view src/share/vm/gc_implementation/g1/heapRegion.hpp @ 5761:b86041bd7b99

8010722: assert: failed: heap size is too big for compressed oops Summary: Use conservative assumptions of required alignment for the various garbage collector components into account when determining the maximum heap size that supports compressed oops. Using this conservative value avoids several circular dependencies in the calculation. Reviewed-by: stefank, dholmes
author tschatzl
date Tue, 18 Apr 2017 06:37:32 +0100
parents 0114a0a4434c
children 2a2721def4a0
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 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
 * 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 if you need additional information or have any
 * questions.


#include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
#include "gc_implementation/g1/g1_specialized_oop_closures.hpp"
#include "gc_implementation/g1/survRateGroup.hpp"
#include "gc_implementation/shared/ageTable.hpp"
#include "gc_implementation/shared/spaceDecorator.hpp"
#include "memory/space.inline.hpp"
#include "memory/watermark.hpp"

#ifndef SERIALGC

// A HeapRegion is the smallest piece of a G1CollectedHeap that
// can be collected independently.

// NOTE: Although a HeapRegion is a Space, its
// Space::initDirtyCardClosure method must not be called.
// The problem is that the existence of this method breaks
// the independence of barrier sets from remembered sets.
// The solution is to remove this method from the definition
// of a Space.

class CompactibleSpace;
class ContiguousSpace;
class HeapRegionRemSet;
class HeapRegionRemSetIterator;
class HeapRegion;
class HeapRegionSetBase;
class nmethod;

#define HR_FORMAT_PARAMS(_hr_) \
                (_hr_)->hrs_index(), \
                (_hr_)->is_survivor() ? "S" : (_hr_)->is_young() ? "E" : \
                (_hr_)->startsHumongous() ? "HS" : \
                (_hr_)->continuesHumongous() ? "HC" : \
                !(_hr_)->is_empty() ? "O" : "F", \
                (_hr_)->bottom(), (_hr_)->top(), (_hr_)->end()

// sentinel value for hrs_index
#define G1_NULL_HRS_INDEX ((uint) -1)

// A dirty card to oop closure for heap regions. It
// knows how to get the G1 heap and how to use the bitmap
// in the concurrent marker used by G1 to filter remembered
// sets.

class HeapRegionDCTOC : public ContiguousSpaceDCTOC {
  // Specification of possible DirtyCardToOopClosure filtering.
  enum FilterKind {

  HeapRegion* _hr;
  FilterKind _fk;
  G1CollectedHeap* _g1;

  void walk_mem_region_with_cl(MemRegion mr,
                               HeapWord* bottom, HeapWord* top,
                               OopClosure* cl);

  // We don't specialize this for FilteringClosure; filtering is handled by
  // the "FilterKind" mechanism.  But we provide this to avoid a compiler
  // warning.
  void walk_mem_region_with_cl(MemRegion mr,
                               HeapWord* bottom, HeapWord* top,
                               FilteringClosure* cl) {
    HeapRegionDCTOC::walk_mem_region_with_cl(mr, bottom, top,

  // Get the actual top of the area on which the closure will
  // operate, given where the top is assumed to be (the end of the
  // memory region passed to do_MemRegion) and where the object
  // at the top is assumed to start. For example, an object may
  // start at the top but actually extend past the assumed top,
  // in which case the top becomes the end of the object.
  HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj) {
    return ContiguousSpaceDCTOC::get_actual_top(top, top_obj);

  // Walk the given memory region from bottom to (actual) top
  // looking for objects and applying the oop closure (_cl) to
  // them. The base implementation of this treats the area as
  // blocks, where a block may or may not be an object. Sub-
  // classes should override this to provide more accurate
  // or possibly more efficient walking.
  void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top) {
    Filtering_DCTOC::walk_mem_region(mr, bottom, top);

  HeapRegionDCTOC(G1CollectedHeap* g1,
                  HeapRegion* hr, OopClosure* cl,
                  CardTableModRefBS::PrecisionStyle precision,
                  FilterKind fk);

// The complicating factor is that BlockOffsetTable diverged
// significantly, and we need functionality that is only in the G1 version.
// So I copied that code, which led to an alternate G1 version of
// OffsetTableContigSpace.  If the two versions of BlockOffsetTable could
// be reconciled, then G1OffsetTableContigSpace could go away.

