
  87   int i;
  88   _n_gens = gen_policy()->number_of_generations();
  89   assert(_n_gens == 2, "There is no support for more than two generations");
  90 
  91   // While there are no constraints in the GC code that HeapWordSize
  92   // be any particular value, there are multiple other areas in the
  93   // system which believe this to be true (e.g. oop->object_size in some
  94   // cases incorrectly returns the size in wordSize units rather than
  95   // HeapWordSize).
  96   guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");
  97 
  98   // The heap must be at least as aligned as generations.
  99   size_t gen_alignment = Generation::GenGrain;
 100 
 101   _gen_specs = gen_policy()->generations();
 102 
 103   // Make sure the sizes are all aligned.
 104   for (i = 0; i < _n_gens; i++) {
 105     _gen_specs[i]->align(gen_alignment);
 106   }
 107 
 108   // Allocate space for the heap.
 109 
 110   char* heap_address;
 111   ReservedSpace heap_rs;
 112 
 113   size_t heap_alignment = collector_policy()->heap_alignment();
 114 
 115   heap_address = allocate(heap_alignment, &heap_rs);
 116 
 117   if (!heap_rs.is_reserved()) {
 118     vm_shutdown_during_initialization(
 119       "Could not reserve enough space for object heap");
 120     return JNI_ENOMEM;
 121   }
 122 
 123   initialize_reserved_region((HeapWord*)heap_rs.base(), (HeapWord*)(heap_rs.base() + heap_rs.size()));
 124 
 125   _rem_set = collector_policy()->create_rem_set(reserved_region());
 126   set_barrier_set(rem_set()->bs());
 127 
 128   _gch = this;
 129 
 130   ReservedSpace young_rs = heap_rs.first_part(_gen_specs[0]->max_size(), false, false);
 131   _young_gen = _gen_specs[0]->init(young_rs, 0, rem_set());
 132   heap_rs = heap_rs.last_part(_gen_specs[0]->max_size());
 133 
 134   ReservedSpace old_rs = heap_rs.first_part(_gen_specs[1]->max_size(), false, false);
 135   _old_gen = _gen_specs[1]->init(old_rs, 1, rem_set());
 136   clear_incremental_collection_failed();
 137 
 138 #if INCLUDE_ALL_GCS
 139   // If we are running CMS, create the collector responsible
 140   // for collecting the CMS generations.
 141   if (collector_policy()->is_concurrent_mark_sweep_policy()) {
 142     bool success = create_cms_collector();
 143     if (!success) return JNI_ENOMEM;
 144   }
 145 #endif // INCLUDE_ALL_GCS
 146 
 147   return JNI_OK;
 148 }
 149 
 150 char* GenCollectedHeap::allocate(size_t alignment,
 151                                  ReservedSpace* heap_rs){
 152   const char overflow_msg[] = "The size of the object heap + VM data exceeds "
 153     "the maximum representable size";
 154 
 155   // Now figure out the total size.
 156   size_t total_reserved = 0;
 157   const size_t pageSize = UseLargePages ?
 158       os::large_page_size() : os::vm_page_size();
 159 
 160   assert(alignment % pageSize == 0, "Must be");
 161 
 162   for (int i = 0; i < _n_gens; i++) {
 163     total_reserved += _gen_specs[i]->max_size();
 164     if (total_reserved < _gen_specs[i]->max_size()) {
 165       vm_exit_during_initialization(overflow_msg);
 166     }
 167   }
 168   assert(total_reserved % alignment == 0,
 169          err_msg("Gen size; total_reserved=" SIZE_FORMAT ", alignment="
 170                  SIZE_FORMAT, total_reserved, alignment));
 171 
 172   *heap_rs = Universe::reserve_heap(total_reserved, alignment);
 173   return heap_rs->base();
 174 }
 175 
 176 void GenCollectedHeap::post_initialize() {
 177   SharedHeap::post_initialize();
 178   GenCollectorPolicy *policy = (GenCollectorPolicy *)collector_policy();
 179   guarantee(policy->is_generation_policy(), "Illegal policy type");
 180   assert((get_gen(0)->kind() == Generation::DefNew) ||
 181          (get_gen(0)->kind() == Generation::ParNew),
 182     "Wrong youngest generation type");
 183   DefNewGeneration* def_new_gen = (DefNewGeneration*)get_gen(0);
 184 
 185   Generation* old_gen = get_gen(1);
 186   assert(old_gen->kind() == Generation::ConcurrentMarkSweep ||
 187          old_gen->kind() == Generation::MarkSweepCompact,
 188     "Wrong generation kind");
 189 
 190   policy->initialize_size_policy(def_new_gen->eden()->capacity(),
 191                                  old_gen->capacity(),
 192                                  def_new_gen->from()->capacity());
 193   policy->initialize_gc_policy_counters();
 194 }
 195 
 196 void GenCollectedHeap::ref_processing_init() {
 197   SharedHeap::ref_processing_init();
 198   _young_gen->ref_processor_init();
 199   _old_gen->ref_processor_init();
 200 }
 201 
 202 size_t GenCollectedHeap::capacity() const {
 203   return _young_gen->capacity() + _old_gen->capacity();
 204 }
 205 
 206 size_t GenCollectedHeap::used() const {
 207   return _young_gen->used() + _old_gen->used();
 208 }
 209 
 210 // Save the "used_region" for generations level and lower.
