view src/share/vm/gc_implementation/g1/heapRegion.cpp @ 2534:6747fd0512e0

7004681: G1: Extend marking verification to Full GCs Summary: Perform a heap verification after the first phase of G1's full GC using objects' mark words to determine liveness. The third parameter of the heap verification routines, which was used in G1 to determine which marking bitmap to use in liveness calculations, has been changed from a boolean to an enum with values defined for using the mark word, and the 'prev' and 'next' bitmaps. Reviewed-by: tonyp, ysr
author johnc
date Tue, 14 Jun 2011 11:01:10 -0700
parents c3f1170908be
children f44782f04dd4
line wrap: on
line source
/*
 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/g1OopClosures.inline.hpp"
#include "gc_implementation/g1/heapRegion.inline.hpp"
#include "gc_implementation/g1/heapRegionRemSet.hpp"
#include "gc_implementation/g1/heapRegionSeq.inline.hpp"
#include "memory/genOopClosures.inline.hpp"
#include "memory/iterator.hpp"
#include "oops/oop.inline.hpp"

int HeapRegion::LogOfHRGrainBytes = 0;
int HeapRegion::LogOfHRGrainWords = 0;
int HeapRegion::GrainBytes        = 0;
int HeapRegion::GrainWords        = 0;
int HeapRegion::CardsPerRegion    = 0;

HeapRegionDCTOC::HeapRegionDCTOC(G1CollectedHeap* g1,
                                 HeapRegion* hr, OopClosure* cl,
                                 CardTableModRefBS::PrecisionStyle precision,
                                 FilterKind fk) :
  ContiguousSpaceDCTOC(hr, cl, precision, NULL),
  _hr(hr), _fk(fk), _g1(g1)
{}

FilterOutOfRegionClosure::FilterOutOfRegionClosure(HeapRegion* r,
                                                   OopClosure* oc) :
  _r_bottom(r->bottom()), _r_end(r->end()),
  _oc(oc), _out_of_region(0)
{}

class VerifyLiveClosure: public OopClosure {
private:
  G1CollectedHeap* _g1h;
  CardTableModRefBS* _bs;
  oop _containing_obj;
  bool _failures;
  int _n_failures;
  VerifyOption _vo;
public:
  // _vo == UsePrevMarking -> use "prev" marking information,
  // _vo == UseNextMarking -> use "next" marking information,
  // _vo == UseMarkWord    -> use mark word from object header.
  VerifyLiveClosure(G1CollectedHeap* g1h, VerifyOption vo) :
    _g1h(g1h), _bs(NULL), _containing_obj(NULL),
    _failures(false), _n_failures(0), _vo(vo)
  {
    BarrierSet* bs = _g1h->barrier_set();
    if (bs->is_a(BarrierSet::CardTableModRef))
      _bs = (CardTableModRefBS*)bs;
  }

  void set_containing_obj(oop obj) {
    _containing_obj = obj;
  }

  bool failures() { return _failures; }
  int n_failures() { return _n_failures; }

  virtual void do_oop(narrowOop* p) { do_oop_work(p); }
  virtual void do_oop(      oop* p) { do_oop_work(p); }

  void print_object(outputStream* out, oop obj) {
#ifdef PRODUCT
    klassOop k = obj->klass();
    const char* class_name = instanceKlass::cast(k)->external_name();
    out->print_cr("class name %s", class_name);
#else // PRODUCT
    obj->print_on(out);
#endif // PRODUCT
  }

