1 /*
   2  * Copyright (c) 2001, 2012, 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 "code/nmethod.hpp"
  27 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
  28 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
  29 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
  30 #include "gc_implementation/g1/heapRegion.inline.hpp"
  31 #include "gc_implementation/g1/heapRegionRemSet.hpp"
  32 #include "gc_implementation/g1/heapRegionSeq.inline.hpp"
  33 #include "memory/genOopClosures.inline.hpp"
  34 #include "memory/iterator.hpp"
  35 #include "oops/oop.inline.hpp"
  36 
  37 int    HeapRegion::LogOfHRGrainBytes = 0;
  38 int    HeapRegion::LogOfHRGrainWords = 0;
  39 size_t HeapRegion::GrainBytes        = 0;
  40 size_t HeapRegion::GrainWords        = 0;
  41 size_t HeapRegion::CardsPerRegion    = 0;
  42 
  43 HeapRegionDCTOC::HeapRegionDCTOC(G1CollectedHeap* g1,
  44                                  HeapRegion* hr, ExtendedOopClosure* cl,
  45                                  CardTableModRefBS::PrecisionStyle precision,
  46                                  FilterKind fk) :
  47   ContiguousSpaceDCTOC(hr, cl, precision, NULL),
  48   _hr(hr), _fk(fk), _g1(g1) { }
  49 
  50 FilterOutOfRegionClosure::FilterOutOfRegionClosure(HeapRegion* r,
  51                                                    OopClosure* oc) :
  52   _r_bottom(r->bottom()), _r_end(r->end()), _oc(oc) { }
  53 
  54 template<class ClosureType>
  55 HeapWord* walk_mem_region_loop(ClosureType* cl, G1CollectedHeap* g1h,
  56                                HeapRegion* hr,
  57                                HeapWord* cur, HeapWord* top) {
  58   oop cur_oop = oop(cur);
  59   int oop_size = cur_oop->size();
  60   HeapWord* next_obj = cur + oop_size;
  61   while (next_obj < top) {
  62     // Keep filtering the remembered set.
  63     if (!g1h->is_obj_dead(cur_oop, hr)) {
  64       // Bottom lies entirely below top, so we can call the
  65       // non-memRegion version of oop_iterate below.
  66       cur_oop->oop_iterate(cl);
  67     }
  68     cur = next_obj;
  69     cur_oop = oop(cur);
  70     oop_size = cur_oop->size();
  71     next_obj = cur + oop_size;
  72   }
  73   return cur;
  74 }
  75 
  76 void HeapRegionDCTOC::walk_mem_region_with_cl(MemRegion mr,
  77                                               HeapWord* bottom,
  78                                               HeapWord* top,
  79                                               ExtendedOopClosure* cl) {
  80   G1CollectedHeap* g1h = _g1;
  81   int oop_size;
  82   ExtendedOopClosure* cl2 = NULL;
  83 
  84   FilterIntoCSClosure intoCSFilt(this, g1h, cl);
  85   FilterOutOfRegionClosure outOfRegionFilt(_hr, cl);
  86 
  87   switch (_fk) {
  88   case NoFilterKind:          cl2 = cl; break;
  89   case IntoCSFilterKind:      cl2 = &intoCSFilt; break;
  90   case OutOfRegionFilterKind: cl2 = &outOfRegionFilt; break;
  91   default:                    ShouldNotReachHere();
  92   }
  93 
  94   // Start filtering what we add to the remembered set. If the object is
  95   // not considered dead, either because it is marked (in the mark bitmap)
  96   // or it was allocated after marking finished, then we add it. Otherwise
  97   // we can safely ignore the object.
  98   if (!g1h->is_obj_dead(oop(bottom), _hr)) {
  99     oop_size = oop(bottom)->oop_iterate(cl2, mr);
 100   } else {
 101     oop_size = oop(bottom)->size();
 102   }
 103 
 104   bottom += oop_size;
 105 
 106   if (bottom < top) {
 107     // We replicate the loop below for several kinds of possible filters.
 108     switch (_fk) {
 109     case NoFilterKind:
 110       bottom = walk_mem_region_loop(cl, g1h, _hr, bottom, top);
 111       break;
 112 
 113     case IntoCSFilterKind: {
 114       FilterIntoCSClosure filt(this, g1h, cl);
 115       bottom = walk_mem_region_loop(&filt, g1h, _hr, bottom, top);
 116       break;
 117     }
 118 
 119     case OutOfRegionFilterKind: {
 120       FilterOutOfRegionClosure filt(_hr, cl);
 121       bottom = walk_mem_region_loop(&filt, g1h, _hr, bottom, top);
 122       break;
 123     }
 124 
 125     default:
 126       ShouldNotReachHere();
 127     }
 128 
 129     // Last object. Need to do dead-obj filtering here too.
 130     if (!g1h->is_obj_dead(oop(bottom), _hr)) {
 131       oop(bottom)->oop_iterate(cl2, mr);
 132     }
 133   }
 134 }
 135 
 136 // Minimum region size; we won't go lower than that.
 137 // We might want to decrease this in the future, to deal with small
 138 // heaps a bit more efficiently.
 139 #define MIN_REGION_SIZE  (      1024 * 1024 )
 140 
 141 // Maximum region size; we don't go higher than that. There's a good
 142 // reason for having an upper bound. We don't want regions to get too
 143 // large, otherwise cleanup's effectiveness would decrease as there
 144 // will be fewer opportunities to find totally empty regions after
 145 // marking.
 146 #define MAX_REGION_SIZE  ( 32 * 1024 * 1024 )
 147 
 148 // The automatic region size calculation will try to have around this
 149 // many regions in the heap (based on the min heap size).