// The idea behind time stamps is the following. Doing a save_marks on
// all regions at every GC pause is time consuming (if I remember
// well, 10ms or so). So, we would like to do that only for regions
// that are GC alloc regions. To achieve this, we use time
// stamps. For every evacuation pause, G1CollectedHeap generates a
// unique time stamp (essentially a counter that gets
// incremented). Every time we want to call save_marks on a region,
// we set the saved_mark_word to top and also copy the current GC
// time stamp to the time stamp field of the space. Reading the
// saved_mark_word involves checking the time stamp of the
// region. If it is the same as the current GC time stamp, then we
// can safely read the saved_mark_word field, as it is valid. If the
// time stamp of the region is not the same as the current GC time
// stamp, then we instead read top, as the saved_mark_word field is
// invalid. Time stamps (on the regions and also on the
// G1CollectedHeap) are reset at every cleanup (we iterate over
// the regions anyway) and at the end of a Full GC. The current scheme
// that uses sequential unsigned ints will fail only if we have 4b
// evacuation pauses between two cleanups, which is _highly_ unlikely.

class G1OffsetTableContigSpace: public ContiguousSpace {
  friend class VMStructs;
  G1BlockOffsetArrayContigSpace _offsets;
  Mutex _par_alloc_lock;
  volatile unsigned _gc_time_stamp;
  // When we need to retire an allocation region, while other threads
  // are also concurrently trying to allocate into it, we typically
  // allocate a dummy object at the end of the region to ensure that
  // no more allocations can take place in it. However, sometimes we
  // want to know where the end of the last "real" object we allocated
  // into the region was and this is what this keeps track.
  HeapWord* _pre_dummy_top;

  // Constructor.  If "is_zeroed" is true, the MemRegion "mr" may be
  // assumed to contain zeros.
  G1OffsetTableContigSpace(G1BlockOffsetSharedArray* sharedOffsetArray,
                           MemRegion mr, bool is_zeroed = false);

  void set_bottom(HeapWord* value);
  void set_end(HeapWord* value);

  virtual HeapWord* saved_mark_word() const;
  virtual void set_saved_mark();
  void reset_gc_time_stamp() { _gc_time_stamp = 0; }
  unsigned get_gc_time_stamp() { return _gc_time_stamp; }

  // See the comment above in the declaration of _pre_dummy_top for an
  // explanation of what it is.
  void set_pre_dummy_top(HeapWord* pre_dummy_top) {
    assert(is_in(pre_dummy_top) && pre_dummy_top <= top(), "pre-condition");
    _pre_dummy_top = pre_dummy_top;
  HeapWord* pre_dummy_top() {
    return (_pre_dummy_top == NULL) ? top() : _pre_dummy_top;
  void reset_pre_dummy_top() { _pre_dummy_top = NULL; }

  virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
  virtual void clear(bool mangle_space);

  HeapWord* block_start(const void* p);
  HeapWord* block_start_const(const void* p) const;

  // Add offset table update.
  virtual HeapWord* allocate(size_t word_size);
  HeapWord* par_allocate(size_t word_size);

  // MarkSweep support phase3
  virtual HeapWord* initialize_threshold();
  virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);

  virtual void print() const;

  void reset_bot() {

  void update_bot_for_object(HeapWord* start, size_t word_size) {
    _offsets.alloc_block(start, word_size);

  void print_bot_on(outputStream* out) {

class HeapRegion: public G1OffsetTableContigSpace {
  friend class VMStructs;

  enum HumongousType {
    NotHumongous = 0,

  // Requires that the region "mr" be dense with objects, and begin and end
  // with an object.
  void oops_in_mr_iterate(MemRegion mr, OopClosure* cl);

  // The remembered set for this region.
  // (Might want to make this "inline" later, to avoid some alloc failure
  // issues.)
  HeapRegionRemSet* _rem_set;

  G1BlockOffsetArrayContigSpace* offsets() { return &_offsets; }

  // The index of this region in the heap region sequence.
  uint  _hrs_index;

  HumongousType _humongous_type;
  // For a humongous region, region in which it starts.
  HeapRegion* _humongous_start_region;
  // For the start region of a humongous sequence, it's original end().
  HeapWord* _orig_end;

  // True iff the region is in current collection_set.
  bool _in_collection_set;