  template <class T> void do_oop_work(T* p) {
    assert(_containing_obj != NULL, "Precondition");
    assert(!_g1h->is_obj_dead_cond(_containing_obj, _vo),
           "Precondition");
    T heap_oop = oopDesc::load_heap_oop(p);
    if (!oopDesc::is_null(heap_oop)) {
      oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
      bool failed = false;
      if (!_g1h->is_in_closed_subset(obj) ||
          _g1h->is_obj_dead_cond(obj, _vo)) {
        if (!_failures) {
          gclog_or_tty->print_cr("");
          gclog_or_tty->print_cr("----------");
        }
        if (!_g1h->is_in_closed_subset(obj)) {
          HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
          gclog_or_tty->print_cr("Field "PTR_FORMAT
                                 " of live obj "PTR_FORMAT" in region "
                                 "["PTR_FORMAT", "PTR_FORMAT")",
                                 p, (void*) _containing_obj,
                                 from->bottom(), from->end());
          print_object(gclog_or_tty, _containing_obj);
          gclog_or_tty->print_cr("points to obj "PTR_FORMAT" not in the heap",
                                 (void*) obj);
        } else {
          HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
          HeapRegion* to   = _g1h->heap_region_containing((HeapWord*)obj);
          gclog_or_tty->print_cr("Field "PTR_FORMAT
                                 " of live obj "PTR_FORMAT" in region "
                                 "["PTR_FORMAT", "PTR_FORMAT")",
                                 p, (void*) _containing_obj,
                                 from->bottom(), from->end());
          print_object(gclog_or_tty, _containing_obj);
          gclog_or_tty->print_cr("points to dead obj "PTR_FORMAT" in region "
                                 "["PTR_FORMAT", "PTR_FORMAT")",
                                 (void*) obj, to->bottom(), to->end());
          print_object(gclog_or_tty, obj);
        }
        gclog_or_tty->print_cr("----------");
        _failures = true;
        failed = true;
        _n_failures++;
      }

      if (!_g1h->full_collection()) {
        HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
        HeapRegion* to   = _g1h->heap_region_containing(obj);
        if (from != NULL && to != NULL &&
            from != to &&
            !to->isHumongous()) {
          jbyte cv_obj = *_bs->byte_for_const(_containing_obj);
          jbyte cv_field = *_bs->byte_for_const(p);
          const jbyte dirty = CardTableModRefBS::dirty_card_val();

          bool is_bad = !(from->is_young()
                          || to->rem_set()->contains_reference(p)
                          || !G1HRRSFlushLogBuffersOnVerify && // buffers were not flushed
                              (_containing_obj->is_objArray() ?
                                  cv_field == dirty
                               : cv_obj == dirty || cv_field == dirty));
          if (is_bad) {
            if (!_failures) {
              gclog_or_tty->print_cr("");
              gclog_or_tty->print_cr("----------");
            }
            gclog_or_tty->print_cr("Missing rem set entry:");
            gclog_or_tty->print_cr("Field "PTR_FORMAT" "
                                   "of obj "PTR_FORMAT", "
                                   "in region "HR_FORMAT,
                                   p, (void*) _containing_obj,
                                   HR_FORMAT_PARAMS(from));
            _containing_obj->print_on(gclog_or_tty);
            gclog_or_tty->print_cr("points to obj "PTR_FORMAT" "
                                   "in region "HR_FORMAT,
                                   (void*) obj,
                                   HR_FORMAT_PARAMS(to));
            obj->print_on(gclog_or_tty);
            gclog_or_tty->print_cr("Obj head CTE = %d, field CTE = %d.",
                          cv_obj, cv_field);
            gclog_or_tty->print_cr("----------");
            _failures = true;
            if (!failed) _n_failures++;
          }
        }
      }
    }
  }
};

template<class ClosureType>
HeapWord* walk_mem_region_loop(ClosureType* cl, G1CollectedHeap* g1h,
                               HeapRegion* hr,
                               HeapWord* cur, HeapWord* top) {
  oop cur_oop = oop(cur);
  int oop_size = cur_oop->size();
  HeapWord* next_obj = cur + oop_size;
  while (next_obj < top) {
    // Keep filtering the remembered set.
    if (!g1h->is_obj_dead(cur_oop, hr)) {
      // Bottom lies entirely below top, so we can call the
      // non-memRegion version of oop_iterate below.
      cur_oop->oop_iterate(cl);
    }
    cur = next_obj;
    cur_oop = oop(cur);
    oop_size = cur_oop->size();
    next_obj = cur + oop_size;
  }
  return cur;
}

void HeapRegionDCTOC::walk_mem_region_with_cl(MemRegion mr,
                                              HeapWord* bottom,
                                              HeapWord* top,
                                              OopClosure* cl) {
  G1CollectedHeap* g1h = _g1;

  int oop_size;

  OopClosure* cl2 = cl;
  FilterIntoCSClosure intoCSFilt(this, g1h, cl);
  FilterOutOfRegionClosure outOfRegionFilt(_hr, cl);
  switch (_fk) {
  case IntoCSFilterKind:      cl2 = &intoCSFilt; break;
  case OutOfRegionFilterKind: cl2 = &outOfRegionFilt; break;
  }