 150 #define TARGET_REGION_NUMBER          2048
 151 
 152 void HeapRegion::setup_heap_region_size(size_t initial_heap_size, size_t max_heap_size) {
 153   uintx region_size = G1HeapRegionSize;
 154   if (FLAG_IS_DEFAULT(G1HeapRegionSize)) {
 155     size_t average_heap_size = (initial_heap_size + max_heap_size) / 2;
 156     region_size = MAX2(average_heap_size / TARGET_REGION_NUMBER,
 157                        (uintx) MIN_REGION_SIZE);
 158   }
 159 
 160   int region_size_log = log2_long((jlong) region_size);
 161   // Recalculate the region size to make sure it's a power of
 162   // 2. This means that region_size is the largest power of 2 that's
 163   // <= what we've calculated so far.
 164   region_size = ((uintx)1 << region_size_log);
 165 
 166   // Now make sure that we don't go over or under our limits.
 167   if (region_size < MIN_REGION_SIZE) {
 168     region_size = MIN_REGION_SIZE;
 169   } else if (region_size > MAX_REGION_SIZE) {
 170     region_size = MAX_REGION_SIZE;
 171   }
 172 
 173   if (region_size != G1HeapRegionSize) {
 174     // Update the flag to make sure that PrintFlagsFinal logs the correct value
 175     FLAG_SET_ERGO(uintx, G1HeapRegionSize, region_size);
 176   }
 177 
 178   // And recalculate the log.
 179   region_size_log = log2_long((jlong) region_size);
 180 
 181   // Now, set up the globals.
 182   guarantee(LogOfHRGrainBytes == 0, "we should only set it once");
 183   LogOfHRGrainBytes = region_size_log;
 184 
 185   guarantee(LogOfHRGrainWords == 0, "we should only set it once");
 186   LogOfHRGrainWords = LogOfHRGrainBytes - LogHeapWordSize;
 187 
 188   guarantee(GrainBytes == 0, "we should only set it once");
 189   // The cast to int is safe, given that we've bounded region_size by
 190   // MIN_REGION_SIZE and MAX_REGION_SIZE.
 191   GrainBytes = (size_t)region_size;
 192 
 193   guarantee(GrainWords == 0, "we should only set it once");
 194   GrainWords = GrainBytes >> LogHeapWordSize;
 195   guarantee((size_t) 1 << LogOfHRGrainWords == GrainWords, "sanity");
 196 
 197   guarantee(CardsPerRegion == 0, "we should only set it once");
 198   CardsPerRegion = GrainBytes >> CardTableModRefBS::card_shift;
 199 }
 200 
 201 void HeapRegion::reset_after_compaction() {
 202   G1OffsetTableContigSpace::reset_after_compaction();
 203   // After a compaction the mark bitmap is invalid, so we must
 204   // treat all objects as being inside the unmarked area.
 205   zero_marked_bytes();
 206   init_top_at_mark_start();
 207 }
 208 
 209 void HeapRegion::hr_clear(bool par, bool clear_space) {
 210   assert(_humongous_type == NotHumongous,
 211          "we should have already filtered out humongous regions");
 212   assert(_humongous_start_region == NULL,
 213          "we should have already filtered out humongous regions");
 214   assert(_end == _orig_end,
 215          "we should have already filtered out humongous regions");
 216 
 217   _in_collection_set = false;
 218 
 219   set_young_index_in_cset(-1);
 220   uninstall_surv_rate_group();
 221   set_young_type(NotYoung);
 222   reset_pre_dummy_top();
 223 
 224   if (!par) {
 225     // If this is parallel, this will be done later.
 226     HeapRegionRemSet* hrrs = rem_set();
 227     hrrs->clear();
 228     _claimed = InitialClaimValue;
 229   }
 230   zero_marked_bytes();
 231 
 232   _offsets.resize(HeapRegion::GrainWords);
 233   init_top_at_mark_start();
 234   if (clear_space) clear(SpaceDecorator::Mangle);
 235 }
 236 
 237 void HeapRegion::par_clear() {
 238   assert(used() == 0, "the region should have been already cleared");
 239   assert(capacity() == HeapRegion::GrainBytes, "should be back to normal");
 240   HeapRegionRemSet* hrrs = rem_set();
 241   hrrs->clear();
 242   CardTableModRefBS* ct_bs =
 243                    (CardTableModRefBS*)G1CollectedHeap::heap()->barrier_set();
 244   ct_bs->clear(MemRegion(bottom(), end()));
 245 }
 246 
 247 void HeapRegion::calc_gc_efficiency() {
 248   // GC efficiency is the ratio of how much space would be
 249   // reclaimed over how long we predict it would take to reclaim it.
 250   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 251   G1CollectorPolicy* g1p = g1h->g1_policy();
 252 
 253   // Retrieve a prediction of the elapsed time for this region for
 254   // a mixed gc because the region will only be evacuated during a
 255   // mixed gc.
