view src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp @ 2684:4f41766176cf

7084509: G1: fix inconsistencies and mistakes in the young list target length calculations Summary: Fixed inconsistencies and mistakes in the young list target length calculations so that a) the calculated target length is optimal (before, it was not), b) other parameters like max survivor size and max gc locker eden expansion are always consistent with the calculated target length (before, they were not always), and c) the resulting target length was always bound by desired min and max values (before, it was not). Reviewed-by: brutisso, johnc
author tonyp
date Thu, 08 Sep 2011 05:16:49 -0400
parents 05550041d664
children af2ab04e0038
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 "code/icBuffer.hpp"
#include "gc_implementation/g1/bufferingOopClosure.hpp"
#include "gc_implementation/g1/concurrentG1Refine.hpp"
#include "gc_implementation/g1/concurrentG1RefineThread.hpp"
#include "gc_implementation/g1/concurrentMarkThread.inline.hpp"
#include "gc_implementation/g1/g1AllocRegion.inline.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/g1CollectorPolicy.hpp"
#include "gc_implementation/g1/g1ErgoVerbose.hpp"
#include "gc_implementation/g1/g1MarkSweep.hpp"
#include "gc_implementation/g1/g1OopClosures.inline.hpp"
#include "gc_implementation/g1/g1RemSet.inline.hpp"
#include "gc_implementation/g1/heapRegionRemSet.hpp"
#include "gc_implementation/g1/heapRegionSeq.inline.hpp"
#include "gc_implementation/g1/vm_operations_g1.hpp"
#include "gc_implementation/shared/isGCActiveMark.hpp"
#include "memory/gcLocker.inline.hpp"
#include "memory/genOopClosures.inline.hpp"
#include "memory/generationSpec.hpp"
#include "oops/oop.inline.hpp"
#include "oops/oop.pcgc.inline.hpp"
#include "runtime/aprofiler.hpp"
#include "runtime/vmThread.hpp"

size_t G1CollectedHeap::_humongous_object_threshold_in_words = 0;

// turn it on so that the contents of the young list (scan-only /
// to-be-collected) are printed at "strategic" points before / during
// / after the collection --- this is useful for debugging
#define YOUNG_LIST_VERBOSE 0
// CURRENT STATUS
// This file is under construction.  Search for "FIXME".

// INVARIANTS/NOTES
//
// All allocation activity covered by the G1CollectedHeap interface is
// serialized by acquiring the HeapLock.  This happens in mem_allocate
// and allocate_new_tlab, which are the "entry" points to the
// allocation code from the rest of the JVM.  (Note that this does not
// apply to TLAB allocation, which is not part of this interface: it
// is done by clients of this interface.)

// Local to this file.

class RefineCardTableEntryClosure: public CardTableEntryClosure {
  SuspendibleThreadSet* _sts;
  G1RemSet* _g1rs;
  ConcurrentG1Refine* _cg1r;
  bool _concurrent;
public:
  RefineCardTableEntryClosure(SuspendibleThreadSet* sts,
                              G1RemSet* g1rs,
                              ConcurrentG1Refine* cg1r) :
    _sts(sts), _g1rs(g1rs), _cg1r(cg1r), _concurrent(true)
  {}
  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    bool oops_into_cset = _g1rs->concurrentRefineOneCard(card_ptr, worker_i, false);
    // This path is executed by the concurrent refine or mutator threads,
    // concurrently, and so we do not care if card_ptr contains references
    // that point into the collection set.
    assert(!oops_into_cset, "should be");

    if (_concurrent && _sts->should_yield()) {
      // Caller will actually yield.
      return false;
    }
    // Otherwise, we finished successfully; return true.
    return true;
  }
  void set_concurrent(bool b) { _concurrent = b; }
};


class ClearLoggedCardTableEntryClosure: public CardTableEntryClosure {
  int _calls;
  G1CollectedHeap* _g1h;
  CardTableModRefBS* _ctbs;
  int _histo[256];
public:
  ClearLoggedCardTableEntryClosure() :
    _calls(0)
  {
    _g1h = G1CollectedHeap::heap();
    _ctbs = (CardTableModRefBS*)_g1h->barrier_set();
    for (int i = 0; i < 256; i++) _histo[i] = 0;
  }
  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    if (_g1h->is_in_reserved(_ctbs->addr_for(card_ptr))) {
      _calls++;
      unsigned char* ujb = (unsigned char*)card_ptr;
      int ind = (int)(*ujb);
      _histo[ind]++;
      *card_ptr = -1;
    }
    return true;
  }
  int calls() { return _calls; }
  void print_histo() {
    gclog_or_tty->print_cr("Card table value histogram:");
    for (int i = 0; i < 256; i++) {
      if (_histo[i] != 0) {
        gclog_or_tty->print_cr("  %d: %d", i, _histo[i]);
      }
    }
  }
};

class RedirtyLoggedCardTableEntryClosure: public CardTableEntryClosure {
  int _calls;
  G1CollectedHeap* _g1h;
  CardTableModRefBS* _ctbs;
public:
  RedirtyLoggedCardTableEntryClosure() :
    _calls(0)
  {
    _g1h = G1CollectedHeap::heap();
    _ctbs = (CardTableModRefBS*)_g1h->barrier_set();
  }
  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    if (_g1h->is_in_reserved(_ctbs->addr_for(card_ptr))) {
      _calls++;
      *card_ptr = 0;
    }
    return true;
  }
  int calls() { return _calls; }
};

class RedirtyLoggedCardTableEntryFastClosure : public CardTableEntryClosure {
public:
  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    *card_ptr = CardTableModRefBS::dirty_card_val();
    return true;
  }
};

YoungList::YoungList(G1CollectedHeap* g1h)
  : _g1h(g1h), _head(NULL),
    _length(0),
    _last_sampled_rs_lengths(0),
    _survivor_head(NULL), _survivor_tail(NULL), _survivor_length(0)
{
  guarantee( check_list_empty(false), "just making sure..." );
}

void YoungList::push_region(HeapRegion *hr) {
  assert(!hr->is_young(), "should not already be young");
  assert(hr->get_next_young_region() == NULL, "cause it should!");

  hr->set_next_young_region(_head);
  _head = hr;

  hr->set_young();
  double yg_surv_rate = _g1h->g1_policy()->predict_yg_surv_rate((int)_length);
  ++_length;
}

void YoungList::add_survivor_region(HeapRegion* hr) {
  assert(hr->is_survivor(), "should be flagged as survivor region");
  assert(hr->get_next_young_region() == NULL, "cause it should!");

  hr->set_next_young_region(_survivor_head);
  if (_survivor_head == NULL) {
    _survivor_tail = hr;
  }
  _survivor_head = hr;

  ++_survivor_length;
}

void YoungList::empty_list(HeapRegion* list) {
  while (list != NULL) {
    HeapRegion* next = list->get_next_young_region();
    list->set_next_young_region(NULL);
    list->uninstall_surv_rate_group();
    list->set_not_young();
    list = next;
  }
}

void YoungList::empty_list() {
  assert(check_list_well_formed(), "young list should be well formed");

  empty_list(_head);
  _head = NULL;
  _length = 0;

  empty_list(_survivor_head);
  _survivor_head = NULL;
  _survivor_tail = NULL;
  _survivor_length = 0;

  _last_sampled_rs_lengths = 0;

  assert(check_list_empty(false), "just making sure...");
}

bool YoungList::check_list_well_formed() {
  bool ret = true;

  size_t length = 0;
  HeapRegion* curr = _head;
  HeapRegion* last = NULL;
  while (curr != NULL) {
    if (!curr->is_young()) {
      gclog_or_tty->print_cr("### YOUNG REGION "PTR_FORMAT"-"PTR_FORMAT" "
                             "incorrectly tagged (y: %d, surv: %d)",
                             curr->bottom(), curr->end(),
                             curr->is_young(), curr->is_survivor());
      ret = false;
    }
    ++length;
    last = curr;
    curr = curr->get_next_young_region();
  }
  ret = ret && (length == _length);

  if (!ret) {
    gclog_or_tty->print_cr("### YOUNG LIST seems not well formed!");
    gclog_or_tty->print_cr("###   list has %d entries, _length is %d",
                           length, _length);
  }

  return ret;
}

bool YoungList::check_list_empty(bool check_sample) {
  bool ret = true;

  if (_length != 0) {
    gclog_or_tty->print_cr("### YOUNG LIST should have 0 length, not %d",
                  _length);
    ret = false;
  }
  if (check_sample && _last_sampled_rs_lengths != 0) {
    gclog_or_tty->print_cr("### YOUNG LIST has non-zero last sampled RS lengths");
    ret = false;
  }
  if (_head != NULL) {
    gclog_or_tty->print_cr("### YOUNG LIST does not have a NULL head");
    ret = false;
  }
  if (!ret) {
    gclog_or_tty->print_cr("### YOUNG LIST does not seem empty");
  }

  return ret;
}

void
YoungList::rs_length_sampling_init() {
  _sampled_rs_lengths = 0;
  _curr               = _head;
}

bool
YoungList::rs_length_sampling_more() {
  return _curr != NULL;
}

void
YoungList::rs_length_sampling_next() {
  assert( _curr != NULL, "invariant" );
  size_t rs_length = _curr->rem_set()->occupied();

  _sampled_rs_lengths += rs_length;

  // The current region may not yet have been added to the
  // incremental collection set (it gets added when it is
  // retired as the current allocation region).
  if (_curr->in_collection_set()) {
    // Update the collection set policy information for this region
    _g1h->g1_policy()->update_incremental_cset_info(_curr, rs_length);
  }

  _curr = _curr->get_next_young_region();
  if (_curr == NULL) {
    _last_sampled_rs_lengths = _sampled_rs_lengths;
    // gclog_or_tty->print_cr("last sampled RS lengths = %d", _last_sampled_rs_lengths);
  }
}

void
YoungList::reset_auxilary_lists() {
  guarantee( is_empty(), "young list should be empty" );
  assert(check_list_well_formed(), "young list should be well formed");

  // Add survivor regions to SurvRateGroup.
  _g1h->g1_policy()->note_start_adding_survivor_regions();
  _g1h->g1_policy()->finished_recalculating_age_indexes(true /* is_survivors */);

  for (HeapRegion* curr = _survivor_head;
       curr != NULL;
       curr = curr->get_next_young_region()) {
    _g1h->g1_policy()->set_region_survivors(curr);

    // The region is a non-empty survivor so let's add it to
    // the incremental collection set for the next evacuation
    // pause.
    _g1h->g1_policy()->add_region_to_incremental_cset_rhs(curr);
  }
  _g1h->g1_policy()->note_stop_adding_survivor_regions();

  _head   = _survivor_head;
  _length = _survivor_length;
  if (_survivor_head != NULL) {
    assert(_survivor_tail != NULL, "cause it shouldn't be");
    assert(_survivor_length > 0, "invariant");
    _survivor_tail->set_next_young_region(NULL);
  }

  // Don't clear the survivor list handles until the start of
  // the next evacuation pause - we need it in order to re-tag
  // the survivor regions from this evacuation pause as 'young'
  // at the start of the next.

  _g1h->g1_policy()->finished_recalculating_age_indexes(false /* is_survivors */);

  assert(check_list_well_formed(), "young list should be well formed");
}

void YoungList::print() {
  HeapRegion* lists[] = {_head,   _survivor_head};
  const char* names[] = {"YOUNG", "SURVIVOR"};

  for (unsigned int list = 0; list < ARRAY_SIZE(lists); ++list) {
    gclog_or_tty->print_cr("%s LIST CONTENTS", names[list]);
    HeapRegion *curr = lists[list];
    if (curr == NULL)
      gclog_or_tty->print_cr("  empty");
    while (curr != NULL) {
      gclog_or_tty->print_cr("  [%08x-%08x], t: %08x, P: %08x, N: %08x, C: %08x, "
                             "age: %4d, y: %d, surv: %d",
                             curr->bottom(), curr->end(),
                             curr->top(),
                             curr->prev_top_at_mark_start(),
                             curr->next_top_at_mark_start(),
                             curr->top_at_conc_mark_count(),
                             curr->age_in_surv_rate_group_cond(),
                             curr->is_young(),
                             curr->is_survivor());
      curr = curr->get_next_young_region();
    }
  }

  gclog_or_tty->print_cr("");
}

void G1CollectedHeap::push_dirty_cards_region(HeapRegion* hr)
{
  // Claim the right to put the region on the dirty cards region list
  // by installing a self pointer.
  HeapRegion* next = hr->get_next_dirty_cards_region();
  if (next == NULL) {
    HeapRegion* res = (HeapRegion*)
      Atomic::cmpxchg_ptr(hr, hr->next_dirty_cards_region_addr(),
                          NULL);
    if (res == NULL) {
      HeapRegion* head;
      do {
        // Put the region to the dirty cards region list.
        head = _dirty_cards_region_list;
        next = (HeapRegion*)
          Atomic::cmpxchg_ptr(hr, &_dirty_cards_region_list, head);
        if (next == head) {
          assert(hr->get_next_dirty_cards_region() == hr,
                 "hr->get_next_dirty_cards_region() != hr");
          if (next == NULL) {
            // The last region in the list points to itself.
            hr->set_next_dirty_cards_region(hr);
          } else {
            hr->set_next_dirty_cards_region(next);
          }
        }
      } while (next != head);
    }
  }
}

HeapRegion* G1CollectedHeap::pop_dirty_cards_region()
{
  HeapRegion* head;
  HeapRegion* hr;
  do {
    head = _dirty_cards_region_list;
    if (head == NULL) {
      return NULL;
    }
    HeapRegion* new_head = head->get_next_dirty_cards_region();
    if (head == new_head) {
      // The last region.
      new_head = NULL;
    }
    hr = (HeapRegion*)Atomic::cmpxchg_ptr(new_head, &_dirty_cards_region_list,
                                          head);
  } while (hr != head);
  assert(hr != NULL, "invariant");
  hr->set_next_dirty_cards_region(NULL);
  return hr;
}

void G1CollectedHeap::stop_conc_gc_threads() {
  _cg1r->stop();
  _cmThread->stop();
}

#ifdef ASSERT
// A region is added to the collection set as it is retired
// so an address p can point to a region which will be in the
// collection set but has not yet been retired.  This method
// therefore is only accurate during a GC pause after all
// regions have been retired.  It is used for debugging
// to check if an nmethod has references to objects that can
// be move during a partial collection.  Though it can be
// inaccurate, it is sufficient for G1 because the conservative
// implementation of is_scavengable() for G1 will indicate that
// all nmethods must be scanned during a partial collection.
bool G1CollectedHeap::is_in_partial_collection(const void* p) {
  HeapRegion* hr = heap_region_containing(p);
  return hr != NULL && hr->in_collection_set();
}
#endif

// Returns true if the reference points to an object that
// can move in an incremental collecction.
bool G1CollectedHeap::is_scavengable(const void* p) {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  G1CollectorPolicy* g1p = g1h->g1_policy();
  HeapRegion* hr = heap_region_containing(p);
  if (hr == NULL) {
     // perm gen (or null)
     return false;
  } else {
    return !hr->isHumongous();
  }
}

void G1CollectedHeap::check_ct_logs_at_safepoint() {
  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
  CardTableModRefBS* ct_bs = (CardTableModRefBS*)barrier_set();

  // Count the dirty cards at the start.
  CountNonCleanMemRegionClosure count1(this);
  ct_bs->mod_card_iterate(&count1);
  int orig_count = count1.n();

  // First clear the logged cards.
  ClearLoggedCardTableEntryClosure clear;
  dcqs.set_closure(&clear);
  dcqs.apply_closure_to_all_completed_buffers();
  dcqs.iterate_closure_all_threads(false);
  clear.print_histo();

  // Now ensure that there's no dirty cards.
  CountNonCleanMemRegionClosure count2(this);
  ct_bs->mod_card_iterate(&count2);
  if (count2.n() != 0) {
    gclog_or_tty->print_cr("Card table has %d entries; %d originally",
                           count2.n(), orig_count);
  }
  guarantee(count2.n() == 0, "Card table should be clean.");

  RedirtyLoggedCardTableEntryClosure redirty;
  JavaThread::dirty_card_queue_set().set_closure(&redirty);
  dcqs.apply_closure_to_all_completed_buffers();
  dcqs.iterate_closure_all_threads(false);
  gclog_or_tty->print_cr("Log entries = %d, dirty cards = %d.",
                         clear.calls(), orig_count);
  guarantee(redirty.calls() == clear.calls(),
            "Or else mechanism is broken.");

  CountNonCleanMemRegionClosure count3(this);
  ct_bs->mod_card_iterate(&count3);
  if (count3.n() != orig_count) {
    gclog_or_tty->print_cr("Should have restored them all: orig = %d, final = %d.",
                           orig_count, count3.n());
    guarantee(count3.n() >= orig_count, "Should have restored them all.");
  }

  JavaThread::dirty_card_queue_set().set_closure(_refine_cte_cl);
}

// Private class members.

G1CollectedHeap* G1CollectedHeap::_g1h;

// Private methods.

HeapRegion*
G1CollectedHeap::new_region_try_secondary_free_list() {
  MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
  while (!_secondary_free_list.is_empty() || free_regions_coming()) {
    if (!_secondary_free_list.is_empty()) {
      if (G1ConcRegionFreeingVerbose) {
        gclog_or_tty->print_cr("G1ConcRegionFreeing [region alloc] : "
                               "secondary_free_list has "SIZE_FORMAT" entries",
                               _secondary_free_list.length());
      }
      // It looks as if there are free regions available on the
      // secondary_free_list. Let's move them to the free_list and try
      // again to allocate from it.
      append_secondary_free_list();

      assert(!_free_list.is_empty(), "if the secondary_free_list was not "
             "empty we should have moved at least one entry to the free_list");
      HeapRegion* res = _free_list.remove_head();
      if (G1ConcRegionFreeingVerbose) {
        gclog_or_tty->print_cr("G1ConcRegionFreeing [region alloc] : "
                               "allocated "HR_FORMAT" from secondary_free_list",
                               HR_FORMAT_PARAMS(res));
      }
      return res;
    }

    // Wait here until we get notifed either when (a) there are no
    // more free regions coming or (b) some regions have been moved on
    // the secondary_free_list.
    SecondaryFreeList_lock->wait(Mutex::_no_safepoint_check_flag);
  }

  if (G1ConcRegionFreeingVerbose) {
    gclog_or_tty->print_cr("G1ConcRegionFreeing [region alloc] : "
                           "could not allocate from secondary_free_list");
  }
  return NULL;
}

HeapRegion* G1CollectedHeap::new_region(size_t word_size, bool do_expand) {
  assert(!isHumongous(word_size) ||
                                  word_size <= (size_t) HeapRegion::GrainWords,
         "the only time we use this to allocate a humongous region is "
         "when we are allocating a single humongous region");

  HeapRegion* res;
  if (G1StressConcRegionFreeing) {
    if (!_secondary_free_list.is_empty()) {
      if (G1ConcRegionFreeingVerbose) {
        gclog_or_tty->print_cr("G1ConcRegionFreeing [region alloc] : "
                               "forced to look at the secondary_free_list");
      }
      res = new_region_try_secondary_free_list();
      if (res != NULL) {
        return res;
      }
    }
  }
  res = _free_list.remove_head_or_null();
  if (res == NULL) {
    if (G1ConcRegionFreeingVerbose) {
      gclog_or_tty->print_cr("G1ConcRegionFreeing [region alloc] : "
                             "res == NULL, trying the secondary_free_list");
    }
    res = new_region_try_secondary_free_list();
  }
  if (res == NULL && do_expand) {
    ergo_verbose1(ErgoHeapSizing,
                  "attempt heap expansion",
                  ergo_format_reason("region allocation request failed")
                  ergo_format_byte("allocation request"),
                  word_size * HeapWordSize);
    if (expand(word_size * HeapWordSize)) {
      // Even though the heap was expanded, it might not have reached
      // the desired size. So, we cannot assume that the allocation
      // will succeed.
      res = _free_list.remove_head_or_null();
    }
  }
  return res;
}

size_t G1CollectedHeap::humongous_obj_allocate_find_first(size_t num_regions,
                                                          size_t word_size) {
  assert(isHumongous(word_size), "word_size should be humongous");
  assert(num_regions * HeapRegion::GrainWords >= word_size, "pre-condition");

  size_t first = G1_NULL_HRS_INDEX;
  if (num_regions == 1) {
    // Only one region to allocate, no need to go through the slower
    // path. The caller will attempt the expasion if this fails, so
    // let's not try to expand here too.
    HeapRegion* hr = new_region(word_size, false /* do_expand */);
    if (hr != NULL) {
      first = hr->hrs_index();
    } else {
      first = G1_NULL_HRS_INDEX;
    }
  } else {
    // We can't allocate humongous regions while cleanupComplete() is
    // running, since some of the regions we find to be empty might not
    // yet be added to the free list and it is not straightforward to
    // know which list they are on so that we can remove them. Note
    // that we only need to do this if we need to allocate more than
    // one region to satisfy the current humongous allocation
    // request. If we are only allocating one region we use the common
    // region allocation code (see above).
    wait_while_free_regions_coming();
    append_secondary_free_list_if_not_empty_with_lock();

    if (free_regions() >= num_regions) {
      first = _hrs.find_contiguous(num_regions);
      if (first != G1_NULL_HRS_INDEX) {
        for (size_t i = first; i < first + num_regions; ++i) {
          HeapRegion* hr = region_at(i);
          assert(hr->is_empty(), "sanity");
          assert(is_on_master_free_list(hr), "sanity");
          hr->set_pending_removal(true);
        }
        _free_list.remove_all_pending(num_regions);
      }
    }
  }
  return first;
}

HeapWord*
G1CollectedHeap::humongous_obj_allocate_initialize_regions(size_t first,
                                                           size_t num_regions,
                                                           size_t word_size) {
  assert(first != G1_NULL_HRS_INDEX, "pre-condition");
  assert(isHumongous(word_size), "word_size should be humongous");
  assert(num_regions * HeapRegion::GrainWords >= word_size, "pre-condition");

  // Index of last region in the series + 1.
  size_t last = first + num_regions;

  // We need to initialize the region(s) we just discovered. This is
  // a bit tricky given that it can happen concurrently with
  // refinement threads refining cards on these regions and
  // potentially wanting to refine the BOT as they are scanning
  // those cards (this can happen shortly after a cleanup; see CR
  // 6991377). So we have to set up the region(s) carefully and in
  // a specific order.