  // Start filtering what we add to the remembered set. If the object is
  // not considered dead, either because it is marked (in the mark bitmap)
  // or it was allocated after marking finished, then we add it. Otherwise
  // we can safely ignore the object.
  if (!g1h->is_obj_dead(oop(bottom), _hr)) {
    oop_size = oop(bottom)->oop_iterate(cl2, mr);
  } else {
    oop_size = oop(bottom)->size();
  }

  bottom += oop_size;

  if (bottom < top) {
    // We replicate the loop below for several kinds of possible filters.
    switch (_fk) {
    case NoFilterKind:
      bottom = walk_mem_region_loop(cl, g1h, _hr, bottom, top);
      break;
    case IntoCSFilterKind: {
      FilterIntoCSClosure filt(this, g1h, cl);
      bottom = walk_mem_region_loop(&filt, g1h, _hr, bottom, top);
      break;
    }
    case OutOfRegionFilterKind: {
      FilterOutOfRegionClosure filt(_hr, cl);
      bottom = walk_mem_region_loop(&filt, g1h, _hr, bottom, top);
      break;
    }
    default:
      ShouldNotReachHere();
    }

    // Last object. Need to do dead-obj filtering here too.
    if (!g1h->is_obj_dead(oop(bottom), _hr)) {
      oop(bottom)->oop_iterate(cl2, mr);
    }
  }
}

// Minimum region size; we won't go lower than that.
// We might want to decrease this in the future, to deal with small
// heaps a bit more efficiently.
#define MIN_REGION_SIZE  (      1024 * 1024 )

// Maximum region size; we don't go higher than that. There's a good
// reason for having an upper bound. We don't want regions to get too
// large, otherwise cleanup's effectiveness would decrease as there
// will be fewer opportunities to find totally empty regions after
// marking.
#define MAX_REGION_SIZE  ( 32 * 1024 * 1024 )

// The automatic region size calculation will try to have around this
// many regions in the heap (based on the min heap size).
#define TARGET_REGION_NUMBER          2048

void HeapRegion::setup_heap_region_size(uintx min_heap_size) {
  // region_size in bytes
  uintx region_size = G1HeapRegionSize;
  if (FLAG_IS_DEFAULT(G1HeapRegionSize)) {
    // We base the automatic calculation on the min heap size. This
    // can be problematic if the spread between min and max is quite
    // wide, imagine -Xms128m -Xmx32g. But, if we decided it based on
    // the max size, the region size might be way too large for the
    // min size. Either way, some users might have to set the region
    // size manually for some -Xms / -Xmx combos.

    region_size = MAX2(min_heap_size / TARGET_REGION_NUMBER,
                       (uintx) MIN_REGION_SIZE);
  }

  int region_size_log = log2_long((jlong) region_size);
  // Recalculate the region size to make sure it's a power of
  // 2. This means that region_size is the largest power of 2 that's
  // <= what we've calculated so far.
  region_size = ((uintx)1 << region_size_log);

  // Now make sure that we don't go over or under our limits.
  if (region_size < MIN_REGION_SIZE) {
    region_size = MIN_REGION_SIZE;
  } else if (region_size > MAX_REGION_SIZE) {
    region_size = MAX_REGION_SIZE;
  }

  // And recalculate the log.
  region_size_log = log2_long((jlong) region_size);

  // Now, set up the globals.
  guarantee(LogOfHRGrainBytes == 0, "we should only set it once");
  LogOfHRGrainBytes = region_size_log;

  guarantee(LogOfHRGrainWords == 0, "we should only set it once");
  LogOfHRGrainWords = LogOfHRGrainBytes - LogHeapWordSize;

  guarantee(GrainBytes == 0, "we should only set it once");
  // The cast to int is safe, given that we've bounded region_size by
  // MIN_REGION_SIZE and MAX_REGION_SIZE.
  GrainBytes = (int) region_size;

  guarantee(GrainWords == 0, "we should only set it once");
  GrainWords = GrainBytes >> LogHeapWordSize;
  guarantee(1 << LogOfHRGrainWords == GrainWords, "sanity");

  guarantee(CardsPerRegion == 0, "we should only set it once");
  CardsPerRegion = GrainBytes >> CardTableModRefBS::card_shift;
}

void HeapRegion::reset_after_compaction() {
  G1OffsetTableContigSpace::reset_after_compaction();
  // After a compaction the mark bitmap is invalid, so we must
  // treat all objects as being inside the unmarked area.
  zero_marked_bytes();
  init_top_at_mark_start();
}