 256   double region_elapsed_time_ms =
 257     g1p->predict_region_elapsed_time_ms(this, false /* for_young_gc */);
 258   _gc_efficiency = (double) reclaimable_bytes() / region_elapsed_time_ms;
 259 }
 260 
 261 void HeapRegion::set_startsHumongous(HeapWord* new_top, HeapWord* new_end) {
 262   assert(!isHumongous(), "sanity / pre-condition");
 263   assert(end() == _orig_end,
 264          "Should be normal before the humongous object allocation");
 265   assert(top() == bottom(), "should be empty");
 266   assert(bottom() <= new_top && new_top <= new_end, "pre-condition");
 267 
 268   _humongous_type = StartsHumongous;
 269   _humongous_start_region = this;
 270 
 271   set_end(new_end);
 272   _offsets.set_for_starts_humongous(new_top);
 273 }
 274 
 275 void HeapRegion::set_continuesHumongous(HeapRegion* first_hr) {
 276   assert(!isHumongous(), "sanity / pre-condition");
 277   assert(end() == _orig_end,
 278          "Should be normal before the humongous object allocation");
 279   assert(top() == bottom(), "should be empty");
 280   assert(first_hr->startsHumongous(), "pre-condition");
 281 
 282   _humongous_type = ContinuesHumongous;
 283   _humongous_start_region = first_hr;
 284 }
 285 
 286 void HeapRegion::set_notHumongous() {
 287   assert(isHumongous(), "pre-condition");
 288 
 289   if (startsHumongous()) {
 290     assert(top() <= end(), "pre-condition");
 291     set_end(_orig_end);
 292     if (top() > end()) {
 293       // at least one "continues humongous" region after it
 294       set_top(end());
 295     }
 296   } else {
 297     // continues humongous
 298     assert(end() == _orig_end, "sanity");
 299   }
 300 
 301   assert(capacity() == HeapRegion::GrainBytes, "pre-condition");
 302   _humongous_type = NotHumongous;
 303   _humongous_start_region = NULL;
 304 }
 305 
 306 bool HeapRegion::claimHeapRegion(jint claimValue) {
 307   jint current = _claimed;
 308   if (current != claimValue) {
 309     jint res = Atomic::cmpxchg(claimValue, &_claimed, current);
 310     if (res == current) {
 311       return true;
 312     }
 313   }
 314   return false;
 315 }
 316 
 317 HeapWord* HeapRegion::next_block_start_careful(HeapWord* addr) {
 318   HeapWord* low = addr;
 319   HeapWord* high = end();
 320   while (low < high) {
 321     size_t diff = pointer_delta(high, low);
 322     // Must add one below to bias toward the high amount.  Otherwise, if
 323   // "high" were at the desired value, and "low" were one less, we
 324     // would not converge on "high".  This is not symmetric, because
 325     // we set "high" to a block start, which might be the right one,
 326     // which we don't do for "low".
 327     HeapWord* middle = low + (diff+1)/2;
 328     if (middle == high) return high;
 329     HeapWord* mid_bs = block_start_careful(middle);
 330     if (mid_bs < addr) {
 331       low = middle;
 332     } else {
 333       high = mid_bs;
 334     }
 335   }
 336   assert(low == high && low >= addr, "Didn't work.");
 337   return low;
 338 }
 339 
 340 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
 341 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 342 #endif // _MSC_VER
 343 
 344 
 345 HeapRegion::HeapRegion(uint hrs_index,
 346                        G1BlockOffsetSharedArray* sharedOffsetArray,
 347                        MemRegion mr) :
 348     G1OffsetTableContigSpace(sharedOffsetArray, mr),
 349     _hrs_index(hrs_index),
 350     _humongous_type(NotHumongous), _humongous_start_region(NULL),
 351     _in_collection_set(false),
 352     _next_in_special_set(NULL), _orig_end(NULL),
 353     _claimed(InitialClaimValue), _evacuation_failed(false),
 354     _prev_marked_bytes(0), _next_marked_bytes(0), _gc_efficiency(0.0),
 355     _young_type(NotYoung), _next_young_region(NULL),
 356     _next_dirty_cards_region(NULL), _next(NULL), _pending_removal(false),
 357 #ifdef ASSERT
 358     _containing_set(NULL),
 359 #endif // ASSERT
 360      _young_index_in_cset(-1), _surv_rate_group(NULL), _age_index(-1),
 361     _rem_set(NULL), _recorded_rs_length(0), _predicted_elapsed_time_ms(0),
 362     _predicted_bytes_to_copy(0)
 363 {
 364   _rem_set = new HeapRegionRemSet(sharedOffsetArray, this);
 365   _orig_end = mr.end();
 366   // Note that initialize() will set the start of the unmarked area of the
 367   // region.
 368   hr_clear(false /*par*/, false /*clear_space*/);
 369   set_top(bottom());
 370   set_saved_mark();
 371 
 372   assert(HeapRegionRemSet::num_par_rem_sets() > 0, "Invariant.");
 373 }
 374 
 375 CompactibleSpace* HeapRegion::next_compaction_space() const {
 376   // We're not using an iterator given that it will wrap around when
 377   // it reaches the last region and this is not what we want here.
 378   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 379   uint index = hrs_index() + 1;
 380   while (index < g1h->n_regions()) {
 381     HeapRegion* hr = g1h->region_at(index);
 382     if (!hr->isHumongous()) {
 383       return hr;
 384     }
 385     index += 1;
 386   }
 387   return NULL;
 388 }
 389 
 390 void HeapRegion::save_marks() {
 391   set_saved_mark();
 392 }
 393 
 394 void HeapRegion::oops_in_mr_iterate(MemRegion mr, ExtendedOopClosure* cl) {
 395   HeapWord* p = mr.start();
 396   HeapWord* e = mr.end();
 397   oop obj;
 398   while (p < e) {
 399     obj = oop(p);
 400     p += obj->oop_iterate(cl);
 401   }
 402   assert(p == e, "bad memregion: doesn't end on obj boundary");
 403 }
 404 
 405 #define HeapRegion_OOP_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
 406 void HeapRegion::oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
 407   ContiguousSpace::oop_since_save_marks_iterate##nv_suffix(cl);              \
 408 }
 409 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(HeapRegion_OOP_SINCE_SAVE_MARKS_DEFN)
 410 
 411 
 412 void HeapRegion::oop_before_save_marks_iterate(ExtendedOopClosure* cl) {
 413   oops_in_mr_iterate(MemRegion(bottom(), saved_mark_word()), cl);
 414 }
 415 
 416 void HeapRegion::note_self_forwarding_removal_start(bool during_initial_mark,
 417                                                     bool during_conc_mark) {
 418   // We always recreate the prev marking info and we'll explicitly
 419   // mark all objects we find to be self-forwarded on the prev
 420   // bitmap. So all objects need to be below PTAMS.