  // The word size sum of all the regions we will allocate.
  size_t word_size_sum = num_regions * HeapRegion::GrainWords;
  assert(word_size <= word_size_sum, "sanity");

  // This will be the "starts humongous" region.
  HeapRegion* first_hr = region_at(first);
  // The header of the new object will be placed at the bottom of
  // the first region.
  HeapWord* new_obj = first_hr->bottom();
  // This will be the new end of the first region in the series that
  // should also match the end of the last region in the seriers.
  HeapWord* new_end = new_obj + word_size_sum;
  // This will be the new top of the first region that will reflect
  // this allocation.
  HeapWord* new_top = new_obj + word_size;

  // First, we need to zero the header of the space that we will be
  // allocating. When we update top further down, some refinement
  // threads might try to scan the region. By zeroing the header we
  // ensure that any thread that will try to scan the region will
  // come across the zero klass word and bail out.
  //
  // NOTE: It would not have been correct to have used
  // CollectedHeap::fill_with_object() and make the space look like
  // an int array. The thread that is doing the allocation will
  // later update the object header to a potentially different array
  // type and, for a very short period of time, the klass and length
  // fields will be inconsistent. This could cause a refinement
  // thread to calculate the object size incorrectly.
  Copy::fill_to_words(new_obj, oopDesc::header_size(), 0);

  // We will set up the first region as "starts humongous". This
  // will also update the BOT covering all the regions to reflect
  // that there is a single object that starts at the bottom of the
  // first region.
  first_hr->set_startsHumongous(new_top, new_end);

  // Then, if there are any, we will set up the "continues
  // humongous" regions.
  HeapRegion* hr = NULL;
  for (size_t i = first + 1; i < last; ++i) {
    hr = region_at(i);
    hr->set_continuesHumongous(first_hr);
  }
  // If we have "continues humongous" regions (hr != NULL), then the
  // end of the last one should match new_end.
  assert(hr == NULL || hr->end() == new_end, "sanity");

  // Up to this point no concurrent thread would have been able to
  // do any scanning on any region in this series. All the top
  // fields still point to bottom, so the intersection between
  // [bottom,top] and [card_start,card_end] will be empty. Before we
  // update the top fields, we'll do a storestore to make sure that
  // no thread sees the update to top before the zeroing of the
  // object header and the BOT initialization.
  OrderAccess::storestore();

  // Now that the BOT and the object header have been initialized,
  // we can update top of the "starts humongous" region.
  assert(first_hr->bottom() < new_top && new_top <= first_hr->end(),
         "new_top should be in this region");
  first_hr->set_top(new_top);
  if (_hr_printer.is_active()) {
    HeapWord* bottom = first_hr->bottom();
    HeapWord* end = first_hr->orig_end();
    if ((first + 1) == last) {
      // the series has a single humongous region
      _hr_printer.alloc(G1HRPrinter::SingleHumongous, first_hr, new_top);
    } else {
      // the series has more than one humongous regions
      _hr_printer.alloc(G1HRPrinter::StartsHumongous, first_hr, end);
    }
  }

  // Now, we will update the top fields of the "continues humongous"
  // regions. The reason we need to do this is that, otherwise,
  // these regions would look empty and this will confuse parts of
  // G1. For example, the code that looks for a consecutive number
  // of empty regions will consider them empty and try to
  // re-allocate them. We can extend is_empty() to also include
  // !continuesHumongous(), but it is easier to just update the top
  // fields here. The way we set top for all regions (i.e., top ==
  // end for all regions but the last one, top == new_top for the
  // last one) is actually used when we will free up the humongous
  // region in free_humongous_region().
  hr = NULL;
  for (size_t i = first + 1; i < last; ++i) {
    hr = region_at(i);
    if ((i + 1) == last) {
      // last continues humongous region
      assert(hr->bottom() < new_top && new_top <= hr->end(),
             "new_top should fall on this region");
      hr->set_top(new_top);
      _hr_printer.alloc(G1HRPrinter::ContinuesHumongous, hr, new_top);
    } else {
      // not last one
      assert(new_top > hr->end(), "new_top should be above this region");
      hr->set_top(hr->end());
      _hr_printer.alloc(G1HRPrinter::ContinuesHumongous, hr, hr->end());
    }
  }
  // If we have continues humongous regions (hr != NULL), then the
  // end of the last one should match new_end and its top should
  // match new_top.
  assert(hr == NULL ||
         (hr->end() == new_end && hr->top() == new_top), "sanity");

  assert(first_hr->used() == word_size * HeapWordSize, "invariant");
  _summary_bytes_used += first_hr->used();
  _humongous_set.add(first_hr);

  return new_obj;
}

// If could fit into free regions w/o expansion, try.
// Otherwise, if can expand, do so.
// Otherwise, if using ex regions might help, try with ex given back.
HeapWord* G1CollectedHeap::humongous_obj_allocate(size_t word_size) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);

  verify_region_sets_optional();

  size_t num_regions =
         round_to(word_size, HeapRegion::GrainWords) / HeapRegion::GrainWords;
  size_t x_size = expansion_regions();
  size_t fs = _hrs.free_suffix();
  size_t first = humongous_obj_allocate_find_first(num_regions, word_size);
  if (first == G1_NULL_HRS_INDEX) {
    // The only thing we can do now is attempt expansion.
    if (fs + x_size >= num_regions) {
      // If the number of regions we're trying to allocate for this
      // object is at most the number of regions in the free suffix,
      // then the call to humongous_obj_allocate_find_first() above
      // should have succeeded and we wouldn't be here.
      //
      // We should only be trying to expand when the free suffix is
      // not sufficient for the object _and_ we have some expansion
      // room available.
      assert(num_regions > fs, "earlier allocation should have succeeded");

      ergo_verbose1(ErgoHeapSizing,
                    "attempt heap expansion",
                    ergo_format_reason("humongous allocation request failed")
                    ergo_format_byte("allocation request"),
                    word_size * HeapWordSize);
      if (expand((num_regions - fs) * HeapRegion::GrainBytes)) {
        // Even though the heap was expanded, it might not have
        // reached the desired size. So, we cannot assume that the
        // allocation will succeed.
        first = humongous_obj_allocate_find_first(num_regions, word_size);
      }
    }
  }

  HeapWord* result = NULL;
  if (first != G1_NULL_HRS_INDEX) {
    result =
      humongous_obj_allocate_initialize_regions(first, num_regions, word_size);
    assert(result != NULL, "it should always return a valid result");
  }

  verify_region_sets_optional();

  return result;
}

HeapWord* G1CollectedHeap::allocate_new_tlab(size_t word_size) {
  assert_heap_not_locked_and_not_at_safepoint();
  assert(!isHumongous(word_size), "we do not allow humongous TLABs");

  unsigned int dummy_gc_count_before;
  return attempt_allocation(word_size, &dummy_gc_count_before);
}

HeapWord*
G1CollectedHeap::mem_allocate(size_t word_size,
                              bool*  gc_overhead_limit_was_exceeded) {
  assert_heap_not_locked_and_not_at_safepoint();

  // Loop until the allocation is satisified, or unsatisfied after GC.
  for (int try_count = 1; /* we'll return */; try_count += 1) {
    unsigned int gc_count_before;

    HeapWord* result = NULL;
    if (!isHumongous(word_size)) {
      result = attempt_allocation(word_size, &gc_count_before);
    } else {
      result = attempt_allocation_humongous(word_size, &gc_count_before);
    }
    if (result != NULL) {
      return result;
    }

    // Create the garbage collection operation...
    VM_G1CollectForAllocation op(gc_count_before, word_size);
    // ...and get the VM thread to execute it.
    VMThread::execute(&op);

    if (op.prologue_succeeded() && op.pause_succeeded()) {
      // If the operation was successful we'll return the result even
      // if it is NULL. If the allocation attempt failed immediately
      // after a Full GC, it's unlikely we'll be able to allocate now.
      HeapWord* result = op.result();
      if (result != NULL && !isHumongous(word_size)) {
        // Allocations that take place on VM operations do not do any
        // card dirtying and we have to do it here. We only have to do
        // this for non-humongous allocations, though.
        dirty_young_block(result, word_size);
      }
      return result;
    } else {
      assert(op.result() == NULL,
             "the result should be NULL if the VM op did not succeed");
    }

    // Give a warning if we seem to be looping forever.
    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
      warning("G1CollectedHeap::mem_allocate retries %d times", try_count);
    }
  }

  ShouldNotReachHere();
  return NULL;
}

HeapWord* G1CollectedHeap::attempt_allocation_slow(size_t word_size,
                                           unsigned int *gc_count_before_ret) {
  // Make sure you read the note in attempt_allocation_humongous().

  assert_heap_not_locked_and_not_at_safepoint();
  assert(!isHumongous(word_size), "attempt_allocation_slow() should not "
         "be called for humongous allocation requests");

  // We should only get here after the first-level allocation attempt
  // (attempt_allocation()) failed to allocate.

  // We will loop until a) we manage to successfully perform the
  // allocation or b) we successfully schedule a collection which
  // fails to perform the allocation. b) is the only case when we'll
  // return NULL.
  HeapWord* result = NULL;
  for (int try_count = 1; /* we'll return */; try_count += 1) {
    bool should_try_gc;
    unsigned int gc_count_before;

    {
      MutexLockerEx x(Heap_lock);

      result = _mutator_alloc_region.attempt_allocation_locked(word_size,
                                                      false /* bot_updates */);
      if (result != NULL) {
        return result;
      }

      // If we reach here, attempt_allocation_locked() above failed to
      // allocate a new region. So the mutator alloc region should be NULL.
      assert(_mutator_alloc_region.get() == NULL, "only way to get here");

      if (GC_locker::is_active_and_needs_gc()) {
        if (g1_policy()->can_expand_young_list()) {
          // No need for an ergo verbose message here,
          // can_expand_young_list() does this when it returns true.
          result = _mutator_alloc_region.attempt_allocation_force(word_size,
                                                      false /* bot_updates */);
          if (result != NULL) {
            return result;
          }
        }
        should_try_gc = false;
      } else {
        // Read the GC count while still holding the Heap_lock.
        gc_count_before = SharedHeap::heap()->total_collections();
        should_try_gc = true;
      }
    }

    if (should_try_gc) {
      bool succeeded;
      result = do_collection_pause(word_size, gc_count_before, &succeeded);
      if (result != NULL) {
        assert(succeeded, "only way to get back a non-NULL result");
        return result;
      }

      if (succeeded) {
        // If we get here we successfully scheduled a collection which
        // failed to allocate. No point in trying to allocate
        // further. We'll just return NULL.
        MutexLockerEx x(Heap_lock);
        *gc_count_before_ret = SharedHeap::heap()->total_collections();
        return NULL;
      }
    } else {
      GC_locker::stall_until_clear();
    }

    // We can reach here if we were unsuccessul in scheduling a
    // collection (because another thread beat us to it) or if we were
    // stalled due to the GC locker. In either can we should retry the
    // allocation attempt in case another thread successfully
    // performed a collection and reclaimed enough space. We do the
    // first attempt (without holding the Heap_lock) here and the
    // follow-on attempt will be at the start of the next loop
    // iteration (after taking the Heap_lock).
    result = _mutator_alloc_region.attempt_allocation(word_size,
                                                      false /* bot_updates */);
    if (result != NULL ){
      return result;
    }

    // Give a warning if we seem to be looping forever.
    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
      warning("G1CollectedHeap::attempt_allocation_slow() "
              "retries %d times", try_count);
    }
  }

  ShouldNotReachHere();
  return NULL;
}

HeapWord* G1CollectedHeap::attempt_allocation_humongous(size_t word_size,
                                          unsigned int * gc_count_before_ret) {
  // The structure of this method has a lot of similarities to
  // attempt_allocation_slow(). The reason these two were not merged
  // into a single one is that such a method would require several "if
  // allocation is not humongous do this, otherwise do that"
  // conditional paths which would obscure its flow. In fact, an early
  // version of this code did use a unified method which was harder to
  // follow and, as a result, it had subtle bugs that were hard to
  // track down. So keeping these two methods separate allows each to
  // be more readable. It will be good to keep these two in sync as
  // much as possible.

  assert_heap_not_locked_and_not_at_safepoint();
  assert(isHumongous(word_size), "attempt_allocation_humongous() "
         "should only be called for humongous allocations");

  // We will loop until a) we manage to successfully perform the
  // allocation or b) we successfully schedule a collection which
  // fails to perform the allocation. b) is the only case when we'll
  // return NULL.
  HeapWord* result = NULL;
  for (int try_count = 1; /* we'll return */; try_count += 1) {
    bool should_try_gc;
    unsigned int gc_count_before;

    {
      MutexLockerEx x(Heap_lock);

      // Given that humongous objects are not allocated in young
      // regions, we'll first try to do the allocation without doing a
      // collection hoping that there's enough space in the heap.
      result = humongous_obj_allocate(word_size);
      if (result != NULL) {
        return result;
      }

      if (GC_locker::is_active_and_needs_gc()) {
        should_try_gc = false;
      } else {
        // Read the GC count while still holding the Heap_lock.
        gc_count_before = SharedHeap::heap()->total_collections();
        should_try_gc = true;
      }
    }

    if (should_try_gc) {
      // If we failed to allocate the humongous object, we should try to
      // do a collection pause (if we're allowed) in case it reclaims
      // enough space for the allocation to succeed after the pause.

      bool succeeded;
      result = do_collection_pause(word_size, gc_count_before, &succeeded);
      if (result != NULL) {
        assert(succeeded, "only way to get back a non-NULL result");
        return result;
      }

      if (succeeded) {
        // If we get here we successfully scheduled a collection which
        // failed to allocate. No point in trying to allocate
        // further. We'll just return NULL.
        MutexLockerEx x(Heap_lock);
        *gc_count_before_ret = SharedHeap::heap()->total_collections();
        return NULL;
      }
    } else {
      GC_locker::stall_until_clear();
    }

    // We can reach here if we were unsuccessul in scheduling a
    // collection (because another thread beat us to it) or if we were
    // stalled due to the GC locker. In either can we should retry the
    // allocation attempt in case another thread successfully
    // performed a collection and reclaimed enough space.  Give a
    // warning if we seem to be looping forever.

    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
      warning("G1CollectedHeap::attempt_allocation_humongous() "
              "retries %d times", try_count);
    }
  }

  ShouldNotReachHere();
  return NULL;
}

HeapWord* G1CollectedHeap::attempt_allocation_at_safepoint(size_t word_size,
                                       bool expect_null_mutator_alloc_region) {
  assert_at_safepoint(true /* should_be_vm_thread */);
  assert(_mutator_alloc_region.get() == NULL ||
                                             !expect_null_mutator_alloc_region,
         "the current alloc region was unexpectedly found to be non-NULL");

  if (!isHumongous(word_size)) {
    return _mutator_alloc_region.attempt_allocation_locked(word_size,
                                                      false /* bot_updates */);
  } else {
    return humongous_obj_allocate(word_size);
  }

  ShouldNotReachHere();
}

class PostMCRemSetClearClosure: public HeapRegionClosure {
  ModRefBarrierSet* _mr_bs;
public:
  PostMCRemSetClearClosure(ModRefBarrierSet* mr_bs) : _mr_bs(mr_bs) {}
  bool doHeapRegion(HeapRegion* r) {
    r->reset_gc_time_stamp();
    if (r->continuesHumongous())
      return false;
    HeapRegionRemSet* hrrs = r->rem_set();
    if (hrrs != NULL) hrrs->clear();
    // You might think here that we could clear just the cards
    // corresponding to the used region.  But no: if we leave a dirty card
    // in a region we might allocate into, then it would prevent that card
    // from being enqueued, and cause it to be missed.
    // Re: the performance cost: we shouldn't be doing full GC anyway!
    _mr_bs->clear(MemRegion(r->bottom(), r->end()));
    return false;
  }
};


class PostMCRemSetInvalidateClosure: public HeapRegionClosure {
  ModRefBarrierSet* _mr_bs;
public:
  PostMCRemSetInvalidateClosure(ModRefBarrierSet* mr_bs) : _mr_bs(mr_bs) {}
  bool doHeapRegion(HeapRegion* r) {
    if (r->continuesHumongous()) return false;
    if (r->used_region().word_size() != 0) {
      _mr_bs->invalidate(r->used_region(), true /*whole heap*/);
    }
    return false;
  }
};

class RebuildRSOutOfRegionClosure: public HeapRegionClosure {
  G1CollectedHeap*   _g1h;
  UpdateRSOopClosure _cl;
  int                _worker_i;
public:
  RebuildRSOutOfRegionClosure(G1CollectedHeap* g1, int worker_i = 0) :
    _cl(g1->g1_rem_set(), worker_i),
    _worker_i(worker_i),
    _g1h(g1)
  { }

  bool doHeapRegion(HeapRegion* r) {
    if (!r->continuesHumongous()) {
      _cl.set_from(r);
      r->oop_iterate(&_cl);
    }
    return false;
  }
};

class ParRebuildRSTask: public AbstractGangTask {
  G1CollectedHeap* _g1;
public:
  ParRebuildRSTask(G1CollectedHeap* g1)
    : AbstractGangTask("ParRebuildRSTask"),
      _g1(g1)
  { }

  void work(int i) {
    RebuildRSOutOfRegionClosure rebuild_rs(_g1, i);
    _g1->heap_region_par_iterate_chunked(&rebuild_rs, i,
                                         HeapRegion::RebuildRSClaimValue);
  }
};

class PostCompactionPrinterClosure: public HeapRegionClosure {
private:
  G1HRPrinter* _hr_printer;
public:
  bool doHeapRegion(HeapRegion* hr) {
    assert(!hr->is_young(), "not expecting to find young regions");
    // We only generate output for non-empty regions.
    if (!hr->is_empty()) {
      if (!hr->isHumongous()) {
        _hr_printer->post_compaction(hr, G1HRPrinter::Old);
      } else if (hr->startsHumongous()) {
        if (hr->capacity() == (size_t) HeapRegion::GrainBytes) {
          // single humongous region
          _hr_printer->post_compaction(hr, G1HRPrinter::SingleHumongous);
        } else {
          _hr_printer->post_compaction(hr, G1HRPrinter::StartsHumongous);
        }
      } else {
        assert(hr->continuesHumongous(), "only way to get here");
        _hr_printer->post_compaction(hr, G1HRPrinter::ContinuesHumongous);
      }
    }
    return false;
  }

  PostCompactionPrinterClosure(G1HRPrinter* hr_printer)
    : _hr_printer(hr_printer) { }
};

bool G1CollectedHeap::do_collection(bool explicit_gc,
                                    bool clear_all_soft_refs,
                                    size_t word_size) {
  assert_at_safepoint(true /* should_be_vm_thread */);

  if (GC_locker::check_active_before_gc()) {
    return false;
  }

  SvcGCMarker sgcm(SvcGCMarker::FULL);
  ResourceMark rm;

  if (PrintHeapAtGC) {
    Universe::print_heap_before_gc();
  }

  verify_region_sets_optional();

  const bool do_clear_all_soft_refs = clear_all_soft_refs ||
                           collector_policy()->should_clear_all_soft_refs();

  ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy());

  {
    IsGCActiveMark x;

    // Timing
    bool system_gc = (gc_cause() == GCCause::_java_lang_system_gc);
    assert(!system_gc || explicit_gc, "invariant");
    gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
    TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
    TraceTime t(system_gc ? "Full GC (System.gc())" : "Full GC",
                PrintGC, true, gclog_or_tty);

    TraceCollectorStats tcs(g1mm()->full_collection_counters());
    TraceMemoryManagerStats tms(true /* fullGC */, gc_cause());

    double start = os::elapsedTime();
    g1_policy()->record_full_collection_start();

    wait_while_free_regions_coming();
    append_secondary_free_list_if_not_empty_with_lock();

    gc_prologue(true);
    increment_total_collections(true /* full gc */);

    size_t g1h_prev_used = used();
    assert(used() == recalculate_used(), "Should be equal");

    if (VerifyBeforeGC && total_collections() >= VerifyGCStartAt) {
      HandleMark hm;  // Discard invalid handles created during verification
      gclog_or_tty->print(" VerifyBeforeGC:");
      prepare_for_verify();
      Universe::verify(/* allow dirty */ true,
                       /* silent      */ false,
                       /* option      */ VerifyOption_G1UsePrevMarking);

    }
    pre_full_gc_dump();

    COMPILER2_PRESENT(DerivedPointerTable::clear());

    // We want to discover references, but not process them yet.
    // This mode is disabled in
    // instanceRefKlass::process_discovered_references if the
    // generation does some collection work, or
    // instanceRefKlass::enqueue_discovered_references if the
    // generation returns without doing any work.
    ref_processor()->disable_discovery();
    ref_processor()->abandon_partial_discovery();
    ref_processor()->verify_no_references_recorded();

    // Abandon current iterations of concurrent marking and concurrent
    // refinement, if any are in progress.
    concurrent_mark()->abort();

    // Make sure we'll choose a new allocation region afterwards.
    release_mutator_alloc_region();
    abandon_gc_alloc_regions();
    g1_rem_set()->cleanupHRRS();
    tear_down_region_lists();

    // We should call this after we retire any currently active alloc
    // regions so that all the ALLOC / RETIRE events are generated
    // before the start GC event.
    _hr_printer.start_gc(true /* full */, (size_t) total_collections());

    // We may have added regions to the current incremental collection
    // set between the last GC or pause and now. We need to clear the
    // incremental collection set and then start rebuilding it afresh
    // after this full GC.
    abandon_collection_set(g1_policy()->inc_cset_head());
    g1_policy()->clear_incremental_cset();
    g1_policy()->stop_incremental_cset_building();

    empty_young_list();
    g1_policy()->set_full_young_gcs(true);

    // See the comment in G1CollectedHeap::ref_processing_init() about
    // how reference processing currently works in G1.

    // Temporarily make reference _discovery_ single threaded (non-MT).
    ReferenceProcessorMTDiscoveryMutator rp_disc_ser(ref_processor(), false);

    // Temporarily make refs discovery atomic
    ReferenceProcessorAtomicMutator rp_disc_atomic(ref_processor(), true);

    // Temporarily clear _is_alive_non_header
    ReferenceProcessorIsAliveMutator rp_is_alive_null(ref_processor(), NULL);

    ref_processor()->enable_discovery();
    ref_processor()->setup_policy(do_clear_all_soft_refs);
    // Do collection work
    {
      HandleMark hm;  // Discard invalid handles created during gc
      G1MarkSweep::invoke_at_safepoint(ref_processor(), do_clear_all_soft_refs);
    }
    assert(free_regions() == 0, "we should not have added any free regions");
    rebuild_region_lists();

    _summary_bytes_used = recalculate_used();

    ref_processor()->enqueue_discovered_references();

    COMPILER2_PRESENT(DerivedPointerTable::update_pointers());

    MemoryService::track_memory_usage();

    if (VerifyAfterGC && total_collections() >= VerifyGCStartAt) {
      HandleMark hm;  // Discard invalid handles created during verification
      gclog_or_tty->print(" VerifyAfterGC:");
      prepare_for_verify();
      Universe::verify(/* allow dirty */ false,
                       /* silent      */ false,
                       /* option      */ VerifyOption_G1UsePrevMarking);

    }
    NOT_PRODUCT(ref_processor()->verify_no_references_recorded());

    reset_gc_time_stamp();
    // Since everything potentially moved, we will clear all remembered
    // sets, and clear all cards.  Later we will rebuild remebered
    // sets. We will also reset the GC time stamps of the regions.
    PostMCRemSetClearClosure rs_clear(mr_bs());
    heap_region_iterate(&rs_clear);

    // Resize the heap if necessary.
    resize_if_necessary_after_full_collection(explicit_gc ? 0 : word_size);

    if (_hr_printer.is_active()) {
      // We should do this after we potentially resize the heap so
      // that all the COMMIT / UNCOMMIT events are generated before
      // the end GC event.

