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/heapRegionManager.inline.hpp"
  36 #include "gc/g1/heapRegionRemSet.hpp"
  37 #include "memory/iterator.hpp"
  38 #include "oops/oop.inline.hpp"
  39 #include "utilities/globalDefinitions.hpp"
  40 #include "utilities/intHisto.hpp"
  41 #include "utilities/stack.inline.hpp"
  42 
  43 G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs)
  44   : _g1(g1), _conc_refine_cards(0),
  45     _ct_bs(ct_bs), _g1p(_g1->g1_policy()),
  46     _cg1r(g1->concurrent_g1_refine()),
  47     _cset_rs_update_cl(NULL),
  48     _prev_period_summary(),
  49     _into_cset_dirty_card_queue_set(false)
  50 {
  51   _cset_rs_update_cl = NEW_C_HEAP_ARRAY(G1ParPushHeapRSClosure*, n_workers(), mtGC);
  52   for (uint i = 0; i < n_workers(); i++) {
  53     _cset_rs_update_cl[i] = NULL;
  54   }
  55   if (G1SummarizeRSetStats) {
  56     _prev_period_summary.initialize(this);
  57   }
  58   // Initialize the card queue set used to hold cards containing
  59   // references into the collection set.
  60   _into_cset_dirty_card_queue_set.initialize(NULL, // Should never be called by the Java code
  61                                              DirtyCardQ_CBL_mon,
  62                                              DirtyCardQ_FL_lock,
  63                                              -1, // never trigger processing
  64                                              -1, // no limit on length
  65                                              Shared_DirtyCardQ_lock,
  66                                              &JavaThread::dirty_card_queue_set());
  67 }
  68 
  69 G1RemSet::~G1RemSet() {
  70   for (uint i = 0; i < n_workers(); i++) {
  71     assert(_cset_rs_update_cl[i] == NULL, "it should be");
  72   }
  73   FREE_C_HEAP_ARRAY(G1ParPushHeapRSClosure*, _cset_rs_update_cl);
  74 }
  75 
  76 class ScanRSClosure : public HeapRegionClosure {
  77   size_t _cards_done, _cards;
  78   G1CollectedHeap* _g1h;
  79 
  80   G1ParPushHeapRSClosure* _oc;
  81   CodeBlobClosure* _code_root_cl;
  82 
  83   G1BlockOffsetSharedArray* _bot_shared;
  84   G1SATBCardTableModRefBS *_ct_bs;
  85 
  86   double _strong_code_root_scan_time_sec;
  87   uint   _worker_i;
  88   size_t _block_size;
  89   bool   _try_claimed;
  90 
  91 public:
  92   ScanRSClosure(G1ParPushHeapRSClosure* oc,
  93                 CodeBlobClosure* code_root_cl,
  94                 uint worker_i) :
  95     _oc(oc),
  96     _code_root_cl(code_root_cl),
  97     _strong_code_root_scan_time_sec(0.0),
  98     _cards(0),
  99     _cards_done(0),
 100     _worker_i(worker_i),
 101     _try_claimed(false)
 102   {
 103     _g1h = G1CollectedHeap::heap();
 104     _bot_shared = _g1h->bot_shared();
 105     _ct_bs = _g1h->g1_barrier_set();
 106     _block_size = MAX2<size_t>(G1RSetScanBlockSize, 1);
 107   }
 108 
 109   void set_try_claimed() { _try_claimed = true; }
 110 
 111   void scanCard(size_t index, HeapRegion *r) {
 112     // Stack allocate the DirtyCardToOopClosure instance
 113     HeapRegionDCTOC cl(_g1h, r, _oc,
 114                        CardTableModRefBS::Precise);
 115 
 116     // Set the "from" region in the closure.
 117     _oc->set_region(r);
 118     MemRegion card_region(_bot_shared->address_for_index(index), G1BlockOffsetSharedArray::N_words);
 119     MemRegion pre_gc_allocated(r->bottom(), r->scan_top());
 120     MemRegion mr = pre_gc_allocated.intersection(card_region);
 121     if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
 122       // We make the card as "claimed" lazily (so races are possible
 123       // but they're benign), which reduces the number of duplicate
 124       // scans (the rsets of the regions in the cset can intersect).
