1 /*
   2  * Copyright (c) 2016, 2019, 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 "gc/g1/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1CollectionSet.hpp"
  28 #include "gc/g1/g1CollectionSetCandidates.hpp"
  29 #include "gc/g1/g1CollectorState.hpp"
  30 #include "gc/g1/g1ParScanThreadState.hpp"
  31 #include "gc/g1/g1Policy.hpp"
  32 #include "gc/g1/heapRegion.inline.hpp"
  33 #include "gc/g1/heapRegionRemSet.hpp"
  34 #include "gc/g1/heapRegionSet.hpp"
  35 #include "logging/logStream.hpp"
  36 #include "utilities/debug.hpp"
  37 #include "utilities/globalDefinitions.hpp"
  38 #include "utilities/quickSort.hpp"
  39 
  40 G1CollectorState* G1CollectionSet::collector_state() {
  41   return _g1h->collector_state();
  42 }
  43 
  44 G1GCPhaseTimes* G1CollectionSet::phase_times() {
  45   return _policy->phase_times();
  46 }
  47 
  48 double G1CollectionSet::predict_region_elapsed_time_ms(HeapRegion* hr) {
  49   return _policy->predict_region_elapsed_time_ms(hr, collector_state()->in_young_only_phase());
  50 }
  51 
  52 G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
  53   _g1h(g1h),
  54   _policy(policy),
  55   _candidates(NULL),
  56   _eden_region_length(0),
  57   _survivor_region_length(0),
  58   _old_region_length(0),
  59   _collection_set_regions(NULL),
  60   _collection_set_cur_length(0),
  61   _collection_set_max_length(0),
  62   _num_optional_regions(0),
  63   _bytes_used_before(0),
  64   _recorded_rs_lengths(0),
  65   _inc_build_state(Inactive),
  66   _inc_part_start(0),
  67   _inc_bytes_used_before(0),
  68   _inc_recorded_rs_lengths(0),
  69   _inc_recorded_rs_lengths_diffs(0),
  70   _inc_predicted_elapsed_time_ms(0.0),
  71   _inc_predicted_elapsed_time_ms_diffs(0.0) {
  72 }
  73 
  74 G1CollectionSet::~G1CollectionSet() {
  75   if (_collection_set_regions != NULL) {
  76     FREE_C_HEAP_ARRAY(uint, _collection_set_regions);
  77   }
  78   free_optional_regions();
  79   clear_candidates();
  80 }
  81 
  82 void G1CollectionSet::init_region_lengths(uint eden_cset_region_length,
  83                                           uint survivor_cset_region_length) {
  84   assert_at_safepoint_on_vm_thread();
  85 
  86   _eden_region_length     = eden_cset_region_length;
  87   _survivor_region_length = survivor_cset_region_length;
  88 
  89   assert((size_t) young_region_length() == _collection_set_cur_length,
  90          "Young region length %u should match collection set length " SIZE_FORMAT, young_region_length(), _collection_set_cur_length);
  91 
  92   _old_region_length = 0;
  93   free_optional_regions();
  94 }
  95 
  96 void G1CollectionSet::initialize(uint max_region_length) {
  97   guarantee(_collection_set_regions == NULL, "Must only initialize once.");
  98   _collection_set_max_length = max_region_length;
  99   _collection_set_regions = NEW_C_HEAP_ARRAY(uint, max_region_length, mtGC);
 100 }
 101 
 102 void G1CollectionSet::free_optional_regions() {
 103   _num_optional_regions = 0;
 104 }
 105 
 106 void G1CollectionSet::clear_candidates() {
 107   delete _candidates;
 108   _candidates = NULL;
 109 }
 110 
 111 void G1CollectionSet::set_recorded_rs_lengths(size_t rs_lengths) {
 112   _recorded_rs_lengths = rs_lengths;
 113 }
 114 
 115 // Add the heap region at the head of the non-incremental collection set
 116 void G1CollectionSet::add_old_region(HeapRegion* hr) {
 117   assert_at_safepoint_on_vm_thread();
 118 
 119   assert(_inc_build_state == Active,
 120          "Precondition, actively building cset or adding optional later on");
 121   assert(hr->is_old(), "the region should be old");
 122 
 123   assert(!hr->in_collection_set(), "should not already be in the collection set");
 124   _g1h->register_old_region_with_region_attr(hr);
 125 
 126   _collection_set_regions[_collection_set_cur_length++] = hr->hrm_index();
 127   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set now larger than maximum size.");
 128 
 129   _bytes_used_before += hr->used();
 130   _recorded_rs_lengths += hr->rem_set()->occupied();
 131   _old_region_length++;
 132 
 133   _g1h->old_set_remove(hr);
 134 }
 135 
 136 void G1CollectionSet::add_optional_region(HeapRegion* hr) {
 137   assert(hr->is_old(), "the region should be old");
 138   assert(!hr->in_collection_set(), "should not already be in the CSet");
 139 
 140   _g1h->register_optional_region_with_region_attr(hr);
 141 
 142   hr->set_index_in_opt_cset(_num_optional_regions++);
 143 }