  // True iff an attempt to evacuate an object in the region failed.
  bool _evacuation_failed;

  // A heap region may be a member one of a number of special subsets, each
  // represented as linked lists through the field below.  Currently, these
  // sets include:
  //   The collection set.
  //   The set of allocation regions used in a collection pause.
  //   Spaces that may contain gray objects.
  HeapRegion* _next_in_special_set;

  // next region in the young "generation" region set
  HeapRegion* _next_young_region;

  // Next region whose cards need cleaning
  HeapRegion* _next_dirty_cards_region;

  // Fields used by the HeapRegionSetBase class and subclasses.
  HeapRegion* _next;
#ifdef ASSERT
  HeapRegionSetBase* _containing_set;
#endif // ASSERT
  bool _pending_removal;

  // For parallel heapRegion traversal.
  jint _claimed;

  // We use concurrent marking to determine the amount of live data
  // in each heap region.
  size_t _prev_marked_bytes;    // Bytes known to be live via last completed marking.
  size_t _next_marked_bytes;    // Bytes known to be live via in-progress marking.

  // The calculated GC efficiency of the region.
  double _gc_efficiency;

  enum YoungType {
    NotYoung,                   // a region is not young
    Young,                      // a region is young
    Survivor                    // a region is young and it contains survivors

  volatile YoungType _young_type;
  int  _young_index_in_cset;
  SurvRateGroup* _surv_rate_group;
  int  _age_index;

  // The start of the unmarked area. The unmarked area extends from this
  // word until the top and/or end of the region, and is the part
  // of the region for which no marking was done, i.e. objects may
  // have been allocated in this part since the last mark phase.
  // "prev" is the top at the start of the last completed marking.
  // "next" is the top at the start of the in-progress marking (if any.)
  HeapWord* _prev_top_at_mark_start;
  HeapWord* _next_top_at_mark_start;
  // If a collection pause is in progress, this is the top at the start
  // of that pause.

  void init_top_at_mark_start() {
    assert(_prev_marked_bytes == 0 &&
           _next_marked_bytes == 0,
           "Must be called after zero_marked_bytes.");
    HeapWord* bot = bottom();
    _prev_top_at_mark_start = bot;
    _next_top_at_mark_start = bot;

  void set_young_type(YoungType new_type) {
    //assert(_young_type != new_type, "setting the same type" );
    // TODO: add more assertions here
    _young_type = new_type;

  // Cached attributes used in the collection set policy information

  // The RSet length that was added to the total value
  // for the collection set.
  size_t _recorded_rs_length;

  // The predicted elapsed time that was added to total value
  // for the collection set.
  double _predicted_elapsed_time_ms;

  // The predicted number of bytes to copy that was added to
  // the total value for the collection set.
  size_t _predicted_bytes_to_copy;

  // If "is_zeroed" is "true", the region "mr" can be assumed to contain zeros.
  HeapRegion(uint hrs_index,
             G1BlockOffsetSharedArray* sharedOffsetArray,
             MemRegion mr, bool is_zeroed);

  static int    LogOfHRGrainBytes;
  static int    LogOfHRGrainWords;

  static size_t GrainBytes;
  static size_t GrainWords;
  static size_t CardsPerRegion;

  static size_t align_up_to_region_byte_size(size_t sz) {
    return (sz + (size_t) GrainBytes - 1) &
                                      ~((1 << (size_t) LogOfHRGrainBytes) - 1);

  static size_t max_region_size();

  // It sets up the heap region size (GrainBytes / GrainWords), as
  // well as other related fields that are based on the heap region
  // size (LogOfHRGrainBytes / LogOfHRGrainWords /
  // CardsPerRegion). All those fields are considered constant
  // throughout the JVM's execution, therefore they should only be set
  // up once during initialization time.
  static void setup_heap_region_size(uintx min_heap_size);

  enum ClaimValues {
    InitialClaimValue          = 0,
    FinalCountClaimValue       = 1,
    NoteEndClaimValue          = 2,
    ScrubRemSetClaimValue      = 3,
    ParVerifyClaimValue        = 4,
    RebuildRSClaimValue        = 5,
    ParEvacFailureClaimValue   = 6,
    AggregateCountClaimValue   = 7,
    VerifyCountClaimValue      = 8,
    ParMarkRootClaimValue      = 9

  inline HeapWord* par_allocate_no_bot_updates(size_t word_size) {
    assert(is_young(), "we can only skip BOT updates on young regions");
    return ContiguousSpace::par_allocate(word_size);
  inline HeapWord* allocate_no_bot_updates(size_t word_size) {
    assert(is_young(), "we can only skip BOT updates on young regions");
    return ContiguousSpace::allocate(word_size);

