1 /*
   2  * Copyright (c) 2001, 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 "gc/g1/concurrentG1Refine.hpp"
  27 #include "gc/g1/concurrentG1RefineThread.hpp"
  28 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
  29 #include "gc/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc/g1/g1CollectorPolicy.hpp"
  31 #include "gc/g1/g1GCPhaseTimes.hpp"
  32 #include "gc/g1/g1HotCardCache.hpp"
  33 #include "gc/g1/g1OopClosures.inline.hpp"
  34 #include "gc/g1/g1RemSet.inline.hpp"
  35 #include "gc/g1/heapRegion.inline.hpp"
  36 #include "gc/g1/heapRegionManager.inline.hpp"
  37 #include "gc/g1/heapRegionRemSet.hpp"
  38 #include "memory/iterator.hpp"
  39 #include "oops/oop.inline.hpp"
  40 #include "utilities/globalDefinitions.hpp"
  41 #include "utilities/intHisto.hpp"
  42 #include "utilities/stack.inline.hpp"
  43 
  44 G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs) :
  45   _g1(g1),
  46   _conc_refine_cards(0),
  47   _ct_bs(ct_bs),
  48   _g1p(_g1->g1_policy()),
  49   _cg1r(g1->concurrent_g1_refine()),
  50   _cset_rs_update_cl(NULL),
  51   _prev_period_summary(),
  52   _into_cset_dirty_card_queue_set(false)
  53 {
  54   _cset_rs_update_cl = NEW_C_HEAP_ARRAY(G1ParPushHeapRSClosure*, n_workers(), mtGC);
  55   for (uint i = 0; i < n_workers(); i++) {
  56     _cset_rs_update_cl[i] = NULL;
  57   }
  58   if (log_is_enabled(Trace, gc, remset)) {
  59     _prev_period_summary.initialize(this);
  60   }
  61   // Initialize the card queue set used to hold cards containing
  62   // references into the collection set.
  63   _into_cset_dirty_card_queue_set.initialize(NULL, // Should never be called by the Java code
  64                                              DirtyCardQ_CBL_mon,
  65                                              DirtyCardQ_FL_lock,
  66                                              -1, // never trigger processing
  67                                              -1, // no limit on length
  68                                              Shared_DirtyCardQ_lock,
  69                                              &JavaThread::dirty_card_queue_set());
  70 }
  71 
  72 G1RemSet::~G1RemSet() {
  73   for (uint i = 0; i < n_workers(); i++) {
  74     assert(_cset_rs_update_cl[i] == NULL, "it should be");
  75   }
  76   FREE_C_HEAP_ARRAY(G1ParPushHeapRSClosure*, _cset_rs_update_cl);
  77 }
  78 
  79 ScanRSClosure::ScanRSClosure(G1ParPushHeapRSClosure* oc,
  80                              CodeBlobClosure* code_root_cl,
  81                              uint worker_i) :
  82   _oc(oc),
  83   _code_root_cl(code_root_cl),
  84   _strong_code_root_scan_time_sec(0.0),
  85   _cards(0),
  86   _cards_done(0),
  87   _worker_i(worker_i),
  88   _try_claimed(false) {
  89   _g1h = G1CollectedHeap::heap();
  90   _bot_shared = _g1h->bot_shared();
  91   _ct_bs = _g1h->g1_barrier_set();
  92   _block_size = MAX2<size_t>(G1RSetScanBlockSize, 1);
  93 }
  94 
  95 void ScanRSClosure::scanCard(size_t index, HeapRegion *r) {
  96   // Stack allocate the DirtyCardToOopClosure instance
  97   HeapRegionDCTOC cl(_g1h, r, _oc,
  98       CardTableModRefBS::Precise);
  99 
 100   // Set the "from" region in the closure.
 101   _oc->set_region(r);
 102   MemRegion card_region(_bot_shared->address_for_index(index), G1BlockOffsetSharedArray::N_words);
 103   MemRegion pre_gc_allocated(r->bottom(), r->scan_top());
 104   MemRegion mr = pre_gc_allocated.intersection(card_region);
 105   if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
 106     // We make the card as "claimed" lazily (so races are possible
 107     // but they're benign), which reduces the number of duplicate
 108     // scans (the rsets of the regions in the cset can intersect).