DirtyCardToOopClosure*
HeapRegion::new_dcto_closure(OopClosure* cl,
                             CardTableModRefBS::PrecisionStyle precision,
                             HeapRegionDCTOC::FilterKind fk) {
  return new HeapRegionDCTOC(G1CollectedHeap::heap(),
                             this, cl, precision, fk);
}

void HeapRegion::hr_clear(bool par, bool clear_space) {
  assert(_humongous_type == NotHumongous,
         "we should have already filtered out humongous regions");
  assert(_humongous_start_region == NULL,
         "we should have already filtered out humongous regions");
  assert(_end == _orig_end,
         "we should have already filtered out humongous regions");

  _in_collection_set = false;
  _is_gc_alloc_region = false;

  set_young_index_in_cset(-1);
  uninstall_surv_rate_group();
  set_young_type(NotYoung);
  reset_pre_dummy_top();

  if (!par) {
    // If this is parallel, this will be done later.
    HeapRegionRemSet* hrrs = rem_set();
    if (hrrs != NULL) hrrs->clear();
    _claimed = InitialClaimValue;
  }
  zero_marked_bytes();
  set_sort_index(-1);

  _offsets.resize(HeapRegion::GrainWords);
  init_top_at_mark_start();
  if (clear_space) clear(SpaceDecorator::Mangle);
}

void HeapRegion::par_clear() {
  assert(used() == 0, "the region should have been already cleared");
  assert(capacity() == (size_t) HeapRegion::GrainBytes,
         "should be back to normal");
  HeapRegionRemSet* hrrs = rem_set();
  hrrs->clear();
  CardTableModRefBS* ct_bs =
                   (CardTableModRefBS*)G1CollectedHeap::heap()->barrier_set();
  ct_bs->clear(MemRegion(bottom(), end()));
}

// <PREDICTION>
void HeapRegion::calc_gc_efficiency() {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  _gc_efficiency = (double) garbage_bytes() /
                            g1h->predict_region_elapsed_time_ms(this, false);
}
// </PREDICTION>

void HeapRegion::set_startsHumongous(HeapWord* new_top, HeapWord* new_end) {
  assert(!isHumongous(), "sanity / pre-condition");
  assert(end() == _orig_end,
         "Should be normal before the humongous object allocation");
  assert(top() == bottom(), "should be empty");
  assert(bottom() <= new_top && new_top <= new_end, "pre-condition");

  _humongous_type = StartsHumongous;
  _humongous_start_region = this;

  set_end(new_end);
  _offsets.set_for_starts_humongous(new_top);
}

void HeapRegion::set_continuesHumongous(HeapRegion* first_hr) {
  assert(!isHumongous(), "sanity / pre-condition");
  assert(end() == _orig_end,
         "Should be normal before the humongous object allocation");
  assert(top() == bottom(), "should be empty");
  assert(first_hr->startsHumongous(), "pre-condition");

  _humongous_type = ContinuesHumongous;
  _humongous_start_region = first_hr;
}

void HeapRegion::set_notHumongous() {
  assert(isHumongous(), "pre-condition");

  if (startsHumongous()) {
    assert(top() <= end(), "pre-condition");
    set_end(_orig_end);
    if (top() > end()) {
      // at least one "continues humongous" region after it
      set_top(end());
    }
  } else {
    // continues humongous
    assert(end() == _orig_end, "sanity");
  }

  assert(capacity() == (size_t) HeapRegion::GrainBytes, "pre-condition");
  _humongous_type = NotHumongous;
  _humongous_start_region = NULL;
}

bool HeapRegion::claimHeapRegion(jint claimValue) {
  jint current = _claimed;
  if (current != claimValue) {
    jint res = Atomic::cmpxchg(claimValue, &_claimed, current);
    if (res == current) {
      return true;
    }
  }
  return false;
}

HeapWord* HeapRegion::next_block_start_careful(HeapWord* addr) {
  HeapWord* low = addr;
  HeapWord* high = end();
  while (low < high) {
    size_t diff = pointer_delta(high, low);
    // Must add one below to bias toward the high amount.  Otherwise, if
  // "high" were at the desired value, and "low" were one less, we
    // would not converge on "high".  This is not symmetric, because
    // we set "high" to a block start, which might be the right one,
    // which we don't do for "low".
    HeapWord* middle = low + (diff+1)/2;
    if (middle == high) return high;
    HeapWord* mid_bs = block_start_careful(middle);
    if (mid_bs < addr) {
      low = middle;
    } else {
      high = mid_bs;
    }
  }
  assert(low == high && low >= addr, "Didn't work.");
  return low;
}

void HeapRegion::initialize(MemRegion mr, bool clear_space, bool mangle_space) {
  G1OffsetTableContigSpace::initialize(mr, false, mangle_space);
  hr_clear(false/*par*/, clear_space);
}
#ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
#pragma warning( disable:4355 ) // 'this' : used in base member initializer list
#endif // _MSC_VER