 211 void GenCollectedHeap::save_used_regions(int level) {
 212   assert(level >= 0, "Illegal level parameter");
 213   assert(level < _n_gens, "Illegal level parameter");
 214   if (level == 1) {
 215     _old_gen->save_used_region();
 216   }
 217   _young_gen->save_used_region();
 218 }
 219 
 220 size_t GenCollectedHeap::max_capacity() const {
 221   return _young_gen->max_capacity() + _old_gen->max_capacity();
 222 }
 223 
 224 // Update the _full_collections_completed counter
 225 // at the end of a stop-world full GC.
 226 unsigned int GenCollectedHeap::update_full_collections_completed() {
 227   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 228   assert(_full_collections_completed <= _total_full_collections,
 229          "Can't complete more collections than were started");
 230   _full_collections_completed = _total_full_collections;
 231   ml.notify_all();
 232   return _full_collections_completed;
 233 }
 234 
 235 // Update the _full_collections_completed counter, as appropriate,
 236 // at the end of a concurrent GC cycle. Note the conditional update
 237 // below to allow this method to be called by a concurrent collector
 238 // without synchronizing in any manner with the VM thread (which
 239 // may already have initiated a STW full collection "concurrently").
 240 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {
 241   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 242   assert((_full_collections_completed <= _total_full_collections) &&
 243          (count <= _total_full_collections),
 244          "Can't complete more collections than were started");
 245   if (count > _full_collections_completed) {
 246     _full_collections_completed = count;
 247     ml.notify_all();
 248   }
 249   return _full_collections_completed;
 250 }
 251 
 252 
 253 #ifndef PRODUCT
 254 // Override of memory state checking method in CollectedHeap:
 255 // Some collectors (CMS for example) can't have badHeapWordVal written
 256 // in the first two words of an object. (For instance , in the case of
 257 // CMS these words hold state used to synchronize between certain
 258 // (concurrent) GC steps and direct allocating mutators.)
 259 // The skip_header_HeapWords() method below, allows us to skip
 260 // over the requisite number of HeapWord's. Note that (for
 261 // generational collectors) this means that those many words are
 262 // skipped in each object, irrespective of the generation in which
 263 // that object lives. The resultant loss of precision seems to be
 264 // harmless and the pain of avoiding that imprecision appears somewhat
 265 // higher than we are prepared to pay for such rudimentary debugging
 266 // support.
 267 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,
 268                                                          size_t size) {
 269   if (CheckMemoryInitialization && ZapUnusedHeapArea) {
 270     // We are asked to check a size in HeapWords,
 271     // but the memory is mangled in juint words.
 272     juint* start = (juint*) (addr + skip_header_HeapWords());
 273     juint* end   = (juint*) (addr + size);
 274     for (juint* slot = start; slot < end; slot += 1) {
 275       assert(*slot == badHeapWordVal,
 276              "Found non badHeapWordValue in pre-allocation check");
 277     }
 278   }
 279 }
 280 #endif
 281 
 282 HeapWord* GenCollectedHeap::attempt_allocation(size_t size,
 283                                                bool is_tlab,
 284                                                bool first_only) {
 285   HeapWord* res = NULL;
 286 
 287   if (_young_gen->should_allocate(size, is_tlab)) {
 288     res = _young_gen->allocate(size, is_tlab);
 289     if (res != NULL || first_only) {
 290       return res;
 291     }
 292   }
 293 
 294   if (_old_gen->should_allocate(size, is_tlab)) {
 295     res = _old_gen->allocate(size, is_tlab);
 296   }
 297 
 298   return res;
 299 }
 300 
 301 HeapWord* GenCollectedHeap::mem_allocate(size_t size,
 302                                          bool* gc_overhead_limit_was_exceeded) {
 303   return collector_policy()->mem_allocate_work(size,
 304                                                false /* is_tlab */,
 305                                                gc_overhead_limit_was_exceeded);
 306 }
 307 
 308 bool GenCollectedHeap::must_clear_all_soft_refs() {
 309   return _gc_cause == GCCause::_last_ditch_collection;
 310 }
 311 
 312 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
 313   return UseConcMarkSweepGC &&
 314          ((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
 315           (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
 316 }
 317 
 318 void GenCollectedHeap::collect_generation(Generation* gen, bool full, size_t size,
 319                                           bool is_tlab, bool run_verification, bool clear_soft_refs,
 320                                           bool restore_marks_for_biased_locking) {
 321   // Timer for individual generations. Last argument is false: no CR
 322   // FIXME: We should try to start the timing earlier to cover more of the GC pause
 323   // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
 324   // so we can assume here that the next GC id is what we want.
 325   GCTraceTime t1(gen->short_name(), PrintGCDetails, false, NULL, GCId::peek());
 326   TraceCollectorStats tcs(gen->counters());
 327   TraceMemoryManagerStats tmms(gen->kind(),gc_cause());
 328 
 329   size_t prev_used = gen->used();
 330   gen->stat_record()->invocations++;
 331   gen->stat_record()->accumulated_time.start();
 332 
 333   // Must be done anew before each collection because
 334   // a previous collection will do mangling and will
 335   // change top of some spaces.
 336   record_gen_tops_before_GC();
 337 
 338   if (PrintGC && Verbose) {
 339     gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,
 340                         gen->level(),
 341                         gen->stat_record()->invocations,
 342                         size * HeapWordSize);
 343   }
 344 
 345   if (run_verification && VerifyBeforeGC) {
 346     HandleMark hm;  // Discard invalid handles created during verification
 347     Universe::verify(" VerifyBeforeGC:");
 348   }
 349   COMPILER2_PRESENT(DerivedPointerTable::clear());
 350 
 351   if (restore_marks_for_biased_locking) {
 352     // We perform this mark word preservation work lazily
 353     // because it's only at this point that we know whether we
 354     // absolutely have to do it; we want to avoid doing it for
 355     // scavenge-only collections where it's unnecessary
 356     BiasedLocking::preserve_marks();
 357   }
 358 
 359   // Do collection work
 360   {
 361     // Note on ref discovery: For what appear to be historical reasons,
 362     // GCH enables and disabled (by enqueing) refs discovery.