 109     _ct_bs->set_card_claimed(index);
 110     _cards_done++;
 111     cl.do_MemRegion(mr);
 112   }
 113 }
 114 
 115 void ScanRSClosure::scan_strong_code_roots(HeapRegion* r) {
 116   double scan_start = os::elapsedTime();
 117   r->strong_code_roots_do(_code_root_cl);
 118   _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 119 }
 120 
 121 bool ScanRSClosure::doHeapRegion(HeapRegion* r) {
 122   assert(r->in_collection_set(), "should only be called on elements of CS.");
 123   HeapRegionRemSet* hrrs = r->rem_set();
 124   if (hrrs->iter_is_complete()) return false; // All done.
 125   if (!_try_claimed && !hrrs->claim_iter()) return false;
 126   // If we ever free the collection set concurrently, we should also
 127   // clear the card table concurrently therefore we won't need to
 128   // add regions of the collection set to the dirty cards region.
 129   _g1h->push_dirty_cards_region(r);
 130   // If we didn't return above, then
 131   //   _try_claimed || r->claim_iter()
 132   // is true: either we're supposed to work on claimed-but-not-complete
 133   // regions, or we successfully claimed the region.
 134 
 135   HeapRegionRemSetIterator iter(hrrs);
 136   size_t card_index;
 137 
 138   // We claim cards in block so as to reduce the contention. The block size is determined by
 139   // the G1RSetScanBlockSize parameter.
 140   size_t jump_to_card = hrrs->iter_claimed_next(_block_size);
 141   for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 142     if (current_card >= jump_to_card + _block_size) {
 143       jump_to_card = hrrs->iter_claimed_next(_block_size);
 144     }
 145     if (current_card < jump_to_card) continue;
 146     HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);
 147 
 148     HeapRegion* card_region = _g1h->heap_region_containing(card_start);
 149     _cards++;
 150 
 151     if (!card_region->is_on_dirty_cards_region_list()) {
 152       _g1h->push_dirty_cards_region(card_region);
 153     }
 154 
 155     // If the card is dirty, then we will scan it during updateRS.
 156     if (!card_region->in_collection_set() &&
 157         !_ct_bs->is_card_dirty(card_index)) {
 158       scanCard(card_index, card_region);
 159     }
 160   }
 161   if (!_try_claimed) {
 162     // Scan the strong code root list attached to the current region
 163     scan_strong_code_roots(r);
 164 
 165     hrrs->set_iter_complete();
 166   }
 167   return false;
 168 }
 169 
 170 size_t G1RemSet::scanRS(G1ParPushHeapRSClosure* oc,
 171                         CodeBlobClosure* heap_region_codeblobs,
 172                         uint worker_i) {
 173   double rs_time_start = os::elapsedTime();
 174 
 175   HeapRegion *startRegion = _g1->start_cset_region_for_worker(worker_i);
 176 
 177   ScanRSClosure scanRScl(oc, heap_region_codeblobs, worker_i);
 178 
 179   _g1->collection_set_iterate_from(startRegion, &scanRScl);
 180   scanRScl.set_try_claimed();
 181   _g1->collection_set_iterate_from(startRegion, &scanRScl);
 182 
 183   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start)
 184                             - scanRScl.strong_code_root_scan_time_sec();
 185 
 186   _g1p->phase_times()->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
 187   _g1p->phase_times()->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, scanRScl.strong_code_root_scan_time_sec());
 188 
 189   return scanRScl.cards_done();
 190 }
 191 
 192 // Closure used for updating RSets and recording references that
 193 // point into the collection set. Only called during an
 194 // evacuation pause.