HeapRegion::
HeapRegion(size_t hrs_index, G1BlockOffsetSharedArray* sharedOffsetArray,
           MemRegion mr, bool is_zeroed)
  : G1OffsetTableContigSpace(sharedOffsetArray, mr, is_zeroed),
    _next_fk(HeapRegionDCTOC::NoFilterKind), _hrs_index(hrs_index),
    _humongous_type(NotHumongous), _humongous_start_region(NULL),
    _in_collection_set(false), _is_gc_alloc_region(false),
    _next_in_special_set(NULL), _orig_end(NULL),
    _claimed(InitialClaimValue), _evacuation_failed(false),
    _prev_marked_bytes(0), _next_marked_bytes(0), _sort_index(-1),
    _young_type(NotYoung), _next_young_region(NULL),
    _next_dirty_cards_region(NULL), _next(NULL), _pending_removal(false),
#ifdef ASSERT
    _containing_set(NULL),
#endif // ASSERT
     _young_index_in_cset(-1), _surv_rate_group(NULL), _age_index(-1),
    _rem_set(NULL), _recorded_rs_length(0), _predicted_elapsed_time_ms(0),
    _predicted_bytes_to_copy(0)
{
  _orig_end = mr.end();
  // Note that initialize() will set the start of the unmarked area of the
  // region.
  this->initialize(mr, !is_zeroed, SpaceDecorator::Mangle);
  set_top(bottom());
  set_saved_mark();

  _rem_set =  new HeapRegionRemSet(sharedOffsetArray, this);

  assert(HeapRegionRemSet::num_par_rem_sets() > 0, "Invariant.");
  // In case the region is allocated during a pause, note the top.
  // We haven't done any counting on a brand new region.
  _top_at_conc_mark_count = bottom();
}

class NextCompactionHeapRegionClosure: public HeapRegionClosure {
  const HeapRegion* _target;
  bool _target_seen;
  HeapRegion* _last;
  CompactibleSpace* _res;
public:
  NextCompactionHeapRegionClosure(const HeapRegion* target) :
    _target(target), _target_seen(false), _res(NULL) {}
  bool doHeapRegion(HeapRegion* cur) {
    if (_target_seen) {
      if (!cur->isHumongous()) {
        _res = cur;
        return true;
      }
    } else if (cur == _target) {
      _target_seen = true;
    }
    return false;
  }
  CompactibleSpace* result() { return _res; }
};

CompactibleSpace* HeapRegion::next_compaction_space() const {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  // cast away const-ness
  HeapRegion* r = (HeapRegion*) this;
  NextCompactionHeapRegionClosure blk(r);
  g1h->heap_region_iterate_from(r, &blk);
  return blk.result();
}

void HeapRegion::save_marks() {
  set_saved_mark();
}

void HeapRegion::oops_in_mr_iterate(MemRegion mr, OopClosure* cl) {
  HeapWord* p = mr.start();
  HeapWord* e = mr.end();
  oop obj;
  while (p < e) {
    obj = oop(p);
    p += obj->oop_iterate(cl);
  }
  assert(p == e, "bad memregion: doesn't end on obj boundary");
}

#define HeapRegion_OOP_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
void HeapRegion::oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
  ContiguousSpace::oop_since_save_marks_iterate##nv_suffix(cl);              \
}
SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(HeapRegion_OOP_SINCE_SAVE_MARKS_DEFN)


void HeapRegion::oop_before_save_marks_iterate(OopClosure* cl) {
  oops_in_mr_iterate(MemRegion(bottom(), saved_mark_word()), cl);
}

HeapWord*
HeapRegion::object_iterate_mem_careful(MemRegion mr,
                                                 ObjectClosure* cl) {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  // We used to use "block_start_careful" here.  But we're actually happy
  // to update the BOT while we do this...
  HeapWord* cur = block_start(mr.start());
  mr = mr.intersection(used_region());
  if (mr.is_empty()) return NULL;
  // Otherwise, find the obj that extends onto mr.start().