 144 
 145 void G1CollectionSet::start_incremental_building() {
 146   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
 147   assert(_inc_build_state == Inactive, "Precondition");
 148 
 149   _inc_bytes_used_before = 0;
 150 
 151   _inc_recorded_rs_lengths = 0;
 152   _inc_recorded_rs_lengths_diffs = 0;
 153   _inc_predicted_elapsed_time_ms = 0.0;
 154   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 155 
 156   update_incremental_marker();
 157 }
 158 
 159 void G1CollectionSet::finalize_incremental_building() {
 160   assert(_inc_build_state == Active, "Precondition");
 161   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
 162 
 163   // The two "main" fields, _inc_recorded_rs_lengths and
 164   // _inc_predicted_elapsed_time_ms, are updated by the thread
 165   // that adds a new region to the CSet. Further updates by the
 166   // concurrent refinement thread that samples the young RSet lengths
 167   // are accumulated in the *_diffs fields. Here we add the diffs to
 168   // the "main" fields.
 169 
 170   if (_inc_recorded_rs_lengths_diffs >= 0) {
 171     _inc_recorded_rs_lengths += _inc_recorded_rs_lengths_diffs;
 172   } else {
 173     // This is defensive. The diff should in theory be always positive
 174     // as RSets can only grow between GCs. However, given that we
 175     // sample their size concurrently with other threads updating them
 176     // it's possible that we might get the wrong size back, which
 177     // could make the calculations somewhat inaccurate.
 178     size_t diffs = (size_t) (-_inc_recorded_rs_lengths_diffs);
 179     if (_inc_recorded_rs_lengths >= diffs) {
 180       _inc_recorded_rs_lengths -= diffs;
 181     } else {
 182       _inc_recorded_rs_lengths = 0;
 183     }
 184   }
 185   _inc_predicted_elapsed_time_ms += _inc_predicted_elapsed_time_ms_diffs;
 186 
 187   _inc_recorded_rs_lengths_diffs = 0;
 188   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 189 }
 190 
 191 void G1CollectionSet::clear() {
 192   assert_at_safepoint_on_vm_thread();
 193   _collection_set_cur_length = 0;
 194 }
 195 
 196 void G1CollectionSet::iterate(HeapRegionClosure* cl) const {
 197   size_t len = _collection_set_cur_length;
 198   OrderAccess::loadload();
 199 
 200   for (uint i = 0; i < len; i++) {
 201     HeapRegion* r = _g1h->region_at(_collection_set_regions[i]);
 202     bool result = cl->do_heap_region(r);
 203     if (result) {
 204       cl->set_incomplete();
 205       return;
 206     }
 207   }
 208 }
 209 
 210 void G1CollectionSet::iterate_optional(HeapRegionClosure* cl) const {
 211   assert_at_safepoint();
 212 
 213   for (uint i = 0; i < _num_optional_regions; i++) {
 214     HeapRegion* r = _candidates->at(i);
 215     bool result = cl->do_heap_region(r);
 216     guarantee(!result, "Must not cancel iteration");
 217   }
 218 }
 219 
 220 void G1CollectionSet::iterate_incremental_part_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const {
 221   assert_at_safepoint();
 222 
 223   size_t len = _collection_set_cur_length - _inc_part_start;
 224   if (len == 0) {
 225     return;
 226   }
 227 
 228   size_t start_pos = (worker_id * len) / total_workers;
 229   size_t cur_pos = start_pos;
 230 
 231   do {
 232     HeapRegion* r = _g1h->region_at(_collection_set_regions[cur_pos + _inc_part_start]);
 233     bool result = cl->do_heap_region(r);
 234     guarantee(!result, "Must not cancel iteration");
 235 
 236     cur_pos++;
 237     if (cur_pos == len) {
 238       cur_pos = 0;
 239     }
 240   } while (cur_pos != start_pos);
 241 }
 242 
 243 void G1CollectionSet::update_young_region_prediction(HeapRegion* hr,
 244                                                      size_t new_rs_length) {
 245   // Update the CSet information that is dependent on the new RS length
 246   assert(hr->is_young(), "Precondition");
 247   assert(!SafepointSynchronize::is_at_safepoint(), "should not be at a safepoint");
 248 
 249   // We could have updated _inc_recorded_rs_lengths and
 250   // _inc_predicted_elapsed_time_ms directly but we'd need to do
 251   // that atomically, as this code is executed by a concurrent
 252   // refinement thread, potentially concurrently with a mutator thread
 253   // allocating a new region and also updating the same fields. To
 254   // avoid the atomic operations we accumulate these updates on two
 255   // separate fields (*_diffs) and we'll just add them to the "main"
 256   // fields at the start of a GC.