 195 
 196 class RefineRecordRefsIntoCSCardTableEntryClosure: public CardTableEntryClosure {
 197   G1RemSet* _g1rs;
 198   DirtyCardQueue* _into_cset_dcq;
 199 public:
 200   RefineRecordRefsIntoCSCardTableEntryClosure(G1CollectedHeap* g1h,
 201                                               DirtyCardQueue* into_cset_dcq) :
 202     _g1rs(g1h->g1_rem_set()), _into_cset_dcq(into_cset_dcq)
 203   {}
 204 
 205   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 206     // The only time we care about recording cards that
 207     // contain references that point into the collection set
 208     // is during RSet updating within an evacuation pause.
 209     // In this case worker_i should be the id of a GC worker thread.
 210     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 211     assert(worker_i < ParallelGCThreads, "should be a GC worker");
 212 
 213     if (_g1rs->refine_card(card_ptr, worker_i, true)) {
 214       // 'card_ptr' contains references that point into the collection
 215       // set. We need to record the card in the DCQS
 216       // (_into_cset_dirty_card_queue_set)
 217       // that's used for that purpose.
 218       //
 219       // Enqueue the card
 220       _into_cset_dcq->enqueue(card_ptr);
 221     }
 222     return true;
 223   }
 224 };
 225 
 226 void G1RemSet::updateRS(DirtyCardQueue* into_cset_dcq, uint worker_i) {
 227   RefineRecordRefsIntoCSCardTableEntryClosure into_cset_update_rs_cl(_g1, into_cset_dcq);
 228 
 229   G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
 230   {
 231     // Apply the closure to the entries of the hot card cache.
 232     G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
 233     _g1->iterate_hcc_closure(&into_cset_update_rs_cl, worker_i);
 234   }
 235   // Apply the closure to all remaining log entries.
 236   _g1->iterate_dirty_card_closure(&into_cset_update_rs_cl, worker_i);
 237 }
 238 
 239 void G1RemSet::cleanupHRRS() {
 240   HeapRegionRemSet::cleanup();
 241 }
 242 
 243 size_t G1RemSet::oops_into_collection_set_do(G1ParPushHeapRSClosure* oc,
 244                                              CodeBlobClosure* heap_region_codeblobs,
 245                                              uint worker_i) {
 246   // We cache the value of 'oc' closure into the appropriate slot in the
 247   // _cset_rs_update_cl for this worker
 248   assert(worker_i < n_workers(), "sanity");
 249   _cset_rs_update_cl[worker_i] = oc;
 250 
 251   // A DirtyCardQueue that is used to hold cards containing references
 252   // that point into the collection set. This DCQ is associated with a
 253   // special DirtyCardQueueSet (see g1CollectedHeap.hpp).  Under normal
 254   // circumstances (i.e. the pause successfully completes), these cards
 255   // are just discarded (there's no need to update the RSets of regions
 256   // that were in the collection set - after the pause these regions
 257   // are wholly 'free' of live objects. In the event of an evacuation
 258   // failure the cards/buffers in this queue set are passed to the
 259   // DirtyCardQueueSet that is used to manage RSet updates
 260   DirtyCardQueue into_cset_dcq(&_into_cset_dirty_card_queue_set);
 261 
 262   updateRS(&into_cset_dcq, worker_i);
 263   size_t cards_scanned = scanRS(oc, heap_region_codeblobs, worker_i);
 264 
 265   // We now clear the cached values of _cset_rs_update_cl for this worker
 266   _cset_rs_update_cl[worker_i] = NULL;
 267   return cards_scanned;
 268 }
 269 
 270 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 271   _g1->set_refine_cte_cl_concurrency(false);
 272   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 273   dcqs.concatenate_logs();
 274 }
 275 
 276 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 277   // Cleanup after copy
 278   _g1->set_refine_cte_cl_concurrency(true);
 279   // Set all cards back to clean.
 280   _g1->cleanUpCardTable();
 281 
 282   DirtyCardQueueSet& into_cset_dcqs = _into_cset_dirty_card_queue_set;
 283   int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();
 284 
 285   if (_g1->evacuation_failed()) {
 286     double restore_remembered_set_start = os::elapsedTime();
 287 
 288     // Restore remembered sets for the regions pointing into the collection set.