  // If this region is a member of a HeapRegionSeq, the index in that
  // sequence, otherwise -1.
  uint hrs_index() const { return _hrs_index; }

  // The number of bytes marked live in the region in the last marking phase.
  size_t marked_bytes()    { return _prev_marked_bytes; }
  size_t live_bytes() {
    return (top() - prev_top_at_mark_start()) * HeapWordSize + marked_bytes();

  // The number of bytes counted in the next marking.
  size_t next_marked_bytes() { return _next_marked_bytes; }
  // The number of bytes live wrt the next marking.
  size_t next_live_bytes() {
      (top() - next_top_at_mark_start()) * HeapWordSize + next_marked_bytes();

  // A lower bound on the amount of garbage bytes in the region.
  size_t garbage_bytes() {
    size_t used_at_mark_start_bytes =
      (prev_top_at_mark_start() - bottom()) * HeapWordSize;
    assert(used_at_mark_start_bytes >= marked_bytes(),
           "Can't mark more than we have.");
    return used_at_mark_start_bytes - marked_bytes();

  // Return the amount of bytes we'll reclaim if we collect this
  // region. This includes not only the known garbage bytes in the
  // region but also any unallocated space in it, i.e., [top, end),
  // since it will also be reclaimed if we collect the region.
  size_t reclaimable_bytes() {
    size_t known_live_bytes = live_bytes();
    assert(known_live_bytes <= capacity(), "sanity");
    return capacity() - known_live_bytes;

  // An upper bound on the number of live bytes in the region.
  size_t max_live_bytes() { return used() - garbage_bytes(); }

  void add_to_marked_bytes(size_t incr_bytes) {
    _next_marked_bytes = _next_marked_bytes + incr_bytes;
    assert(_next_marked_bytes <= used(), "invariant" );

  void zero_marked_bytes()      {
    _prev_marked_bytes = _next_marked_bytes = 0;

  bool isHumongous() const { return _humongous_type != NotHumongous; }
  bool startsHumongous() const { return _humongous_type == StartsHumongous; }
  bool continuesHumongous() const { return _humongous_type == ContinuesHumongous; }
  // For a humongous region, region in which it starts.
  HeapRegion* humongous_start_region() const {
    return _humongous_start_region;

  // Return the number of distinct regions that are covered by this region:
  // 1 if the region is not humongous, >= 1 if the region is humongous.
  uint region_num() const {
    if (!isHumongous()) {
      return 1U;
    } else {
      assert(startsHumongous(), "doesn't make sense on HC regions");
      assert(capacity() % HeapRegion::GrainBytes == 0, "sanity");
      return (uint) (capacity() >> HeapRegion::LogOfHRGrainBytes);

  // Return the index + 1 of the last HC regions that's associated
  // with this HS region.
  uint last_hc_index() const {
    assert(startsHumongous(), "don't call this otherwise");
    return hrs_index() + region_num();

  // Same as Space::is_in_reserved, but will use the original size of the region.
  // The original size is different only for start humongous regions. They get
  // their _end set up to be the end of the last continues region of the
  // corresponding humongous object.
  bool is_in_reserved_raw(const void* p) const {
    return _bottom <= p && p < _orig_end;

  // Makes the current region be a "starts humongous" region, i.e.,
  // the first region in a series of one or more contiguous regions
  // that will contain a single "humongous" object. The two parameters
  // are as follows:
  // new_top : The new value of the top field of this region which
  // points to the end of the humongous object that's being
  // allocated. If there is more than one region in the series, top
  // will lie beyond this region's original end field and on the last
  // region in the series.
  // new_end : The new value of the end field of this region which
  // points to the end of the last region in the series. If there is
  // one region in the series (namely: this one) end will be the same
  // as the original end of this region.
  // Updating top and end as described above makes this region look as
  // if it spans the entire space taken up by all the regions in the
  // series and an single allocation moved its top to new_top. This
  // ensures that the space (capacity / allocated) taken up by all
  // humongous regions can be calculated by just looking at the
  // "starts humongous" regions and by ignoring the "continues
  // humongous" regions.
  void set_startsHumongous(HeapWord* new_top, HeapWord* new_end);