 257 
 258   ssize_t old_rs_length = (ssize_t) hr->recorded_rs_length();
 259   ssize_t rs_lengths_diff = (ssize_t) new_rs_length - old_rs_length;
 260   _inc_recorded_rs_lengths_diffs += rs_lengths_diff;
 261 
 262   double old_elapsed_time_ms = hr->predicted_elapsed_time_ms();
 263   double new_region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 264   double elapsed_ms_diff = new_region_elapsed_time_ms - old_elapsed_time_ms;
 265   _inc_predicted_elapsed_time_ms_diffs += elapsed_ms_diff;
 266 
 267   hr->set_recorded_rs_length(new_rs_length);
 268   hr->set_predicted_elapsed_time_ms(new_region_elapsed_time_ms);
 269 }
 270 
 271 void G1CollectionSet::add_young_region_common(HeapRegion* hr) {
 272   assert(hr->is_young(), "invariant");
 273   assert(_inc_build_state == Active, "Precondition");
 274 
 275   size_t collection_set_length = _collection_set_cur_length;
 276   assert(collection_set_length <= INT_MAX, "Collection set is too large with %d entries", (int)collection_set_length);
 277   hr->set_young_index_in_cset((int)collection_set_length);
 278 
 279   _collection_set_regions[collection_set_length] = hr->hrm_index();
 280   // Concurrent readers must observe the store of the value in the array before an
 281   // update to the length field.
 282   OrderAccess::storestore();
 283   _collection_set_cur_length++;
 284   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set larger than maximum allowed.");
 285 
 286   // This routine is used when:
 287   // * adding survivor regions to the incremental cset at the end of an
 288   //   evacuation pause or
 289   // * adding the current allocation region to the incremental cset
 290   //   when it is retired.
 291   // Therefore this routine may be called at a safepoint by the
 292   // VM thread, or in-between safepoints by mutator threads (when
 293   // retiring the current allocation region)
 294   // We need to clear and set the cached recorded/cached collection set
 295   // information in the heap region here (before the region gets added
 296   // to the collection set). An individual heap region's cached values
 297   // are calculated, aggregated with the policy collection set info,
 298   // and cached in the heap region here (initially) and (subsequently)
 299   // by the Young List sampling code.
 300   // Ignore calls to this due to retirement during full gc.
 301 
 302   if (!_g1h->collector_state()->in_full_gc()) {
 303     size_t rs_length = hr->rem_set()->occupied();
 304     double region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 305 
 306     // Cache the values we have added to the aggregated information
 307     // in the heap region in case we have to remove this region from
 308     // the incremental collection set, or it is updated by the
 309     // rset sampling code
 310     hr->set_recorded_rs_length(rs_length);
 311     hr->set_predicted_elapsed_time_ms(region_elapsed_time_ms);
 312 
 313     _inc_recorded_rs_lengths += rs_length;
 314     _inc_predicted_elapsed_time_ms += region_elapsed_time_ms;
 315     _inc_bytes_used_before += hr->used();
 316   }
 317 
 318   assert(!hr->in_collection_set(), "invariant");
 319   _g1h->register_young_region_with_region_attr(hr);
 320 }
 321 
 322 void G1CollectionSet::add_survivor_regions(HeapRegion* hr) {
 323   assert(hr->is_survivor(), "Must only add survivor regions, but is %s", hr->get_type_str());
 324   add_young_region_common(hr);
 325 }
 326 
 327 void G1CollectionSet::add_eden_region(HeapRegion* hr) {
 328   assert(hr->is_eden(), "Must only add eden regions, but is %s", hr->get_type_str());
 329   add_young_region_common(hr);
 330 }
 331 
 332 #ifndef PRODUCT
 333 class G1VerifyYoungAgesClosure : public HeapRegionClosure {
 334 public:
 335   bool _valid;
 336 public:
 337   G1VerifyYoungAgesClosure() : HeapRegionClosure(), _valid(true) { }
 338 
 339   virtual bool do_heap_region(HeapRegion* r) {
 340     guarantee(r->is_young(), "Region must be young but is %s", r->get_type_str());
 341 
 342     SurvRateGroup* group = r->surv_rate_group();
 343 
 344     if (group == NULL) {
 345       log_error(gc, verify)("## encountered NULL surv_rate_group in young region");
 346       _valid = false;
 347     }
 348 
 349     if (r->age_in_surv_rate_group() < 0) {
 350       log_error(gc, verify)("## encountered negative age in young region");