 289     // We just need to transfer the completed buffers from the DirtyCardQueueSet
 290     // used to hold cards that contain references that point into the collection set
 291     // to the DCQS used to hold the deferred RS updates.
 292     _g1->dirty_card_queue_set().merge_bufferlists(&into_cset_dcqs);
 293     _g1->g1_policy()->phase_times()->record_evac_fail_restore_remsets((os::elapsedTime() - restore_remembered_set_start) * 1000.0);
 294   }
 295 
 296   // Free any completed buffers in the DirtyCardQueueSet used to hold cards
 297   // which contain references that point into the collection.
 298   _into_cset_dirty_card_queue_set.clear();
 299   assert(_into_cset_dirty_card_queue_set.completed_buffers_num() == 0,
 300          "all buffers should be freed");
 301   _into_cset_dirty_card_queue_set.clear_n_completed_buffers();
 302 }
 303 
 304 class ScrubRSClosure: public HeapRegionClosure {
 305   G1CollectedHeap* _g1h;
 306   BitMap* _region_bm;
 307   BitMap* _card_bm;
 308   CardTableModRefBS* _ctbs;
 309 public:
 310   ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :
 311     _g1h(G1CollectedHeap::heap()),
 312     _region_bm(region_bm), _card_bm(card_bm),
 313     _ctbs(_g1h->g1_barrier_set()) {}
 314 
 315   bool doHeapRegion(HeapRegion* r) {
 316     if (!r->is_continues_humongous()) {
 317       r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);
 318     }
 319     return false;
 320   }
 321 };
 322 
 323 void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm, uint worker_num, HeapRegionClaimer *hrclaimer) {
 324   ScrubRSClosure scrub_cl(region_bm, card_bm);
 325   _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
 326 }
 327 
 328 G1TriggerClosure::G1TriggerClosure() :
 329   _triggered(false) { }
 330 
 331 G1InvokeIfNotTriggeredClosure::G1InvokeIfNotTriggeredClosure(G1TriggerClosure* t_cl,
 332                                                              OopClosure* oop_cl)  :
 333   _trigger_cl(t_cl), _oop_cl(oop_cl) { }
 334 
 335 G1Mux2Closure::G1Mux2Closure(OopClosure *c1, OopClosure *c2) :
 336   _c1(c1), _c2(c2) { }
 337 
 338 G1UpdateRSOrPushRefOopClosure::
 339 G1UpdateRSOrPushRefOopClosure(G1CollectedHeap* g1h,
 340                               G1RemSet* rs,
 341                               G1ParPushHeapRSClosure* push_ref_cl,
 342                               bool record_refs_into_cset,
 343                               uint worker_i) :
 344   _g1(g1h), _g1_rem_set(rs), _from(NULL),
 345   _record_refs_into_cset(record_refs_into_cset),
 346   _push_ref_cl(push_ref_cl), _worker_i(worker_i) { }
 347 
 348 // Returns true if the given card contains references that point
 349 // into the collection set, if we're checking for such references;
 350 // false otherwise.
 351 
 352 bool G1RemSet::refine_card(jbyte* card_ptr, uint worker_i,
 353                            bool check_for_refs_into_cset) {
 354   assert(_g1->is_in_exact(_ct_bs->addr_for(card_ptr)),
 355          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 356          p2i(card_ptr),
 357          _ct_bs->index_for(_ct_bs->addr_for(card_ptr)),
 358          p2i(_ct_bs->addr_for(card_ptr)),
 359          _g1->addr_to_region(_ct_bs->addr_for(card_ptr)));
 360 
 361   // If the card is no longer dirty, nothing to do.
 362   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 363     // No need to return that this card contains refs that point
 364     // into the collection set.
 365     return false;
 366   }
 367 
 368   // Construct the region representing the card.
 369   HeapWord* start = _ct_bs->addr_for(card_ptr);
 370   // And find the region containing it.