 125       _ct_bs->set_card_claimed(index);
 126       _cards_done++;
 127       cl.do_MemRegion(mr);
 128     }
 129   }
 130 
 131   void printCard(HeapRegion* card_region, size_t card_index,
 132                  HeapWord* card_start) {
 133     gclog_or_tty->print_cr("T %u Region [" PTR_FORMAT ", " PTR_FORMAT ") "
 134                            "RS names card " SIZE_FORMAT_HEX ": "
 135                            "[" PTR_FORMAT ", " PTR_FORMAT ")",
 136                            _worker_i,
 137                            p2i(card_region->bottom()), p2i(card_region->end()),
 138                            card_index,
 139                            p2i(card_start), p2i(card_start + G1BlockOffsetSharedArray::N_words));
 140   }
 141 
 142   void scan_strong_code_roots(HeapRegion* r) {
 143     double scan_start = os::elapsedTime();
 144     r->strong_code_roots_do(_code_root_cl);
 145     _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 146   }
 147 
 148   bool doHeapRegion(HeapRegion* r) {
 149     assert(r->in_collection_set(), "should only be called on elements of CS.");
 150     HeapRegionRemSet* hrrs = r->rem_set();
 151     if (hrrs->iter_is_complete()) return false; // All done.
 152     if (!_try_claimed && !hrrs->claim_iter()) return false;
 153     // If we ever free the collection set concurrently, we should also
 154     // clear the card table concurrently therefore we won't need to
 155     // add regions of the collection set to the dirty cards region.
 156     _g1h->push_dirty_cards_region(r);
 157     // If we didn't return above, then
 158     //   _try_claimed || r->claim_iter()
 159     // is true: either we're supposed to work on claimed-but-not-complete
 160     // regions, or we successfully claimed the region.
 161 
 162     HeapRegionRemSetIterator iter(hrrs);
 163     size_t card_index;
 164 
 165     // We claim cards in block so as to reduce the contention. The block size is determined by
 166     // the G1RSetScanBlockSize parameter.
 167     size_t jump_to_card = hrrs->iter_claimed_next(_block_size);
 168     for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 169       if (current_card >= jump_to_card + _block_size) {
 170         jump_to_card = hrrs->iter_claimed_next(_block_size);
 171       }
 172       if (current_card < jump_to_card) continue;
 173       HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);
 174 #if 0
 175       gclog_or_tty->print("Rem set iteration yielded card [" PTR_FORMAT ", " PTR_FORMAT ").\n",
 176                           card_start, card_start + CardTableModRefBS::card_size_in_words);
 177 #endif
 178 
 179       HeapRegion* card_region = _g1h->heap_region_containing(card_start);
 180       _cards++;
 181 
 182       if (!card_region->is_on_dirty_cards_region_list()) {
 183         _g1h->push_dirty_cards_region(card_region);
 184       }
 185 
 186       // If the card is dirty, then we will scan it during updateRS.
 187       if (!card_region->in_collection_set() &&
 188           !_ct_bs->is_card_dirty(card_index)) {
 189         scanCard(card_index, card_region);
 190       }
 191     }
 192     if (!_try_claimed) {
 193       // Scan the strong code root list attached to the current region
 194       scan_strong_code_roots(r);
 195 
 196       hrrs->set_iter_complete();
 197     }
 198     return false;
 199   }
 200 
 201   double strong_code_root_scan_time_sec() {
 202     return _strong_code_root_scan_time_sec;
 203   }
 204 
 205   size_t cards_done() { return _cards_done;}
 206   size_t cards_looked_up() { return _cards;}
 207 };
 208 
 209 size_t G1RemSet::scanRS(G1ParPushHeapRSClosure* oc,
 210                         CodeBlobClosure* heap_region_codeblobs,
 211                         uint worker_i) {
 212   double rs_time_start = os::elapsedTime();
 213 
 214   HeapRegion *startRegion = _g1->start_cset_region_for_worker(worker_i);
 215 
 216   ScanRSClosure scanRScl(oc, heap_region_codeblobs, worker_i);
 217 
 218   _g1->collection_set_iterate_from(startRegion, &scanRScl);
 219   scanRScl.set_try_claimed();
 220   _g1->collection_set_iterate_from(startRegion, &scanRScl);
 221 
 222   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start)
 223                             - scanRScl.strong_code_root_scan_time_sec();
 224 
 225   _g1p->phase_times()->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
 226   _g1p->phase_times()->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, scanRScl.strong_code_root_scan_time_sec());
 227 
 228   return scanRScl.cards_done();
 229 }
 230 
 231 // Closure used for updating RSets and recording references that
 232 // point into the collection set. Only called during an
 233 // evacuation pause.