 363     // In the future this should be moved into the generation's
 364     // collect method so that ref discovery and enqueueing concerns
 365     // are local to a generation. The collect method could return
 366     // an appropriate indication in the case that notification on
 367     // the ref lock was needed. This will make the treatment of
 368     // weak refs more uniform (and indeed remove such concerns
 369     // from GCH). XXX
 370 
 371     HandleMark hm;  // Discard invalid handles created during gc
 372     save_marks();   // save marks for all gens
 373     // We want to discover references, but not process them yet.
 374     // This mode is disabled in process_discovered_references if the
 375     // generation does some collection work, or in
 376     // enqueue_discovered_references if the generation returns
 377     // without doing any work.
 378     ReferenceProcessor* rp = gen->ref_processor();
 379     // If the discovery of ("weak") refs in this generation is
 380     // atomic wrt other collectors in this configuration, we
 381     // are guaranteed to have empty discovered ref lists.
 382     if (rp->discovery_is_atomic()) {
 383       rp->enable_discovery();
 384       rp->setup_policy(clear_soft_refs);
 385     } else {
 386       // collect() below will enable discovery as appropriate
 387     }
 388     gen->collect(full, clear_soft_refs, size, is_tlab);
 389     if (!rp->enqueuing_is_done()) {
 390       rp->enqueue_discovered_references();
 391     } else {
 392       rp->set_enqueuing_is_done(false);
 393     }
 394     rp->verify_no_references_recorded();
 395   }
 396 
 397   COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 398 
 399   gen->stat_record()->accumulated_time.stop();
 400 
 401   update_gc_stats(gen->level(), full);
 402 
 403   if (run_verification && VerifyAfterGC) {
 404     HandleMark hm;  // Discard invalid handles created during verification
 405     Universe::verify(" VerifyAfterGC:");
 406   }
 407 
 408   if (PrintGCDetails) {
 409     gclog_or_tty->print(":");
 410     gen->print_heap_change(prev_used);
 411   }
 412 }
 413 
 414 void GenCollectedHeap::do_collection(bool   full,
 415                                      bool   clear_all_soft_refs,
 416                                      size_t size,
 417                                      bool   is_tlab,
 418                                      int    max_level) {
 419   ResourceMark rm;
 420   DEBUG_ONLY(Thread* my_thread = Thread::current();)
 421 
 422   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
 423   assert(my_thread->is_VM_thread() ||
 424          my_thread->is_ConcurrentGC_thread(),
 425          "incorrect thread type capability");
 426   assert(Heap_lock->is_locked(),
 427          "the requesting thread should have the Heap_lock");
 428   guarantee(!is_gc_active(), "collection is not reentrant");
 429   assert(max_level < n_gens(), "sanity check");
 430 
 431   if (GC_locker::check_active_before_gc()) {
 432     return; // GC is disabled (e.g. JNI GetXXXCritical operation)
 433   }
 434 
 435   const bool do_clear_all_soft_refs = clear_all_soft_refs ||
 436                           collector_policy()->should_clear_all_soft_refs();
 437 
 438   ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy());
 439 
 440   const size_t metadata_prev_used = MetaspaceAux::used_bytes();
 441 
 442   print_heap_before_gc();
 443 
 444   {
 445     FlagSetting fl(_is_gc_active, true);
 446 
 447     bool complete = full && (max_level == (n_gens()-1));
 448     const char* gc_cause_prefix = complete ? "Full GC" : "GC";
 449     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 450     // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
 451     // so we can assume here that the next GC id is what we want.
 452     GCTraceTime t(GCCauseString(gc_cause_prefix, gc_cause()), PrintGCDetails, false, NULL, GCId::peek());
 453 
 454     gc_prologue(complete);
 455     increment_total_collections(complete);
 456 
 457     size_t gch_prev_used = used();
 458     bool run_verification = total_collections() >= VerifyGCStartAt;
 459 
 460     bool prepared_for_verification = false;
 461     int max_level_collected = 0;
 462     bool old_collects_young = (max_level == 1) &&
 463                               full &&
 464                               _old_gen->full_collects_younger_generations();
 465     if (!old_collects_young &&
 466         _young_gen->should_collect(full, size, is_tlab)) {
 467       if (run_verification && VerifyGCLevel <= 0 && VerifyBeforeGC) {
 468         prepare_for_verify();
 469         prepared_for_verification = true;
 470       }
 471 
 472       assert(!_young_gen->performs_in_place_marking(), "No young generation do in place marking");
 473       collect_generation(_young_gen,
 474                          full,
 475                          size,
 476                          is_tlab,
 477                          run_verification && VerifyGCLevel <= 0,
 478                          do_clear_all_soft_refs,
 479                          false);
 480 
 481       if (size > 0 && (!is_tlab || _young_gen->supports_tlab_allocation()) &&
 482           size * HeapWordSize <= _young_gen->unsafe_max_alloc_nogc()) {
 483         // Allocation request was met by young GC.