      PostCompactionPrinterClosure cl(hr_printer());
      heap_region_iterate(&cl);

      _hr_printer.end_gc(true /* full */, (size_t) total_collections());
    }

    if (_cg1r->use_cache()) {
      _cg1r->clear_and_record_card_counts();
      _cg1r->clear_hot_cache();
    }

    // Rebuild remembered sets of all regions.

    if (G1CollectedHeap::use_parallel_gc_threads()) {
      ParRebuildRSTask rebuild_rs_task(this);
      assert(check_heap_region_claim_values(
             HeapRegion::InitialClaimValue), "sanity check");
      set_par_threads(workers()->total_workers());
      workers()->run_task(&rebuild_rs_task);
      set_par_threads(0);
      assert(check_heap_region_claim_values(
             HeapRegion::RebuildRSClaimValue), "sanity check");
      reset_heap_region_claim_values();
    } else {
      RebuildRSOutOfRegionClosure rebuild_rs(this);
      heap_region_iterate(&rebuild_rs);
    }

    if (PrintGC) {
      print_size_transition(gclog_or_tty, g1h_prev_used, used(), capacity());
    }

    if (true) { // FIXME
      // Ask the permanent generation to adjust size for full collections
      perm()->compute_new_size();
    }

    // Start a new incremental collection set for the next pause
    assert(g1_policy()->collection_set() == NULL, "must be");
    g1_policy()->start_incremental_cset_building();

    // Clear the _cset_fast_test bitmap in anticipation of adding
    // regions to the incremental collection set for the next
    // evacuation pause.
    clear_cset_fast_test();

    init_mutator_alloc_region();

    double end = os::elapsedTime();
    g1_policy()->record_full_collection_end();

#ifdef TRACESPINNING
    ParallelTaskTerminator::print_termination_counts();
#endif

    gc_epilogue(true);

    // Discard all rset updates
    JavaThread::dirty_card_queue_set().abandon_logs();
    assert(!G1DeferredRSUpdate
           || (G1DeferredRSUpdate && (dirty_card_queue_set().completed_buffers_num() == 0)), "Should not be any");
  }

  _young_list->reset_sampled_info();
  // At this point there should be no regions in the
  // entire heap tagged as young.
  assert( check_young_list_empty(true /* check_heap */),
    "young list should be empty at this point");

  // Update the number of full collections that have been completed.
  increment_full_collections_completed(false /* concurrent */);

  _hrs.verify_optional();
  verify_region_sets_optional();

  if (PrintHeapAtGC) {
    Universe::print_heap_after_gc();
  }
  g1mm()->update_counters();
  post_full_gc_dump();

  return true;
}

void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs) {
  // do_collection() will return whether it succeeded in performing
  // the GC. Currently, there is no facility on the
  // do_full_collection() API to notify the caller than the collection
  // did not succeed (e.g., because it was locked out by the GC
  // locker). So, right now, we'll ignore the return value.
  bool dummy = do_collection(true,                /* explicit_gc */
                             clear_all_soft_refs,
                             0                    /* word_size */);
}

// This code is mostly copied from TenuredGeneration.
void
G1CollectedHeap::
resize_if_necessary_after_full_collection(size_t word_size) {
  assert(MinHeapFreeRatio <= MaxHeapFreeRatio, "sanity check");

  // Include the current allocation, if any, and bytes that will be
  // pre-allocated to support collections, as "used".
  const size_t used_after_gc = used();
  const size_t capacity_after_gc = capacity();
  const size_t free_after_gc = capacity_after_gc - used_after_gc;

  // This is enforced in arguments.cpp.
  assert(MinHeapFreeRatio <= MaxHeapFreeRatio,
         "otherwise the code below doesn't make sense");

  // We don't have floating point command-line arguments
  const double minimum_free_percentage = (double) MinHeapFreeRatio / 100.0;
  const double maximum_used_percentage = 1.0 - minimum_free_percentage;
  const double maximum_free_percentage = (double) MaxHeapFreeRatio / 100.0;
  const double minimum_used_percentage = 1.0 - maximum_free_percentage;

  const size_t min_heap_size = collector_policy()->min_heap_byte_size();
  const size_t max_heap_size = collector_policy()->max_heap_byte_size();

  // We have to be careful here as these two calculations can overflow
  // 32-bit size_t's.
  double used_after_gc_d = (double) used_after_gc;
  double minimum_desired_capacity_d = used_after_gc_d / maximum_used_percentage;
  double maximum_desired_capacity_d = used_after_gc_d / minimum_used_percentage;

  // Let's make sure that they are both under the max heap size, which
  // by default will make them fit into a size_t.
  double desired_capacity_upper_bound = (double) max_heap_size;
  minimum_desired_capacity_d = MIN2(minimum_desired_capacity_d,
                                    desired_capacity_upper_bound);
  maximum_desired_capacity_d = MIN2(maximum_desired_capacity_d,
                                    desired_capacity_upper_bound);

  // We can now safely turn them into size_t's.
  size_t minimum_desired_capacity = (size_t) minimum_desired_capacity_d;
  size_t maximum_desired_capacity = (size_t) maximum_desired_capacity_d;

  // This assert only makes sense here, before we adjust them
  // with respect to the min and max heap size.
  assert(minimum_desired_capacity <= maximum_desired_capacity,
         err_msg("minimum_desired_capacity = "SIZE_FORMAT", "
                 "maximum_desired_capacity = "SIZE_FORMAT,
                 minimum_desired_capacity, maximum_desired_capacity));

  // Should not be greater than the heap max size. No need to adjust
  // it with respect to the heap min size as it's a lower bound (i.e.,
  // we'll try to make the capacity larger than it, not smaller).
  minimum_desired_capacity = MIN2(minimum_desired_capacity, max_heap_size);
  // Should not be less than the heap min size. No need to adjust it
  // with respect to the heap max size as it's an upper bound (i.e.,
  // we'll try to make the capacity smaller than it, not greater).
  maximum_desired_capacity =  MAX2(maximum_desired_capacity, min_heap_size);

  if (capacity_after_gc < minimum_desired_capacity) {
    // Don't expand unless it's significant
    size_t expand_bytes = minimum_desired_capacity - capacity_after_gc;
    ergo_verbose4(ErgoHeapSizing,
                  "attempt heap expansion",
                  ergo_format_reason("capacity lower than "
                                     "min desired capacity after Full GC")
                  ergo_format_byte("capacity")
                  ergo_format_byte("occupancy")
                  ergo_format_byte_perc("min desired capacity"),
                  capacity_after_gc, used_after_gc,
                  minimum_desired_capacity, (double) MinHeapFreeRatio);
    expand(expand_bytes);

    // No expansion, now see if we want to shrink
  } else if (capacity_after_gc > maximum_desired_capacity) {
    // Capacity too large, compute shrinking size
    size_t shrink_bytes = capacity_after_gc - maximum_desired_capacity;
    ergo_verbose4(ErgoHeapSizing,
                  "attempt heap shrinking",
                  ergo_format_reason("capacity higher than "
                                     "max desired capacity after Full GC")
                  ergo_format_byte("capacity")
                  ergo_format_byte("occupancy")
                  ergo_format_byte_perc("max desired capacity"),
                  capacity_after_gc, used_after_gc,
                  maximum_desired_capacity, (double) MaxHeapFreeRatio);
    shrink(shrink_bytes);
  }
}


HeapWord*
G1CollectedHeap::satisfy_failed_allocation(size_t word_size,
                                           bool* succeeded) {
  assert_at_safepoint(true /* should_be_vm_thread */);

  *succeeded = true;
  // Let's attempt the allocation first.
  HeapWord* result =
    attempt_allocation_at_safepoint(word_size,
                                 false /* expect_null_mutator_alloc_region */);
  if (result != NULL) {
    assert(*succeeded, "sanity");
    return result;
  }

  // In a G1 heap, we're supposed to keep allocation from failing by
  // incremental pauses.  Therefore, at least for now, we'll favor
  // expansion over collection.  (This might change in the future if we can
  // do something smarter than full collection to satisfy a failed alloc.)
  result = expand_and_allocate(word_size);
  if (result != NULL) {
    assert(*succeeded, "sanity");
    return result;
  }

  // Expansion didn't work, we'll try to do a Full GC.
  bool gc_succeeded = do_collection(false, /* explicit_gc */
                                    false, /* clear_all_soft_refs */
                                    word_size);
  if (!gc_succeeded) {
    *succeeded = false;
    return NULL;
  }

  // Retry the allocation
  result = attempt_allocation_at_safepoint(word_size,
                                  true /* expect_null_mutator_alloc_region */);
  if (result != NULL) {
    assert(*succeeded, "sanity");
    return result;
  }

  // Then, try a Full GC that will collect all soft references.
  gc_succeeded = do_collection(false, /* explicit_gc */
                               true,  /* clear_all_soft_refs */
                               word_size);
  if (!gc_succeeded) {
    *succeeded = false;
    return NULL;
  }

  // Retry the allocation once more
  result = attempt_allocation_at_safepoint(word_size,
                                  true /* expect_null_mutator_alloc_region */);
  if (result != NULL) {
    assert(*succeeded, "sanity");
    return result;
  }

  assert(!collector_policy()->should_clear_all_soft_refs(),
         "Flag should have been handled and cleared prior to this point");

  // What else?  We might try synchronous finalization later.  If the total
  // space available is large enough for the allocation, then a more
  // complete compaction phase than we've tried so far might be
  // appropriate.
  assert(*succeeded, "sanity");
  return NULL;
}

// Attempting to expand the heap sufficiently
// to support an allocation of the given "word_size".  If
// successful, perform the allocation and return the address of the
// allocated block, or else "NULL".

HeapWord* G1CollectedHeap::expand_and_allocate(size_t word_size) {
  assert_at_safepoint(true /* should_be_vm_thread */);

  verify_region_sets_optional();

  size_t expand_bytes = MAX2(word_size * HeapWordSize, MinHeapDeltaBytes);
  ergo_verbose1(ErgoHeapSizing,
                "attempt heap expansion",
                ergo_format_reason("allocation request failed")
                ergo_format_byte("allocation request"),
                word_size * HeapWordSize);
  if (expand(expand_bytes)) {
    _hrs.verify_optional();
    verify_region_sets_optional();
    return attempt_allocation_at_safepoint(word_size,
                                 false /* expect_null_mutator_alloc_region */);
  }
  return NULL;
}

void G1CollectedHeap::update_committed_space(HeapWord* old_end,
                                             HeapWord* new_end) {
  assert(old_end != new_end, "don't call this otherwise");
  assert((HeapWord*) _g1_storage.high() == new_end, "invariant");

  // Update the committed mem region.
  _g1_committed.set_end(new_end);
  // Tell the card table about the update.
  Universe::heap()->barrier_set()->resize_covered_region(_g1_committed);
  // Tell the BOT about the update.
  _bot_shared->resize(_g1_committed.word_size());
}

bool G1CollectedHeap::expand(size_t expand_bytes) {
  size_t old_mem_size = _g1_storage.committed_size();
  size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
  aligned_expand_bytes = align_size_up(aligned_expand_bytes,
                                       HeapRegion::GrainBytes);
  ergo_verbose2(ErgoHeapSizing,
                "expand the heap",
                ergo_format_byte("requested expansion amount")
                ergo_format_byte("attempted expansion amount"),
                expand_bytes, aligned_expand_bytes);

  // First commit the memory.
  HeapWord* old_end = (HeapWord*) _g1_storage.high();
  bool successful = _g1_storage.expand_by(aligned_expand_bytes);
  if (successful) {
    // Then propagate this update to the necessary data structures.
    HeapWord* new_end = (HeapWord*) _g1_storage.high();
    update_committed_space(old_end, new_end);

    FreeRegionList expansion_list("Local Expansion List");
    MemRegion mr = _hrs.expand_by(old_end, new_end, &expansion_list);
    assert(mr.start() == old_end, "post-condition");
    // mr might be a smaller region than what was requested if
    // expand_by() was unable to allocate the HeapRegion instances
    assert(mr.end() <= new_end, "post-condition");

    size_t actual_expand_bytes = mr.byte_size();
    assert(actual_expand_bytes <= aligned_expand_bytes, "post-condition");
    assert(actual_expand_bytes == expansion_list.total_capacity_bytes(),
           "post-condition");
    if (actual_expand_bytes < aligned_expand_bytes) {
      // We could not expand _hrs to the desired size. In this case we
      // need to shrink the committed space accordingly.
      assert(mr.end() < new_end, "invariant");

      size_t diff_bytes = aligned_expand_bytes - actual_expand_bytes;
      // First uncommit the memory.
      _g1_storage.shrink_by(diff_bytes);
      // Then propagate this update to the necessary data structures.
      update_committed_space(new_end, mr.end());
    }
    _free_list.add_as_tail(&expansion_list);

    if (_hr_printer.is_active()) {
      HeapWord* curr = mr.start();
      while (curr < mr.end()) {
        HeapWord* curr_end = curr + HeapRegion::GrainWords;
        _hr_printer.commit(curr, curr_end);
        curr = curr_end;
      }
      assert(curr == mr.end(), "post-condition");
    }
    g1_policy()->calculate_reserve(n_regions());
  } else {
    ergo_verbose0(ErgoHeapSizing,
                  "did not expand the heap",
                  ergo_format_reason("heap expansion operation failed"));
    // The expansion of the virtual storage space was unsuccessful.
    // Let's see if it was because we ran out of swap.
    if (G1ExitOnExpansionFailure &&
        _g1_storage.uncommitted_size() >= aligned_expand_bytes) {
      // We had head room...
      vm_exit_out_of_memory(aligned_expand_bytes, "G1 heap expansion");
    }
  }
  return successful;
}

void G1CollectedHeap::shrink_helper(size_t shrink_bytes) {
  size_t old_mem_size = _g1_storage.committed_size();
  size_t aligned_shrink_bytes =
    ReservedSpace::page_align_size_down(shrink_bytes);
  aligned_shrink_bytes = align_size_down(aligned_shrink_bytes,
                                         HeapRegion::GrainBytes);
  size_t num_regions_deleted = 0;
  MemRegion mr = _hrs.shrink_by(aligned_shrink_bytes, &num_regions_deleted);
  HeapWord* old_end = (HeapWord*) _g1_storage.high();
  assert(mr.end() == old_end, "post-condition");

  ergo_verbose3(ErgoHeapSizing,
                "shrink the heap",
                ergo_format_byte("requested shrinking amount")
                ergo_format_byte("aligned shrinking amount")
                ergo_format_byte("attempted shrinking amount"),
                shrink_bytes, aligned_shrink_bytes, mr.byte_size());
  if (mr.byte_size() > 0) {
    if (_hr_printer.is_active()) {
      HeapWord* curr = mr.end();
      while (curr > mr.start()) {
        HeapWord* curr_end = curr;
        curr -= HeapRegion::GrainWords;
        _hr_printer.uncommit(curr, curr_end);
      }
      assert(curr == mr.start(), "post-condition");
    }

    _g1_storage.shrink_by(mr.byte_size());
    HeapWord* new_end = (HeapWord*) _g1_storage.high();
    assert(mr.start() == new_end, "post-condition");

    _expansion_regions += num_regions_deleted;
    update_committed_space(old_end, new_end);
    HeapRegionRemSet::shrink_heap(n_regions());
    g1_policy()->calculate_reserve(n_regions());
  } else {
    ergo_verbose0(ErgoHeapSizing,
                  "did not shrink the heap",
                  ergo_format_reason("heap shrinking operation failed"));
  }
}

void G1CollectedHeap::shrink(size_t shrink_bytes) {
  verify_region_sets_optional();

  // We should only reach here at the end of a Full GC which means we
  // should not not be holding to any GC alloc regions. The method
  // below will make sure of that and do any remaining clean up.
  abandon_gc_alloc_regions();

  // Instead of tearing down / rebuilding the free lists here, we
  // could instead use the remove_all_pending() method on free_list to
  // remove only the ones that we need to remove.
  tear_down_region_lists();  // We will rebuild them in a moment.
  shrink_helper(shrink_bytes);
  rebuild_region_lists();

  _hrs.verify_optional();
  verify_region_sets_optional();
}

// Public methods.

#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


G1CollectedHeap::G1CollectedHeap(G1CollectorPolicy* policy_) :
  SharedHeap(policy_),
  _g1_policy(policy_),
  _dirty_card_queue_set(false),
  _into_cset_dirty_card_queue_set(false),
  _is_alive_closure(this),
  _ref_processor(NULL),
  _process_strong_tasks(new SubTasksDone(G1H_PS_NumElements)),
  _bot_shared(NULL),
  _objs_with_preserved_marks(NULL), _preserved_marks_of_objs(NULL),
  _evac_failure_scan_stack(NULL) ,
  _mark_in_progress(false),
  _cg1r(NULL), _summary_bytes_used(0),
  _refine_cte_cl(NULL),
  _full_collection(false),
  _free_list("Master Free List"),
  _secondary_free_list("Secondary Free List"),
  _humongous_set("Master Humongous Set"),
  _free_regions_coming(false),
  _young_list(new YoungList(this)),
  _gc_time_stamp(0),
  _retained_old_gc_alloc_region(NULL),
  _surviving_young_words(NULL),
  _full_collections_completed(0),
  _in_cset_fast_test(NULL),
  _in_cset_fast_test_base(NULL),
  _dirty_cards_region_list(NULL) {
  _g1h = this; // To catch bugs.
  if (_process_strong_tasks == NULL || !_process_strong_tasks->valid()) {
    vm_exit_during_initialization("Failed necessary allocation.");
  }

  _humongous_object_threshold_in_words = HeapRegion::GrainWords / 2;

  int n_queues = MAX2((int)ParallelGCThreads, 1);
  _task_queues = new RefToScanQueueSet(n_queues);

  int n_rem_sets = HeapRegionRemSet::num_par_rem_sets();
  assert(n_rem_sets > 0, "Invariant.");

  HeapRegionRemSetIterator** iter_arr =
    NEW_C_HEAP_ARRAY(HeapRegionRemSetIterator*, n_queues);
  for (int i = 0; i < n_queues; i++) {
    iter_arr[i] = new HeapRegionRemSetIterator();
  }
  _rem_set_iterator = iter_arr;

  for (int i = 0; i < n_queues; i++) {
    RefToScanQueue* q = new RefToScanQueue();
    q->initialize();
    _task_queues->register_queue(i, q);
  }

  guarantee(_task_queues != NULL, "task_queues allocation failure.");
}

jint G1CollectedHeap::initialize() {
  CollectedHeap::pre_initialize();
  os::enable_vtime();

  // Necessary to satisfy locking discipline assertions.

  MutexLocker x(Heap_lock);

  // We have to initialize the printer before committing the heap, as
  // it will be used then.
  _hr_printer.set_active(G1PrintHeapRegions);

  // While there are no constraints in the GC code that HeapWordSize
  // be any particular value, there are multiple other areas in the
  // system which believe this to be true (e.g. oop->object_size in some
  // cases incorrectly returns the size in wordSize units rather than
  // HeapWordSize).
  guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");

  size_t init_byte_size = collector_policy()->initial_heap_byte_size();
  size_t max_byte_size = collector_policy()->max_heap_byte_size();

  // Ensure that the sizes are properly aligned.
  Universe::check_alignment(init_byte_size, HeapRegion::GrainBytes, "g1 heap");
  Universe::check_alignment(max_byte_size, HeapRegion::GrainBytes, "g1 heap");

  _cg1r = new ConcurrentG1Refine();

  // Reserve the maximum.
  PermanentGenerationSpec* pgs = collector_policy()->permanent_generation();
  // Includes the perm-gen.

  // When compressed oops are enabled, the preferred heap base
  // is calculated by subtracting the requested size from the
  // 32Gb boundary and using the result as the base address for
  // heap reservation. If the requested size is not aligned to
  // HeapRegion::GrainBytes (i.e. the alignment that is passed
  // into the ReservedHeapSpace constructor) then the actual
  // base of the reserved heap may end up differing from the
  // address that was requested (i.e. the preferred heap base).
  // If this happens then we could end up using a non-optimal
  // compressed oops mode.

  // Since max_byte_size is aligned to the size of a heap region (checked
  // above), we also need to align the perm gen size as it might not be.
  const size_t total_reserved = max_byte_size +
                                align_size_up(pgs->max_size(), HeapRegion::GrainBytes);
  Universe::check_alignment(total_reserved, HeapRegion::GrainBytes, "g1 heap and perm");

  char* addr = Universe::preferred_heap_base(total_reserved, Universe::UnscaledNarrowOop);

  ReservedHeapSpace heap_rs(total_reserved, HeapRegion::GrainBytes,
                            UseLargePages, addr);

  if (UseCompressedOops) {
    if (addr != NULL && !heap_rs.is_reserved()) {
      // Failed to reserve at specified address - the requested memory
      // region is taken already, for example, by 'java' launcher.
      // Try again to reserver heap higher.
      addr = Universe::preferred_heap_base(total_reserved, Universe::ZeroBasedNarrowOop);

      ReservedHeapSpace heap_rs0(total_reserved, HeapRegion::GrainBytes,
                                 UseLargePages, addr);

      if (addr != NULL && !heap_rs0.is_reserved()) {
        // Failed to reserve at specified address again - give up.
        addr = Universe::preferred_heap_base(total_reserved, Universe::HeapBasedNarrowOop);
        assert(addr == NULL, "");

        ReservedHeapSpace heap_rs1(total_reserved, HeapRegion::GrainBytes,
                                   UseLargePages, addr);
        heap_rs = heap_rs1;
      } else {
        heap_rs = heap_rs0;
      }
    }
  }

  if (!heap_rs.is_reserved()) {
    vm_exit_during_initialization("Could not reserve enough space for object heap");
    return JNI_ENOMEM;
  }

  // It is important to do this in a way such that concurrent readers can't
  // temporarily think somethings in the heap.  (I've actually seen this
  // happen in asserts: DLD.)
  _reserved.set_word_size(0);
  _reserved.set_start((HeapWord*)heap_rs.base());
  _reserved.set_end((HeapWord*)(heap_rs.base() + heap_rs.size()));

  _expansion_regions = max_byte_size/HeapRegion::GrainBytes;

  // Create the gen rem set (and barrier set) for the entire reserved region.
  _rem_set = collector_policy()->create_rem_set(_reserved, 2);
  set_barrier_set(rem_set()->bs());
  if (barrier_set()->is_a(BarrierSet::ModRef)) {
    _mr_bs = (ModRefBarrierSet*)_barrier_set;
  } else {
    vm_exit_during_initialization("G1 requires a mod ref bs.");
    return JNI_ENOMEM;
  }

  // Also create a G1 rem set.
  if (mr_bs()->is_a(BarrierSet::CardTableModRef)) {
    _g1_rem_set = new G1RemSet(this, (CardTableModRefBS*)mr_bs());
  } else {
    vm_exit_during_initialization("G1 requires a cardtable mod ref bs.");
    return JNI_ENOMEM;
  }

  // Carve out the G1 part of the heap.