 234 
 235 class RefineRecordRefsIntoCSCardTableEntryClosure: public CardTableEntryClosure {
 236   G1RemSet* _g1rs;
 237   DirtyCardQueue* _into_cset_dcq;
 238 public:
 239   RefineRecordRefsIntoCSCardTableEntryClosure(G1CollectedHeap* g1h,
 240                                               DirtyCardQueue* into_cset_dcq) :
 241     _g1rs(g1h->g1_rem_set()), _into_cset_dcq(into_cset_dcq)
 242   {}
 243 
 244   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 245     // The only time we care about recording cards that
 246     // contain references that point into the collection set
 247     // is during RSet updating within an evacuation pause.
 248     // In this case worker_i should be the id of a GC worker thread.
 249     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 250     assert(worker_i < ParallelGCThreads, "should be a GC worker");
 251 
 252     if (_g1rs->refine_card(card_ptr, worker_i, true)) {
 253       // 'card_ptr' contains references that point into the collection
 254       // set. We need to record the card in the DCQS
 255       // (_into_cset_dirty_card_queue_set)
 256       // that's used for that purpose.
 257       //
 258       // Enqueue the card
 259       _into_cset_dcq->enqueue(card_ptr);
 260     }
 261     return true;
 262   }
 263 };
 264 
 265 void G1RemSet::updateRS(DirtyCardQueue* into_cset_dcq, uint worker_i) {
 266   RefineRecordRefsIntoCSCardTableEntryClosure into_cset_update_rs_cl(_g1, into_cset_dcq);
 267 
 268   G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
 269   {
 270     // Apply the closure to the entries of the hot card cache.
 271     G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
 272     _g1->iterate_hcc_closure(&into_cset_update_rs_cl, worker_i);
 273   }
 274   // Apply the closure to all remaining log entries.
 275   _g1->iterate_dirty_card_closure(&into_cset_update_rs_cl, worker_i);
 276 }
 277 
 278 void G1RemSet::cleanupHRRS() {
 279   HeapRegionRemSet::cleanup();
 280 }
 281 
 282 size_t G1RemSet::oops_into_collection_set_do(G1ParPushHeapRSClosure* oc,
 283                                              CodeBlobClosure* heap_region_codeblobs,
 284                                              uint worker_i) {
 285   // We cache the value of 'oc' closure into the appropriate slot in the
 286   // _cset_rs_update_cl for this worker
 287   assert(worker_i < n_workers(), "sanity");
 288   _cset_rs_update_cl[worker_i] = oc;
 289 
 290   // A DirtyCardQueue that is used to hold cards containing references
 291   // that point into the collection set. This DCQ is associated with a
 292   // special DirtyCardQueueSet (see g1CollectedHeap.hpp).  Under normal
 293   // circumstances (i.e. the pause successfully completes), these cards
 294   // are just discarded (there's no need to update the RSets of regions
 295   // that were in the collection set - after the pause these regions
 296   // are wholly 'free' of live objects. In the event of an evacuation
 297   // failure the cards/buffers in this queue set are passed to the
 298   // DirtyCardQueueSet that is used to manage RSet updates
 299   DirtyCardQueue into_cset_dcq(&_into_cset_dirty_card_queue_set);
 300 
 301   updateRS(&into_cset_dcq, worker_i);
 302   size_t cards_scanned = scanRS(oc, heap_region_codeblobs, worker_i);
 303 
 304   // We now clear the cached values of _cset_rs_update_cl for this worker
 305   _cset_rs_update_cl[worker_i] = NULL;
 306   return cards_scanned;
 307 }
 308 
 309 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 310   cleanupHRRS();
 311   _g1->set_refine_cte_cl_concurrency(false);
 312   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 313   dcqs.concatenate_logs();
 314 }
 315 
 316 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 317   // Cleanup after copy
 318   _g1->set_refine_cte_cl_concurrency(true);
 319   // Set all cards back to clean.