 484         size = 0;
 485       }
 486     }
 487 
 488     bool must_restore_marks_for_biased_locking = false;
 489 
 490     if (max_level == 1 && _old_gen->should_collect(full, size, is_tlab)) {
 491       if (!complete) {
 492         // The full_collections increment was missed above.
 493         increment_total_full_collections();
 494       }
 495 
 496       pre_full_gc_dump(NULL);    // do any pre full gc dumps
 497 
 498       if (!prepared_for_verification && run_verification &&
 499           VerifyGCLevel <= 1 && VerifyBeforeGC) {
 500         prepare_for_verify();
 501       }
 502 
 503       assert(_old_gen->performs_in_place_marking(), "All old generations do in place marking");
 504       collect_generation(_old_gen,
 505                          full,
 506                          size,
 507                          is_tlab,
 508                          run_verification && VerifyGCLevel <= 1,
 509                          do_clear_all_soft_refs,
 510                          true);
 511 
 512       must_restore_marks_for_biased_locking = true;
 513       max_level_collected = 1;
 514     }
 515 
 516     // Update "complete" boolean wrt what actually transpired --
 517     // for instance, a promotion failure could have led to
 518     // a whole heap collection.
 519     complete = complete || (max_level_collected == n_gens() - 1);
 520 
 521     if (complete) { // We did a "major" collection
 522       // FIXME: See comment at pre_full_gc_dump call
 523       post_full_gc_dump(NULL);   // do any post full gc dumps
 524     }
 525 
 526     if (PrintGCDetails) {
 527       print_heap_change(gch_prev_used);
 528 
 529       // Print metaspace info for full GC with PrintGCDetails flag.
 530       if (complete) {
 531         MetaspaceAux::print_metaspace_change(metadata_prev_used);
 532       }
 533     }
 534 
 535     // Adjust generation sizes.
 536     if (max_level_collected == 1) {
 537       _old_gen->compute_new_size();
 538     }
 539     _young_gen->compute_new_size();
 540 
 541     if (complete) {
 542       // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 543       ClassLoaderDataGraph::purge();
 544       MetaspaceAux::verify_metrics();
 545       // Resize the metaspace capacity after full collections
 546       MetaspaceGC::compute_new_size();
 547       update_full_collections_completed();
 548     }
 549 
 550     // Track memory usage and detect low memory after GC finishes
 551     MemoryService::track_memory_usage();
 552 
 553     gc_epilogue(complete);
 554 
 555     if (must_restore_marks_for_biased_locking) {
 556       BiasedLocking::restore_marks();
 557     }
 558   }
 559 
 560   print_heap_after_gc();
 561 
 562 #ifdef TRACESPINNING
 563   ParallelTaskTerminator::print_termination_counts();
 564 #endif
 565 }
 566 
 567 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {
 568   return collector_policy()->satisfy_failed_allocation(size, is_tlab);
 569 }
 570 
 571 void GenCollectedHeap::set_par_threads(uint t) {
 572   SharedHeap::set_par_threads(t);
 573   _gen_process_roots_tasks->set_n_threads(t);
 574 }
 575 
 576 void GenCollectedHeap::
 577 gen_process_roots(int level,
 578                   bool younger_gens_as_roots,
 579                   bool activate_scope,
 580                   SharedHeap::ScanningOption so,
 581                   OopsInGenClosure* not_older_gens,
 582                   OopsInGenClosure* weak_roots,
 583                   OopsInGenClosure* older_gens,
 584                   CLDClosure* cld_closure,
 585                   CLDClosure* weak_cld_closure,
 586                   CodeBlobClosure* code_closure) {
 587 
 588   // General roots.
 589   SharedHeap::process_roots(activate_scope, so,
 590                             not_older_gens, weak_roots,
 591                             cld_closure, weak_cld_closure,
 592                             code_closure);
 593 
 594   if (younger_gens_as_roots) {
 595     if (!_gen_process_roots_tasks->is_task_claimed(GCH_PS_younger_gens)) {
 596       if (level == 1) {
 597         not_older_gens->set_generation(_young_gen);
 598         _young_gen->oop_iterate(not_older_gens);
 599       }
 600       not_older_gens->reset_generation();
 601     }
 602   }
 603   // When collection is parallel, all threads get to cooperate to do
 604   // older-gen scanning.