  assert(cur <= mr.start()
         && (oop(cur)->klass_or_null() == NULL ||
             cur + oop(cur)->size() > mr.start()),
         "postcondition of block_start");
  oop obj;
  while (cur < mr.end()) {
    obj = oop(cur);
    if (obj->klass_or_null() == NULL) {
      // Ran into an unparseable point.
      return cur;
    } else if (!g1h->is_obj_dead(obj)) {
      cl->do_object(obj);
    }
    if (cl->abort()) return cur;
    // The check above must occur before the operation below, since an
    // abort might invalidate the "size" operation.
    cur += obj->size();
  }
  return NULL;
}

HeapWord*
HeapRegion::
oops_on_card_seq_iterate_careful(MemRegion mr,
                                 FilterOutOfRegionClosure* cl,
                                 bool filter_young,
                                 jbyte* card_ptr) {
  // Currently, we should only have to clean the card if filter_young
  // is true and vice versa.
  if (filter_young) {
    assert(card_ptr != NULL, "pre-condition");
  } else {
    assert(card_ptr == NULL, "pre-condition");
  }
  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  // If we're within a stop-world GC, then we might look at a card in a
  // GC alloc region that extends onto a GC LAB, which may not be
  // parseable.  Stop such at the "saved_mark" of the region.
  if (G1CollectedHeap::heap()->is_gc_active()) {
    mr = mr.intersection(used_region_at_save_marks());
  } else {
    mr = mr.intersection(used_region());
  }
  if (mr.is_empty()) return NULL;
  // Otherwise, find the obj that extends onto mr.start().

  // The intersection of the incoming mr (for the card) and the
  // allocated part of the region is non-empty. This implies that
  // we have actually allocated into this region. The code in
  // G1CollectedHeap.cpp that allocates a new region sets the
  // is_young tag on the region before allocating. Thus we
  // safely know if this region is young.
  if (is_young() && filter_young) {
    return NULL;
  }

  assert(!is_young(), "check value of filter_young");

  // We can only clean the card here, after we make the decision that
  // the card is not young. And we only clean the card if we have been
  // asked to (i.e., card_ptr != NULL).
  if (card_ptr != NULL) {
    *card_ptr = CardTableModRefBS::clean_card_val();
    // We must complete this write before we do any of the reads below.
    OrderAccess::storeload();
  }

  // We used to use "block_start_careful" here.  But we're actually happy
  // to update the BOT while we do this...
  HeapWord* cur = block_start(mr.start());
  assert(cur <= mr.start(), "Postcondition");

  while (cur <= mr.start()) {
    if (oop(cur)->klass_or_null() == NULL) {
      // Ran into an unparseable point.
      return cur;
    }
    // Otherwise...
    int sz = oop(cur)->size();
    if (cur + sz > mr.start()) break;
    // Otherwise, go on.
    cur = cur + sz;
  }
  oop obj;
  obj = oop(cur);
  // If we finish this loop...
  assert(cur <= mr.start()
         && obj->klass_or_null() != NULL
         && cur + obj->size() > mr.start(),
         "Loop postcondition");
  if (!g1h->is_obj_dead(obj)) {
    obj->oop_iterate(cl, mr);
  }

  HeapWord* next;
  while (cur < mr.end()) {
    obj = oop(cur);
    if (obj->klass_or_null() == NULL) {
      // Ran into an unparseable point.
      return cur;
    };
    // Otherwise:
    next = (cur + obj->size());
    if (!g1h->is_obj_dead(obj)) {
      if (next < mr.end()) {
        obj->oop_iterate(cl);
      } else {
        // this obj spans the boundary.  If it's an array, stop at the
        // boundary.
        if (obj->is_objArray()) {
          obj->oop_iterate(cl, mr);
        } else {
          obj->oop_iterate(cl);
        }
      }
    }
    cur = next;
  }
  return NULL;
}

void HeapRegion::print() const { print_on(gclog_or_tty); }
void HeapRegion::print_on(outputStream* st) const {
  if (isHumongous()) {
    if (startsHumongous())
      st->print(" HS");
    else
      st->print(" HC");
  } else {
    st->print("   ");
  }
  if (in_collection_set())
    st->print(" CS");
  else if (is_gc_alloc_region())
    st->print(" A ");
  else
    st->print("   ");
  if (is_young())
    st->print(is_survivor() ? " SU" : " Y ");
  else
    st->print("   ");
  if (is_empty())
    st->print(" F");
  else
    st->print("  ");
  st->print(" %5d", _gc_time_stamp);
  st->print(" PTAMS "PTR_FORMAT" NTAMS "PTR_FORMAT,
            prev_top_at_mark_start(), next_top_at_mark_start());
  G1OffsetTableContigSpace::print_on(st);
}

void HeapRegion::verify(bool allow_dirty) const {
  bool dummy = false;
  verify(allow_dirty, VerifyOption_G1UsePrevMarking, /* failures */ &dummy);
}