 320   _g1->cleanUpCardTable();
 321 
 322   DirtyCardQueueSet& into_cset_dcqs = _into_cset_dirty_card_queue_set;
 323   int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();
 324 
 325   if (_g1->evacuation_failed()) {
 326     double restore_remembered_set_start = os::elapsedTime();
 327 
 328     // Restore remembered sets for the regions pointing into the collection set.
 329     // We just need to transfer the completed buffers from the DirtyCardQueueSet
 330     // used to hold cards that contain references that point into the collection set
 331     // to the DCQS used to hold the deferred RS updates.
 332     _g1->dirty_card_queue_set().merge_bufferlists(&into_cset_dcqs);
 333     _g1->g1_policy()->phase_times()->record_evac_fail_restore_remsets((os::elapsedTime() - restore_remembered_set_start) * 1000.0);
 334   }
 335 
 336   // Free any completed buffers in the DirtyCardQueueSet used to hold cards
 337   // which contain references that point into the collection.
 338   _into_cset_dirty_card_queue_set.clear();
 339   assert(_into_cset_dirty_card_queue_set.completed_buffers_num() == 0,
 340          "all buffers should be freed");
 341   _into_cset_dirty_card_queue_set.clear_n_completed_buffers();
 342 }
 343 
 344 class ScrubRSClosure: public HeapRegionClosure {
 345   G1CollectedHeap* _g1h;
 346   BitMap* _region_bm;
 347   BitMap* _card_bm;
 348   CardTableModRefBS* _ctbs;
 349 public:
 350   ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :
 351     _g1h(G1CollectedHeap::heap()),
 352     _region_bm(region_bm), _card_bm(card_bm),
 353     _ctbs(_g1h->g1_barrier_set()) {}
 354 
 355   bool doHeapRegion(HeapRegion* r) {
 356     if (!r->is_continues_humongous()) {
 357       r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);
 358     }
 359     return false;
 360   }
 361 };
 362 
 363 void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm, uint worker_num, HeapRegionClaimer *hrclaimer) {
 364   ScrubRSClosure scrub_cl(region_bm, card_bm);
 365   _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
 366 }
 367 
 368 G1TriggerClosure::G1TriggerClosure() :
 369   _triggered(false) { }
 370 
 371 G1InvokeIfNotTriggeredClosure::G1InvokeIfNotTriggeredClosure(G1TriggerClosure* t_cl,
 372                                                              OopClosure* oop_cl)  :
 373   _trigger_cl(t_cl), _oop_cl(oop_cl) { }
 374 
 375 G1Mux2Closure::G1Mux2Closure(OopClosure *c1, OopClosure *c2) :
 376   _c1(c1), _c2(c2) { }
 377 
 378 G1UpdateRSOrPushRefOopClosure::
 379 G1UpdateRSOrPushRefOopClosure(G1CollectedHeap* g1h,
 380                               G1RemSet* rs,
 381                               G1ParPushHeapRSClosure* push_ref_cl,
 382                               bool record_refs_into_cset,
 383                               uint worker_i) :
 384   _g1(g1h), _g1_rem_set(rs), _from(NULL),
 385   _record_refs_into_cset(record_refs_into_cset),
 386   _push_ref_cl(push_ref_cl), _worker_i(worker_i) { }
 387 
 388 // Returns true if the given card contains references that point
 389 // into the collection set, if we're checking for such references;
 390 // false otherwise.
 391 
 392 bool G1RemSet::refine_card(jbyte* card_ptr, uint worker_i,
 393                            bool check_for_refs_into_cset) {
 394   assert(_g1->is_in_exact(_ct_bs->addr_for(card_ptr)),
 395          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 396          p2i(card_ptr),
 397          _ct_bs->index_for(_ct_bs->addr_for(card_ptr)),
 398          p2i(_ct_bs->addr_for(card_ptr)),
 399          _g1->addr_to_region(_ct_bs->addr_for(card_ptr)));
 400 
 401   // If the card is no longer dirty, nothing to do.
 402   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 403     // No need to return that this card contains refs that point
 404     // into the collection set.