 371   HeapRegion* r = _g1->heap_region_containing(start);
 372 
 373   // Why do we have to check here whether a card is on a young region,
 374   // given that we dirty young regions and, as a result, the
 375   // post-barrier is supposed to filter them out and never to enqueue
 376   // them? When we allocate a new region as the "allocation region" we
 377   // actually dirty its cards after we release the lock, since card
 378   // dirtying while holding the lock was a performance bottleneck. So,
 379   // as a result, it is possible for other threads to actually
 380   // allocate objects in the region (after the acquire the lock)
 381   // before all the cards on the region are dirtied. This is unlikely,
 382   // and it doesn't happen often, but it can happen. So, the extra
 383   // check below filters out those cards.
 384   if (r->is_young()) {
 385     return false;
 386   }
 387 
 388   // While we are processing RSet buffers during the collection, we
 389   // actually don't want to scan any cards on the collection set,
 390   // since we don't want to update remembered sets with entries that
 391   // point into the collection set, given that live objects from the
 392   // collection set are about to move and such entries will be stale
 393   // very soon. This change also deals with a reliability issue which
 394   // involves scanning a card in the collection set and coming across
 395   // an array that was being chunked and looking malformed. Note,
 396   // however, that if evacuation fails, we have to scan any objects
 397   // that were not moved and create any missing entries.
 398   if (r->in_collection_set()) {
 399     return false;
 400   }
 401 
 402   // The result from the hot card cache insert call is either:
 403   //   * pointer to the current card
 404   //     (implying that the current card is not 'hot'),
 405   //   * null
 406   //     (meaning we had inserted the card ptr into the "hot" card cache,
 407   //     which had some headroom),
 408   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 409   //
 410 
 411   G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 412   if (hot_card_cache->use_cache()) {
 413     assert(!check_for_refs_into_cset, "sanity");
 414     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 415 
 416     card_ptr = hot_card_cache->insert(card_ptr);
 417     if (card_ptr == NULL) {
 418       // There was no eviction. Nothing to do.
 419       return false;
 420     }
 421 
 422     start = _ct_bs->addr_for(card_ptr);
 423     r = _g1->heap_region_containing(start);
 424 
 425     // Checking whether the region we got back from the cache
 426     // is young here is inappropriate. The region could have been
 427     // freed, reallocated and tagged as young while in the cache.
 428     // Hence we could see its young type change at any time.
 429   }
 430 
 431   // Don't use addr_for(card_ptr + 1) which can ask for
 432   // a card beyond the heap.  This is not safe without a perm
 433   // gen at the upper end of the heap.
 434   HeapWord* end   = start + CardTableModRefBS::card_size_in_words;
 435   MemRegion dirtyRegion(start, end);
 436 
 437   G1ParPushHeapRSClosure* oops_in_heap_closure = NULL;
 438   if (check_for_refs_into_cset) {
 439     // ConcurrentG1RefineThreads have worker numbers larger than what
 440     // _cset_rs_update_cl[] is set up to handle. But those threads should
 441     // only be active outside of a collection which means that when they
 442     // reach here they should have check_for_refs_into_cset == false.
 443     assert((size_t)worker_i < n_workers(), "index of worker larger than _cset_rs_update_cl[].length");
 444     oops_in_heap_closure = _cset_rs_update_cl[worker_i];
 445   }
 446   G1UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,
 447                                                  _g1->g1_rem_set(),
 448                                                  oops_in_heap_closure,
 449                                                  check_for_refs_into_cset,
 450                                                  worker_i);
 451   update_rs_oop_cl.set_from(r);
 452 
 453   G1TriggerClosure trigger_cl;
 454   FilterIntoCSClosure into_cs_cl(_g1, &trigger_cl);
 455   G1InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);
 456   G1Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);
 457 
 458   FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,
 459                         (check_for_refs_into_cset ?
 460                                 (OopClosure*)&mux :
 461                                 (OopClosure*)&update_rs_oop_cl));
 462 
 463   // The region for the current card may be a young region. The
 464   // current card may have been a card that was evicted from the
 465   // card cache. When the card was inserted into the cache, we had
 466   // determined that its region was non-young. While in the cache,
 467   // the region may have been freed during a cleanup pause, reallocated
 468   // and tagged as young.