  ReservedSpace g1_rs   = heap_rs.first_part(max_byte_size);
  _g1_reserved = MemRegion((HeapWord*)g1_rs.base(),
                           g1_rs.size()/HeapWordSize);
  ReservedSpace perm_gen_rs = heap_rs.last_part(max_byte_size);

  _perm_gen = pgs->init(perm_gen_rs, pgs->init_size(), rem_set());

  _g1_storage.initialize(g1_rs, 0);
  _g1_committed = MemRegion((HeapWord*)_g1_storage.low(), (size_t) 0);
  _hrs.initialize((HeapWord*) _g1_reserved.start(),
                  (HeapWord*) _g1_reserved.end(),
                  _expansion_regions);

  // 6843694 - ensure that the maximum region index can fit
  // in the remembered set structures.
  const size_t max_region_idx = ((size_t)1 << (sizeof(RegionIdx_t)*BitsPerByte-1)) - 1;
  guarantee((max_regions() - 1) <= max_region_idx, "too many regions");

  size_t max_cards_per_region = ((size_t)1 << (sizeof(CardIdx_t)*BitsPerByte-1)) - 1;
  guarantee(HeapRegion::CardsPerRegion > 0, "make sure it's initialized");
  guarantee((size_t) HeapRegion::CardsPerRegion < max_cards_per_region,
            "too many cards per region");

  HeapRegionSet::set_unrealistically_long_length(max_regions() + 1);

  _bot_shared = new G1BlockOffsetSharedArray(_reserved,
                                             heap_word_size(init_byte_size));

  _g1h = this;

   _in_cset_fast_test_length = max_regions();
   _in_cset_fast_test_base = NEW_C_HEAP_ARRAY(bool, _in_cset_fast_test_length);

   // We're biasing _in_cset_fast_test to avoid subtracting the
   // beginning of the heap every time we want to index; basically
   // it's the same with what we do with the card table.
   _in_cset_fast_test = _in_cset_fast_test_base -
                ((size_t) _g1_reserved.start() >> HeapRegion::LogOfHRGrainBytes);

   // Clear the _cset_fast_test bitmap in anticipation of adding
   // regions to the incremental collection set for the first
   // evacuation pause.
   clear_cset_fast_test();

  // Create the ConcurrentMark data structure and thread.
  // (Must do this late, so that "max_regions" is defined.)
  _cm       = new ConcurrentMark(heap_rs, (int) max_regions());
  _cmThread = _cm->cmThread();

  // Initialize the from_card cache structure of HeapRegionRemSet.
  HeapRegionRemSet::init_heap(max_regions());

  // Now expand into the initial heap size.
  if (!expand(init_byte_size)) {
    vm_exit_during_initialization("Failed to allocate initial heap.");
    return JNI_ENOMEM;
  }

  // Perform any initialization actions delegated to the policy.
  g1_policy()->init();

  g1_policy()->note_start_of_mark_thread();

  _refine_cte_cl =
    new RefineCardTableEntryClosure(ConcurrentG1RefineThread::sts(),
                                    g1_rem_set(),
                                    concurrent_g1_refine());
  JavaThread::dirty_card_queue_set().set_closure(_refine_cte_cl);

  JavaThread::satb_mark_queue_set().initialize(SATB_Q_CBL_mon,
                                               SATB_Q_FL_lock,
                                               G1SATBProcessCompletedThreshold,
                                               Shared_SATB_Q_lock);

  JavaThread::dirty_card_queue_set().initialize(DirtyCardQ_CBL_mon,
                                                DirtyCardQ_FL_lock,
                                                concurrent_g1_refine()->yellow_zone(),
                                                concurrent_g1_refine()->red_zone(),
                                                Shared_DirtyCardQ_lock);

  if (G1DeferredRSUpdate) {
    dirty_card_queue_set().initialize(DirtyCardQ_CBL_mon,
                                      DirtyCardQ_FL_lock,
                                      -1, // never trigger processing
                                      -1, // no limit on length
                                      Shared_DirtyCardQ_lock,
                                      &JavaThread::dirty_card_queue_set());
  }

  // Initialize the card queue set used to hold cards containing
  // references into the collection set.
  _into_cset_dirty_card_queue_set.initialize(DirtyCardQ_CBL_mon,
                                             DirtyCardQ_FL_lock,
                                             -1, // never trigger processing
                                             -1, // no limit on length
                                             Shared_DirtyCardQ_lock,
                                             &JavaThread::dirty_card_queue_set());

  // In case we're keeping closure specialization stats, initialize those
  // counts and that mechanism.
  SpecializationStats::clear();

  // Do later initialization work for concurrent refinement.
  _cg1r->init();

  // Here we allocate the dummy full region that is required by the
  // G1AllocRegion class. If we don't pass an address in the reserved
  // space here, lots of asserts fire.

  HeapRegion* dummy_region = new_heap_region(0 /* index of bottom region */,
                                             _g1_reserved.start());
  // We'll re-use the same region whether the alloc region will
  // require BOT updates or not and, if it doesn't, then a non-young
  // region will complain that it cannot support allocations without
  // BOT updates. So we'll tag the dummy region as young to avoid that.
  dummy_region->set_young();
  // Make sure it's full.
  dummy_region->set_top(dummy_region->end());
  G1AllocRegion::setup(this, dummy_region);

  init_mutator_alloc_region();

  // Do create of the monitoring and management support so that
  // values in the heap have been properly initialized.
  _g1mm = new G1MonitoringSupport(this, &_g1_storage);

  return JNI_OK;
}

void G1CollectedHeap::ref_processing_init() {
  // Reference processing in G1 currently works as follows:
  //
  // * There is only one reference processor instance that
  //   'spans' the entire heap. It is created by the code
  //   below.
  // * Reference discovery is not enabled during an incremental
  //   pause (see 6484982).
  // * Discoverered refs are not enqueued nor are they processed
  //   during an incremental pause (see 6484982).
  // * Reference discovery is enabled at initial marking.
  // * Reference discovery is disabled and the discovered
  //   references processed etc during remarking.
  // * Reference discovery is MT (see below).
  // * Reference discovery requires a barrier (see below).
  // * Reference processing is currently not MT (see 6608385).
  // * A full GC enables (non-MT) reference discovery and
  //   processes any discovered references.

  SharedHeap::ref_processing_init();
  MemRegion mr = reserved_region();
  _ref_processor =
    new ReferenceProcessor(mr,    // span
                           ParallelRefProcEnabled && (ParallelGCThreads > 1),    // mt processing
                           (int) ParallelGCThreads,   // degree of mt processing
                           ParallelGCThreads > 1 || ConcGCThreads > 1,  // mt discovery
                           (int) MAX2(ParallelGCThreads, ConcGCThreads), // degree of mt discovery
                           false,                     // Reference discovery is not atomic
                           &_is_alive_closure,        // is alive closure for efficiency
                           true);                     // Setting next fields of discovered
                                                      // lists requires a barrier.
}

size_t G1CollectedHeap::capacity() const {
  return _g1_committed.byte_size();
}

void G1CollectedHeap::iterate_dirty_card_closure(CardTableEntryClosure* cl,
                                                 DirtyCardQueue* into_cset_dcq,
                                                 bool concurrent,
                                                 int worker_i) {
  // Clean cards in the hot card cache
  concurrent_g1_refine()->clean_up_cache(worker_i, g1_rem_set(), into_cset_dcq);

  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
  int n_completed_buffers = 0;
  while (dcqs.apply_closure_to_completed_buffer(cl, worker_i, 0, true)) {
    n_completed_buffers++;
  }
  g1_policy()->record_update_rs_processed_buffers(worker_i,
                                                  (double) n_completed_buffers);
  dcqs.clear_n_completed_buffers();
  assert(!dcqs.completed_buffers_exist_dirty(), "Completed buffers exist!");
}


// Computes the sum of the storage used by the various regions.

size_t G1CollectedHeap::used() const {
  assert(Heap_lock->owner() != NULL,
         "Should be owned on this thread's behalf.");
  size_t result = _summary_bytes_used;
  // Read only once in case it is set to NULL concurrently
  HeapRegion* hr = _mutator_alloc_region.get();
  if (hr != NULL)
    result += hr->used();
  return result;
}

size_t G1CollectedHeap::used_unlocked() const {
  size_t result = _summary_bytes_used;
  return result;
}

class SumUsedClosure: public HeapRegionClosure {
  size_t _used;
public:
  SumUsedClosure() : _used(0) {}
  bool doHeapRegion(HeapRegion* r) {
    if (!r->continuesHumongous()) {
      _used += r->used();
    }
    return false;
  }
  size_t result() { return _used; }
};

size_t G1CollectedHeap::recalculate_used() const {
  SumUsedClosure blk;
  heap_region_iterate(&blk);
  return blk.result();
}

size_t G1CollectedHeap::unsafe_max_alloc() {
  if (free_regions() > 0) return HeapRegion::GrainBytes;
  // otherwise, is there space in the current allocation region?

  // We need to store the current allocation region in a local variable
  // here. The problem is that this method doesn't take any locks and
  // there may be other threads which overwrite the current allocation
  // region field. attempt_allocation(), for example, sets it to NULL
  // and this can happen *after* the NULL check here but before the call
  // to free(), resulting in a SIGSEGV. Note that this doesn't appear
  // to be a problem in the optimized build, since the two loads of the
  // current allocation region field are optimized away.
  HeapRegion* hr = _mutator_alloc_region.get();
  if (hr == NULL) {
    return 0;
  }
  return hr->free();
}

bool G1CollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
  return
    ((cause == GCCause::_gc_locker           && GCLockerInvokesConcurrent) ||
     (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
}

#ifndef PRODUCT
void G1CollectedHeap::allocate_dummy_regions() {
  // Let's fill up most of the region
  size_t word_size = HeapRegion::GrainWords - 1024;
  // And as a result the region we'll allocate will be humongous.
  guarantee(isHumongous(word_size), "sanity");

  for (uintx i = 0; i < G1DummyRegionsPerGC; ++i) {
    // Let's use the existing mechanism for the allocation
    HeapWord* dummy_obj = humongous_obj_allocate(word_size);
    if (dummy_obj != NULL) {
      MemRegion mr(dummy_obj, word_size);
      CollectedHeap::fill_with_object(mr);
    } else {
      // If we can't allocate once, we probably cannot allocate
      // again. Let's get out of the loop.
      break;
    }
  }
}
#endif // !PRODUCT

void G1CollectedHeap::increment_full_collections_completed(bool concurrent) {
  MonitorLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);

  // We assume that if concurrent == true, then the caller is a
  // concurrent thread that was joined the Suspendible Thread
  // Set. If there's ever a cheap way to check this, we should add an
  // assert here.

  // We have already incremented _total_full_collections at the start
  // of the GC, so total_full_collections() represents how many full
  // collections have been started.
  unsigned int full_collections_started = total_full_collections();

  // Given that this method is called at the end of a Full GC or of a
  // concurrent cycle, and those can be nested (i.e., a Full GC can
  // interrupt a concurrent cycle), the number of full collections
  // completed should be either one (in the case where there was no
  // nesting) or two (when a Full GC interrupted a concurrent cycle)
  // behind the number of full collections started.

  // This is the case for the inner caller, i.e. a Full GC.
  assert(concurrent ||
         (full_collections_started == _full_collections_completed + 1) ||
         (full_collections_started == _full_collections_completed + 2),
         err_msg("for inner caller (Full GC): full_collections_started = %u "
                 "is inconsistent with _full_collections_completed = %u",
                 full_collections_started, _full_collections_completed));

  // This is the case for the outer caller, i.e. the concurrent cycle.
  assert(!concurrent ||
         (full_collections_started == _full_collections_completed + 1),
         err_msg("for outer caller (concurrent cycle): "
                 "full_collections_started = %u "
                 "is inconsistent with _full_collections_completed = %u",
                 full_collections_started, _full_collections_completed));

  _full_collections_completed += 1;

  // We need to clear the "in_progress" flag in the CM thread before
  // we wake up any waiters (especially when ExplicitInvokesConcurrent
  // is set) so that if a waiter requests another System.gc() it doesn't
  // incorrectly see that a marking cyle is still in progress.
  if (concurrent) {
    _cmThread->clear_in_progress();
  }

  // This notify_all() will ensure that a thread that called
  // System.gc() with (with ExplicitGCInvokesConcurrent set or not)
  // and it's waiting for a full GC to finish will be woken up. It is
  // waiting in VM_G1IncCollectionPause::doit_epilogue().
  FullGCCount_lock->notify_all();
}

void G1CollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
  assert_at_safepoint(true /* should_be_vm_thread */);
  GCCauseSetter gcs(this, cause);
  switch (cause) {
    case GCCause::_heap_inspection:
    case GCCause::_heap_dump: {
      HandleMark hm;
      do_full_collection(false);         // don't clear all soft refs
      break;
    }
    default: // XXX FIX ME
      ShouldNotReachHere(); // Unexpected use of this function
  }
}

void G1CollectedHeap::collect(GCCause::Cause cause) {
  // The caller doesn't have the Heap_lock
  assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");

  unsigned int gc_count_before;
  unsigned int full_gc_count_before;
  {
    MutexLocker ml(Heap_lock);

    // Read the GC count while holding the Heap_lock
    gc_count_before = SharedHeap::heap()->total_collections();
    full_gc_count_before = SharedHeap::heap()->total_full_collections();
  }

  if (should_do_concurrent_full_gc(cause)) {
    // Schedule an initial-mark evacuation pause that will start a
    // concurrent cycle. We're setting word_size to 0 which means that
    // we are not requesting a post-GC allocation.
    VM_G1IncCollectionPause op(gc_count_before,
                               0,     /* word_size */
                               true,  /* should_initiate_conc_mark */
                               g1_policy()->max_pause_time_ms(),
                               cause);
    VMThread::execute(&op);
  } else {
    if (cause == GCCause::_gc_locker
        DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {

      // Schedule a standard evacuation pause. We're setting word_size
      // to 0 which means that we are not requesting a post-GC allocation.
      VM_G1IncCollectionPause op(gc_count_before,
                                 0,     /* word_size */
                                 false, /* should_initiate_conc_mark */
                                 g1_policy()->max_pause_time_ms(),
                                 cause);
      VMThread::execute(&op);
    } else {
      // Schedule a Full GC.
      VM_G1CollectFull op(gc_count_before, full_gc_count_before, cause);
      VMThread::execute(&op);
    }
  }
}

bool G1CollectedHeap::is_in(const void* p) const {
  HeapRegion* hr = _hrs.addr_to_region((HeapWord*) p);
  if (hr != NULL) {
    return hr->is_in(p);
  } else {
    return _perm_gen->as_gen()->is_in(p);
  }
}

// Iteration functions.

// Iterates an OopClosure over all ref-containing fields of objects
// within a HeapRegion.

class IterateOopClosureRegionClosure: public HeapRegionClosure {
  MemRegion _mr;
  OopClosure* _cl;
public:
  IterateOopClosureRegionClosure(MemRegion mr, OopClosure* cl)
    : _mr(mr), _cl(cl) {}
  bool doHeapRegion(HeapRegion* r) {
    if (! r->continuesHumongous()) {
      r->oop_iterate(_cl);
    }
    return false;
  }
};

void G1CollectedHeap::oop_iterate(OopClosure* cl, bool do_perm) {
  IterateOopClosureRegionClosure blk(_g1_committed, cl);
  heap_region_iterate(&blk);
  if (do_perm) {
    perm_gen()->oop_iterate(cl);
  }
}

void G1CollectedHeap::oop_iterate(MemRegion mr, OopClosure* cl, bool do_perm) {
  IterateOopClosureRegionClosure blk(mr, cl);
  heap_region_iterate(&blk);
  if (do_perm) {
    perm_gen()->oop_iterate(cl);
  }
}

// Iterates an ObjectClosure over all objects within a HeapRegion.

class IterateObjectClosureRegionClosure: public HeapRegionClosure {
  ObjectClosure* _cl;
public:
  IterateObjectClosureRegionClosure(ObjectClosure* cl) : _cl(cl) {}
  bool doHeapRegion(HeapRegion* r) {
    if (! r->continuesHumongous()) {
      r->object_iterate(_cl);
    }
    return false;
  }
};

void G1CollectedHeap::object_iterate(ObjectClosure* cl, bool do_perm) {
  IterateObjectClosureRegionClosure blk(cl);
  heap_region_iterate(&blk);
  if (do_perm) {
    perm_gen()->object_iterate(cl);
  }
}

void G1CollectedHeap::object_iterate_since_last_GC(ObjectClosure* cl) {
  // FIXME: is this right?
  guarantee(false, "object_iterate_since_last_GC not supported by G1 heap");
}

// Calls a SpaceClosure on a HeapRegion.

class SpaceClosureRegionClosure: public HeapRegionClosure {
  SpaceClosure* _cl;
public:
  SpaceClosureRegionClosure(SpaceClosure* cl) : _cl(cl) {}
  bool doHeapRegion(HeapRegion* r) {
    _cl->do_space(r);
    return false;
  }
};

void G1CollectedHeap::space_iterate(SpaceClosure* cl) {
  SpaceClosureRegionClosure blk(cl);
  heap_region_iterate(&blk);
}

void G1CollectedHeap::heap_region_iterate(HeapRegionClosure* cl) const {
  _hrs.iterate(cl);
}

void G1CollectedHeap::heap_region_iterate_from(HeapRegion* r,
                                               HeapRegionClosure* cl) const {
  _hrs.iterate_from(r, cl);
}

void
G1CollectedHeap::heap_region_par_iterate_chunked(HeapRegionClosure* cl,
                                                 int worker,
                                                 jint claim_value) {
  const size_t regions = n_regions();
  const size_t worker_num = (G1CollectedHeap::use_parallel_gc_threads() ? ParallelGCThreads : 1);
  // try to spread out the starting points of the workers
  const size_t start_index = regions / worker_num * (size_t) worker;

  // each worker will actually look at all regions
  for (size_t count = 0; count < regions; ++count) {
    const size_t index = (start_index + count) % regions;
    assert(0 <= index && index < regions, "sanity");
    HeapRegion* r = region_at(index);
    // we'll ignore "continues humongous" regions (we'll process them
    // when we come across their corresponding "start humongous"
    // region) and regions already claimed
    if (r->claim_value() == claim_value || r->continuesHumongous()) {
      continue;
    }
    // OK, try to claim it
    if (r->claimHeapRegion(claim_value)) {
      // success!
      assert(!r->continuesHumongous(), "sanity");
      if (r->startsHumongous()) {
        // If the region is "starts humongous" we'll iterate over its
        // "continues humongous" first; in fact we'll do them
        // first. The order is important. In on case, calling the
        // closure on the "starts humongous" region might de-allocate
        // and clear all its "continues humongous" regions and, as a
        // result, we might end up processing them twice. So, we'll do
        // them first (notice: most closures will ignore them anyway) and
        // then we'll do the "starts humongous" region.
        for (size_t ch_index = index + 1; ch_index < regions; ++ch_index) {
          HeapRegion* chr = region_at(ch_index);

          // if the region has already been claimed or it's not
          // "continues humongous" we're done
          if (chr->claim_value() == claim_value ||
              !chr->continuesHumongous()) {
            break;
          }

          // Noone should have claimed it directly. We can given
          // that we claimed its "starts humongous" region.
          assert(chr->claim_value() != claim_value, "sanity");
          assert(chr->humongous_start_region() == r, "sanity");

          if (chr->claimHeapRegion(claim_value)) {
            // we should always be able to claim it; noone else should
            // be trying to claim this region

            bool res2 = cl->doHeapRegion(chr);
            assert(!res2, "Should not abort");

            // Right now, this holds (i.e., no closure that actually
            // does something with "continues humongous" regions
            // clears them). We might have to weaken it in the future,
            // but let's leave these two asserts here for extra safety.
            assert(chr->continuesHumongous(), "should still be the case");
            assert(chr->humongous_start_region() == r, "sanity");
          } else {
            guarantee(false, "we should not reach here");
          }
        }
      }

      assert(!r->continuesHumongous(), "sanity");
      bool res = cl->doHeapRegion(r);
      assert(!res, "Should not abort");
    }
  }
}

class ResetClaimValuesClosure: public HeapRegionClosure {
public:
  bool doHeapRegion(HeapRegion* r) {
    r->set_claim_value(HeapRegion::InitialClaimValue);
    return false;
  }
};

void
G1CollectedHeap::reset_heap_region_claim_values() {
  ResetClaimValuesClosure blk;
  heap_region_iterate(&blk);
}

#ifdef ASSERT
// This checks whether all regions in the heap have the correct claim
// value. I also piggy-backed on this a check to ensure that the
// humongous_start_region() information on "continues humongous"
// regions is correct.

class CheckClaimValuesClosure : public HeapRegionClosure {
private:
  jint _claim_value;
  size_t _failures;
  HeapRegion* _sh_region;
public:
  CheckClaimValuesClosure(jint claim_value) :
    _claim_value(claim_value), _failures(0), _sh_region(NULL) { }
  bool doHeapRegion(HeapRegion* r) {
    if (r->claim_value() != _claim_value) {
      gclog_or_tty->print_cr("Region ["PTR_FORMAT","PTR_FORMAT"), "
                             "claim value = %d, should be %d",
                             r->bottom(), r->end(), r->claim_value(),
                             _claim_value);
      ++_failures;
    }
    if (!r->isHumongous()) {
      _sh_region = NULL;
    } else if (r->startsHumongous()) {
      _sh_region = r;
    } else if (r->continuesHumongous()) {
      if (r->humongous_start_region() != _sh_region) {
        gclog_or_tty->print_cr("Region ["PTR_FORMAT","PTR_FORMAT"), "
                               "HS = "PTR_FORMAT", should be "PTR_FORMAT,
                               r->bottom(), r->end(),
                               r->humongous_start_region(),
                               _sh_region);
        ++_failures;
      }
    }
    return false;
  }
  size_t failures() {
    return _failures;
  }
};

bool G1CollectedHeap::check_heap_region_claim_values(jint claim_value) {
  CheckClaimValuesClosure cl(claim_value);
  heap_region_iterate(&cl);
  return cl.failures() == 0;
}
#endif // ASSERT

void G1CollectedHeap::collection_set_iterate(HeapRegionClosure* cl) {
  HeapRegion* r = g1_policy()->collection_set();
  while (r != NULL) {
    HeapRegion* next = r->next_in_collection_set();
    if (cl->doHeapRegion(r)) {
      cl->incomplete();
      return;
    }
    r = next;
  }
}

void G1CollectedHeap::collection_set_iterate_from(HeapRegion* r,
                                                  HeapRegionClosure *cl) {
  if (r == NULL) {
    // The CSet is empty so there's nothing to do.
    return;
  }

  assert(r->in_collection_set(),
         "Start region must be a member of the collection set.");
  HeapRegion* cur = r;
  while (cur != NULL) {
    HeapRegion* next = cur->next_in_collection_set();
    if (cl->doHeapRegion(cur) && false) {
      cl->incomplete();
      return;
    }
    cur = next;
  }
  cur = g1_policy()->collection_set();
  while (cur != r) {
    HeapRegion* next = cur->next_in_collection_set();
    if (cl->doHeapRegion(cur) && false) {
      cl->incomplete();
      return;
    }
    cur = next;
  }
}

CompactibleSpace* G1CollectedHeap::first_compactible_space() {
  return n_regions() > 0 ? region_at(0) : NULL;
}


Space* G1CollectedHeap::space_containing(const void* addr) const {
  Space* res = heap_region_containing(addr);
  if (res == NULL)
    res = perm_gen()->space_containing(addr);
  return res;
}

HeapWord* G1CollectedHeap::block_start(const void* addr) const {
  Space* sp = space_containing(addr);
  if (sp != NULL) {
    return sp->block_start(addr);
  }
  return NULL;
}

size_t G1CollectedHeap::block_size(const HeapWord* addr) const {
  Space* sp = space_containing(addr);
  assert(sp != NULL, "block_size of address outside of heap");
  return sp->block_size(addr);
}

bool G1CollectedHeap::block_is_obj(const HeapWord* addr) const {
  Space* sp = space_containing(addr);
  return sp->block_is_obj(addr);
}

bool G1CollectedHeap::supports_tlab_allocation() const {
  return true;
}

size_t G1CollectedHeap::tlab_capacity(Thread* ignored) const {
  return HeapRegion::GrainBytes;
}

size_t G1CollectedHeap::unsafe_max_tlab_alloc(Thread* ignored) const {
  // Return the remaining space in the cur alloc region, but not less than
  // the min TLAB size.

  // Also, this value can be at most the humongous object threshold,
  // since we can't allow tlabs to grow big enough to accomodate
  // humongous objects.