 405     return false;
 406   }
 407 
 408   // Construct the region representing the card.
 409   HeapWord* start = _ct_bs->addr_for(card_ptr);
 410   // And find the region containing it.
 411   HeapRegion* r = _g1->heap_region_containing(start);
 412 
 413   // Why do we have to check here whether a card is on a young region,
 414   // given that we dirty young regions and, as a result, the
 415   // post-barrier is supposed to filter them out and never to enqueue
 416   // them? When we allocate a new region as the "allocation region" we
 417   // actually dirty its cards after we release the lock, since card
 418   // dirtying while holding the lock was a performance bottleneck. So,
 419   // as a result, it is possible for other threads to actually
 420   // allocate objects in the region (after the acquire the lock)
 421   // before all the cards on the region are dirtied. This is unlikely,
 422   // and it doesn't happen often, but it can happen. So, the extra
 423   // check below filters out those cards.
 424   if (r->is_young()) {
 425     return false;
 426   }
 427 
 428   // While we are processing RSet buffers during the collection, we
 429   // actually don't want to scan any cards on the collection set,
 430   // since we don't want to update remembered sets with entries that
 431   // point into the collection set, given that live objects from the
 432   // collection set are about to move and such entries will be stale
 433   // very soon. This change also deals with a reliability issue which
 434   // involves scanning a card in the collection set and coming across
 435   // an array that was being chunked and looking malformed. Note,
 436   // however, that if evacuation fails, we have to scan any objects
 437   // that were not moved and create any missing entries.
 438   if (r->in_collection_set()) {
 439     return false;
 440   }
 441 
 442   // The result from the hot card cache insert call is either:
 443   //   * pointer to the current card
 444   //     (implying that the current card is not 'hot'),
 445   //   * null
 446   //     (meaning we had inserted the card ptr into the "hot" card cache,
 447   //     which had some headroom),
 448   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 449   //
 450 
 451   G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 452   if (hot_card_cache->use_cache()) {
 453     assert(!check_for_refs_into_cset, "sanity");
 454     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 455 
 456     card_ptr = hot_card_cache->insert(card_ptr);
 457     if (card_ptr == NULL) {
 458       // There was no eviction. Nothing to do.
 459       return false;
 460     }
 461 
 462     start = _ct_bs->addr_for(card_ptr);
 463     r = _g1->heap_region_containing(start);
 464 
 465     // Checking whether the region we got back from the cache
 466     // is young here is inappropriate. The region could have been
 467     // freed, reallocated and tagged as young while in the cache.
 468     // Hence we could see its young type change at any time.
 469   }
 470 
 471   // Don't use addr_for(card_ptr + 1) which can ask for
 472   // a card beyond the heap.  This is not safe without a perm
 473   // gen at the upper end of the heap.
 474   HeapWord* end   = start + CardTableModRefBS::card_size_in_words;
 475   MemRegion dirtyRegion(start, end);
 476 
 477   G1ParPushHeapRSClosure* oops_in_heap_closure = NULL;
 478   if (check_for_refs_into_cset) {
 479     // ConcurrentG1RefineThreads have worker numbers larger than what
 480     // _cset_rs_update_cl[] is set up to handle. But those threads should
 481     // only be active outside of a collection which means that when they
 482     // reach here they should have check_for_refs_into_cset == false.
 483     assert((size_t)worker_i < n_workers(), "index of worker larger than _cset_rs_update_cl[].length");
 484     oops_in_heap_closure = _cset_rs_update_cl[worker_i];
 485   }
 486   G1UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,
 487                                                  _g1->g1_rem_set(),
 488                                                  oops_in_heap_closure,
 489                                                  check_for_refs_into_cset,
 490                                                  worker_i);
 491   update_rs_oop_cl.set_from(r);
 492 
 493   G1TriggerClosure trigger_cl;
 494   FilterIntoCSClosure into_cs_cl(NULL, _g1, &trigger_cl);
 495   G1InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);
 496   G1Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);
 497 
 498   FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,
 499                         (check_for_refs_into_cset ?
 500                                 (OopClosure*)&mux :
 501                                 (OopClosure*)&update_rs_oop_cl));
 502 
 503   // The region for the current card may be a young region. The
 504   // current card may have been a card that was evicted from the
 505   // card cache. When the card was inserted into the cache, we had
 506   // determined that its region was non-young. While in the cache,
 507   // the region may have been freed during a cleanup pause, reallocated
 508   // and tagged as young.