 421   _prev_top_at_mark_start = top();
 422   _prev_marked_bytes = 0;
 423 
 424   if (during_initial_mark) {
 425     // During initial-mark, we'll also explicitly mark all objects
 426     // we find to be self-forwarded on the next bitmap. So all
 427     // objects need to be below NTAMS.
 428     _next_top_at_mark_start = top();
 429     _next_marked_bytes = 0;
 430   } else if (during_conc_mark) {
 431     // During concurrent mark, all objects in the CSet (including
 432     // the ones we find to be self-forwarded) are implicitly live.
 433     // So all objects need to be above NTAMS.
 434     _next_top_at_mark_start = bottom();
 435     _next_marked_bytes = 0;
 436   }
 437 }
 438 
 439 void HeapRegion::note_self_forwarding_removal_end(bool during_initial_mark,
 440                                                   bool during_conc_mark,
 441                                                   size_t marked_bytes) {
 442   assert(0 <= marked_bytes && marked_bytes <= used(),
 443          err_msg("marked: "SIZE_FORMAT" used: "SIZE_FORMAT,
 444                  marked_bytes, used()));
 445   _prev_marked_bytes = marked_bytes;
 446 }
 447 
 448 HeapWord*
 449 HeapRegion::object_iterate_mem_careful(MemRegion mr,
 450                                                  ObjectClosure* cl) {
 451   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 452   // We used to use "block_start_careful" here.  But we're actually happy
 453   // to update the BOT while we do this...
 454   HeapWord* cur = block_start(mr.start());
 455   mr = mr.intersection(used_region());
 456   if (mr.is_empty()) return NULL;
 457   // Otherwise, find the obj that extends onto mr.start().
 458 
 459   assert(cur <= mr.start()
 460          && (oop(cur)->klass_or_null() == NULL ||
 461              cur + oop(cur)->size() > mr.start()),
 462          "postcondition of block_start");
 463   oop obj;
 464   while (cur < mr.end()) {
 465     obj = oop(cur);
 466     if (obj->klass_or_null() == NULL) {
 467       // Ran into an unparseable point.
 468       return cur;
 469     } else if (!g1h->is_obj_dead(obj)) {
 470       cl->do_object(obj);
 471     }
 472     if (cl->abort()) return cur;
 473     // The check above must occur before the operation below, since an
 474     // abort might invalidate the "size" operation.
 475     cur += obj->size();
 476   }
 477   return NULL;
 478 }
 479 
 480 HeapWord*
 481 HeapRegion::
 482 oops_on_card_seq_iterate_careful(MemRegion mr,
 483                                  FilterOutOfRegionClosure* cl,
 484                                  bool filter_young,
 485                                  jbyte* card_ptr) {
 486   // Currently, we should only have to clean the card if filter_young
 487   // is true and vice versa.
 488   if (filter_young) {
 489     assert(card_ptr != NULL, "pre-condition");
 490   } else {
 491     assert(card_ptr == NULL, "pre-condition");
 492   }
 493   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 494 
 495   // If we're within a stop-world GC, then we might look at a card in a
 496   // GC alloc region that extends onto a GC LAB, which may not be
 497   // parseable.  Stop such at the "saved_mark" of the region.
 498   if (g1h->is_gc_active()) {
 499     mr = mr.intersection(used_region_at_save_marks());
 500   } else {
 501     mr = mr.intersection(used_region());
 502   }
 503   if (mr.is_empty()) return NULL;
 504   // Otherwise, find the obj that extends onto mr.start().
 505 
 506   // The intersection of the incoming mr (for the card) and the
 507   // allocated part of the region is non-empty. This implies that
 508   // we have actually allocated into this region. The code in
 509   // G1CollectedHeap.cpp that allocates a new region sets the
 510   // is_young tag on the region before allocating. Thus we
 511   // safely know if this region is young.
 512   if (is_young() && filter_young) {
 513     return NULL;
 514   }
 515 
 516   assert(!is_young(), "check value of filter_young");
 517 
 518   // We can only clean the card here, after we make the decision that
 519   // the card is not young. And we only clean the card if we have been
 520   // asked to (i.e., card_ptr != NULL).
 521   if (card_ptr != NULL) {
 522     *card_ptr = CardTableModRefBS::clean_card_val();
 523     // We must complete this write before we do any of the reads below.
 524     OrderAccess::storeload();
 525   }
 526 
 527   // Cache the boundaries of the memory region in some const locals
 528   HeapWord* const start = mr.start();
 529   HeapWord* const end = mr.end();
 530 
 531   // We used to use "block_start_careful" here.  But we're actually happy
 532   // to update the BOT while we do this...
 533   HeapWord* cur = block_start(start);
 534   assert(cur <= start, "Postcondition");
 535 
 536   oop obj;
 537 
 538   HeapWord* next = cur;
 539   while (next <= start) {
 540     cur = next;
 541     obj = oop(cur);
 542     if (obj->klass_or_null() == NULL) {
 543       // Ran into an unparseable point.
 544       return cur;
 545     }
 546     // Otherwise...
 547     next = (cur + obj->size());
 548   }
 549 
 550   // If we finish the above loop...We have a parseable object that
 551   // begins on or before the start of the memory region, and ends
 552   // inside or spans the entire region.
 553 
 554   assert(obj == oop(cur), "sanity");
 555   assert(cur <= start &&
 556          obj->klass_or_null() != NULL &&
 557          (cur + obj->size()) > start,
 558          "Loop postcondition");
 559 
 560   if (!g1h->is_obj_dead(obj)) {
 561     obj->oop_iterate(cl, mr);
 562   }
 563 
 564   while (cur < end) {
 565     obj = oop(cur);
 566     if (obj->klass_or_null() == NULL) {
 567       // Ran into an unparseable point.