 605   if (level == 0) {
 606     older_gens->set_generation(_old_gen);
 607     rem_set()->younger_refs_iterate(_old_gen, older_gens);
 608     older_gens->reset_generation();
 609   }
 610 
 611   _gen_process_roots_tasks->all_tasks_completed();
 612 }
 613 
 614 void GenCollectedHeap::
 615 gen_process_roots(int level,
 616                   bool younger_gens_as_roots,
 617                   bool activate_scope,
 618                   SharedHeap::ScanningOption so,
 619                   bool only_strong_roots,
 620                   OopsInGenClosure* not_older_gens,
 621                   OopsInGenClosure* older_gens,
 622                   CLDClosure* cld_closure) {
 623 
 624   const bool is_adjust_phase = !only_strong_roots && !younger_gens_as_roots;
 625 
 626   bool is_moving_collection = false;
 627   if (level == 0 || is_adjust_phase) {
 628     // young collections are always moving
 629     is_moving_collection = true;
 630   }
 631 
 632   MarkingCodeBlobClosure mark_code_closure(not_older_gens, is_moving_collection);
 633   CodeBlobClosure* code_closure = &mark_code_closure;
 634 
 635   gen_process_roots(level,
 636                     younger_gens_as_roots,
 637                     activate_scope, so,
 638                     not_older_gens, only_strong_roots ? NULL : not_older_gens,
 639                     older_gens,
 640                     cld_closure, only_strong_roots ? NULL : cld_closure,
 641                     code_closure);
 642 
 643 }
 644 
 645 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) {
 646   SharedHeap::process_weak_roots(root_closure);
 647   // "Local" "weak" refs
 648   _young_gen->ref_processor()->weak_oops_do(root_closure);
 649   _old_gen->ref_processor()->weak_oops_do(root_closure);
 650 }
 651 
 652 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix)    \
 653 void GenCollectedHeap::                                                 \
 654 oop_since_save_marks_iterate(int level,                                 \
 655                              OopClosureType* cur,                       \
 656                              OopClosureType* older) {                   \
 657   if (level == 0) {                                                     \
 658     _young_gen->oop_since_save_marks_iterate##nv_suffix(cur);           \
 659     _old_gen->oop_since_save_marks_iterate##nv_suffix(older);           \
 660   } else {                                                              \
 661     _old_gen->oop_since_save_marks_iterate##nv_suffix(cur);             \
 662   }                                                                     \
 663 }
 664 
 665 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)
 666 
 667 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN
 668 
 669 bool GenCollectedHeap::no_allocs_since_save_marks(int level) {
 670   if (level == 0 && !_young_gen->no_allocs_since_save_marks()) {
 671     return false;
 672   }
 673   return _old_gen->no_allocs_since_save_marks();
 674 }
 675 
 676 bool GenCollectedHeap::supports_inline_contig_alloc() const {
 677   return _young_gen->supports_inline_contig_alloc();
 678 }
 679 
 680 HeapWord** GenCollectedHeap::top_addr() const {
 681   return _young_gen->top_addr();
 682 }
 683 
 684 HeapWord** GenCollectedHeap::end_addr() const {
 685   return _young_gen->end_addr();
 686 }
 687 
 688 // public collection interfaces
 689 
 690 void GenCollectedHeap::collect(GCCause::Cause cause) {
 691   if (should_do_concurrent_full_gc(cause)) {
 692 #if INCLUDE_ALL_GCS
 693     // mostly concurrent full collection
 694     collect_mostly_concurrent(cause);
 695 #else  // INCLUDE_ALL_GCS
 696     ShouldNotReachHere();
 697 #endif // INCLUDE_ALL_GCS
 698   } else if (cause == GCCause::_wb_young_gc) {
 699     // minor collection for WhiteBox API
 700     collect(cause, 0);
 701   } else {
 702 #ifdef ASSERT
 703   if (cause == GCCause::_scavenge_alot) {
 704     // minor collection only
 705     collect(cause, 0);
 706   } else {
 707     // Stop-the-world full collection
 708     collect(cause, n_gens() - 1);
 709   }
 710 #else
 711     // Stop-the-world full collection
 712     collect(cause, n_gens() - 1);
 713 #endif
 714   }
 715 }
 716 
 717 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {
 718   // The caller doesn't have the Heap_lock
 719   assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
 720   MutexLocker ml(Heap_lock);
 721   collect_locked(cause, max_level);
 722 }
 723 
 724 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
 725   // The caller has the Heap_lock
 726   assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
 727   collect_locked(cause, n_gens() - 1);
 728 }
 729 
 730 // this is the private collection interface
 731 // The Heap_lock is expected to be held on entry.
 732 
 733 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
 734   // Read the GC count while holding the Heap_lock
 735   unsigned int gc_count_before      = total_collections();
 736   unsigned int full_gc_count_before = total_full_collections();
 737   {
 738     MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back
 739     VM_GenCollectFull op(gc_count_before, full_gc_count_before,
 740                          cause, max_level);
 741     VMThread::execute(&op);
 742   }
 743 }
 744 
 745 #if INCLUDE_ALL_GCS
 746 bool GenCollectedHeap::create_cms_collector() {
 747 
 748   assert(_old_gen->kind() == Generation::ConcurrentMarkSweep,
 749          "Unexpected generation kinds");
 750   // Skip two header words in the block content verification
 751   NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)
 752   CMSCollector* collector = new CMSCollector(
 753     (ConcurrentMarkSweepGeneration*)_old_gen,
 754     _rem_set->as_CardTableRS(),
 755     (ConcurrentMarkSweepPolicy*) collector_policy());
 756 
 757   if (collector == NULL || !collector->completed_initialization()) {
 758     if (collector) {
 759       delete collector;  // Be nice in embedded situation
 760     }
 761     vm_shutdown_during_initialization("Could not create CMS collector");
 762     return false;
 763   }
 764   return true;  // success
 765 }
 766 
 767 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {
 768   assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");
 769 
 770   MutexLocker ml(Heap_lock);
 771   // Read the GC counts while holding the Heap_lock
 772   unsigned int full_gc_count_before = total_full_collections();
 773   unsigned int gc_count_before      = total_collections();
 774   {
 775     MutexUnlocker mu(Heap_lock);
 776     VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);
 777     VMThread::execute(&op);
 778   }
 779 }
 780 #endif // INCLUDE_ALL_GCS
 781 
 782 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
 783    do_full_collection(clear_all_soft_refs, _n_gens - 1);
 784 }
 785 
 786 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
 787                                           int max_level) {
 788   int local_max_level;
 789   if (!incremental_collection_will_fail(false /* don't consult_young */) &&
 790       gc_cause() == GCCause::_gc_locker) {
 791     local_max_level = 0;
 792   } else {
 793     local_max_level = max_level;
 794   }
 795 
 796   do_collection(true                 /* full */,
 797                 clear_all_soft_refs  /* clear_all_soft_refs */,
 798                 0                    /* size */,
 799                 false                /* is_tlab */,
 800                 local_max_level      /* max_level */);
 801   // Hack XXX FIX ME !!!