 509   //
 510   // We wish to filter out cards for such a region but the current
 511   // thread, if we're running concurrently, may "see" the young type
 512   // change at any time (so an earlier "is_young" check may pass or
 513   // fail arbitrarily). We tell the iteration code to perform this
 514   // filtering when it has been determined that there has been an actual
 515   // allocation in this region and making it safe to check the young type.
 516   bool filter_young = true;
 517 
 518   HeapWord* stop_point =
 519     r->oops_on_card_seq_iterate_careful(dirtyRegion,
 520                                         &filter_then_update_rs_oop_cl,
 521                                         filter_young,
 522                                         card_ptr);
 523 
 524   // If stop_point is non-null, then we encountered an unallocated region
 525   // (perhaps the unfilled portion of a TLAB.)  For now, we'll dirty the
 526   // card and re-enqueue: if we put off the card until a GC pause, then the
 527   // unallocated portion will be filled in.  Alternatively, we might try
 528   // the full complexity of the technique used in "regular" precleaning.
 529   if (stop_point != NULL) {
 530     // The card might have gotten re-dirtied and re-enqueued while we
 531     // worked.  (In fact, it's pretty likely.)
 532     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 533       *card_ptr = CardTableModRefBS::dirty_card_val();
 534       MutexLockerEx x(Shared_DirtyCardQ_lock,
 535                       Mutex::_no_safepoint_check_flag);
 536       DirtyCardQueue* sdcq =
 537         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 538       sdcq->enqueue(card_ptr);
 539     }
 540   } else {
 541     _conc_refine_cards++;
 542   }
 543 
 544   // This gets set to true if the card being refined has
 545   // references that point into the collection set.
 546   bool has_refs_into_cset = trigger_cl.triggered();
 547 
 548   // We should only be detecting that the card contains references
 549   // that point into the collection set if the current thread is
 550   // a GC worker thread.
 551   assert(!has_refs_into_cset || SafepointSynchronize::is_at_safepoint(),
 552            "invalid result at non safepoint");
 553 
 554   return has_refs_into_cset;
 555 }
 556 
 557 void G1RemSet::print_periodic_summary_info(const char* header) {
 558   G1RemSetSummary current;
 559   current.initialize(this);
 560 
 561   _prev_period_summary.subtract_from(&current);
 562   print_summary_info(&_prev_period_summary, header);
 563 
 564   _prev_period_summary.set(&current);
 565 }
 566 
 567 void G1RemSet::print_summary_info() {
 568   G1RemSetSummary current;
 569   current.initialize(this);
 570 
 571   print_summary_info(&current, " Cumulative RS summary");
 572 }
 573 
 574 void G1RemSet::print_summary_info(G1RemSetSummary * summary, const char * header) {
 575   assert(summary != NULL, "just checking");
 576 
 577   if (header != NULL) {
 578     gclog_or_tty->print_cr("%s", header);
 579   }
 580 
 581   summary->print_on(gclog_or_tty);
 582 }
 583 
 584 void G1RemSet::prepare_for_verify() {
 585   if (G1HRRSFlushLogBuffersOnVerify &&
 586       (VerifyBeforeGC || VerifyAfterGC)
 587       &&  (!_g1->collector_state()->full_collection() || G1VerifyRSetsDuringFullGC)) {
 588     cleanupHRRS();
 589     _g1->set_refine_cte_cl_concurrency(false);
 590     if (SafepointSynchronize::is_at_safepoint()) {
 591       DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 592       dcqs.concatenate_logs();
 593     }
 594 
 595     G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 596     bool use_hot_card_cache = hot_card_cache->use_cache();
 597     hot_card_cache->set_use_cache(false);
 598 
 599     DirtyCardQueue into_cset_dcq(&_into_cset_dirty_card_queue_set);
 600     updateRS(&into_cset_dcq, 0);
 601     _into_cset_dirty_card_queue_set.clear();
 602 
 603     hot_card_cache->set_use_cache(use_hot_card_cache);
 604     assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");
 605   }
 606 }
--- EOF ---