 568       return cur;
 569     };
 570 
 571     // Otherwise:
 572     next = (cur + obj->size());
 573 
 574     if (!g1h->is_obj_dead(obj)) {
 575       if (next < end || !obj->is_objArray()) {
 576         // This object either does not span the MemRegion
 577         // boundary, or if it does it's not an array.
 578         // Apply closure to whole object.
 579         obj->oop_iterate(cl);
 580       } else {
 581         // This obj is an array that spans the boundary.
 582         // Stop at the boundary.
 583         obj->oop_iterate(cl, mr);
 584       }
 585     }
 586     cur = next;
 587   }
 588   return NULL;
 589 }
 590 
 591 // Code roots support
 592 
 593 void HeapRegion::add_strong_code_root(nmethod* nm) {
 594   HeapRegionRemSet* hrrs = rem_set();
 595   hrrs->add_strong_code_root(nm);
 596 }
 597 
 598 void HeapRegion::remove_strong_code_root(nmethod* nm) {
 599   HeapRegionRemSet* hrrs = rem_set();
 600   hrrs->remove_strong_code_root(nm);
 601 }
 602 
 603 void HeapRegion::migrate_strong_code_roots() {
 604   assert(in_collection_set(), "only collection set regions");
 605   assert(!isHumongous(), "not humongous regions");
 606 
 607   HeapRegionRemSet* hrrs = rem_set();
 608   hrrs->migrate_strong_code_roots();
 609 }
 610 
 611 void HeapRegion::strong_code_roots_do(CodeBlobClosure* blk) const {
 612   HeapRegionRemSet* hrrs = rem_set();
 613   hrrs->strong_code_roots_do(blk);
 614 }
 615 
 616 class VerifyStrongCodeRootOopClosure: public OopClosure {
 617   const HeapRegion* _hr;
 618   nmethod* _nm;
 619   bool _failures;
 620   bool _has_oops_in_region;
 621 
 622   template <class T> void do_oop_work(T* p) {
 623     T heap_oop = oopDesc::load_heap_oop(p);
 624     if (!oopDesc::is_null(heap_oop)) {
 625       oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 626 
 627       // Note: not all the oops embedded in the nmethod are in the
 628       // current region. We only look at those which are.
 629       if (_hr->is_in(obj)) {
 630         // Object is in the region. Check that its less than top
 631         if (_hr->top() <= (HeapWord*)obj) {
 632           // Object is above top
 633           gclog_or_tty->print_cr("Object "PTR_FORMAT" in region "
 634                                  "["PTR_FORMAT", "PTR_FORMAT") is above "
 635                                  "top "PTR_FORMAT,
 636                                  obj, _hr->bottom(), _hr->end(), _hr->top());
 637           _failures = true;
 638           return;
 639         }
 640         // Nmethod has at least one oop in the current region
 641         _has_oops_in_region = true;
 642       }
 643     }
 644   }
 645 
 646 public:
 647   VerifyStrongCodeRootOopClosure(const HeapRegion* hr, nmethod* nm):
 648     _hr(hr), _failures(false), _has_oops_in_region(false) {}
 649 
 650   void do_oop(narrowOop* p) { do_oop_work(p); }
 651   void do_oop(oop* p)       { do_oop_work(p); }
 652 
 653   bool failures()           { return _failures; }
 654   bool has_oops_in_region() { return _has_oops_in_region; }
 655 };
 656 
 657 class VerifyStrongCodeRootCodeBlobClosure: public CodeBlobClosure {
 658   const HeapRegion* _hr;
 659   bool _failures;
 660 public:
 661   VerifyStrongCodeRootCodeBlobClosure(const HeapRegion* hr) :
 662     _hr(hr), _failures(false) {}
 663 
 664   void do_code_blob(CodeBlob* cb) {
 665     nmethod* nm = (cb == NULL) ? NULL : cb->as_nmethod_or_null();
 666     if (nm != NULL) {
 667       // Verify that the nemthod is live
 668       if (!nm->is_alive()) {
 669         gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] has dead nmethod "
 670                                PTR_FORMAT" in its strong code roots",
 671                                _hr->bottom(), _hr->end(), nm);
 672         _failures = true;
 673       } else {
 674         VerifyStrongCodeRootOopClosure oop_cl(_hr, nm);
 675         nm->oops_do(&oop_cl);
 676         if (!oop_cl.has_oops_in_region()) {
 677           gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] has nmethod "
 678                                  PTR_FORMAT" in its strong code roots "
 679                                  "with no pointers into region",
 680                                  _hr->bottom(), _hr->end(), nm);
 681           _failures = true;
 682         } else if (oop_cl.failures()) {
 683           gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] has other "
 684                                  "failures for nmethod "PTR_FORMAT,
 685                                  _hr->bottom(), _hr->end(), nm);
 686           _failures = true;
 687         }
 688       }
 689     }
 690   }
 691 
 692   bool failures()       { return _failures; }
 693 };
 694 
 695 void HeapRegion::verify_strong_code_roots(VerifyOption vo, bool* failures) const {
 696   if (!G1VerifyHeapRegionCodeRoots) {
 697     // We're not verifying code roots.
 698     return;
 699   }
 700   if (vo == VerifyOption_G1UseMarkWord) {
 701     // Marking verification during a full GC is performed after class
 702     // unloading, code cache unloading, etc so the strong code roots
 703     // attached to each heap region are in an inconsistent state. They won't
 704     // be consistent until the strong code roots are rebuilt after the
 705     // actual GC. Skip verifying the strong code roots in this particular
 706     // time.