  HeapRegion* hr = _mutator_alloc_region.get();
  size_t max_tlab_size = _humongous_object_threshold_in_words * wordSize;
  if (hr == NULL) {
    return max_tlab_size;
  } else {
    return MIN2(MAX2(hr->free(), (size_t) MinTLABSize), max_tlab_size);
  }
}

size_t G1CollectedHeap::max_capacity() const {
  return _g1_reserved.byte_size();
}

jlong G1CollectedHeap::millis_since_last_gc() {
  // assert(false, "NYI");
  return 0;
}

void G1CollectedHeap::prepare_for_verify() {
  if (SafepointSynchronize::is_at_safepoint() || ! UseTLAB) {
    ensure_parsability(false);
  }
  g1_rem_set()->prepare_for_verify();
}

class VerifyLivenessOopClosure: public OopClosure {
  G1CollectedHeap* _g1h;
  VerifyOption _vo;
public:
  VerifyLivenessOopClosure(G1CollectedHeap* g1h, VerifyOption vo):
    _g1h(g1h), _vo(vo)
  { }
  void do_oop(narrowOop *p) { do_oop_work(p); }
  void do_oop(      oop *p) { do_oop_work(p); }

  template <class T> void do_oop_work(T *p) {
    oop obj = oopDesc::load_decode_heap_oop(p);
    guarantee(obj == NULL || !_g1h->is_obj_dead_cond(obj, _vo),
              "Dead object referenced by a not dead object");
  }
};

class VerifyObjsInRegionClosure: public ObjectClosure {
private:
  G1CollectedHeap* _g1h;
  size_t _live_bytes;
  HeapRegion *_hr;
  VerifyOption _vo;
public:
  // _vo == UsePrevMarking -> use "prev" marking information,
  // _vo == UseNextMarking -> use "next" marking information,
  // _vo == UseMarkWord    -> use mark word from object header.
  VerifyObjsInRegionClosure(HeapRegion *hr, VerifyOption vo)
    : _live_bytes(0), _hr(hr), _vo(vo) {
    _g1h = G1CollectedHeap::heap();
  }
  void do_object(oop o) {
    VerifyLivenessOopClosure isLive(_g1h, _vo);
    assert(o != NULL, "Huh?");
    if (!_g1h->is_obj_dead_cond(o, _vo)) {
      // If the object is alive according to the mark word,
      // then verify that the marking information agrees.
      // Note we can't verify the contra-positive of the
      // above: if the object is dead (according to the mark
      // word), it may not be marked, or may have been marked
      // but has since became dead, or may have been allocated
      // since the last marking.
      if (_vo == VerifyOption_G1UseMarkWord) {
        guarantee(!_g1h->is_obj_dead(o), "mark word and concurrent mark mismatch");
      }

      o->oop_iterate(&isLive);
      if (!_hr->obj_allocated_since_prev_marking(o)) {
        size_t obj_size = o->size();    // Make sure we don't overflow
        _live_bytes += (obj_size * HeapWordSize);
      }
    }
  }
  size_t live_bytes() { return _live_bytes; }
};

class PrintObjsInRegionClosure : public ObjectClosure {
  HeapRegion *_hr;
  G1CollectedHeap *_g1;
public:
  PrintObjsInRegionClosure(HeapRegion *hr) : _hr(hr) {
    _g1 = G1CollectedHeap::heap();
  };

  void do_object(oop o) {
    if (o != NULL) {
      HeapWord *start = (HeapWord *) o;
      size_t word_sz = o->size();
      gclog_or_tty->print("\nPrinting obj "PTR_FORMAT" of size " SIZE_FORMAT
                          " isMarkedPrev %d isMarkedNext %d isAllocSince %d\n",
                          (void*) o, word_sz,
                          _g1->isMarkedPrev(o),
                          _g1->isMarkedNext(o),
                          _hr->obj_allocated_since_prev_marking(o));
      HeapWord *end = start + word_sz;
      HeapWord *cur;
      int *val;
      for (cur = start; cur < end; cur++) {
        val = (int *) cur;
        gclog_or_tty->print("\t "PTR_FORMAT":"PTR_FORMAT"\n", val, *val);
      }
    }
  }
};

class VerifyRegionClosure: public HeapRegionClosure {
private:
  bool         _allow_dirty;
  bool         _par;
  VerifyOption _vo;
  bool         _failures;
public:
  // _vo == UsePrevMarking -> use "prev" marking information,
  // _vo == UseNextMarking -> use "next" marking information,
  // _vo == UseMarkWord    -> use mark word from object header.
  VerifyRegionClosure(bool allow_dirty, bool par, VerifyOption vo)
    : _allow_dirty(allow_dirty),
      _par(par),
      _vo(vo),
      _failures(false) {}

  bool failures() {
    return _failures;
  }

  bool doHeapRegion(HeapRegion* r) {
    guarantee(_par || r->claim_value() == HeapRegion::InitialClaimValue,
              "Should be unclaimed at verify points.");
    if (!r->continuesHumongous()) {
      bool failures = false;
      r->verify(_allow_dirty, _vo, &failures);
      if (failures) {
        _failures = true;
      } else {
        VerifyObjsInRegionClosure not_dead_yet_cl(r, _vo);
        r->object_iterate(&not_dead_yet_cl);
        if (r->max_live_bytes() < not_dead_yet_cl.live_bytes()) {
          gclog_or_tty->print_cr("["PTR_FORMAT","PTR_FORMAT"] "
                                 "max_live_bytes "SIZE_FORMAT" "
                                 "< calculated "SIZE_FORMAT,
                                 r->bottom(), r->end(),
                                 r->max_live_bytes(),
                                 not_dead_yet_cl.live_bytes());
          _failures = true;
        }
      }
    }
    return false; // stop the region iteration if we hit a failure
  }
};

class VerifyRootsClosure: public OopsInGenClosure {
private:
  G1CollectedHeap* _g1h;
  VerifyOption     _vo;
  bool             _failures;
public:
  // _vo == UsePrevMarking -> use "prev" marking information,
  // _vo == UseNextMarking -> use "next" marking information,
  // _vo == UseMarkWord    -> use mark word from object header.
  VerifyRootsClosure(VerifyOption vo) :
    _g1h(G1CollectedHeap::heap()),
    _vo(vo),
    _failures(false) { }

  bool failures() { return _failures; }

  template <class T> void do_oop_nv(T* p) {
    T heap_oop = oopDesc::load_heap_oop(p);
    if (!oopDesc::is_null(heap_oop)) {
      oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
      if (_g1h->is_obj_dead_cond(obj, _vo)) {
        gclog_or_tty->print_cr("Root location "PTR_FORMAT" "
                              "points to dead obj "PTR_FORMAT, p, (void*) obj);
        if (_vo == VerifyOption_G1UseMarkWord) {
          gclog_or_tty->print_cr("  Mark word: "PTR_FORMAT, (void*)(obj->mark()));
        }
        obj->print_on(gclog_or_tty);
        _failures = true;
      }
    }
  }

  void do_oop(oop* p)       { do_oop_nv(p); }
  void do_oop(narrowOop* p) { do_oop_nv(p); }
};

// This is the task used for parallel heap verification.

class G1ParVerifyTask: public AbstractGangTask {
private:
  G1CollectedHeap* _g1h;
  bool             _allow_dirty;
  VerifyOption     _vo;
  bool             _failures;

public:
  // _vo == UsePrevMarking -> use "prev" marking information,
  // _vo == UseNextMarking -> use "next" marking information,
  // _vo == UseMarkWord    -> use mark word from object header.
  G1ParVerifyTask(G1CollectedHeap* g1h, bool allow_dirty, VerifyOption vo) :
    AbstractGangTask("Parallel verify task"),
    _g1h(g1h),
    _allow_dirty(allow_dirty),
    _vo(vo),
    _failures(false) { }

  bool failures() {
    return _failures;
  }

  void work(int worker_i) {
    HandleMark hm;
    VerifyRegionClosure blk(_allow_dirty, true, _vo);
    _g1h->heap_region_par_iterate_chunked(&blk, worker_i,
                                          HeapRegion::ParVerifyClaimValue);
    if (blk.failures()) {
      _failures = true;
    }
  }
};

void G1CollectedHeap::verify(bool allow_dirty, bool silent) {
  verify(allow_dirty, silent, VerifyOption_G1UsePrevMarking);
}

void G1CollectedHeap::verify(bool allow_dirty,
                             bool silent,
                             VerifyOption vo) {
  if (SafepointSynchronize::is_at_safepoint() || ! UseTLAB) {
    if (!silent) { gclog_or_tty->print("Roots (excluding permgen) "); }
    VerifyRootsClosure rootsCl(vo);
    CodeBlobToOopClosure blobsCl(&rootsCl, /*do_marking=*/ false);

    // We apply the relevant closures to all the oops in the
    // system dictionary, the string table and the code cache.
    const int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;

    process_strong_roots(true,      // activate StrongRootsScope
                         true,      // we set "collecting perm gen" to true,
                                    // so we don't reset the dirty cards in the perm gen.
                         SharedHeap::ScanningOption(so),  // roots scanning options
                         &rootsCl,
                         &blobsCl,
                         &rootsCl);

    // If we're verifying after the marking phase of a Full GC then we can't
    // treat the perm gen as roots into the G1 heap. Some of the objects in
    // the perm gen may be dead and hence not marked. If one of these dead
    // objects is considered to be a root then we may end up with a false
    // "Root location <x> points to dead ob <y>" failure.
    if (vo != VerifyOption_G1UseMarkWord) {
      // Since we used "collecting_perm_gen" == true above, we will not have
      // checked the refs from perm into the G1-collected heap. We check those
      // references explicitly below. Whether the relevant cards are dirty
      // is checked further below in the rem set verification.
      if (!silent) { gclog_or_tty->print("Permgen roots "); }
      perm_gen()->oop_iterate(&rootsCl);
    }
    bool failures = rootsCl.failures();

    if (vo != VerifyOption_G1UseMarkWord) {
      // If we're verifying during a full GC then the region sets
      // will have been torn down at the start of the GC. Therefore
      // verifying the region sets will fail. So we only verify
      // the region sets when not in a full GC.
      if (!silent) { gclog_or_tty->print("HeapRegionSets "); }
      verify_region_sets();
    }

    if (!silent) { gclog_or_tty->print("HeapRegions "); }
    if (GCParallelVerificationEnabled && ParallelGCThreads > 1) {
      assert(check_heap_region_claim_values(HeapRegion::InitialClaimValue),
             "sanity check");

      G1ParVerifyTask task(this, allow_dirty, vo);
      int n_workers = workers()->total_workers();
      set_par_threads(n_workers);
      workers()->run_task(&task);
      set_par_threads(0);
      if (task.failures()) {
        failures = true;
      }

      assert(check_heap_region_claim_values(HeapRegion::ParVerifyClaimValue),
             "sanity check");

      reset_heap_region_claim_values();

      assert(check_heap_region_claim_values(HeapRegion::InitialClaimValue),
             "sanity check");
    } else {
      VerifyRegionClosure blk(allow_dirty, false, vo);
      heap_region_iterate(&blk);
      if (blk.failures()) {
        failures = true;
      }
    }
    if (!silent) gclog_or_tty->print("RemSet ");
    rem_set()->verify();

    if (failures) {
      gclog_or_tty->print_cr("Heap:");
      print_on(gclog_or_tty, true /* extended */);
      gclog_or_tty->print_cr("");
#ifndef PRODUCT
      if (VerifyDuringGC && G1VerifyDuringGCPrintReachable) {
        concurrent_mark()->print_reachable("at-verification-failure",
                                           vo, false /* all */);
      }
#endif
      gclog_or_tty->flush();
    }
    guarantee(!failures, "there should not have been any failures");
  } else {
    if (!silent) gclog_or_tty->print("(SKIPPING roots, heapRegions, remset) ");
  }
}

class PrintRegionClosure: public HeapRegionClosure {
  outputStream* _st;
public:
  PrintRegionClosure(outputStream* st) : _st(st) {}
  bool doHeapRegion(HeapRegion* r) {
    r->print_on(_st);
    return false;
  }
};

void G1CollectedHeap::print() const { print_on(tty); }

void G1CollectedHeap::print_on(outputStream* st) const {
  print_on(st, PrintHeapAtGCExtended);
}

void G1CollectedHeap::print_on(outputStream* st, bool extended) const {
  st->print(" %-20s", "garbage-first heap");
  st->print(" total " SIZE_FORMAT "K, used " SIZE_FORMAT "K",
            capacity()/K, used_unlocked()/K);
  st->print(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", " INTPTR_FORMAT ")",
            _g1_storage.low_boundary(),
            _g1_storage.high(),
            _g1_storage.high_boundary());
  st->cr();
  st->print("  region size " SIZE_FORMAT "K, ",
            HeapRegion::GrainBytes/K);
  size_t young_regions = _young_list->length();
  st->print(SIZE_FORMAT " young (" SIZE_FORMAT "K), ",
            young_regions, young_regions * HeapRegion::GrainBytes / K);
  size_t survivor_regions = g1_policy()->recorded_survivor_regions();
  st->print(SIZE_FORMAT " survivors (" SIZE_FORMAT "K)",
            survivor_regions, survivor_regions * HeapRegion::GrainBytes / K);
  st->cr();
  perm()->as_gen()->print_on(st);
  if (extended) {
    st->cr();
    print_on_extended(st);
  }
}

void G1CollectedHeap::print_on_extended(outputStream* st) const {
  PrintRegionClosure blk(st);
  heap_region_iterate(&blk);
}

void G1CollectedHeap::print_gc_threads_on(outputStream* st) const {
  if (G1CollectedHeap::use_parallel_gc_threads()) {
    workers()->print_worker_threads_on(st);
  }
  _cmThread->print_on(st);
  st->cr();
  _cm->print_worker_threads_on(st);
  _cg1r->print_worker_threads_on(st);
  st->cr();
}

void G1CollectedHeap::gc_threads_do(ThreadClosure* tc) const {
  if (G1CollectedHeap::use_parallel_gc_threads()) {
    workers()->threads_do(tc);
  }
  tc->do_thread(_cmThread);
  _cg1r->threads_do(tc);
}

void G1CollectedHeap::print_tracing_info() const {
  // We'll overload this to mean "trace GC pause statistics."
  if (TraceGen0Time || TraceGen1Time) {
    // The "G1CollectorPolicy" is keeping track of these stats, so delegate
    // to that.
    g1_policy()->print_tracing_info();
  }
  if (G1SummarizeRSetStats) {
    g1_rem_set()->print_summary_info();
  }
  if (G1SummarizeConcMark) {
    concurrent_mark()->print_summary_info();
  }
  g1_policy()->print_yg_surv_rate_info();
  SpecializationStats::print();
}

#ifndef PRODUCT
// Helpful for debugging RSet issues.

class PrintRSetsClosure : public HeapRegionClosure {
private:
  const char* _msg;
  size_t _occupied_sum;

public:
  bool doHeapRegion(HeapRegion* r) {
    HeapRegionRemSet* hrrs = r->rem_set();
    size_t occupied = hrrs->occupied();
    _occupied_sum += occupied;

    gclog_or_tty->print_cr("Printing RSet for region "HR_FORMAT,
                           HR_FORMAT_PARAMS(r));
    if (occupied == 0) {
      gclog_or_tty->print_cr("  RSet is empty");
    } else {
      hrrs->print();
    }
    gclog_or_tty->print_cr("----------");
    return false;
  }

  PrintRSetsClosure(const char* msg) : _msg(msg), _occupied_sum(0) {
    gclog_or_tty->cr();
    gclog_or_tty->print_cr("========================================");
    gclog_or_tty->print_cr(msg);
    gclog_or_tty->cr();
  }

  ~PrintRSetsClosure() {
    gclog_or_tty->print_cr("Occupied Sum: "SIZE_FORMAT, _occupied_sum);
    gclog_or_tty->print_cr("========================================");
    gclog_or_tty->cr();
  }
};

void G1CollectedHeap::print_cset_rsets() {
  PrintRSetsClosure cl("Printing CSet RSets");
  collection_set_iterate(&cl);
}

void G1CollectedHeap::print_all_rsets() {
  PrintRSetsClosure cl("Printing All RSets");;
  heap_region_iterate(&cl);
}
#endif // PRODUCT

G1CollectedHeap* G1CollectedHeap::heap() {
  assert(_sh->kind() == CollectedHeap::G1CollectedHeap,
         "not a garbage-first heap");
  return _g1h;
}

void G1CollectedHeap::gc_prologue(bool full /* Ignored */) {
  // always_do_update_barrier = false;
  assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
  // Call allocation profiler
  AllocationProfiler::iterate_since_last_gc();
  // Fill TLAB's and such
  ensure_parsability(true);
}

void G1CollectedHeap::gc_epilogue(bool full /* Ignored */) {
  // FIXME: what is this about?
  // I'm ignoring the "fill_newgen()" call if "alloc_event_enabled"
  // is set.
  COMPILER2_PRESENT(assert(DerivedPointerTable::is_empty(),
                        "derived pointer present"));
  // always_do_update_barrier = true;
}

HeapWord* G1CollectedHeap::do_collection_pause(size_t word_size,
                                               unsigned int gc_count_before,
                                               bool* succeeded) {
  assert_heap_not_locked_and_not_at_safepoint();
  g1_policy()->record_stop_world_start();
  VM_G1IncCollectionPause op(gc_count_before,
                             word_size,
                             false, /* should_initiate_conc_mark */
                             g1_policy()->max_pause_time_ms(),
                             GCCause::_g1_inc_collection_pause);
  VMThread::execute(&op);

  HeapWord* result = op.result();
  bool ret_succeeded = op.prologue_succeeded() && op.pause_succeeded();
  assert(result == NULL || ret_succeeded,
         "the result should be NULL if the VM did not succeed");
  *succeeded = ret_succeeded;

  assert_heap_not_locked();
  return result;
}

void
G1CollectedHeap::doConcurrentMark() {
  MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
  if (!_cmThread->in_progress()) {
    _cmThread->set_started();
    CGC_lock->notify();
  }
}

// <NEW PREDICTION>

double G1CollectedHeap::predict_region_elapsed_time_ms(HeapRegion *hr,
                                                       bool young) {
  return _g1_policy->predict_region_elapsed_time_ms(hr, young);
}

void G1CollectedHeap::check_if_region_is_too_expensive(double
                                                           predicted_time_ms) {
  _g1_policy->check_if_region_is_too_expensive(predicted_time_ms);
}

size_t G1CollectedHeap::pending_card_num() {
  size_t extra_cards = 0;
  JavaThread *curr = Threads::first();
  while (curr != NULL) {
    DirtyCardQueue& dcq = curr->dirty_card_queue();
    extra_cards += dcq.size();
    curr = curr->next();
  }
  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
  size_t buffer_size = dcqs.buffer_size();
  size_t buffer_num = dcqs.completed_buffers_num();
  return buffer_size * buffer_num + extra_cards;
}

size_t G1CollectedHeap::max_pending_card_num() {
  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
  size_t buffer_size = dcqs.buffer_size();
  size_t buffer_num  = dcqs.completed_buffers_num();
  int thread_num  = Threads::number_of_threads();
  return (buffer_num + thread_num) * buffer_size;
}

size_t G1CollectedHeap::cards_scanned() {
  return g1_rem_set()->cardsScanned();
}

void
G1CollectedHeap::setup_surviving_young_words() {
  guarantee( _surviving_young_words == NULL, "pre-condition" );
  size_t array_length = g1_policy()->young_cset_length();
  _surviving_young_words = NEW_C_HEAP_ARRAY(size_t, array_length);
  if (_surviving_young_words == NULL) {
    vm_exit_out_of_memory(sizeof(size_t) * array_length,
                          "Not enough space for young surv words summary.");
  }
  memset(_surviving_young_words, 0, array_length * sizeof(size_t));
#ifdef ASSERT
  for (size_t i = 0;  i < array_length; ++i) {
    assert( _surviving_young_words[i] == 0, "memset above" );
  }
#endif // !ASSERT
}

void
G1CollectedHeap::update_surviving_young_words(size_t* surv_young_words) {
  MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
  size_t array_length = g1_policy()->young_cset_length();
  for (size_t i = 0; i < array_length; ++i)
    _surviving_young_words[i] += surv_young_words[i];
}

void
G1CollectedHeap::cleanup_surviving_young_words() {
  guarantee( _surviving_young_words != NULL, "pre-condition" );
  FREE_C_HEAP_ARRAY(size_t, _surviving_young_words);
  _surviving_young_words = NULL;
}

// </NEW PREDICTION>

#ifdef ASSERT
class VerifyCSetClosure: public HeapRegionClosure {
public:
  bool doHeapRegion(HeapRegion* hr) {
    // Here we check that the CSet region's RSet is ready for parallel
    // iteration. The fields that we'll verify are only manipulated
    // when the region is part of a CSet and is collected. Afterwards,
    // we reset these fields when we clear the region's RSet (when the
    // region is freed) so they are ready when the region is
    // re-allocated. The only exception to this is if there's an
    // evacuation failure and instead of freeing the region we leave
    // it in the heap. In that case, we reset these fields during
    // evacuation failure handling.
    guarantee(hr->rem_set()->verify_ready_for_par_iteration(), "verification");

    // Here's a good place to add any other checks we'd like to
    // perform on CSet regions.
    return false;
  }
};
#endif // ASSERT

#if TASKQUEUE_STATS
void G1CollectedHeap::print_taskqueue_stats_hdr(outputStream* const st) {
  st->print_raw_cr("GC Task Stats");
  st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
  st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
}

void G1CollectedHeap::print_taskqueue_stats(outputStream* const st) const {
  print_taskqueue_stats_hdr(st);

  TaskQueueStats totals;
  const int n = workers() != NULL ? workers()->total_workers() : 1;
  for (int i = 0; i < n; ++i) {
    st->print("%3d ", i); task_queue(i)->stats.print(st); st->cr();
    totals += task_queue(i)->stats;
  }
  st->print_raw("tot "); totals.print(st); st->cr();

  DEBUG_ONLY(totals.verify());
}

void G1CollectedHeap::reset_taskqueue_stats() {
  const int n = workers() != NULL ? workers()->total_workers() : 1;
  for (int i = 0; i < n; ++i) {
    task_queue(i)->stats.reset();
  }
}
#endif // TASKQUEUE_STATS

bool
G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
  assert_at_safepoint(true /* should_be_vm_thread */);
  guarantee(!is_gc_active(), "collection is not reentrant");

  if (GC_locker::check_active_before_gc()) {
    return false;
  }

  SvcGCMarker sgcm(SvcGCMarker::MINOR);
  ResourceMark rm;

  if (PrintHeapAtGC) {
    Universe::print_heap_before_gc();
  }

  verify_region_sets_optional();
  verify_dirty_young_regions();

  {
    // This call will decide whether this pause is an initial-mark
    // pause. If it is, during_initial_mark_pause() will return true
    // for the duration of this pause.
    g1_policy()->decide_on_conc_mark_initiation();

    char verbose_str[128];
    sprintf(verbose_str, "GC pause ");
    if (g1_policy()->full_young_gcs()) {
      strcat(verbose_str, "(young)");
    } else {
      strcat(verbose_str, "(partial)");
    }
    if (g1_policy()->during_initial_mark_pause()) {
      strcat(verbose_str, " (initial-mark)");
      // We are about to start a marking cycle, so we increment the
      // full collection counter.
      increment_total_full_collections();
    }