// This really ought to be commoned up into OffsetTableContigSpace somehow.
// We would need a mechanism to make that code skip dead objects.

void HeapRegion::verify(bool allow_dirty,
                        VerifyOption vo,
                        bool* failures) const {
  G1CollectedHeap* g1 = G1CollectedHeap::heap();
  *failures = false;
  HeapWord* p = bottom();
  HeapWord* prev_p = NULL;
  VerifyLiveClosure vl_cl(g1, vo);
  bool is_humongous = isHumongous();
  bool do_bot_verify = !is_young();
  size_t object_num = 0;
  while (p < top()) {
    oop obj = oop(p);
    size_t obj_size = obj->size();
    object_num += 1;

    if (is_humongous != g1->isHumongous(obj_size)) {
      gclog_or_tty->print_cr("obj "PTR_FORMAT" is of %shumongous size ("
                             SIZE_FORMAT" words) in a %shumongous region",
                             p, g1->isHumongous(obj_size) ? "" : "non-",
                             obj_size, is_humongous ? "" : "non-");
       *failures = true;
       return;
    }

    // If it returns false, verify_for_object() will output the
    // appropriate messasge.
    if (do_bot_verify && !_offsets.verify_for_object(p, obj_size)) {
      *failures = true;
      return;
    }

    if (!g1->is_obj_dead_cond(obj, this, vo)) {
      if (obj->is_oop()) {
        klassOop klass = obj->klass();
        if (!klass->is_perm()) {
          gclog_or_tty->print_cr("klass "PTR_FORMAT" of object "PTR_FORMAT" "
                                 "not in perm", klass, obj);
          *failures = true;
          return;
        } else if (!klass->is_klass()) {
          gclog_or_tty->print_cr("klass "PTR_FORMAT" of object "PTR_FORMAT" "
                                 "not a klass", klass, obj);
          *failures = true;
          return;
        } else {
          vl_cl.set_containing_obj(obj);
          obj->oop_iterate(&vl_cl);
          if (vl_cl.failures()) {
            *failures = true;
          }
          if (G1MaxVerifyFailures >= 0 &&
              vl_cl.n_failures() >= G1MaxVerifyFailures) {
            return;
          }
        }
      } else {
        gclog_or_tty->print_cr(PTR_FORMAT" no an oop", obj);
        *failures = true;
        return;
      }
    }
    prev_p = p;
    p += obj_size;
  }

  if (p != top()) {
    gclog_or_tty->print_cr("end of last object "PTR_FORMAT" "
                           "does not match top "PTR_FORMAT, p, top());
    *failures = true;
    return;
  }

  HeapWord* the_end = end();
  assert(p == top(), "it should still hold");
  // Do some extra BOT consistency checking for addresses in the
  // range [top, end). BOT look-ups in this range should yield
  // top. No point in doing that if top == end (there's nothing there).
  if (p < the_end) {
    // Look up top
    HeapWord* addr_1 = p;
    HeapWord* b_start_1 = _offsets.block_start_const(addr_1);
    if (b_start_1 != p) {
      gclog_or_tty->print_cr("BOT look up for top: "PTR_FORMAT" "
                             " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
                             addr_1, b_start_1, p);
      *failures = true;
      return;
    }

    // Look up top + 1
    HeapWord* addr_2 = p + 1;
    if (addr_2 < the_end) {
      HeapWord* b_start_2 = _offsets.block_start_const(addr_2);
      if (b_start_2 != p) {
        gclog_or_tty->print_cr("BOT look up for top + 1: "PTR_FORMAT" "
                               " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
                               addr_2, b_start_2, p);
        *failures = true;
        return;
      }
    }