 707     assert(VerifyDuringGC, "only way to get here");
 708     return;
 709   }
 710 
 711   HeapRegionRemSet* hrrs = rem_set();
 712   int strong_code_roots_length = hrrs->strong_code_roots_list_length();
 713 
 714   // if this region is empty then there should be no entries
 715   // on its strong code root list
 716   if (is_empty()) {
 717     if (strong_code_roots_length > 0) {
 718       gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] is empty "
 719                              "but has "INT32_FORMAT" code root entries",
 720                              bottom(), end(), strong_code_roots_length);
 721       *failures = true;
 722     }
 723     return;
 724   }
 725 
 726   // An H-region should have an empty strong code root list
 727   if (isHumongous()) {
 728     if (strong_code_roots_length > 0) {
 729       gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] is humongous "
 730                              "but has "INT32_FORMAT" code root entries",
 731                              bottom(), end(), strong_code_roots_length);
 732       *failures = true;
 733     }
 734     return;
 735   }
 736 
 737   VerifyStrongCodeRootCodeBlobClosure cb_cl(this);
 738   strong_code_roots_do(&cb_cl);
 739 
 740   if (cb_cl.failures()) {
 741     *failures = true;
 742   }
 743 }
 744 
 745 void HeapRegion::print() const { print_on(gclog_or_tty); }
 746 void HeapRegion::print_on(outputStream* st) const {
 747   if (isHumongous()) {
 748     if (startsHumongous())
 749       st->print(" HS");
 750     else
 751       st->print(" HC");
 752   } else {
 753     st->print("   ");
 754   }
 755   if (in_collection_set())
 756     st->print(" CS");
 757   else
 758     st->print("   ");
 759   if (is_young())
 760     st->print(is_survivor() ? " SU" : " Y ");
 761   else
 762     st->print("   ");
 763   if (is_empty())
 764     st->print(" F");
 765   else
 766     st->print("  ");
 767   st->print(" TS %5d", _gc_time_stamp);
 768   st->print(" PTAMS "PTR_FORMAT" NTAMS "PTR_FORMAT,
 769             prev_top_at_mark_start(), next_top_at_mark_start());
 770   G1OffsetTableContigSpace::print_on(st);
 771 }
 772 
 773 class VerifyLiveClosure: public OopClosure {
 774 private:
 775   G1CollectedHeap* _g1h;
 776   CardTableModRefBS* _bs;
 777   oop _containing_obj;
 778   bool _failures;
 779   int _n_failures;
 780   VerifyOption _vo;
 781 public:
 782   // _vo == UsePrevMarking -> use "prev" marking information,
 783   // _vo == UseNextMarking -> use "next" marking information,
 784   // _vo == UseMarkWord    -> use mark word from object header.
 785   VerifyLiveClosure(G1CollectedHeap* g1h, VerifyOption vo) :
 786     _g1h(g1h), _bs(NULL), _containing_obj(NULL),
 787     _failures(false), _n_failures(0), _vo(vo)
 788   {
 789     BarrierSet* bs = _g1h->barrier_set();
 790     if (bs->is_a(BarrierSet::CardTableModRef))
 791       _bs = (CardTableModRefBS*)bs;
 792   }
 793 
 794   void set_containing_obj(oop obj) {
 795     _containing_obj = obj;
 796   }
 797 
 798   bool failures() { return _failures; }
 799   int n_failures() { return _n_failures; }
 800 
 801   virtual void do_oop(narrowOop* p) { do_oop_work(p); }
 802   virtual void do_oop(      oop* p) { do_oop_work(p); }
 803 
 804   void print_object(outputStream* out, oop obj) {
 805 #ifdef PRODUCT
 806     Klass* k = obj->klass();
 807     const char* class_name = InstanceKlass::cast(k)->external_name();
 808     out->print_cr("class name %s", class_name);
 809 #else // PRODUCT
 810     obj->print_on(out);
 811 #endif // PRODUCT
 812   }
 813 
 814   template <class T>
 815   void do_oop_work(T* p) {
 816     assert(_containing_obj != NULL, "Precondition");
 817     assert(!_g1h->is_obj_dead_cond(_containing_obj, _vo),
 818            "Precondition");
 819     T heap_oop = oopDesc::load_heap_oop(p);
 820     if (!oopDesc::is_null(heap_oop)) {
 821       oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 822       bool failed = false;
 823       if (!_g1h->is_in_closed_subset(obj) || _g1h->is_obj_dead_cond(obj, _vo)) {
 824         MutexLockerEx x(ParGCRareEvent_lock,
 825                         Mutex::_no_safepoint_check_flag);
 826 
 827         if (!_failures) {
 828           gclog_or_tty->print_cr("");
 829           gclog_or_tty->print_cr("----------");
 830         }
 831         if (!_g1h->is_in_closed_subset(obj)) {
 832           HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
 833           gclog_or_tty->print_cr("Field "PTR_FORMAT
 834                                  " of live obj "PTR_FORMAT" in region "
 835                                  "["PTR_FORMAT", "PTR_FORMAT")",
 836                                  p, (void*) _containing_obj,
 837                                  from->bottom(), from->end());
 838           print_object(gclog_or_tty, _containing_obj);
 839           gclog_or_tty->print_cr("points to obj "PTR_FORMAT" not in the heap",
 840                                  (void*) obj);
 841         } else {
 842           HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
 843           HeapRegion* to   = _g1h->heap_region_containing((HeapWord*)obj);
 844           gclog_or_tty->print_cr("Field "PTR_FORMAT
 845                                  " of live obj "PTR_FORMAT" in region "
 846                                  "["PTR_FORMAT", "PTR_FORMAT")",
 847                                  p, (void*) _containing_obj,
 848                                  from->bottom(), from->end());
 849           print_object(gclog_or_tty, _containing_obj);
 850           gclog_or_tty->print_cr("points to dead obj "PTR_FORMAT" in region "
 851                                  "["PTR_FORMAT", "PTR_FORMAT")",
 852                                  (void*) obj, to->bottom(), to->end());
 853           print_object(gclog_or_tty, obj);
 854         }
 855         gclog_or_tty->print_cr("----------");
 856         gclog_or_tty->flush();
 857         _failures = true;
 858         failed = true;
 859         _n_failures++;
 860       }
 861 
 862       if (!_g1h->full_collection() || G1VerifyRSetsDuringFullGC) {
 863         HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
 864         HeapRegion* to   = _g1h->heap_region_containing(obj);
 865         if (from != NULL && to != NULL &&
 866             from != to &&
 867             !to->isHumongous()) {
 868           jbyte cv_obj = *_bs->byte_for_const(_containing_obj);
 869           jbyte cv_field = *_bs->byte_for_const(p);
 870           const jbyte dirty = CardTableModRefBS::dirty_card_val();
 871 
 872           bool is_bad = !(from->is_young()
 873                           || to->rem_set()->contains_reference(p)
 874                           || !G1HRRSFlushLogBuffersOnVerify && // buffers were not flushed
 875                               (_containing_obj->is_objArray() ?