 351       _valid = false;
 352     }
 353 
 354     return false;
 355   }
 356 
 357   bool valid() const { return _valid; }
 358 };
 359 
 360 bool G1CollectionSet::verify_young_ages() {
 361   assert_at_safepoint_on_vm_thread();
 362 
 363   G1VerifyYoungAgesClosure cl;
 364   iterate(&cl);
 365 
 366   if (!cl.valid()) {
 367     LogStreamHandle(Error, gc, verify) log;
 368     print(&log);
 369   }
 370 
 371   return cl.valid();
 372 }
 373 
 374 class G1PrintCollectionSetDetailClosure : public HeapRegionClosure {
 375   outputStream* _st;
 376 public:
 377   G1PrintCollectionSetDetailClosure(outputStream* st) : HeapRegionClosure(), _st(st) { }
 378 
 379   virtual bool do_heap_region(HeapRegion* r) {
 380     assert(r->in_collection_set(), "Region %u should be in collection set", r->hrm_index());
 381     _st->print_cr("  " HR_FORMAT ", P: " PTR_FORMAT "N: " PTR_FORMAT ", age: %4d",
 382                   HR_FORMAT_PARAMS(r),
 383                   p2i(r->prev_top_at_mark_start()),
 384                   p2i(r->next_top_at_mark_start()),
 385                   r->age_in_surv_rate_group_cond());
 386     return false;
 387   }
 388 };
 389 
 390 void G1CollectionSet::print(outputStream* st) {
 391   st->print_cr("\nCollection_set:");
 392 
 393   G1PrintCollectionSetDetailClosure cl(st);
 394   iterate(&cl);
 395 }
 396 #endif // !PRODUCT
 397 
 398 double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
 399   double young_start_time_sec = os::elapsedTime();
 400 
 401   finalize_incremental_building();
 402 
 403   guarantee(target_pause_time_ms > 0.0,
 404             "target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
 405 
 406   size_t pending_cards = _policy->pending_cards();
 407   double base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
 408   double time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, 0.0);
 409 
 410   log_trace(gc, ergo, cset)("Start choosing CSet. pending cards: " SIZE_FORMAT " predicted base time: %1.2fms remaining time: %1.2fms target pause time: %1.2fms",
 411                             pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);
 412 
 413   // The young list is laid with the survivor regions from the previous
 414   // pause are appended to the RHS of the young list, i.e.
 415   //   [Newly Young Regions ++ Survivors from last pause].
 416 
 417   uint survivor_region_length = survivors->length();
 418   uint eden_region_length = _g1h->eden_regions_count();
 419   init_region_lengths(eden_region_length, survivor_region_length);
 420 
 421   verify_young_cset_indices();
 422 
 423   // Clear the fields that point to the survivor list - they are all young now.
 424   survivors->convert_to_eden();
 425 
 426   _bytes_used_before = _inc_bytes_used_before;
 427   time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, 0.0);
 428 
 429   log_trace(gc, ergo, cset)("Add young regions to CSet. eden: %u regions, survivors: %u regions, predicted young region time: %1.2fms, target pause time: %1.2fms",
 430                             eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);
 431 
 432   // The number of recorded young regions is the incremental
 433   // collection set's current size
 434   set_recorded_rs_lengths(_inc_recorded_rs_lengths);
 435 
 436   double young_end_time_sec = os::elapsedTime();
 437   phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * 1000.0);
 438 
 439   return time_remaining_ms;
 440 }
 441 
 442 static int compare_region_idx(const uint a, const uint b) {
 443   if (a > b) {
 444     return 1;
 445   } else if (a == b) {
 446     return 0;
 447   } else {
 448     return -1;
 449   }
 450 }
 451 
 452 void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
 453   double non_young_start_time_sec = os::elapsedTime();
 454 
 455   if (collector_state()->in_mixed_phase()) {
 456     candidates()->verify();
 457 
 458     uint num_initial_old_regions;
 459     uint num_optional_old_regions;
 460 
 461     _policy->calculate_old_collection_set_regions(candidates(),
 462                                                   time_remaining_ms,
 463                                                   num_initial_old_regions,
 464                                                   num_optional_old_regions);
 465 
 466     // Prepare initial old regions.