    // Look up an address between top and end
    size_t diff = pointer_delta(the_end, p) / 2;
    HeapWord* addr_3 = p + diff;
    if (addr_3 < the_end) {
      HeapWord* b_start_3 = _offsets.block_start_const(addr_3);
      if (b_start_3 != p) {
        gclog_or_tty->print_cr("BOT look up for top + diff: "PTR_FORMAT" "
                               " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
                               addr_3, b_start_3, p);
        *failures = true;
        return;
      }
    }

    // Loook up end - 1
    HeapWord* addr_4 = the_end - 1;
    HeapWord* b_start_4 = _offsets.block_start_const(addr_4);
    if (b_start_4 != p) {
      gclog_or_tty->print_cr("BOT look up for end - 1: "PTR_FORMAT" "
                             " yielded "PTR_FORMAT", expecting "PTR_FORMAT,
                             addr_4, b_start_4, p);
      *failures = true;
      return;
    }
  }

  if (is_humongous && object_num > 1) {
    gclog_or_tty->print_cr("region ["PTR_FORMAT","PTR_FORMAT"] is humongous "
                           "but has "SIZE_FORMAT", objects",
                           bottom(), end(), object_num);
    *failures = true;
    return;
  }
}

// G1OffsetTableContigSpace code; copied from space.cpp.  Hope this can go
// away eventually.

void G1OffsetTableContigSpace::initialize(MemRegion mr, bool clear_space, bool mangle_space) {
  // false ==> we'll do the clearing if there's clearing to be done.
  ContiguousSpace::initialize(mr, false, mangle_space);
  _offsets.zero_bottom_entry();
  _offsets.initialize_threshold();
  if (clear_space) clear(mangle_space);
}

void G1OffsetTableContigSpace::clear(bool mangle_space) {
  ContiguousSpace::clear(mangle_space);
  _offsets.zero_bottom_entry();
  _offsets.initialize_threshold();
}

void G1OffsetTableContigSpace::set_bottom(HeapWord* new_bottom) {
  Space::set_bottom(new_bottom);
  _offsets.set_bottom(new_bottom);
}

void G1OffsetTableContigSpace::set_end(HeapWord* new_end) {
  Space::set_end(new_end);
  _offsets.resize(new_end - bottom());
}

void G1OffsetTableContigSpace::print() const {
  print_short();
  gclog_or_tty->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", "
                INTPTR_FORMAT ", " INTPTR_FORMAT ")",
                bottom(), top(), _offsets.threshold(), end());
}

HeapWord* G1OffsetTableContigSpace::initialize_threshold() {
  return _offsets.initialize_threshold();
}

HeapWord* G1OffsetTableContigSpace::cross_threshold(HeapWord* start,
                                                    HeapWord* end) {
  _offsets.alloc_block(start, end);
  return _offsets.threshold();
}

HeapWord* G1OffsetTableContigSpace::saved_mark_word() const {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  assert( _gc_time_stamp <= g1h->get_gc_time_stamp(), "invariant" );
  if (_gc_time_stamp < g1h->get_gc_time_stamp())
    return top();
  else
    return ContiguousSpace::saved_mark_word();
}

void G1OffsetTableContigSpace::set_saved_mark() {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  unsigned curr_gc_time_stamp = g1h->get_gc_time_stamp();

  if (_gc_time_stamp < curr_gc_time_stamp) {
    // The order of these is important, as another thread might be
    // about to start scanning this region. If it does so after
    // set_saved_mark and before _gc_time_stamp = ..., then the latter
    // will be false, and it will pick up top() as the high water mark
    // of region. If it does so after _gc_time_stamp = ..., then it
    // will pick up the right saved_mark_word() as the high water mark
    // of the region. Either way, the behaviour will be correct.
    ContiguousSpace::set_saved_mark();
    OrderAccess::storestore();
    _gc_time_stamp = curr_gc_time_stamp;
    // No need to do another barrier to flush the writes above. If
    // this is called in parallel with other threads trying to
    // allocate into the region, the caller should call this while
    // holding a lock and when the lock is released the writes will be
    // flushed.
  }
}

G1OffsetTableContigSpace::
G1OffsetTableContigSpace(G1BlockOffsetSharedArray* sharedOffsetArray,
                         MemRegion mr, bool is_zeroed) :
  _offsets(sharedOffsetArray, mr),
  _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true),
  _gc_time_stamp(0)
{
  _offsets.set_space(this);
  initialize(mr, !is_zeroed, SpaceDecorator::Mangle);
}