  // Makes the current region be a "continues humongous'
  // region. first_hr is the "start humongous" region of the series
  // which this region will be part of.
  void set_continuesHumongous(HeapRegion* first_hr);

  // Unsets the humongous-related fields on the region.
  void set_notHumongous();

  // If the region has a remembered set, return a pointer to it.
  HeapRegionRemSet* rem_set() const {
    return _rem_set;

  // True iff the region is in current collection_set.
  bool in_collection_set() const {
    return _in_collection_set;
  void set_in_collection_set(bool b) {
    _in_collection_set = b;
  HeapRegion* next_in_collection_set() {
    assert(in_collection_set(), "should only invoke on member of CS.");
    assert(_next_in_special_set == NULL ||
           "Malformed CS.");
    return _next_in_special_set;
  void set_next_in_collection_set(HeapRegion* r) {
    assert(in_collection_set(), "should only invoke on member of CS.");
    assert(r == NULL || r->in_collection_set(), "Malformed CS.");
    _next_in_special_set = r;

  // Methods used by the HeapRegionSetBase class and subclasses.

  // Getter and setter for the next field used to link regions into
  // linked lists.
  HeapRegion* next()              { return _next; }

  void set_next(HeapRegion* next) { _next = next; }

  // Every region added to a set is tagged with a reference to that
  // set. This is used for doing consistency checking to make sure that
  // the contents of a set are as they should be and it's only
  // available in non-product builds.
#ifdef ASSERT
  void set_containing_set(HeapRegionSetBase* containing_set) {
    assert((containing_set == NULL && _containing_set != NULL) ||
           (containing_set != NULL && _containing_set == NULL),
           err_msg("containing_set: "PTR_FORMAT" "
                   "_containing_set: "PTR_FORMAT,
                   containing_set, _containing_set));

    _containing_set = containing_set;

  HeapRegionSetBase* containing_set() { return _containing_set; }
#else // ASSERT
  void set_containing_set(HeapRegionSetBase* containing_set) { }

  // containing_set() is only used in asserts so there's no reason
  // to provide a dummy version of it.
#endif // ASSERT

  // If we want to remove regions from a list in bulk we can simply tag
  // them with the pending_removal tag and call the
  // remove_all_pending() method on the list.

  bool pending_removal() { return _pending_removal; }

  void set_pending_removal(bool pending_removal) {
    if (pending_removal) {
      assert(!_pending_removal && containing_set() != NULL,
             "can only set pending removal to true if it's false and "
             "the region belongs to a region set");
    } else {
      assert( _pending_removal && containing_set() == NULL,
              "can only set pending removal to false if it's true and "
              "the region does not belong to a region set");

    _pending_removal = pending_removal;

  HeapRegion* get_next_young_region() { return _next_young_region; }
  void set_next_young_region(HeapRegion* hr) {
    _next_young_region = hr;

  HeapRegion* get_next_dirty_cards_region() const { return _next_dirty_cards_region; }
  HeapRegion** next_dirty_cards_region_addr() { return &_next_dirty_cards_region; }
  void set_next_dirty_cards_region(HeapRegion* hr) { _next_dirty_cards_region = hr; }
  bool is_on_dirty_cards_region_list() const { return get_next_dirty_cards_region() != NULL; }

  HeapWord* orig_end() { return _orig_end; }

  // Allows logical separation between objects allocated before and after.
  void save_marks();

  // Reset HR stuff to default values.
  void hr_clear(bool par, bool clear_space);
  void par_clear();

  void initialize(MemRegion mr, bool clear_space, bool mangle_space);

  // Get the start of the unmarked area in this region.
  HeapWord* prev_top_at_mark_start() const { return _prev_top_at_mark_start; }
  HeapWord* next_top_at_mark_start() const { return _next_top_at_mark_start; }

  // Apply "cl->do_oop" to (the addresses of) all reference fields in objects
  // allocated in the current region before the last call to "save_mark".
  void oop_before_save_marks_iterate(OopClosure* cl);

  // Note the start or end of marking. This tells the heap region
  // that the collector is about to start or has finished (concurrently)
  // marking the heap.