    // if PrintGCDetails is on, we'll print long statistics information
    // in the collector policy code, so let's not print this as the output
    // is messy if we do.
    gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
    TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
    TraceTime t(verbose_str, PrintGC && !PrintGCDetails, true, gclog_or_tty);

    TraceCollectorStats tcs(g1mm()->incremental_collection_counters());
    TraceMemoryManagerStats tms(false /* fullGC */, gc_cause());

    // If the secondary_free_list is not empty, append it to the
    // free_list. No need to wait for the cleanup operation to finish;
    // the region allocation code will check the secondary_free_list
    // and wait if necessary. If the G1StressConcRegionFreeing flag is
    // set, skip this step so that the region allocation code has to
    // get entries from the secondary_free_list.
    if (!G1StressConcRegionFreeing) {
      append_secondary_free_list_if_not_empty_with_lock();
    }

    assert(check_young_list_well_formed(),
      "young list should be well formed");

    { // Call to jvmpi::post_class_unload_events must occur outside of active GC
      IsGCActiveMark x;

      gc_prologue(false);
      increment_total_collections(false /* full gc */);
      increment_gc_time_stamp();

      if (VerifyBeforeGC && total_collections() >= VerifyGCStartAt) {
        HandleMark hm;  // Discard invalid handles created during verification
        gclog_or_tty->print(" VerifyBeforeGC:");
        prepare_for_verify();
        Universe::verify(/* allow dirty */ false,
                         /* silent      */ false,
                         /* option      */ VerifyOption_G1UsePrevMarking);

      }

      COMPILER2_PRESENT(DerivedPointerTable::clear());

      // Please see comment in G1CollectedHeap::ref_processing_init()
      // to see how reference processing currently works in G1.
      //
      // We want to turn off ref discovery, if necessary, and turn it back on
      // on again later if we do. XXX Dubious: why is discovery disabled?
      bool was_enabled = ref_processor()->discovery_enabled();
      if (was_enabled) ref_processor()->disable_discovery();

      // Forget the current alloc region (we might even choose it to be part
      // of the collection set!).
      release_mutator_alloc_region();

      // We should call this after we retire the mutator alloc
      // region(s) so that all the ALLOC / RETIRE events are generated
      // before the start GC event.
      _hr_printer.start_gc(false /* full */, (size_t) total_collections());

      // The elapsed time induced by the start time below deliberately elides
      // the possible verification above.
      double start_time_sec = os::elapsedTime();
      size_t start_used_bytes = used();

#if YOUNG_LIST_VERBOSE
      gclog_or_tty->print_cr("\nBefore recording pause start.\nYoung_list:");
      _young_list->print();
      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
#endif // YOUNG_LIST_VERBOSE

      g1_policy()->record_collection_pause_start(start_time_sec,
                                                 start_used_bytes);

#if YOUNG_LIST_VERBOSE
      gclog_or_tty->print_cr("\nAfter recording pause start.\nYoung_list:");
      _young_list->print();
#endif // YOUNG_LIST_VERBOSE

      if (g1_policy()->during_initial_mark_pause()) {
        concurrent_mark()->checkpointRootsInitialPre();
      }
      perm_gen()->save_marks();

      // We must do this before any possible evacuation that should propagate
      // marks.
      if (mark_in_progress()) {
        double start_time_sec = os::elapsedTime();

        _cm->drainAllSATBBuffers();
        double finish_mark_ms = (os::elapsedTime() - start_time_sec) * 1000.0;
        g1_policy()->record_satb_drain_time(finish_mark_ms);
      }
      // Record the number of elements currently on the mark stack, so we
      // only iterate over these.  (Since evacuation may add to the mark
      // stack, doing more exposes race conditions.)  If no mark is in
      // progress, this will be zero.
      _cm->set_oops_do_bound();

      if (mark_in_progress()) {
        concurrent_mark()->newCSet();
      }

#if YOUNG_LIST_VERBOSE
      gclog_or_tty->print_cr("\nBefore choosing collection set.\nYoung_list:");
      _young_list->print();
      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
#endif // YOUNG_LIST_VERBOSE

      g1_policy()->choose_collection_set(target_pause_time_ms);

      if (_hr_printer.is_active()) {
        HeapRegion* hr = g1_policy()->collection_set();
        while (hr != NULL) {
          G1HRPrinter::RegionType type;
          if (!hr->is_young()) {
            type = G1HRPrinter::Old;
          } else if (hr->is_survivor()) {
            type = G1HRPrinter::Survivor;
          } else {
            type = G1HRPrinter::Eden;
          }
          _hr_printer.cset(hr);
          hr = hr->next_in_collection_set();
        }
      }

      // We have chosen the complete collection set. If marking is
      // active then, we clear the region fields of any of the
      // concurrent marking tasks whose region fields point into
      // the collection set as these values will become stale. This
      // will cause the owning marking threads to claim a new region
      // when marking restarts.
      if (mark_in_progress()) {
        concurrent_mark()->reset_active_task_region_fields_in_cset();
      }

#ifdef ASSERT
      VerifyCSetClosure cl;
      collection_set_iterate(&cl);
#endif // ASSERT

      setup_surviving_young_words();

      // Initialize the GC alloc regions.
      init_gc_alloc_regions();

      // Actually do the work...
      evacuate_collection_set();

      free_collection_set(g1_policy()->collection_set());
      g1_policy()->clear_collection_set();

      cleanup_surviving_young_words();

      // Start a new incremental collection set for the next pause.
      g1_policy()->start_incremental_cset_building();

      // Clear the _cset_fast_test bitmap in anticipation of adding
      // regions to the incremental collection set for the next
      // evacuation pause.
      clear_cset_fast_test();

      _young_list->reset_sampled_info();

      // Don't check the whole heap at this point as the
      // GC alloc regions from this pause have been tagged
      // as survivors and moved on to the survivor list.
      // Survivor regions will fail the !is_young() check.
      assert(check_young_list_empty(false /* check_heap */),
        "young list should be empty");

#if YOUNG_LIST_VERBOSE
      gclog_or_tty->print_cr("Before recording survivors.\nYoung List:");
      _young_list->print();
#endif // YOUNG_LIST_VERBOSE

      g1_policy()->record_survivor_regions(_young_list->survivor_length(),
        _young_list->first_survivor_region(),
        _young_list->last_survivor_region());

      _young_list->reset_auxilary_lists();

      if (evacuation_failed()) {
        _summary_bytes_used = recalculate_used();
      } else {
        // The "used" of the the collection set have already been subtracted
        // when they were freed.  Add in the bytes evacuated.
        _summary_bytes_used += g1_policy()->bytes_copied_during_gc();
      }

      if (g1_policy()->during_initial_mark_pause()) {
        concurrent_mark()->checkpointRootsInitialPost();
        set_marking_started();
        // CAUTION: after the doConcurrentMark() call below,
        // the concurrent marking thread(s) could be running
        // concurrently with us. Make sure that anything after
        // this point does not assume that we are the only GC thread
        // running. Note: of course, the actual marking work will
        // not start until the safepoint itself is released in
        // ConcurrentGCThread::safepoint_desynchronize().
        doConcurrentMark();
      }

      allocate_dummy_regions();

#if YOUNG_LIST_VERBOSE
      gclog_or_tty->print_cr("\nEnd of the pause.\nYoung_list:");
      _young_list->print();
      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
#endif // YOUNG_LIST_VERBOSE

      init_mutator_alloc_region();

      double end_time_sec = os::elapsedTime();
      double pause_time_ms = (end_time_sec - start_time_sec) * MILLIUNITS;
      g1_policy()->record_pause_time_ms(pause_time_ms);
      g1_policy()->record_collection_pause_end();

      MemoryService::track_memory_usage();

      // In prepare_for_verify() below we'll need to scan the deferred
      // update buffers to bring the RSets up-to-date if
      // G1HRRSFlushLogBuffersOnVerify has been set. While scanning
      // the update buffers we'll probably need to scan cards on the
      // regions we just allocated to (i.e., the GC alloc
      // regions). However, during the last GC we called
      // set_saved_mark() on all the GC alloc regions, so card
      // scanning might skip the [saved_mark_word()...top()] area of
      // those regions (i.e., the area we allocated objects into
      // during the last GC). But it shouldn't. Given that
      // saved_mark_word() is conditional on whether the GC time stamp
      // on the region is current or not, by incrementing the GC time
      // stamp here we invalidate all the GC time stamps on all the
      // regions and saved_mark_word() will simply return top() for
      // all the regions. This is a nicer way of ensuring this rather
      // than iterating over the regions and fixing them. In fact, the
      // GC time stamp increment here also ensures that
      // saved_mark_word() will return top() between pauses, i.e.,
      // during concurrent refinement. So we don't need the
      // is_gc_active() check to decided which top to use when
      // scanning cards (see CR 7039627).
      increment_gc_time_stamp();

      if (VerifyAfterGC && total_collections() >= VerifyGCStartAt) {
        HandleMark hm;  // Discard invalid handles created during verification
        gclog_or_tty->print(" VerifyAfterGC:");
        prepare_for_verify();
        Universe::verify(/* allow dirty */ true,
                         /* silent      */ false,
                         /* option      */ VerifyOption_G1UsePrevMarking);
      }

      if (was_enabled) ref_processor()->enable_discovery();

      {
        size_t expand_bytes = g1_policy()->expansion_amount();
        if (expand_bytes > 0) {
          size_t bytes_before = capacity();
          // No need for an ergo verbose message here,
          // expansion_amount() does this when it returns a value > 0.
          if (!expand(expand_bytes)) {
            // We failed to expand the heap so let's verify that
            // committed/uncommitted amount match the backing store
            assert(capacity() == _g1_storage.committed_size(), "committed size mismatch");
            assert(max_capacity() == _g1_storage.reserved_size(), "reserved size mismatch");
          }
        }
      }

      // We should do this after we potentially expand the heap so
      // that all the COMMIT events are generated before the end GC
      // event, and after we retire the GC alloc regions so that all
      // RETIRE events are generated before the end GC event.
      _hr_printer.end_gc(false /* full */, (size_t) total_collections());

      // We have to do this after we decide whether to expand the heap or not.
      g1_policy()->print_heap_transition();

      if (mark_in_progress()) {
        concurrent_mark()->update_g1_committed();
      }

#ifdef TRACESPINNING
      ParallelTaskTerminator::print_termination_counts();
#endif

      gc_epilogue(false);
    }

    if (ExitAfterGCNum > 0 && total_collections() == ExitAfterGCNum) {
      gclog_or_tty->print_cr("Stopping after GC #%d", ExitAfterGCNum);
      print_tracing_info();
      vm_exit(-1);
    }
  }

  _hrs.verify_optional();
  verify_region_sets_optional();

  TASKQUEUE_STATS_ONLY(if (ParallelGCVerbose) print_taskqueue_stats());
  TASKQUEUE_STATS_ONLY(reset_taskqueue_stats());

  if (PrintHeapAtGC) {
    Universe::print_heap_after_gc();
  }
  g1mm()->update_counters();

  if (G1SummarizeRSetStats &&
      (G1SummarizeRSetStatsPeriod > 0) &&
      (total_collections() % G1SummarizeRSetStatsPeriod == 0)) {
    g1_rem_set()->print_summary_info();
  }

  return true;
}

size_t G1CollectedHeap::desired_plab_sz(GCAllocPurpose purpose)
{
  size_t gclab_word_size;
  switch (purpose) {
    case GCAllocForSurvived:
      gclab_word_size = YoungPLABSize;
      break;
    case GCAllocForTenured:
      gclab_word_size = OldPLABSize;
      break;
    default:
      assert(false, "unknown GCAllocPurpose");
      gclab_word_size = OldPLABSize;
      break;
  }
  return gclab_word_size;
}

void G1CollectedHeap::init_mutator_alloc_region() {
  assert(_mutator_alloc_region.get() == NULL, "pre-condition");
  _mutator_alloc_region.init();
}

void G1CollectedHeap::release_mutator_alloc_region() {
  _mutator_alloc_region.release();
  assert(_mutator_alloc_region.get() == NULL, "post-condition");
}

void G1CollectedHeap::init_gc_alloc_regions() {
  assert_at_safepoint(true /* should_be_vm_thread */);

  _survivor_gc_alloc_region.init();
  _old_gc_alloc_region.init();
  HeapRegion* retained_region = _retained_old_gc_alloc_region;
  _retained_old_gc_alloc_region = NULL;

  // We will discard the current GC alloc region if:
  // a) it's in the collection set (it can happen!),
  // b) it's already full (no point in using it),
  // c) it's empty (this means that it was emptied during
  // a cleanup and it should be on the free list now), or
  // d) it's humongous (this means that it was emptied
  // during a cleanup and was added to the free list, but
  // has been subseqently used to allocate a humongous
  // object that may be less than the region size).
  if (retained_region != NULL &&
      !retained_region->in_collection_set() &&
      !(retained_region->top() == retained_region->end()) &&
      !retained_region->is_empty() &&
      !retained_region->isHumongous()) {
    retained_region->set_saved_mark();
    _old_gc_alloc_region.set(retained_region);
    _hr_printer.reuse(retained_region);
  }
}

void G1CollectedHeap::release_gc_alloc_regions() {
  _survivor_gc_alloc_region.release();
  // If we have an old GC alloc region to release, we'll save it in
  // _retained_old_gc_alloc_region. If we don't
  // _retained_old_gc_alloc_region will become NULL. This is what we
  // want either way so no reason to check explicitly for either
  // condition.
  _retained_old_gc_alloc_region = _old_gc_alloc_region.release();
}

void G1CollectedHeap::abandon_gc_alloc_regions() {
  assert(_survivor_gc_alloc_region.get() == NULL, "pre-condition");
  assert(_old_gc_alloc_region.get() == NULL, "pre-condition");
  _retained_old_gc_alloc_region = NULL;
}

void G1CollectedHeap::init_for_evac_failure(OopsInHeapRegionClosure* cl) {
  _drain_in_progress = false;
  set_evac_failure_closure(cl);
  _evac_failure_scan_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(40, true);
}

void G1CollectedHeap::finalize_for_evac_failure() {
  assert(_evac_failure_scan_stack != NULL &&
         _evac_failure_scan_stack->length() == 0,
         "Postcondition");
  assert(!_drain_in_progress, "Postcondition");
  delete _evac_failure_scan_stack;
  _evac_failure_scan_stack = NULL;
}

// *** Sequential G1 Evacuation

class G1IsAliveClosure: public BoolObjectClosure {
  G1CollectedHeap* _g1;
public:
  G1IsAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}
  void do_object(oop p) { assert(false, "Do not call."); }
  bool do_object_b(oop p) {
    // It is reachable if it is outside the collection set, or is inside
    // and forwarded.
    return !_g1->obj_in_cs(p) || p->is_forwarded();
  }
};

class G1KeepAliveClosure: public OopClosure {
  G1CollectedHeap* _g1;
public:
  G1KeepAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}
  void do_oop(narrowOop* p) { guarantee(false, "Not needed"); }
  void do_oop(      oop* p) {
    oop obj = *p;
    if (_g1->obj_in_cs(obj)) {
      assert( obj->is_forwarded(), "invariant" );
      *p = obj->forwardee();
    }
  }
};

class UpdateRSetDeferred : public OopsInHeapRegionClosure {
private:
  G1CollectedHeap* _g1;
  DirtyCardQueue *_dcq;
  CardTableModRefBS* _ct_bs;

public:
  UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
    _g1(g1), _ct_bs((CardTableModRefBS*)_g1->barrier_set()), _dcq(dcq) {}

  virtual void do_oop(narrowOop* p) { do_oop_work(p); }
  virtual void do_oop(      oop* p) { do_oop_work(p); }
  template <class T> void do_oop_work(T* p) {
    assert(_from->is_in_reserved(p), "paranoia");
    if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
        !_from->is_survivor()) {
      size_t card_index = _ct_bs->index_for(p);
      if (_ct_bs->mark_card_deferred(card_index)) {
        _dcq->enqueue((jbyte*)_ct_bs->byte_for_index(card_index));
      }
    }
  }
};

class RemoveSelfPointerClosure: public ObjectClosure {
private:
  G1CollectedHeap* _g1;
  ConcurrentMark* _cm;
  HeapRegion* _hr;
  size_t _prev_marked_bytes;
  size_t _next_marked_bytes;
  OopsInHeapRegionClosure *_cl;
public:
  RemoveSelfPointerClosure(G1CollectedHeap* g1, HeapRegion* hr,
                           OopsInHeapRegionClosure* cl) :
    _g1(g1), _hr(hr), _cm(_g1->concurrent_mark()),  _prev_marked_bytes(0),
    _next_marked_bytes(0), _cl(cl) {}

  size_t prev_marked_bytes() { return _prev_marked_bytes; }
  size_t next_marked_bytes() { return _next_marked_bytes; }

  // <original comment>
  // The original idea here was to coalesce evacuated and dead objects.
  // However that caused complications with the block offset table (BOT).
  // In particular if there were two TLABs, one of them partially refined.
  // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
  // The BOT entries of the unrefined part of TLAB_2 point to the start
  // of TLAB_2. If the last object of the TLAB_1 and the first object
  // of TLAB_2 are coalesced, then the cards of the unrefined part
  // would point into middle of the filler object.
  // The current approach is to not coalesce and leave the BOT contents intact.
  // </original comment>
  //
  // We now reset the BOT when we start the object iteration over the
  // region and refine its entries for every object we come across. So
  // the above comment is not really relevant and we should be able
  // to coalesce dead objects if we want to.
  void do_object(oop obj) {
    HeapWord* obj_addr = (HeapWord*) obj;
    assert(_hr->is_in(obj_addr), "sanity");
    size_t obj_size = obj->size();
    _hr->update_bot_for_object(obj_addr, obj_size);
    if (obj->is_forwarded() && obj->forwardee() == obj) {
      // The object failed to move.
      assert(!_g1->is_obj_dead(obj), "We should not be preserving dead objs.");
      _cm->markPrev(obj);
      assert(_cm->isPrevMarked(obj), "Should be marked!");
      _prev_marked_bytes += (obj_size * HeapWordSize);
      if (_g1->mark_in_progress() && !_g1->is_obj_ill(obj)) {
        _cm->markAndGrayObjectIfNecessary(obj);
      }
      obj->set_mark(markOopDesc::prototype());
      // While we were processing RSet buffers during the
      // collection, we actually didn't scan any cards on the
      // collection set, since we didn't want to update remebered
      // sets with entries that point into the collection set, given
      // that live objects fromthe collection set are about to move
      // and such entries will be stale very soon. This change also
      // dealt with a reliability issue which involved scanning a
      // card in the collection set and coming across an array that
      // was being chunked and looking malformed. The problem is
      // that, if evacuation fails, we might have remembered set
      // entries missing given that we skipped cards on the
      // collection set. So, we'll recreate such entries now.
      obj->oop_iterate(_cl);
      assert(_cm->isPrevMarked(obj), "Should be marked!");
    } else {
      // The object has been either evacuated or is dead. Fill it with a
      // dummy object.
      MemRegion mr((HeapWord*)obj, obj_size);
      CollectedHeap::fill_with_object(mr);
      _cm->clearRangeBothMaps(mr);
    }
  }
};

void G1CollectedHeap::remove_self_forwarding_pointers() {
  UpdateRSetImmediate immediate_update(_g1h->g1_rem_set());
  DirtyCardQueue dcq(&_g1h->dirty_card_queue_set());
  UpdateRSetDeferred deferred_update(_g1h, &dcq);
  OopsInHeapRegionClosure *cl;
  if (G1DeferredRSUpdate) {
    cl = &deferred_update;
  } else {
    cl = &immediate_update;
  }
  HeapRegion* cur = g1_policy()->collection_set();
  while (cur != NULL) {
    assert(g1_policy()->assertMarkedBytesDataOK(), "Should be!");
    assert(!cur->isHumongous(), "sanity");

    if (cur->evacuation_failed()) {
      assert(cur->in_collection_set(), "bad CS");
      RemoveSelfPointerClosure rspc(_g1h, cur, cl);

      // In the common case we make sure that this is done when the
      // region is freed so that it is "ready-to-go" when it's
      // re-allocated. However, when evacuation failure happens, a
      // region will remain in the heap and might ultimately be added
      // to a CSet in the future. So we have to be careful here and
      // make sure the region's RSet is ready for parallel iteration
      // whenever this might be required in the future.
      cur->rem_set()->reset_for_par_iteration();
      cur->reset_bot();
      cl->set_region(cur);
      cur->object_iterate(&rspc);

      // A number of manipulations to make the TAMS be the current top,
      // and the marked bytes be the ones observed in the iteration.
      if (_g1h->concurrent_mark()->at_least_one_mark_complete()) {
        // The comments below are the postconditions achieved by the
        // calls.  Note especially the last such condition, which says that
        // the count of marked bytes has been properly restored.
        cur->note_start_of_marking(false);
        // _next_top_at_mark_start == top, _next_marked_bytes == 0
        cur->add_to_marked_bytes(rspc.prev_marked_bytes());
        // _next_marked_bytes == prev_marked_bytes.
        cur->note_end_of_marking();
        // _prev_top_at_mark_start == top(),
        // _prev_marked_bytes == prev_marked_bytes
      }
      // If there is no mark in progress, we modified the _next variables
      // above needlessly, but harmlessly.
      if (_g1h->mark_in_progress()) {
        cur->note_start_of_marking(false);
        // _next_top_at_mark_start == top, _next_marked_bytes == 0
        // _next_marked_bytes == next_marked_bytes.
      }

      // Now make sure the region has the right index in the sorted array.
      g1_policy()->note_change_in_marked_bytes(cur);
    }
    cur = cur->next_in_collection_set();
  }
  assert(g1_policy()->assertMarkedBytesDataOK(), "Should be!");

  // Now restore saved marks, if any.
  if (_objs_with_preserved_marks != NULL) {
    assert(_preserved_marks_of_objs != NULL, "Both or none.");
    guarantee(_objs_with_preserved_marks->length() ==
              _preserved_marks_of_objs->length(), "Both or none.");
    for (int i = 0; i < _objs_with_preserved_marks->length(); i++) {
      oop obj   = _objs_with_preserved_marks->at(i);
      markOop m = _preserved_marks_of_objs->at(i);
      obj->set_mark(m);
    }
    // Delete the preserved marks growable arrays (allocated on the C heap).
    delete _objs_with_preserved_marks;
    delete _preserved_marks_of_objs;
    _objs_with_preserved_marks = NULL;
    _preserved_marks_of_objs = NULL;
  }
}

void G1CollectedHeap::push_on_evac_failure_scan_stack(oop obj) {
  _evac_failure_scan_stack->push(obj);
}

void G1CollectedHeap::drain_evac_failure_scan_stack() {
  assert(_evac_failure_scan_stack != NULL, "precondition");

  while (_evac_failure_scan_stack->length() > 0) {
     oop obj = _evac_failure_scan_stack->pop();
     _evac_failure_closure->set_region(heap_region_containing(obj));
     obj->oop_iterate_backwards(_evac_failure_closure);
  }
}

oop
G1CollectedHeap::handle_evacuation_failure_par(OopsInHeapRegionClosure* cl,
                                               oop old) {
  assert(obj_in_cs(old),
         err_msg("obj: "PTR_FORMAT" should still be in the CSet",
                 (HeapWord*) old));
  markOop m = old->mark();
  oop forward_ptr = old->forward_to_atomic(old);
  if (forward_ptr == NULL) {
    // Forward-to-self succeeded.
    if (_evac_failure_closure != cl) {
      MutexLockerEx x(EvacFailureStack_lock, Mutex::_no_safepoint_check_flag);
      assert(!_drain_in_progress,
             "Should only be true while someone holds the lock.");
      // Set the global evac-failure closure to the current thread's.
      assert(_evac_failure_closure == NULL, "Or locking has failed.");
      set_evac_failure_closure(cl);
      // Now do the common part.
      handle_evacuation_failure_common(old, m);
      // Reset to NULL.
      set_evac_failure_closure(NULL);
    } else {
      // The lock is already held, and this is recursive.
      assert(_drain_in_progress, "This should only be the recursive case.");
      handle_evacuation_failure_common(old, m);
    }
    return old;
  } else {
    // Forward-to-self failed. Either someone else managed to allocate
    // space for this object (old != forward_ptr) or they beat us in
    // self-forwarding it (old == forward_ptr).
    assert(old == forward_ptr || !obj_in_cs(forward_ptr),
           err_msg("obj: "PTR_FORMAT" forwarded to: "PTR_FORMAT" "
                   "should not be in the CSet",
                   (HeapWord*) old, (HeapWord*) forward_ptr));
    return forward_ptr;
  }
}

void G1CollectedHeap::handle_evacuation_failure_common(oop old, markOop m) {
  set_evacuation_failed(true);

  preserve_mark_if_necessary(old, m);