 802   // A scavenge may not have been attempted, or may have
 803   // been attempted and failed, because the old gen was too full
 804   if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
 805       incremental_collection_will_fail(false /* don't consult_young */)) {
 806     if (PrintGCDetails) {
 807       gclog_or_tty->print_cr("GC locker: Trying a full collection "
 808                              "because scavenge failed");
 809     }
 810     // This time allow the old gen to be collected as well
 811     do_collection(true                 /* full */,
 812                   clear_all_soft_refs  /* clear_all_soft_refs */,
 813                   0                    /* size */,
 814                   false                /* is_tlab */,
 815                   n_gens() - 1         /* max_level */);
 816   }
 817 }
 818 
 819 bool GenCollectedHeap::is_in_young(oop p) {
 820   bool result = ((HeapWord*)p) < _old_gen->reserved().start();
 821   assert(result == _young_gen->is_in_reserved(p),
 822          err_msg("incorrect test - result=%d, p=" INTPTR_FORMAT, result, p2i((void*)p)));
 823   return result;
 824 }
 825 
 826 // Returns "TRUE" iff "p" points into the committed areas of the heap.
 827 bool GenCollectedHeap::is_in(const void* p) const {
 828   #ifndef ASSERT
 829   guarantee(VerifyBeforeGC      ||
 830             VerifyDuringGC      ||
 831             VerifyBeforeExit    ||
 832             VerifyDuringStartup ||
 833             PrintAssembly       ||
 834             tty->count() != 0   ||   // already printing
 835             VerifyAfterGC       ||
 836     VMError::fatal_error_in_progress(), "too expensive");
 837 
 838   #endif
 839   return _young_gen->is_in(p) || _old_gen->is_in(p);
 840 }
 841 
 842 #ifdef ASSERT
 843 // Don't implement this by using is_in_young().  This method is used
 844 // in some cases to check that is_in_young() is correct.
 845 bool GenCollectedHeap::is_in_partial_collection(const void* p) {
 846   assert(is_in_reserved(p) || p == NULL,
 847     "Does not work if address is non-null and outside of the heap");
 848   return p < _young_gen->reserved().end() && p != NULL;
 849 }
 850 #endif
 851 
 852 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) {
 853   _young_gen->oop_iterate(cl);
 854   _old_gen->oop_iterate(cl);
 855 }
 856 
 857 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
 858   _young_gen->object_iterate(cl);
 859   _old_gen->object_iterate(cl);
 860 }
 861 
 862 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
 863   _young_gen->safe_object_iterate(cl);
 864   _old_gen->safe_object_iterate(cl);
 865 }
 866 
 867 Space* GenCollectedHeap::space_containing(const void* addr) const {
 868   Space* res = _young_gen->space_containing(addr);
 869   if (res != NULL) {
 870     return res;
 871   }
 872   res = _old_gen->space_containing(addr);
 873   assert(res != NULL, "Could not find containing space");
 874   return res;
 875 }
 876 
 877 HeapWord* GenCollectedHeap::block_start(const void* addr) const {
 878   assert(is_in_reserved(addr), "block_start of address outside of heap");
 879   if (_young_gen->is_in_reserved(addr)) {
 880     assert(_young_gen->is_in(addr), "addr should be in allocated part of generation");
 881     return _young_gen->block_start(addr);
 882   }
 883 
 884   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
 885   assert(_old_gen->is_in(addr), "addr should be in allocated part of generation");
 886   return _old_gen->block_start(addr);
 887 }
 888 
 889 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
 890   assert(is_in_reserved(addr), "block_size of address outside of heap");
 891   if (_young_gen->is_in_reserved(addr)) {
 892     assert(_young_gen->is_in(addr), "addr should be in allocated part of generation");
 893     return _young_gen->block_size(addr);
 894   }
 895 
 896   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
 897   assert(_old_gen->is_in(addr), "addr should be in allocated part of generation");
 898   return _old_gen->block_size(addr);
 899 }
 900 
 901 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
 902   assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
 903   assert(block_start(addr) == addr, "addr must be a block start");
 904   if (_young_gen->is_in_reserved(addr)) {
 905     return _young_gen->block_is_obj(addr);
 906   }
 907 
 908   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
 909   return _old_gen->block_is_obj(addr);
 910 }
 911 
 912 bool GenCollectedHeap::supports_tlab_allocation() const {
 913   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
 914   return _young_gen->supports_tlab_allocation();
 915 }
 916 
 917 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
 918   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
 919   if (_young_gen->supports_tlab_allocation()) {
 920     return _young_gen->tlab_capacity();
 921   }
 922   return 0;
 923 }
 924 
 925 size_t GenCollectedHeap::tlab_used(Thread* thr) const {
 926   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
 927   if (_young_gen->supports_tlab_allocation()) {
 928     return _young_gen->tlab_used();
 929   }
 930   return 0;
 931 }
 932 
 933 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
 934   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
 935   if (_young_gen->supports_tlab_allocation()) {
 936     return _young_gen->unsafe_max_tlab_alloc();
 937   }
 938   return 0;
 939 }
 940 
 941 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
 942   bool gc_overhead_limit_was_exceeded;
 943   return collector_policy()->mem_allocate_work(size /* size */,
 944                                                true /* is_tlab */,
 945                                                &gc_overhead_limit_was_exceeded);
 946 }
 947 
 948 // Requires "*prev_ptr" to be non-NULL.  Deletes and a block of minimal size
 949 // from the list headed by "*prev_ptr".