 876                                   cv_field == dirty
 877                                : cv_obj == dirty || cv_field == dirty));
 878           if (is_bad) {
 879             MutexLockerEx x(ParGCRareEvent_lock,
 880                             Mutex::_no_safepoint_check_flag);
 881 
 882             if (!_failures) {
 883               gclog_or_tty->print_cr("");
 884               gclog_or_tty->print_cr("----------");
 885             }
 886             gclog_or_tty->print_cr("Missing rem set entry:");
 887             gclog_or_tty->print_cr("Field "PTR_FORMAT" "
 888                                    "of obj "PTR_FORMAT", "
 889                                    "in region "HR_FORMAT,
 890                                    p, (void*) _containing_obj,
 891                                    HR_FORMAT_PARAMS(from));
 892             _containing_obj->print_on(gclog_or_tty);
 893             gclog_or_tty->print_cr("points to obj "PTR_FORMAT" "
 894                                    "in region "HR_FORMAT,
 895                                    (void*) obj,
 896                                    HR_FORMAT_PARAMS(to));
 897             obj->print_on(gclog_or_tty);
 898             gclog_or_tty->print_cr("Obj head CTE = %d, field CTE = %d.",
 899                           cv_obj, cv_field);
 900             gclog_or_tty->print_cr("----------");
 901             gclog_or_tty->flush();
 902             _failures = true;
 903             if (!failed) _n_failures++;
 904           }
 905         }
 906       }
 907     }
 908   }
 909 };
 910 
 911 // This really ought to be commoned up into OffsetTableContigSpace somehow.
 912 // We would need a mechanism to make that code skip dead objects.
 913 
 914 void HeapRegion::verify(VerifyOption vo,
 915                         bool* failures) const {
 916   G1CollectedHeap* g1 = G1CollectedHeap::heap();
 917   *failures = false;
 918   HeapWord* p = bottom();
 919   HeapWord* prev_p = NULL;
 920   VerifyLiveClosure vl_cl(g1, vo);
 921   bool is_humongous = isHumongous();
 922   bool do_bot_verify = !is_young();
 923   size_t object_num = 0;
 924   while (p < top()) {
 925     oop obj = oop(p);
 926     size_t obj_size = obj->size();
 927     object_num += 1;
 928 
 929     if (is_humongous != g1->isHumongous(obj_size)) {
 930       gclog_or_tty->print_cr("obj "PTR_FORMAT" is of %shumongous size ("
 931                              SIZE_FORMAT" words) in a %shumongous region",
 932                              p, g1->isHumongous(obj_size) ? "" : "non-",
 933                              obj_size, is_humongous ? "" : "non-");
 934        *failures = true;
 935        return;
 936     }
 937 
 938     // If it returns false, verify_for_object() will output the
 939     // appropriate messasge.
 940     if (do_bot_verify && !_offsets.verify_for_object(p, obj_size)) {
 941       *failures = true;
 942       return;
 943     }
 944 
 945     if (!g1->is_obj_dead_cond(obj, this, vo)) {
 946       if (obj->is_oop()) {
 947         Klass* klass = obj->klass();
 948         if (!klass->is_metaspace_object()) {
 949           gclog_or_tty->print_cr("klass "PTR_FORMAT" of object "PTR_FORMAT" "
 950                                  "not metadata", klass, obj);
 951           *failures = true;
 952           return;
 953         } else if (!klass->is_klass()) {
 954           gclog_or_tty->print_cr("klass "PTR_FORMAT" of object "PTR_FORMAT" "
 955                                  "not a klass", klass, obj);
 956           *failures = true;
 957           return;
 958         } else {
 959           vl_cl.set_containing_obj(obj);
 960           obj->oop_iterate_no_header(&vl_cl);
 961           if (vl_cl.failures()) {
 962             *failures = true;
 963           }
 964           if (G1MaxVerifyFailures >= 0 &&
 965               vl_cl.n_failures() >= G1MaxVerifyFailures) {
 966             return;
 967           }
 968         }
 969       } else {
 970         gclog_or_tty->print_cr(PTR_FORMAT" no an oop", obj);
 971         *failures = true;
 972         return;
 973       }
 974     }
 975     prev_p = p;
 976     p += obj_size;
 977   }
 978 
 979   if (p != top()) {
 980     gclog_or_tty->print_cr("end of last object "PTR_FORMAT" "
 981                            "does not match top "PTR_FORMAT, p, top());
 982     *failures = true;
 983     return;
 984   }
 985 
 986   HeapWord* the_end = end();
 987   assert(p == top(), "it should still hold");
 988   // Do some extra BOT consistency checking for addresses in the
 989   // range [top, end). BOT look-ups in this range should yield
 990   // top. No point in doing that if top == end (there's nothing there).