  HeapRegion* r = heap_region_containing(old);
  if (!r->evacuation_failed()) {
    r->set_evacuation_failed(true);
    _hr_printer.evac_failure(r);
  }

  push_on_evac_failure_scan_stack(old);

  if (!_drain_in_progress) {
    // prevent recursion in copy_to_survivor_space()
    _drain_in_progress = true;
    drain_evac_failure_scan_stack();
    _drain_in_progress = false;
  }
}

void G1CollectedHeap::preserve_mark_if_necessary(oop obj, markOop m) {
  assert(evacuation_failed(), "Oversaving!");
  // We want to call the "for_promotion_failure" version only in the
  // case of a promotion failure.
  if (m->must_be_preserved_for_promotion_failure(obj)) {
    if (_objs_with_preserved_marks == NULL) {
      assert(_preserved_marks_of_objs == NULL, "Both or none.");
      _objs_with_preserved_marks =
        new (ResourceObj::C_HEAP) GrowableArray<oop>(40, true);
      _preserved_marks_of_objs =
        new (ResourceObj::C_HEAP) GrowableArray<markOop>(40, true);
    }
    _objs_with_preserved_marks->push(obj);
    _preserved_marks_of_objs->push(m);
  }
}

HeapWord* G1CollectedHeap::par_allocate_during_gc(GCAllocPurpose purpose,
                                                  size_t word_size) {
  if (purpose == GCAllocForSurvived) {
    HeapWord* result = survivor_attempt_allocation(word_size);
    if (result != NULL) {
      return result;
    } else {
      // Let's try to allocate in the old gen in case we can fit the
      // object there.
      return old_attempt_allocation(word_size);
    }
  } else {
    assert(purpose ==  GCAllocForTenured, "sanity");
    HeapWord* result = old_attempt_allocation(word_size);
    if (result != NULL) {
      return result;
    } else {
      // Let's try to allocate in the survivors in case we can fit the
      // object there.
      return survivor_attempt_allocation(word_size);
    }
  }

  ShouldNotReachHere();
  // Trying to keep some compilers happy.
  return NULL;
}

#ifndef PRODUCT
bool GCLabBitMapClosure::do_bit(size_t offset) {
  HeapWord* addr = _bitmap->offsetToHeapWord(offset);
  guarantee(_cm->isMarked(oop(addr)), "it should be!");
  return true;
}
#endif // PRODUCT

G1ParGCAllocBuffer::G1ParGCAllocBuffer(size_t gclab_word_size) :
  ParGCAllocBuffer(gclab_word_size),
  _should_mark_objects(false),
  _bitmap(G1CollectedHeap::heap()->reserved_region().start(), gclab_word_size),
  _retired(false)
{
  //_should_mark_objects is set to true when G1ParCopyHelper needs to
  // mark the forwarded location of an evacuated object.
  // We set _should_mark_objects to true if marking is active, i.e. when we
  // need to propagate a mark, or during an initial mark pause, i.e. when we
  // need to mark objects immediately reachable by the roots.
  if (G1CollectedHeap::heap()->mark_in_progress() ||
      G1CollectedHeap::heap()->g1_policy()->during_initial_mark_pause()) {
    _should_mark_objects = true;
  }
}

G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h, int queue_num)
  : _g1h(g1h),
    _refs(g1h->task_queue(queue_num)),
    _dcq(&g1h->dirty_card_queue_set()),
    _ct_bs((CardTableModRefBS*)_g1h->barrier_set()),
    _g1_rem(g1h->g1_rem_set()),
    _hash_seed(17), _queue_num(queue_num),
    _term_attempts(0),
    _surviving_alloc_buffer(g1h->desired_plab_sz(GCAllocForSurvived)),
    _tenured_alloc_buffer(g1h->desired_plab_sz(GCAllocForTenured)),
    _age_table(false),
    _strong_roots_time(0), _term_time(0),
    _alloc_buffer_waste(0), _undo_waste(0)
{
  // we allocate G1YoungSurvRateNumRegions plus one entries, since
  // we "sacrifice" entry 0 to keep track of surviving bytes for
  // non-young regions (where the age is -1)
  // We also add a few elements at the beginning and at the end in
  // an attempt to eliminate cache contention
  size_t real_length = 1 + _g1h->g1_policy()->young_cset_length();
  size_t array_length = PADDING_ELEM_NUM +
                        real_length +
                        PADDING_ELEM_NUM;
  _surviving_young_words_base = NEW_C_HEAP_ARRAY(size_t, array_length);
  if (_surviving_young_words_base == NULL)
    vm_exit_out_of_memory(array_length * sizeof(size_t),
                          "Not enough space for young surv histo.");
  _surviving_young_words = _surviving_young_words_base + PADDING_ELEM_NUM;
  memset(_surviving_young_words, 0, real_length * sizeof(size_t));

  _alloc_buffers[GCAllocForSurvived] = &_surviving_alloc_buffer;
  _alloc_buffers[GCAllocForTenured]  = &_tenured_alloc_buffer;

  _start = os::elapsedTime();
}

void
G1ParScanThreadState::print_termination_stats_hdr(outputStream* const st)
{
  st->print_raw_cr("GC Termination Stats");
  st->print_raw_cr("     elapsed  --strong roots-- -------termination-------"
                   " ------waste (KiB)------");
  st->print_raw_cr("thr     ms        ms      %        ms      %    attempts"
                   "  total   alloc    undo");
  st->print_raw_cr("--- --------- --------- ------ --------- ------ --------"
                   " ------- ------- -------");
}

void
G1ParScanThreadState::print_termination_stats(int i,
                                              outputStream* const st) const
{
  const double elapsed_ms = elapsed_time() * 1000.0;
  const double s_roots_ms = strong_roots_time() * 1000.0;
  const double term_ms    = term_time() * 1000.0;
  st->print_cr("%3d %9.2f %9.2f %6.2f "
               "%9.2f %6.2f " SIZE_FORMAT_W(8) " "
               SIZE_FORMAT_W(7) " " SIZE_FORMAT_W(7) " " SIZE_FORMAT_W(7),
               i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
               term_ms, term_ms * 100 / elapsed_ms, term_attempts(),
               (alloc_buffer_waste() + undo_waste()) * HeapWordSize / K,
               alloc_buffer_waste() * HeapWordSize / K,
               undo_waste() * HeapWordSize / K);
}

#ifdef ASSERT
bool G1ParScanThreadState::verify_ref(narrowOop* ref) const {
  assert(ref != NULL, "invariant");
  assert(UseCompressedOops, "sanity");
  assert(!has_partial_array_mask(ref), err_msg("ref=" PTR_FORMAT, ref));
  oop p = oopDesc::load_decode_heap_oop(ref);
  assert(_g1h->is_in_g1_reserved(p),
         err_msg("ref=" PTR_FORMAT " p=" PTR_FORMAT, ref, intptr_t(p)));
  return true;
}

bool G1ParScanThreadState::verify_ref(oop* ref) const {
  assert(ref != NULL, "invariant");
  if (has_partial_array_mask(ref)) {
    // Must be in the collection set--it's already been copied.
    oop p = clear_partial_array_mask(ref);
    assert(_g1h->obj_in_cs(p),
           err_msg("ref=" PTR_FORMAT " p=" PTR_FORMAT, ref, intptr_t(p)));
  } else {
    oop p = oopDesc::load_decode_heap_oop(ref);
    assert(_g1h->is_in_g1_reserved(p),
           err_msg("ref=" PTR_FORMAT " p=" PTR_FORMAT, ref, intptr_t(p)));
  }
  return true;
}

bool G1ParScanThreadState::verify_task(StarTask ref) const {
  if (ref.is_narrow()) {
    return verify_ref((narrowOop*) ref);
  } else {
    return verify_ref((oop*) ref);
  }
}
#endif // ASSERT

void G1ParScanThreadState::trim_queue() {
  StarTask ref;
  do {
    // Drain the overflow stack first, so other threads can steal.
    while (refs()->pop_overflow(ref)) {
      deal_with_reference(ref);
    }
    while (refs()->pop_local(ref)) {
      deal_with_reference(ref);
    }
  } while (!refs()->is_empty());
}

G1ParClosureSuper::G1ParClosureSuper(G1CollectedHeap* g1, G1ParScanThreadState* par_scan_state) :
  _g1(g1), _g1_rem(_g1->g1_rem_set()), _cm(_g1->concurrent_mark()),
  _par_scan_state(par_scan_state),
  _during_initial_mark(_g1->g1_policy()->during_initial_mark_pause()),
  _mark_in_progress(_g1->mark_in_progress()) { }

template <class T> void G1ParCopyHelper::mark_object(T* p) {
  // This is called from do_oop_work for objects that are not
  // in the collection set. Objects in the collection set
  // are marked after they have been evacuated.

  T heap_oop = oopDesc::load_heap_oop(p);
  if (!oopDesc::is_null(heap_oop)) {
    oop obj = oopDesc::decode_heap_oop(heap_oop);
    HeapWord* addr = (HeapWord*)obj;
    if (_g1->is_in_g1_reserved(addr)) {
      _cm->grayRoot(oop(addr));
    }
  }
}

oop G1ParCopyHelper::copy_to_survivor_space(oop old, bool should_mark_copy) {
  size_t    word_sz = old->size();
  HeapRegion* from_region = _g1->heap_region_containing_raw(old);
  // +1 to make the -1 indexes valid...
  int       young_index = from_region->young_index_in_cset()+1;
  assert( (from_region->is_young() && young_index > 0) ||
          (!from_region->is_young() && young_index == 0), "invariant" );
  G1CollectorPolicy* g1p = _g1->g1_policy();
  markOop m = old->mark();
  int age = m->has_displaced_mark_helper() ? m->displaced_mark_helper()->age()
                                           : m->age();
  GCAllocPurpose alloc_purpose = g1p->evacuation_destination(from_region, age,
                                                             word_sz);
  HeapWord* obj_ptr = _par_scan_state->allocate(alloc_purpose, word_sz);
  oop       obj     = oop(obj_ptr);

  if (obj_ptr == NULL) {
    // This will either forward-to-self, or detect that someone else has
    // installed a forwarding pointer.
    OopsInHeapRegionClosure* cl = _par_scan_state->evac_failure_closure();
    return _g1->handle_evacuation_failure_par(cl, old);
  }

  // We're going to allocate linearly, so might as well prefetch ahead.
  Prefetch::write(obj_ptr, PrefetchCopyIntervalInBytes);

  oop forward_ptr = old->forward_to_atomic(obj);
  if (forward_ptr == NULL) {
    Copy::aligned_disjoint_words((HeapWord*) old, obj_ptr, word_sz);
    if (g1p->track_object_age(alloc_purpose)) {
      // We could simply do obj->incr_age(). However, this causes a
      // performance issue. obj->incr_age() will first check whether
      // the object has a displaced mark by checking its mark word;
      // getting the mark word from the new location of the object
      // stalls. So, given that we already have the mark word and we
      // are about to install it anyway, it's better to increase the
      // age on the mark word, when the object does not have a
      // displaced mark word. We're not expecting many objects to have
      // a displaced marked word, so that case is not optimized
      // further (it could be...) and we simply call obj->incr_age().

      if (m->has_displaced_mark_helper()) {
        // in this case, we have to install the mark word first,
        // otherwise obj looks to be forwarded (the old mark word,
        // which contains the forward pointer, was copied)
        obj->set_mark(m);
        obj->incr_age();
      } else {
        m = m->incr_age();
        obj->set_mark(m);
      }
      _par_scan_state->age_table()->add(obj, word_sz);
    } else {
      obj->set_mark(m);
    }

    // Mark the evacuated object or propagate "next" mark bit
    if (should_mark_copy) {
      if (!use_local_bitmaps ||
          !_par_scan_state->alloc_buffer(alloc_purpose)->mark(obj_ptr)) {
        // if we couldn't mark it on the local bitmap (this happens when
        // the object was not allocated in the GCLab), we have to bite
        // the bullet and do the standard parallel mark
        _cm->markAndGrayObjectIfNecessary(obj);
      }

      if (_g1->isMarkedNext(old)) {
        // Unmark the object's old location so that marking
        // doesn't think the old object is alive.
        _cm->nextMarkBitMap()->parClear((HeapWord*)old);
      }
    }

    size_t* surv_young_words = _par_scan_state->surviving_young_words();
    surv_young_words[young_index] += word_sz;

    if (obj->is_objArray() && arrayOop(obj)->length() >= ParGCArrayScanChunk) {
      arrayOop(old)->set_length(0);
      oop* old_p = set_partial_array_mask(old);
      _par_scan_state->push_on_queue(old_p);
    } else {
      // No point in using the slower heap_region_containing() method,
      // given that we know obj is in the heap.
      _scanner->set_region(_g1->heap_region_containing_raw(obj));
      obj->oop_iterate_backwards(_scanner);
    }
  } else {
    _par_scan_state->undo_allocation(alloc_purpose, obj_ptr, word_sz);
    obj = forward_ptr;
  }
  return obj;
}

template <bool do_gen_barrier, G1Barrier barrier, bool do_mark_object>
template <class T>
void G1ParCopyClosure<do_gen_barrier, barrier, do_mark_object>
::do_oop_work(T* p) {
  oop obj = oopDesc::load_decode_heap_oop(p);
  assert(barrier != G1BarrierRS || obj != NULL,
         "Precondition: G1BarrierRS implies obj is nonNull");

  // Marking:
  // If the object is in the collection set, then the thread
  // that copies the object should mark, or propagate the
  // mark to, the evacuated object.
  // If the object is not in the collection set then we
  // should call the mark_object() method depending on the
  // value of the template parameter do_mark_object (which will
  // be true for root scanning closures during an initial mark
  // pause).
  // The mark_object() method first checks whether the object
  // is marked and, if not, attempts to mark the object.

  // here the null check is implicit in the cset_fast_test() test
  if (_g1->in_cset_fast_test(obj)) {
    if (obj->is_forwarded()) {
      oopDesc::encode_store_heap_oop(p, obj->forwardee());
      // If we are a root scanning closure during an initial
      // mark pause (i.e. do_mark_object will be true) then
      // we also need to handle marking of roots in the
      // event of an evacuation failure. In the event of an
      // evacuation failure, the object is forwarded to itself
      // and not copied so let's mark it here.
      if (do_mark_object && obj->forwardee() == obj) {
        mark_object(p);
      }
    } else {
      // We need to mark the copied object if we're a root scanning
      // closure during an initial mark pause (i.e. do_mark_object
      // will be true), or the object is already marked and we need
      // to propagate the mark to the evacuated copy.
      bool should_mark_copy = do_mark_object ||
                              _during_initial_mark ||
                              (_mark_in_progress && !_g1->is_obj_ill(obj));

      oop copy_oop = copy_to_survivor_space(obj, should_mark_copy);
      oopDesc::encode_store_heap_oop(p, copy_oop);
    }
    // When scanning the RS, we only care about objs in CS.
    if (barrier == G1BarrierRS) {
      _par_scan_state->update_rs(_from, p, _par_scan_state->queue_num());
    }
  } else {
    // The object is not in collection set. If we're a root scanning
    // closure during an initial mark pause (i.e. do_mark_object will
    // be true) then attempt to mark the object.
    if (do_mark_object) {
      mark_object(p);
    }
  }

  if (barrier == G1BarrierEvac && obj != NULL) {
    _par_scan_state->update_rs(_from, p, _par_scan_state->queue_num());
  }

  if (do_gen_barrier && obj != NULL) {
    par_do_barrier(p);
  }
}

template void G1ParCopyClosure<false, G1BarrierEvac, false>::do_oop_work(oop* p);
template void G1ParCopyClosure<false, G1BarrierEvac, false>::do_oop_work(narrowOop* p);

template <class T> void G1ParScanPartialArrayClosure::do_oop_nv(T* p) {
  assert(has_partial_array_mask(p), "invariant");
  oop old = clear_partial_array_mask(p);
  assert(old->is_objArray(), "must be obj array");
  assert(old->is_forwarded(), "must be forwarded");
  assert(Universe::heap()->is_in_reserved(old), "must be in heap.");

  objArrayOop obj = objArrayOop(old->forwardee());
  assert((void*)old != (void*)old->forwardee(), "self forwarding here?");
  // Process ParGCArrayScanChunk elements now
  // and push the remainder back onto queue
  int start     = arrayOop(old)->length();
  int end       = obj->length();
  int remainder = end - start;
  assert(start <= end, "just checking");
  if (remainder > 2 * ParGCArrayScanChunk) {
    // Test above combines last partial chunk with a full chunk
    end = start + ParGCArrayScanChunk;
    arrayOop(old)->set_length(end);
    // Push remainder.
    oop* old_p = set_partial_array_mask(old);
    assert(arrayOop(old)->length() < obj->length(), "Empty push?");
    _par_scan_state->push_on_queue(old_p);
  } else {
    // Restore length so that the heap remains parsable in
    // case of evacuation failure.
    arrayOop(old)->set_length(end);
  }
  _scanner.set_region(_g1->heap_region_containing_raw(obj));
  // process our set of indices (include header in first chunk)
  obj->oop_iterate_range(&_scanner, start, end);
}

class G1ParEvacuateFollowersClosure : public VoidClosure {
protected:
  G1CollectedHeap*              _g1h;
  G1ParScanThreadState*         _par_scan_state;
  RefToScanQueueSet*            _queues;
  ParallelTaskTerminator*       _terminator;

  G1ParScanThreadState*   par_scan_state() { return _par_scan_state; }
  RefToScanQueueSet*      queues()         { return _queues; }
  ParallelTaskTerminator* terminator()     { return _terminator; }

public:
  G1ParEvacuateFollowersClosure(G1CollectedHeap* g1h,
                                G1ParScanThreadState* par_scan_state,
                                RefToScanQueueSet* queues,
                                ParallelTaskTerminator* terminator)
    : _g1h(g1h), _par_scan_state(par_scan_state),
      _queues(queues), _terminator(terminator) {}

  void do_void();

private:
  inline bool offer_termination();
};

bool G1ParEvacuateFollowersClosure::offer_termination() {
  G1ParScanThreadState* const pss = par_scan_state();
  pss->start_term_time();
  const bool res = terminator()->offer_termination();
  pss->end_term_time();
  return res;
}

void G1ParEvacuateFollowersClosure::do_void() {
  StarTask stolen_task;
  G1ParScanThreadState* const pss = par_scan_state();
  pss->trim_queue();

  do {
    while (queues()->steal(pss->queue_num(), pss->hash_seed(), stolen_task)) {
      assert(pss->verify_task(stolen_task), "sanity");
      if (stolen_task.is_narrow()) {
        pss->deal_with_reference((narrowOop*) stolen_task);
      } else {
        pss->deal_with_reference((oop*) stolen_task);
      }

      // We've just processed a reference and we might have made
      // available new entries on the queues. So we have to make sure
      // we drain the queues as necessary.
      pss->trim_queue();
    }
  } while (!offer_termination());

  pss->retire_alloc_buffers();
}

class G1ParTask : public AbstractGangTask {
protected:
  G1CollectedHeap*       _g1h;
  RefToScanQueueSet      *_queues;
  ParallelTaskTerminator _terminator;
  int _n_workers;

  Mutex _stats_lock;
  Mutex* stats_lock() { return &_stats_lock; }

  size_t getNCards() {
    return (_g1h->capacity() + G1BlockOffsetSharedArray::N_bytes - 1)
      / G1BlockOffsetSharedArray::N_bytes;
  }

public:
  G1ParTask(G1CollectedHeap* g1h, int workers, RefToScanQueueSet *task_queues)
    : AbstractGangTask("G1 collection"),
      _g1h(g1h),
      _queues(task_queues),
      _terminator(workers, _queues),
      _stats_lock(Mutex::leaf, "parallel G1 stats lock", true),
      _n_workers(workers)
  {}

  RefToScanQueueSet* queues() { return _queues; }

  RefToScanQueue *work_queue(int i) {
    return queues()->queue(i);
  }

  void work(int i) {
    if (i >= _n_workers) return;  // no work needed this round

    double start_time_ms = os::elapsedTime() * 1000.0;
    _g1h->g1_policy()->record_gc_worker_start_time(i, start_time_ms);

    ResourceMark rm;
    HandleMark   hm;

    G1ParScanThreadState            pss(_g1h, i);
    G1ParScanHeapEvacClosure        scan_evac_cl(_g1h, &pss);
    G1ParScanHeapEvacFailureClosure evac_failure_cl(_g1h, &pss);
    G1ParScanPartialArrayClosure    partial_scan_cl(_g1h, &pss);

    pss.set_evac_closure(&scan_evac_cl);
    pss.set_evac_failure_closure(&evac_failure_cl);
    pss.set_partial_scan_closure(&partial_scan_cl);

    G1ParScanExtRootClosure         only_scan_root_cl(_g1h, &pss);
    G1ParScanPermClosure            only_scan_perm_cl(_g1h, &pss);
    G1ParScanHeapRSClosure          only_scan_heap_rs_cl(_g1h, &pss);
    G1ParPushHeapRSClosure          push_heap_rs_cl(_g1h, &pss);

    G1ParScanAndMarkExtRootClosure  scan_mark_root_cl(_g1h, &pss);
    G1ParScanAndMarkPermClosure     scan_mark_perm_cl(_g1h, &pss);
    G1ParScanAndMarkHeapRSClosure   scan_mark_heap_rs_cl(_g1h, &pss);

    OopsInHeapRegionClosure        *scan_root_cl;
    OopsInHeapRegionClosure        *scan_perm_cl;

    if (_g1h->g1_policy()->during_initial_mark_pause()) {
      scan_root_cl = &scan_mark_root_cl;
      scan_perm_cl = &scan_mark_perm_cl;
    } else {
      scan_root_cl = &only_scan_root_cl;
      scan_perm_cl = &only_scan_perm_cl;
    }

    pss.start_strong_roots();
    _g1h->g1_process_strong_roots(/* not collecting perm */ false,
                                  SharedHeap::SO_AllClasses,
                                  scan_root_cl,
                                  &push_heap_rs_cl,
                                  scan_perm_cl,
                                  i);
    pss.end_strong_roots();