 950 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
 951   bool first = true;
 952   size_t min_size = 0;   // "first" makes this conceptually infinite.
 953   ScratchBlock **smallest_ptr, *smallest;
 954   ScratchBlock  *cur = *prev_ptr;
 955   while (cur) {
 956     assert(*prev_ptr == cur, "just checking");
 957     if (first || cur->num_words < min_size) {
 958       smallest_ptr = prev_ptr;
 959       smallest     = cur;
 960       min_size     = smallest->num_words;
 961       first        = false;
 962     }
 963     prev_ptr = &cur->next;
 964     cur     =  cur->next;
 965   }
 966   smallest      = *smallest_ptr;
 967   *smallest_ptr = smallest->next;
 968   return smallest;
 969 }
 970 
 971 // Sort the scratch block list headed by res into decreasing size order,
 972 // and set "res" to the result.
 973 static void sort_scratch_list(ScratchBlock*& list) {
 974   ScratchBlock* sorted = NULL;
 975   ScratchBlock* unsorted = list;
 976   while (unsorted) {
 977     ScratchBlock *smallest = removeSmallestScratch(&unsorted);
 978     smallest->next  = sorted;
 979     sorted          = smallest;
 980   }
 981   list = sorted;
 982 }
 983 
 984 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
 985                                                size_t max_alloc_words) {
 986   ScratchBlock* res = NULL;
 987   _young_gen->contribute_scratch(res, requestor, max_alloc_words);
 988   _old_gen->contribute_scratch(res, requestor, max_alloc_words);
 989   sort_scratch_list(res);
 990   return res;
 991 }
 992 
 993 void GenCollectedHeap::release_scratch() {
 994   _young_gen->reset_scratch();
 995   _old_gen->reset_scratch();
 996 }
 997 
 998 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
 999   void do_generation(Generation* gen) {
1000     gen->prepare_for_verify();
1001   }
1002 };
1003 
1004 void GenCollectedHeap::prepare_for_verify() {
1005   ensure_parsability(false);        // no need to retire TLABs
1006   GenPrepareForVerifyClosure blk;
1007   generation_iterate(&blk, false);
1008 }
1009 
1010 void GenCollectedHeap::generation_iterate(GenClosure* cl,
1011                                           bool old_to_young) {
1012   if (old_to_young) {
1013     cl->do_generation(_old_gen);
1014     cl->do_generation(_young_gen);
1015   } else {
1016     cl->do_generation(_young_gen);
1017     cl->do_generation(_old_gen);
1018   }
1019 }
1020 
1021 void GenCollectedHeap::space_iterate(SpaceClosure* cl) {
1022   _young_gen->space_iterate(cl, true);
1023   _old_gen->space_iterate(cl, true);
1024 }
1025 
1026 bool GenCollectedHeap::is_maximal_no_gc() const {
1027   return _young_gen->is_maximal_no_gc() && _old_gen->is_maximal_no_gc();
1028 }
1029 
1030 void GenCollectedHeap::save_marks() {
1031   _young_gen->save_marks();
1032   _old_gen->save_marks();
1033 }
1034 
1035 GenCollectedHeap* GenCollectedHeap::heap() {
1036   assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");
1037   assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");
1038   return _gch;
1039 }
1040 
1041 
1042 void GenCollectedHeap::prepare_for_compaction() {
1043   guarantee(_n_gens = 2, "Wrong number of generations");
1044   // Start by compacting into same gen.
1045   CompactPoint cp(_old_gen);
1046   _old_gen->prepare_for_compaction(&cp);
1047   _young_gen->prepare_for_compaction(&cp);
1048 }
1049 
1050 GCStats* GenCollectedHeap::gc_stats(int level) const {
1051   if (level == 0) {
1052     return _young_gen->gc_stats();
1053   } else {
1054     return _old_gen->gc_stats();
1055   }
1056 }
1057 
1058 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) {
1059   if (!silent) {
1060     gclog_or_tty->print("%s", _old_gen->name());
1061     gclog_or_tty->print(" ");
1062   }
1063   _old_gen->verify();
1064 
1065   if (!silent) {
1066     gclog_or_tty->print("%s", _young_gen->name());
1067     gclog_or_tty->print(" ");
1068   }
1069   _young_gen->verify();
1070 
1071   if (!silent) {
1072     gclog_or_tty->print("remset ");
1073   }
1074   rem_set()->verify();
1075 }
1076 
1077 void GenCollectedHeap::print_on(outputStream* st) const {
1078   _young_gen->print_on(st);
1079   _old_gen->print_on(st);
1080   MetaspaceAux::print_on(st);
1081 }
1082 
1083 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
1084   if (workers() != NULL) {
1085     workers()->threads_do(tc);
1086   }
1087 #if INCLUDE_ALL_GCS
1088   if (UseConcMarkSweepGC) {
1089     ConcurrentMarkSweepThread::threads_do(tc);
1090   }
1091 #endif // INCLUDE_ALL_GCS
1092 }
1093 
1094 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
1095 #if INCLUDE_ALL_GCS
1096   if (UseConcMarkSweepGC) {
1097     workers()->print_worker_threads_on(st);
1098     ConcurrentMarkSweepThread::print_all_on(st);
1099   }
1100 #endif // INCLUDE_ALL_GCS
1101 }
1102 
1103 void GenCollectedHeap::print_on_error(outputStream* st) const {
1104   this->CollectedHeap::print_on_error(st);
1105 
1106 #if INCLUDE_ALL_GCS
1107   if (UseConcMarkSweepGC) {
1108     st->cr();
1109     CMSCollector::print_on_error(st);
1110   }
1111 #endif // INCLUDE_ALL_GCS
1112 }
1113 
1114 void GenCollectedHeap::print_tracing_info() const {
1115   if (TraceYoungGenTime) {