 991   if (p < the_end) {
 992     // Look up top
 993     HeapWord* addr_1 = p;
 994     HeapWord* b_start_1 = _offsets.block_start_const(addr_1);
 995     if (b_start_1 != p) {
 996       gclog_or_tty->print_cr("BOT look up for top: "PTR_FORMAT" "
 997                              " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
 998                              addr_1, b_start_1, p);
 999       *failures = true;
1000       return;
1001     }
1002 
1003     // Look up top + 1
1004     HeapWord* addr_2 = p + 1;
1005     if (addr_2 < the_end) {
1006       HeapWord* b_start_2 = _offsets.block_start_const(addr_2);
1007       if (b_start_2 != p) {
1008         gclog_or_tty->print_cr("BOT look up for top + 1: "PTR_FORMAT" "
1009                                " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
1010                                addr_2, b_start_2, p);
1011         *failures = true;
1012         return;
1013       }
1014     }
1015 
1016     // Look up an address between top and end
1017     size_t diff = pointer_delta(the_end, p) / 2;
1018     HeapWord* addr_3 = p + diff;
1019     if (addr_3 < the_end) {
1020       HeapWord* b_start_3 = _offsets.block_start_const(addr_3);
1021       if (b_start_3 != p) {
1022         gclog_or_tty->print_cr("BOT look up for top + diff: "PTR_FORMAT" "
1023                                " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
1024                                addr_3, b_start_3, p);
1025         *failures = true;
1026         return;
1027       }
1028     }
1029 
1030     // Loook up end - 1
1031     HeapWord* addr_4 = the_end - 1;
1032     HeapWord* b_start_4 = _offsets.block_start_const(addr_4);
1033     if (b_start_4 != p) {
1034       gclog_or_tty->print_cr("BOT look up for end - 1: "PTR_FORMAT" "
1035                              " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
1036                              addr_4, b_start_4, p);
1037       *failures = true;
1038       return;
1039     }
1040   }
1041 
1042   if (is_humongous && object_num > 1) {
1043     gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] is humongous "
1044                            "but has "SIZE_FORMAT", objects",
1045                            bottom(), end(), object_num);
1046     *failures = true;
1047     return;
1048   }
1049 
1050   verify_strong_code_roots(vo, failures);
1051 }
1052 
1053 void HeapRegion::verify() const {
1054   bool dummy = false;
1055   verify(VerifyOption_G1UsePrevMarking, /* failures */ &dummy);
1056 }
1057 
1058 // G1OffsetTableContigSpace code; copied from space.cpp.  Hope this can go
1059 // away eventually.
1060 
1061 void G1OffsetTableContigSpace::clear(bool mangle_space) {
1062   ContiguousSpace::clear(mangle_space);
1063   _offsets.zero_bottom_entry();
1064   _offsets.initialize_threshold();
1065 }
1066 
1067 void G1OffsetTableContigSpace::set_bottom(HeapWord* new_bottom) {
1068   Space::set_bottom(new_bottom);
1069   _offsets.set_bottom(new_bottom);
1070 }
1071 
1072 void G1OffsetTableContigSpace::set_end(HeapWord* new_end) {
1073   Space::set_end(new_end);
1074   _offsets.resize(new_end - bottom());
1075 }
1076 
1077 void G1OffsetTableContigSpace::print() const {
1078   print_short();
1079   gclog_or_tty->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", "
1080                 INTPTR_FORMAT ", " INTPTR_FORMAT ")",
1081                 bottom(), top(), _offsets.threshold(), end());
1082 }
1083 
1084 HeapWord* G1OffsetTableContigSpace::initialize_threshold() {
1085   return _offsets.initialize_threshold();
1086 }
1087 
1088 HeapWord* G1OffsetTableContigSpace::cross_threshold(HeapWord* start,
1089                                                     HeapWord* end) {
1090   _offsets.alloc_block(start, end);
1091   return _offsets.threshold();
1092 }
1093 
1094 HeapWord* G1OffsetTableContigSpace::saved_mark_word() const {
1095   G1CollectedHeap* g1h = G1CollectedHeap::heap();
1096   assert( _gc_time_stamp <= g1h->get_gc_time_stamp(), "invariant" );
1097   if (_gc_time_stamp < g1h->get_gc_time_stamp())
1098     return top();
1099   else
1100     return ContiguousSpace::saved_mark_word();
1101 }
1102 
1103 void G1OffsetTableContigSpace::set_saved_mark() {
1104   G1CollectedHeap* g1h = G1CollectedHeap::heap();
1105   unsigned curr_gc_time_stamp = g1h->get_gc_time_stamp();
1106 
1107   if (_gc_time_stamp < curr_gc_time_stamp) {
1108     // The order of these is important, as another thread might be
1109     // about to start scanning this region. If it does so after
1110     // set_saved_mark and before _gc_time_stamp = ..., then the latter
1111     // will be false, and it will pick up top() as the high water mark
1112     // of region. If it does so after _gc_time_stamp = ..., then it
1113     // will pick up the right saved_mark_word() as the high water mark
1114     // of the region. Either way, the behaviour will be correct.
1115     ContiguousSpace::set_saved_mark();
1116     OrderAccess::storestore();
1117     _gc_time_stamp = curr_gc_time_stamp;
1118     // No need to do another barrier to flush the writes above. If
1119     // this is called in parallel with other threads trying to
1120     // allocate into the region, the caller should call this while
1121     // holding a lock and when the lock is released the writes will be
1122     // flushed.
1123   }
1124 }
1125 
1126 G1OffsetTableContigSpace::
1127 G1OffsetTableContigSpace(G1BlockOffsetSharedArray* sharedOffsetArray,
1128                          MemRegion mr) :
1129   _offsets(sharedOffsetArray, mr),
1130   _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true),
1131   _gc_time_stamp(0)
1132 {
1133   _offsets.set_space(this);
1134   // false ==> we'll do the clearing if there's clearing to be done.
1135   ContiguousSpace::initialize(mr, false, SpaceDecorator::Mangle);
1136   _offsets.zero_bottom_entry();
1137   _offsets.initialize_threshold();
1138 }