 469   //
 470   // We wish to filter out cards for such a region but the current
 471   // thread, if we're running concurrently, may "see" the young type
 472   // change at any time (so an earlier "is_young" check may pass or
 473   // fail arbitrarily). We tell the iteration code to perform this
 474   // filtering when it has been determined that there has been an actual
 475   // allocation in this region and making it safe to check the young type.
 476   bool filter_young = true;
 477 
 478   HeapWord* stop_point =
 479     r->oops_on_card_seq_iterate_careful(dirtyRegion,
 480                                         &filter_then_update_rs_oop_cl,
 481                                         filter_young,
 482                                         card_ptr);
 483 
 484   // If stop_point is non-null, then we encountered an unallocated region
 485   // (perhaps the unfilled portion of a TLAB.)  For now, we'll dirty the
 486   // card and re-enqueue: if we put off the card until a GC pause, then the
 487   // unallocated portion will be filled in.  Alternatively, we might try
 488   // the full complexity of the technique used in "regular" precleaning.
 489   if (stop_point != NULL) {
 490     // The card might have gotten re-dirtied and re-enqueued while we
 491     // worked.  (In fact, it's pretty likely.)
 492     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 493       *card_ptr = CardTableModRefBS::dirty_card_val();
 494       MutexLockerEx x(Shared_DirtyCardQ_lock,
 495                       Mutex::_no_safepoint_check_flag);
 496       DirtyCardQueue* sdcq =
 497         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 498       sdcq->enqueue(card_ptr);
 499     }
 500   } else {
 501     _conc_refine_cards++;
 502   }
 503 
 504   // This gets set to true if the card being refined has
 505   // references that point into the collection set.
 506   bool has_refs_into_cset = trigger_cl.triggered();
 507 
 508   // We should only be detecting that the card contains references
 509   // that point into the collection set if the current thread is
 510   // a GC worker thread.
 511   assert(!has_refs_into_cset || SafepointSynchronize::is_at_safepoint(),
 512            "invalid result at non safepoint");
 513 
 514   return has_refs_into_cset;
 515 }
 516 
 517 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
 518   if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
 519       (period_count % G1SummarizeRSetStatsPeriod == 0)) {
 520 
 521     if (!_prev_period_summary.initialized()) {
 522       _prev_period_summary.initialize(this);
 523     }
 524 
 525     G1RemSetSummary current;
 526     current.initialize(this);
 527     _prev_period_summary.subtract_from(&current);
 528 
 529     LogHandle(gc, remset) log;
 530     log.trace("%s", header);
 531     ResourceMark rm;
 532     _prev_period_summary.print_on(log.trace_stream());
 533 
 534     _prev_period_summary.set(&current);
 535   }
 536 }
 537 
 538 void G1RemSet::print_summary_info() {
 539   LogHandle(gc, remset, exit) log;
 540   if (log.is_trace()) {
 541     log.trace(" Cumulative RS summary");
 542     G1RemSetSummary current;
 543     current.initialize(this);
 544     ResourceMark rm;
 545     current.print_on(log.trace_stream());
 546   }
 547 }
 548 
 549 void G1RemSet::prepare_for_verify() {
 550   if (G1HRRSFlushLogBuffersOnVerify &&
 551       (VerifyBeforeGC || VerifyAfterGC)
 552       &&  (!_g1->collector_state()->full_collection() || G1VerifyRSetsDuringFullGC)) {
 553     cleanupHRRS();
 554     _g1->set_refine_cte_cl_concurrency(false);
 555     if (SafepointSynchronize::is_at_safepoint()) {
 556       DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 557       dcqs.concatenate_logs();
 558     }
 559 
 560     G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 561     bool use_hot_card_cache = hot_card_cache->use_cache();
 562     hot_card_cache->set_use_cache(false);
 563 
 564     DirtyCardQueue into_cset_dcq(&_into_cset_dirty_card_queue_set);
 565     updateRS(&into_cset_dcq, 0);
 566     _into_cset_dirty_card_queue_set.clear();
 567 
 568     hot_card_cache->set_use_cache(use_hot_card_cache);
 569     assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");
 570   }
 571 }