 467     move_candidates_to_collection_set(num_initial_old_regions);
 468 
 469     // Prepare optional old regions for evacuation.
 470     uint candidate_idx = candidates()->cur_idx();
 471     for (uint i = 0; i < num_optional_old_regions; i++) {
 472       add_optional_region(candidates()->at(candidate_idx + i));
 473     }
 474 
 475     candidates()->verify();
 476   }
 477 
 478   stop_incremental_building();
 479 
 480   double non_young_end_time_sec = os::elapsedTime();
 481   phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
 482 
 483   QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx, true);
 484 }
 485 
 486 void G1CollectionSet::move_candidates_to_collection_set(uint num_old_candidate_regions) {
 487   if (num_old_candidate_regions == 0) {
 488     return;
 489   }
 490   uint candidate_idx = candidates()->cur_idx();
 491   for (uint i = 0; i < num_old_candidate_regions; i++) {
 492     HeapRegion* r = candidates()->at(candidate_idx + i);
 493     // This potentially optional candidate region is going to be an actual collection
 494     // set region. Clear cset marker.
 495     _g1h->clear_region_attr(r);
 496     add_old_region(r);
 497   }
 498   candidates()->remove(num_old_candidate_regions);
 499 
 500   candidates()->verify();
 501 }
 502 
 503 void G1CollectionSet::finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) {
 504   double time_remaining_ms = finalize_young_part(target_pause_time_ms, survivor);
 505   finalize_old_part(time_remaining_ms);
 506 }
 507 
 508 bool G1CollectionSet::finalize_optional_for_evacuation(double remaining_pause_time) {
 509   update_incremental_marker();
 510 
 511   uint num_selected_regions;
 512   _policy->calculate_optional_collection_set_regions(candidates(),
 513                                                      _num_optional_regions,
 514                                                      remaining_pause_time,
 515                                                      num_selected_regions);
 516 
 517   move_candidates_to_collection_set(num_selected_regions);
 518 
 519   _num_optional_regions -= num_selected_regions;
 520 
 521   stop_incremental_building();
 522   return num_selected_regions > 0;
 523 }
 524 
 525 void G1CollectionSet::abandon_optional_collection_set(G1ParScanThreadStateSet* pss) {
 526   for (uint i = 0; i < _num_optional_regions; i++) {
 527     HeapRegion* r = candidates()->at(candidates()->cur_idx() + i);
 528     pss->record_unused_optional_region(r);
 529     _g1h->clear_region_attr(r);
 530     r->clear_index_in_opt_cset();
 531   }
 532   free_optional_regions();
 533 }
 534 
 535 #ifdef ASSERT
 536 class G1VerifyYoungCSetIndicesClosure : public HeapRegionClosure {
 537 private:
 538   size_t _young_length;
 539   int* _heap_region_indices;
 540 public:
 541   G1VerifyYoungCSetIndicesClosure(size_t young_length) : HeapRegionClosure(), _young_length(young_length) {
 542     _heap_region_indices = NEW_C_HEAP_ARRAY(int, young_length, mtGC);
 543     for (size_t i = 0; i < young_length; i++) {
 544       _heap_region_indices[i] = -1;
 545     }
 546   }
 547   ~G1VerifyYoungCSetIndicesClosure() {
 548     FREE_C_HEAP_ARRAY(int, _heap_region_indices);
 549   }
 550 
 551   virtual bool do_heap_region(HeapRegion* r) {
 552     const int idx = r->young_index_in_cset();
 553 
 554     assert(idx > -1, "Young index must be set for all regions in the incremental collection set but is not for region %u.", r->hrm_index());
 555     assert((size_t)idx < _young_length, "Young cset index too large for region %u", r->hrm_index());
 556 
 557     assert(_heap_region_indices[idx] == -1,
 558            "Index %d used by multiple regions, first use by region %u, second by region %u",
 559            idx, _heap_region_indices[idx], r->hrm_index());
 560 
 561     _heap_region_indices[idx] = r->hrm_index();
 562 
 563     return false;
 564   }
 565 };
 566 
 567 void G1CollectionSet::verify_young_cset_indices() const {
 568   assert_at_safepoint_on_vm_thread();
 569 
 570   G1VerifyYoungCSetIndicesClosure cl(_collection_set_cur_length);
 571   iterate(&cl);
 572 }
 573 #endif