  // Notify the region that concurrent marking is starting. Initialize
  // all fields related to the next marking info.
  inline void note_start_of_marking();

  // Notify the region that concurrent marking has finished. Copy the
  // (now finalized) next marking info fields into the prev marking
  // info fields.
  inline void note_end_of_marking();

  // Notify the region that it will be used as to-space during a GC
  // and we are about to start copying objects into it.
  inline void note_start_of_copying(bool during_initial_mark);

  // Notify the region that it ceases being to-space during a GC and
  // we will not copy objects into it any more.
  inline void note_end_of_copying(bool during_initial_mark);

  // Notify the region that we are about to start processing
  // self-forwarded objects during evac failure handling.
  void note_self_forwarding_removal_start(bool during_initial_mark,
                                          bool during_conc_mark);

  // Notify the region that we have finished processing self-forwarded
  // objects during evac failure handling.
  void note_self_forwarding_removal_end(bool during_initial_mark,
                                        bool during_conc_mark,
                                        size_t marked_bytes);

  // Returns "false" iff no object in the region was allocated when the
  // last mark phase ended.
  bool is_marked() { return _prev_top_at_mark_start != bottom(); }

  void reset_during_compaction() {
    assert(isHumongous() && startsHumongous(),
           "should only be called for starts humongous regions");


  void calc_gc_efficiency(void);
  double gc_efficiency() { return _gc_efficiency;}

  bool is_young() const     { return _young_type != NotYoung; }
  bool is_survivor() const  { return _young_type == Survivor; }

  int  young_index_in_cset() const { return _young_index_in_cset; }
  void set_young_index_in_cset(int index) {
    assert( (index == -1) || is_young(), "pre-condition" );
    _young_index_in_cset = index;

  int age_in_surv_rate_group() {
    assert( _surv_rate_group != NULL, "pre-condition" );
    assert( _age_index > -1, "pre-condition" );
    return _surv_rate_group->age_in_group(_age_index);

  void record_surv_words_in_group(size_t words_survived) {
    assert( _surv_rate_group != NULL, "pre-condition" );
    assert( _age_index > -1, "pre-condition" );
    int age_in_group = age_in_surv_rate_group();
    _surv_rate_group->record_surviving_words(age_in_group, words_survived);

  int age_in_surv_rate_group_cond() {
    if (_surv_rate_group != NULL)
      return age_in_surv_rate_group();
      return -1;

  SurvRateGroup* surv_rate_group() {
    return _surv_rate_group;

  void install_surv_rate_group(SurvRateGroup* surv_rate_group) {
    assert( surv_rate_group != NULL, "pre-condition" );
    assert( _surv_rate_group == NULL, "pre-condition" );
    assert( is_young(), "pre-condition" );

    _surv_rate_group = surv_rate_group;
    _age_index = surv_rate_group->next_age_index();

  void uninstall_surv_rate_group() {
    if (_surv_rate_group != NULL) {
      assert( _age_index > -1, "pre-condition" );
      assert( is_young(), "pre-condition" );

      _surv_rate_group = NULL;
      _age_index = -1;
    } else {
      assert( _age_index == -1, "pre-condition" );

  void set_young() { set_young_type(Young); }

  void set_survivor() { set_young_type(Survivor); }

  void set_not_young() { set_young_type(NotYoung); }

  // Determine if an object has been allocated since the last
  // mark performed by the collector. This returns true iff the object
  // is within the unmarked area of the region.
  bool obj_allocated_since_prev_marking(oop obj) const {
    return (HeapWord *) obj >= prev_top_at_mark_start();
  bool obj_allocated_since_next_marking(oop obj) const {
    return (HeapWord *) obj >= next_top_at_mark_start();

  // For parallel heapRegion traversal.
  bool claimHeapRegion(int claimValue);
  jint claim_value() { return _claimed; }
  // Use this carefully: only when you're sure no one is claiming...
  void set_claim_value(int claimValue) { _claimed = claimValue; }

  // Returns the "evacuation_failed" property of the region.
  bool evacuation_failed() { return _evacuation_failed; }

  // Sets the "evacuation_failed" property of the region.
  void set_evacuation_failed(bool b) {
    _evacuation_failed = b;

    if (b) {
      _next_marked_bytes = 0;