1116     get_gen(0)->print_summary_info();
1117   }
1118   if (TraceOldGenTime) {
1119     get_gen(1)->print_summary_info();
1120   }
1121 }
1122 
1123 void GenCollectedHeap::print_heap_change(size_t prev_used) const {
1124   if (PrintGCDetails && Verbose) {
1125     gclog_or_tty->print(" "  SIZE_FORMAT
1126                         "->" SIZE_FORMAT
1127                         "("  SIZE_FORMAT ")",
1128                         prev_used, used(), capacity());
1129   } else {
1130     gclog_or_tty->print(" "  SIZE_FORMAT "K"
1131                         "->" SIZE_FORMAT "K"
1132                         "("  SIZE_FORMAT "K)",
1133                         prev_used / K, used() / K, capacity() / K);
1134   }
1135 }
1136 
1137 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
1138  private:
1139   bool _full;
1140  public:
1141   void do_generation(Generation* gen) {
1142     gen->gc_prologue(_full);
1143   }
1144   GenGCPrologueClosure(bool full) : _full(full) {};
1145 };
1146 
1147 void GenCollectedHeap::gc_prologue(bool full) {
1148   assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
1149 
1150   always_do_update_barrier = false;
1151   // Fill TLAB's and such
1152   CollectedHeap::accumulate_statistics_all_tlabs();
1153   ensure_parsability(true);   // retire TLABs
1154 
1155   // Walk generations
1156   GenGCPrologueClosure blk(full);
1157   generation_iterate(&blk, false);  // not old-to-young.
1158 };
1159 
1160 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
1161  private:
1162   bool _full;
1163  public:
1164   void do_generation(Generation* gen) {
1165     gen->gc_epilogue(_full);
1166   }
1167   GenGCEpilogueClosure(bool full) : _full(full) {};
1168 };
1169 
1170 void GenCollectedHeap::gc_epilogue(bool full) {
1171 #ifdef COMPILER2
1172   assert(DerivedPointerTable::is_empty(), "derived pointer present");
1173   size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
1174   guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
1175 #endif /* COMPILER2 */
1176 
1177   resize_all_tlabs();
1178 
1179   GenGCEpilogueClosure blk(full);
1180   generation_iterate(&blk, false);  // not old-to-young.
1181 
1182   if (!CleanChunkPoolAsync) {
1183     Chunk::clean_chunk_pool();
1184   }
1185 
1186   MetaspaceCounters::update_performance_counters();
1187   CompressedClassSpaceCounters::update_performance_counters();
1188 
1189   always_do_update_barrier = UseConcMarkSweepGC;
1190 };
1191 
1192 #ifndef PRODUCT
1193 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
1194  private:
1195  public:
1196   void do_generation(Generation* gen) {
1197     gen->record_spaces_top();
1198   }
1199 };
1200 
1201 void GenCollectedHeap::record_gen_tops_before_GC() {
1202   if (ZapUnusedHeapArea) {
1203     GenGCSaveTopsBeforeGCClosure blk;
1204     generation_iterate(&blk, false);  // not old-to-young.
1205   }
1206 }
1207 #endif  // not PRODUCT
1208 
1209 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
1210  public:
1211   void do_generation(Generation* gen) {
1212     gen->ensure_parsability();
1213   }
1214 };
1215 
1216 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
1217   CollectedHeap::ensure_parsability(retire_tlabs);
1218   GenEnsureParsabilityClosure ep_cl;
1219   generation_iterate(&ep_cl, false);
1220 }
1221 
1222 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
1223                                               oop obj,
1224                                               size_t obj_size) {
1225   guarantee(old_gen->level() == 1, "We only get here with an old generation");
1226   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1227   HeapWord* result = NULL;
1228 
1229   result = old_gen->expand_and_allocate(obj_size, false);
1230 
1231   if (result != NULL) {
1232     Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
1233   }
1234   return oop(result);
1235 }
1236 
1237 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
1238   jlong _time;   // in ms
1239   jlong _now;    // in ms
1240 
1241  public:
1242   GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
1243 
1244   jlong time() { return _time; }
1245 
1246   void do_generation(Generation* gen) {
1247     _time = MIN2(_time, gen->time_of_last_gc(_now));
1248   }
1249 };
1250 
1251 jlong GenCollectedHeap::millis_since_last_gc() {
1252   // We need a monotonically non-decreasing time in ms but
1253   // os::javaTimeMillis() does not guarantee monotonicity.
1254   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1255   GenTimeOfLastGCClosure tolgc_cl(now);
1256   // iterate over generations getting the oldest
1257   // time that a generation was collected
1258   generation_iterate(&tolgc_cl, false);
1259 
1260   // javaTimeNanos() is guaranteed to be monotonically non-decreasing
1261   // provided the underlying platform provides such a time source
1262   // (and it is bug free). So we still have to guard against getting
1263   // back a time later than 'now'.
1264   jlong retVal = now - tolgc_cl.time();
1265   if (retVal < 0) {
1266     NOT_PRODUCT(warning("time warp: "INT64_FORMAT, (int64_t) retVal);)
1267     return 0;
1268   }
1269   return retVal;
1270 }