  // Requires that "mr" be entirely within the region.
  // Apply "cl->do_object" to all objects that intersect with "mr".
  // If the iteration encounters an unparseable portion of the region,
  // or if "cl->abort()" is true after a closure application,
  // terminate the iteration and return the address of the start of the
  // subregion that isn't done.  (The two can be distinguished by querying
  // "cl->abort()".)  Return of "NULL" indicates that the iteration
  // completed.
  object_iterate_mem_careful(MemRegion mr, ObjectClosure* cl);

  // filter_young: if true and the region is a young region then we
  // skip the iteration.
  // card_ptr: if not NULL, and we decide that the card is not young
  // and we iterate over it, we'll clean the card before we start the
  // iteration.
  oops_on_card_seq_iterate_careful(MemRegion mr,
                                   FilterOutOfRegionClosure* cl,
                                   bool filter_young,
                                   jbyte* card_ptr);

  // A version of block start that is guaranteed to find *some* block
  // boundary at or before "p", but does not object iteration, and may
  // therefore be used safely when the heap is unparseable.
  HeapWord* block_start_careful(const void* p) const {
    return _offsets.block_start_careful(p);

  // Requires that "addr" is within the region.  Returns the start of the
  // first ("careful") block that starts at or after "addr", or else the
  // "end" of the region if there is no such block.
  HeapWord* next_block_start_careful(HeapWord* addr);

  size_t recorded_rs_length() const        { return _recorded_rs_length; }
  double predicted_elapsed_time_ms() const { return _predicted_elapsed_time_ms; }
  size_t predicted_bytes_to_copy() const   { return _predicted_bytes_to_copy; }

  void set_recorded_rs_length(size_t rs_length) {
    _recorded_rs_length = rs_length;

  void set_predicted_elapsed_time_ms(double ms) {
    _predicted_elapsed_time_ms = ms;

  void set_predicted_bytes_to_copy(size_t bytes) {
    _predicted_bytes_to_copy = bytes;

#define HeapRegion_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \
  virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);

  virtual CompactibleSpace* next_compaction_space() const;

  virtual void reset_after_compaction();

  // Routines for managing a list of code roots (attached to the
  // this region's RSet) that point into this heap region.
  void add_strong_code_root(nmethod* nm);
  void remove_strong_code_root(nmethod* nm);

  // During a collection, migrate the successfully evacuated
  // strong code roots that referenced into this region to the
  // new regions that they now point into. Unsuccessfully
  // evacuated code roots are not migrated.
  void migrate_strong_code_roots();

  // Applies blk->do_code_blob() to each of the entries in
  // the strong code roots list for this region
  void strong_code_roots_do(CodeBlobClosure* blk) const;

  // Verify that the entries on the strong code root list for this
  // region are live and include at least one pointer into this region.
  void verify_strong_code_roots(VerifyOption vo, bool* failures) const;

  void print() const;
  void print_on(outputStream* st) const;

  // vo == UsePrevMarking  -> use "prev" marking information,
  // vo == UseNextMarking -> use "next" marking information
  // vo == UseMarkWord    -> use the mark word in the object header
  // NOTE: Only the "prev" marking information is guaranteed to be
  // consistent most of the time, so most calls to this should use
  // vo == UsePrevMarking.
  // Currently, there is only one case where this is called with
  // vo == UseNextMarking, which is to verify the "next" marking
  // information at the end of remark.
  // Currently there is only one place where this is called with
  // vo == UseMarkWord, which is to verify the marking during a
  // full GC.
  void verify(VerifyOption vo, bool *failures) const;

  // Override; it uses the "prev" marking information
  virtual void verify() const;

// HeapRegionClosure is used for iterating over regions.
// Terminates the iteration when the "doHeapRegion" method returns "true".
class HeapRegionClosure : public StackObj {
  friend class HeapRegionSeq;
  friend class G1CollectedHeap;

  bool _complete;
  void incomplete() { _complete = false; }

  HeapRegionClosure(): _complete(true) {}

  // Typically called on each region until it returns true.
  virtual bool doHeapRegion(HeapRegion* r) = 0;

  // True after iteration if the closure was applied to all heap regions
  // and returned "false" in all cases.
  bool complete() { return _complete; }

#endif // SERIALGC