    {
      double start = os::elapsedTime();
      G1ParEvacuateFollowersClosure evac(_g1h, &pss, _queues, &_terminator);
      evac.do_void();
      double elapsed_ms = (os::elapsedTime()-start)*1000.0;
      double term_ms = pss.term_time()*1000.0;
      _g1h->g1_policy()->record_obj_copy_time(i, elapsed_ms-term_ms);
      _g1h->g1_policy()->record_termination(i, term_ms, pss.term_attempts());
    }
    _g1h->g1_policy()->record_thread_age_table(pss.age_table());
    _g1h->update_surviving_young_words(pss.surviving_young_words()+1);

    // Clean up any par-expanded rem sets.
    HeapRegionRemSet::par_cleanup();

    if (ParallelGCVerbose) {
      MutexLocker x(stats_lock());
      pss.print_termination_stats(i);
    }

    assert(pss.refs()->is_empty(), "should be empty");
    double end_time_ms = os::elapsedTime() * 1000.0;
    _g1h->g1_policy()->record_gc_worker_end_time(i, end_time_ms);
  }
};

// *** Common G1 Evacuation Stuff

// This method is run in a GC worker.

void
G1CollectedHeap::
g1_process_strong_roots(bool collecting_perm_gen,
                        SharedHeap::ScanningOption so,
                        OopClosure* scan_non_heap_roots,
                        OopsInHeapRegionClosure* scan_rs,
                        OopsInGenClosure* scan_perm,
                        int worker_i) {
  // First scan the strong roots, including the perm gen.
  double ext_roots_start = os::elapsedTime();
  double closure_app_time_sec = 0.0;

  BufferingOopClosure buf_scan_non_heap_roots(scan_non_heap_roots);
  BufferingOopsInGenClosure buf_scan_perm(scan_perm);
  buf_scan_perm.set_generation(perm_gen());

  // Walk the code cache w/o buffering, because StarTask cannot handle
  // unaligned oop locations.
  CodeBlobToOopClosure eager_scan_code_roots(scan_non_heap_roots, /*do_marking=*/ true);

  process_strong_roots(false, // no scoping; this is parallel code
                       collecting_perm_gen, so,
                       &buf_scan_non_heap_roots,
                       &eager_scan_code_roots,
                       &buf_scan_perm);

  // Now the ref_processor roots.
  if (!_process_strong_tasks->is_task_claimed(G1H_PS_refProcessor_oops_do)) {
    // We need to treat the discovered reference lists as roots and
    // keep entries (which are added by the marking threads) on them
    // live until they can be processed at the end of marking.
    ref_processor()->weak_oops_do(&buf_scan_non_heap_roots);
  }

  // Finish up any enqueued closure apps (attributed as object copy time).
  buf_scan_non_heap_roots.done();
  buf_scan_perm.done();

  double ext_roots_end = os::elapsedTime();

  g1_policy()->reset_obj_copy_time(worker_i);
  double obj_copy_time_sec = buf_scan_perm.closure_app_seconds() +
                                buf_scan_non_heap_roots.closure_app_seconds();
  g1_policy()->record_obj_copy_time(worker_i, obj_copy_time_sec * 1000.0);

  double ext_root_time_ms =
    ((ext_roots_end - ext_roots_start) - obj_copy_time_sec) * 1000.0;

  g1_policy()->record_ext_root_scan_time(worker_i, ext_root_time_ms);

  // Scan strong roots in mark stack.
  if (!_process_strong_tasks->is_task_claimed(G1H_PS_mark_stack_oops_do)) {
    concurrent_mark()->oops_do(scan_non_heap_roots);
  }
  double mark_stack_scan_ms = (os::elapsedTime() - ext_roots_end) * 1000.0;
  g1_policy()->record_mark_stack_scan_time(worker_i, mark_stack_scan_ms);

  // Now scan the complement of the collection set.
  if (scan_rs != NULL) {
    g1_rem_set()->oops_into_collection_set_do(scan_rs, worker_i);
  }

  _process_strong_tasks->all_tasks_completed();
}

void
G1CollectedHeap::g1_process_weak_roots(OopClosure* root_closure,
                                       OopClosure* non_root_closure) {
  CodeBlobToOopClosure roots_in_blobs(root_closure, /*do_marking=*/ false);
  SharedHeap::process_weak_roots(root_closure, &roots_in_blobs, non_root_closure);
}

void G1CollectedHeap::evacuate_collection_set() {
  set_evacuation_failed(false);

  g1_rem_set()->prepare_for_oops_into_collection_set_do();
  concurrent_g1_refine()->set_use_cache(false);
  concurrent_g1_refine()->clear_hot_cache_claimed_index();

  int n_workers = (ParallelGCThreads > 0 ? workers()->total_workers() : 1);
  set_par_threads(n_workers);
  G1ParTask g1_par_task(this, n_workers, _task_queues);

  init_for_evac_failure(NULL);

  rem_set()->prepare_for_younger_refs_iterate(true);

  assert(dirty_card_queue_set().completed_buffers_num() == 0, "Should be empty");
  double start_par = os::elapsedTime();
  if (G1CollectedHeap::use_parallel_gc_threads()) {
    // The individual threads will set their evac-failure closures.
    StrongRootsScope srs(this);
    if (ParallelGCVerbose) G1ParScanThreadState::print_termination_stats_hdr();
    workers()->run_task(&g1_par_task);
  } else {
    StrongRootsScope srs(this);
    g1_par_task.work(0);
  }

  double par_time = (os::elapsedTime() - start_par) * 1000.0;
  g1_policy()->record_par_time(par_time);
  set_par_threads(0);

  // Weak root processing.
  // Note: when JSR 292 is enabled and code blobs can contain
  // non-perm oops then we will need to process the code blobs
  // here too.
  {
    G1IsAliveClosure is_alive(this);
    G1KeepAliveClosure keep_alive(this);
    JNIHandles::weak_oops_do(&is_alive, &keep_alive);
  }
  release_gc_alloc_regions();
  g1_rem_set()->cleanup_after_oops_into_collection_set_do();

  concurrent_g1_refine()->clear_hot_cache();
  concurrent_g1_refine()->set_use_cache(true);

  finalize_for_evac_failure();

  // Must do this before removing self-forwarding pointers, which clears
  // the per-region evac-failure flags.
  concurrent_mark()->complete_marking_in_collection_set();

  if (evacuation_failed()) {
    remove_self_forwarding_pointers();
    if (PrintGCDetails) {
      gclog_or_tty->print(" (to-space overflow)");
    } else if (PrintGC) {
      gclog_or_tty->print("--");
    }
  }

  if (G1DeferredRSUpdate) {
    RedirtyLoggedCardTableEntryFastClosure redirty;
    dirty_card_queue_set().set_closure(&redirty);
    dirty_card_queue_set().apply_closure_to_all_completed_buffers();

    DirtyCardQueueSet& dcq = JavaThread::dirty_card_queue_set();
    dcq.merge_bufferlists(&dirty_card_queue_set());
    assert(dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");
  }
  COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
}

void G1CollectedHeap::free_region_if_empty(HeapRegion* hr,
                                     size_t* pre_used,
                                     FreeRegionList* free_list,
                                     HumongousRegionSet* humongous_proxy_set,
                                     HRRSCleanupTask* hrrs_cleanup_task,
                                     bool par) {
  if (hr->used() > 0 && hr->max_live_bytes() == 0 && !hr->is_young()) {
    if (hr->isHumongous()) {
      assert(hr->startsHumongous(), "we should only see starts humongous");
      free_humongous_region(hr, pre_used, free_list, humongous_proxy_set, par);
    } else {
      free_region(hr, pre_used, free_list, par);
    }
  } else {
    hr->rem_set()->do_cleanup_work(hrrs_cleanup_task);
  }
}

void G1CollectedHeap::free_region(HeapRegion* hr,
                                  size_t* pre_used,
                                  FreeRegionList* free_list,
                                  bool par) {
  assert(!hr->isHumongous(), "this is only for non-humongous regions");
  assert(!hr->is_empty(), "the region should not be empty");
  assert(free_list != NULL, "pre-condition");

  *pre_used += hr->used();
  hr->hr_clear(par, true /* clear_space */);
  free_list->add_as_head(hr);
}

void G1CollectedHeap::free_humongous_region(HeapRegion* hr,
                                     size_t* pre_used,
                                     FreeRegionList* free_list,
                                     HumongousRegionSet* humongous_proxy_set,
                                     bool par) {
  assert(hr->startsHumongous(), "this is only for starts humongous regions");
  assert(free_list != NULL, "pre-condition");
  assert(humongous_proxy_set != NULL, "pre-condition");

  size_t hr_used = hr->used();
  size_t hr_capacity = hr->capacity();
  size_t hr_pre_used = 0;
  _humongous_set.remove_with_proxy(hr, humongous_proxy_set);
  hr->set_notHumongous();
  free_region(hr, &hr_pre_used, free_list, par);

  size_t i = hr->hrs_index() + 1;
  size_t num = 1;
  while (i < n_regions()) {
    HeapRegion* curr_hr = region_at(i);
    if (!curr_hr->continuesHumongous()) {
      break;
    }
    curr_hr->set_notHumongous();
    free_region(curr_hr, &hr_pre_used, free_list, par);
    num += 1;
    i += 1;
  }
  assert(hr_pre_used == hr_used,
         err_msg("hr_pre_used: "SIZE_FORMAT" and hr_used: "SIZE_FORMAT" "
                 "should be the same", hr_pre_used, hr_used));
  *pre_used += hr_pre_used;
}

void G1CollectedHeap::update_sets_after_freeing_regions(size_t pre_used,
                                       FreeRegionList* free_list,
                                       HumongousRegionSet* humongous_proxy_set,
                                       bool par) {
  if (pre_used > 0) {
    Mutex* lock = (par) ? ParGCRareEvent_lock : NULL;
    MutexLockerEx x(lock, Mutex::_no_safepoint_check_flag);
    assert(_summary_bytes_used >= pre_used,
           err_msg("invariant: _summary_bytes_used: "SIZE_FORMAT" "
                   "should be >= pre_used: "SIZE_FORMAT,
                   _summary_bytes_used, pre_used));
    _summary_bytes_used -= pre_used;
  }
  if (free_list != NULL && !free_list->is_empty()) {
    MutexLockerEx x(FreeList_lock, Mutex::_no_safepoint_check_flag);
    _free_list.add_as_head(free_list);
  }
  if (humongous_proxy_set != NULL && !humongous_proxy_set->is_empty()) {
    MutexLockerEx x(OldSets_lock, Mutex::_no_safepoint_check_flag);
    _humongous_set.update_from_proxy(humongous_proxy_set);
  }
}

class G1ParCleanupCTTask : public AbstractGangTask {
  CardTableModRefBS* _ct_bs;
  G1CollectedHeap* _g1h;
  HeapRegion* volatile _su_head;
public:
  G1ParCleanupCTTask(CardTableModRefBS* ct_bs,
                     G1CollectedHeap* g1h) :
    AbstractGangTask("G1 Par Cleanup CT Task"),
    _ct_bs(ct_bs), _g1h(g1h) { }

  void work(int i) {
    HeapRegion* r;
    while (r = _g1h->pop_dirty_cards_region()) {
      clear_cards(r);
    }
  }

  void clear_cards(HeapRegion* r) {
    // Cards of the survivors should have already been dirtied.
    if (!r->is_survivor()) {
      _ct_bs->clear(MemRegion(r->bottom(), r->end()));
    }
  }
};

#ifndef PRODUCT
class G1VerifyCardTableCleanup: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  CardTableModRefBS* _ct_bs;
public:
  G1VerifyCardTableCleanup(G1CollectedHeap* g1h, CardTableModRefBS* ct_bs)
    : _g1h(g1h), _ct_bs(ct_bs) { }
  virtual bool doHeapRegion(HeapRegion* r) {
    if (r->is_survivor()) {
      _g1h->verify_dirty_region(r);
    } else {
      _g1h->verify_not_dirty_region(r);
    }
    return false;
  }
};

void G1CollectedHeap::verify_not_dirty_region(HeapRegion* hr) {
  // All of the region should be clean.
  CardTableModRefBS* ct_bs = (CardTableModRefBS*)barrier_set();
  MemRegion mr(hr->bottom(), hr->end());
  ct_bs->verify_not_dirty_region(mr);
}

void G1CollectedHeap::verify_dirty_region(HeapRegion* hr) {
  // We cannot guarantee that [bottom(),end()] is dirty.  Threads
  // dirty allocated blocks as they allocate them. The thread that
  // retires each region and replaces it with a new one will do a
  // maximal allocation to fill in [pre_dummy_top(),end()] but will
  // not dirty that area (one less thing to have to do while holding
  // a lock). So we can only verify that [bottom(),pre_dummy_top()]
  // is dirty.
  CardTableModRefBS* ct_bs = (CardTableModRefBS*) barrier_set();
  MemRegion mr(hr->bottom(), hr->pre_dummy_top());
  ct_bs->verify_dirty_region(mr);
}

void G1CollectedHeap::verify_dirty_young_list(HeapRegion* head) {
  CardTableModRefBS* ct_bs = (CardTableModRefBS*) barrier_set();
  for (HeapRegion* hr = head; hr != NULL; hr = hr->get_next_young_region()) {
    verify_dirty_region(hr);
  }
}

void G1CollectedHeap::verify_dirty_young_regions() {
  verify_dirty_young_list(_young_list->first_region());
  verify_dirty_young_list(_young_list->first_survivor_region());
}
#endif

void G1CollectedHeap::cleanUpCardTable() {
  CardTableModRefBS* ct_bs = (CardTableModRefBS*) (barrier_set());
  double start = os::elapsedTime();

  // Iterate over the dirty cards region list.
  G1ParCleanupCTTask cleanup_task(ct_bs, this);

  if (ParallelGCThreads > 0) {
    set_par_threads(workers()->total_workers());
    workers()->run_task(&cleanup_task);
    set_par_threads(0);
  } else {
    while (_dirty_cards_region_list) {
      HeapRegion* r = _dirty_cards_region_list;
      cleanup_task.clear_cards(r);
      _dirty_cards_region_list = r->get_next_dirty_cards_region();
      if (_dirty_cards_region_list == r) {
        // The last region.
        _dirty_cards_region_list = NULL;
      }
      r->set_next_dirty_cards_region(NULL);
    }
  }

  double elapsed = os::elapsedTime() - start;
  g1_policy()->record_clear_ct_time( elapsed * 1000.0);
#ifndef PRODUCT
  if (G1VerifyCTCleanup || VerifyAfterGC) {
    G1VerifyCardTableCleanup cleanup_verifier(this, ct_bs);
    heap_region_iterate(&cleanup_verifier);
  }
#endif
}

void G1CollectedHeap::free_collection_set(HeapRegion* cs_head) {
  size_t pre_used = 0;
  FreeRegionList local_free_list("Local List for CSet Freeing");

  double young_time_ms     = 0.0;
  double non_young_time_ms = 0.0;

  // Since the collection set is a superset of the the young list,
  // all we need to do to clear the young list is clear its
  // head and length, and unlink any young regions in the code below
  _young_list->clear();

  G1CollectorPolicy* policy = g1_policy();

  double start_sec = os::elapsedTime();
  bool non_young = true;

  HeapRegion* cur = cs_head;
  int age_bound = -1;
  size_t rs_lengths = 0;

  while (cur != NULL) {
    assert(!is_on_master_free_list(cur), "sanity");

    if (non_young) {
      if (cur->is_young()) {
        double end_sec = os::elapsedTime();
        double elapsed_ms = (end_sec - start_sec) * 1000.0;
        non_young_time_ms += elapsed_ms;

        start_sec = os::elapsedTime();
        non_young = false;
      }
    } else {
      double end_sec = os::elapsedTime();
      double elapsed_ms = (end_sec - start_sec) * 1000.0;
      young_time_ms += elapsed_ms;

      start_sec = os::elapsedTime();
      non_young = true;
    }

    rs_lengths += cur->rem_set()->occupied();

    HeapRegion* next = cur->next_in_collection_set();
    assert(cur->in_collection_set(), "bad CS");
    cur->set_next_in_collection_set(NULL);
    cur->set_in_collection_set(false);

    if (cur->is_young()) {
      int index = cur->young_index_in_cset();
      guarantee( index != -1, "invariant" );
      guarantee( (size_t)index < policy->young_cset_length(), "invariant" );
      size_t words_survived = _surviving_young_words[index];
      cur->record_surv_words_in_group(words_survived);

      // At this point the we have 'popped' cur from the collection set
      // (linked via next_in_collection_set()) but it is still in the
      // young list (linked via next_young_region()). Clear the
      // _next_young_region field.
      cur->set_next_young_region(NULL);
    } else {
      int index = cur->young_index_in_cset();
      guarantee( index == -1, "invariant" );
    }

    assert( (cur->is_young() && cur->young_index_in_cset() > -1) ||
            (!cur->is_young() && cur->young_index_in_cset() == -1),
            "invariant" );

    if (!cur->evacuation_failed()) {
      // And the region is empty.
      assert(!cur->is_empty(), "Should not have empty regions in a CS.");
      free_region(cur, &pre_used, &local_free_list, false /* par */);
    } else {
      cur->uninstall_surv_rate_group();
      if (cur->is_young())
        cur->set_young_index_in_cset(-1);
      cur->set_not_young();
      cur->set_evacuation_failed(false);
    }
    cur = next;
  }

  policy->record_max_rs_lengths(rs_lengths);
  policy->cset_regions_freed();

  double end_sec = os::elapsedTime();
  double elapsed_ms = (end_sec - start_sec) * 1000.0;
  if (non_young)
    non_young_time_ms += elapsed_ms;
  else
    young_time_ms += elapsed_ms;

  update_sets_after_freeing_regions(pre_used, &local_free_list,
                                    NULL /* humongous_proxy_set */,
                                    false /* par */);
  policy->record_young_free_cset_time_ms(young_time_ms);
  policy->record_non_young_free_cset_time_ms(non_young_time_ms);
}

// This routine is similar to the above but does not record
// any policy statistics or update free lists; we are abandoning
// the current incremental collection set in preparation of a
// full collection. After the full GC we will start to build up
// the incremental collection set again.
// This is only called when we're doing a full collection
// and is immediately followed by the tearing down of the young list.

void G1CollectedHeap::abandon_collection_set(HeapRegion* cs_head) {
  HeapRegion* cur = cs_head;

  while (cur != NULL) {
    HeapRegion* next = cur->next_in_collection_set();
    assert(cur->in_collection_set(), "bad CS");
    cur->set_next_in_collection_set(NULL);
    cur->set_in_collection_set(false);
    cur->set_young_index_in_cset(-1);
    cur = next;
  }
}

void G1CollectedHeap::set_free_regions_coming() {
  if (G1ConcRegionFreeingVerbose) {
    gclog_or_tty->print_cr("G1ConcRegionFreeing [cm thread] : "
                           "setting free regions coming");
  }

  assert(!free_regions_coming(), "pre-condition");
  _free_regions_coming = true;
}

void G1CollectedHeap::reset_free_regions_coming() {
  {
    assert(free_regions_coming(), "pre-condition");
    MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
    _free_regions_coming = false;
    SecondaryFreeList_lock->notify_all();
  }

  if (G1ConcRegionFreeingVerbose) {
    gclog_or_tty->print_cr("G1ConcRegionFreeing [cm thread] : "
                           "reset free regions coming");
  }
}

void G1CollectedHeap::wait_while_free_regions_coming() {
  // Most of the time we won't have to wait, so let's do a quick test
  // first before we take the lock.
  if (!free_regions_coming()) {
    return;
  }

  if (G1ConcRegionFreeingVerbose) {
    gclog_or_tty->print_cr("G1ConcRegionFreeing [other] : "
                           "waiting for free regions");
  }

  {
    MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
    while (free_regions_coming()) {
      SecondaryFreeList_lock->wait(Mutex::_no_safepoint_check_flag);
    }
  }

  if (G1ConcRegionFreeingVerbose) {
    gclog_or_tty->print_cr("G1ConcRegionFreeing [other] : "
                           "done waiting for free regions");
  }
}

void G1CollectedHeap::set_region_short_lived_locked(HeapRegion* hr) {
  assert(heap_lock_held_for_gc(),
              "the heap lock should already be held by or for this thread");
  _young_list->push_region(hr);
  g1_policy()->set_region_short_lived(hr);
}

class NoYoungRegionsClosure: public HeapRegionClosure {
private:
  bool _success;
public:
  NoYoungRegionsClosure() : _success(true) { }
  bool doHeapRegion(HeapRegion* r) {
    if (r->is_young()) {
      gclog_or_tty->print_cr("Region ["PTR_FORMAT", "PTR_FORMAT") tagged as young",
                             r->bottom(), r->end());
      _success = false;
    }
    return false;
  }
  bool success() { return _success; }
};

bool G1CollectedHeap::check_young_list_empty(bool check_heap, bool check_sample) {
  bool ret = _young_list->check_list_empty(check_sample);

  if (check_heap) {
    NoYoungRegionsClosure closure;
    heap_region_iterate(&closure);
    ret = ret && closure.success();
  }

  return ret;
}

void G1CollectedHeap::empty_young_list() {
  assert(heap_lock_held_for_gc(),
              "the heap lock should already be held by or for this thread");

  _young_list->empty_list();
}

// Done at the start of full GC.
void G1CollectedHeap::tear_down_region_lists() {
  _free_list.remove_all();
}

class RegionResetter: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  FreeRegionList _local_free_list;

public:
  RegionResetter() : _g1h(G1CollectedHeap::heap()),
                     _local_free_list("Local Free List for RegionResetter") { }

  bool doHeapRegion(HeapRegion* r) {
    if (r->continuesHumongous()) return false;
    if (r->top() > r->bottom()) {
      if (r->top() < r->end()) {
        Copy::fill_to_words(r->top(),
                          pointer_delta(r->end(), r->top()));
      }
    } else {
      assert(r->is_empty(), "tautology");
      _local_free_list.add_as_tail(r);
    }
    return false;
  }

  void update_free_lists() {
    _g1h->update_sets_after_freeing_regions(0, &_local_free_list, NULL,
                                            false /* par */);
  }
};

// Done at the end of full GC.
void G1CollectedHeap::rebuild_region_lists() {
  // This needs to go at the end of the full GC.
  RegionResetter rs;
  heap_region_iterate(&rs);
  rs.update_free_lists();
}

void G1CollectedHeap::set_refine_cte_cl_concurrency(bool concurrent) {
  _refine_cte_cl->set_concurrent(concurrent);
}

bool G1CollectedHeap::is_in_closed_subset(const void* p) const {
  HeapRegion* hr = heap_region_containing(p);
  if (hr == NULL) {
    return is_in_permanent(p);
  } else {
    return hr->is_in(p);
  }
}

// Methods for the mutator alloc region

HeapRegion* G1CollectedHeap::new_mutator_alloc_region(size_t word_size,
                                                      bool force) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);
  assert(!force || g1_policy()->can_expand_young_list(),
         "if force is true we should be able to expand the young list");
  bool young_list_full = g1_policy()->is_young_list_full();
  if (force || !young_list_full) {
    HeapRegion* new_alloc_region = new_region(word_size,
                                              false /* do_expand */);
    if (new_alloc_region != NULL) {
      g1_policy()->update_region_num(true /* next_is_young */);
      set_region_short_lived_locked(new_alloc_region);
      _hr_printer.alloc(new_alloc_region, G1HRPrinter::Eden, young_list_full);
      g1mm()->update_eden_counters();
      return new_alloc_region;
    }
  }
  return NULL;
}

void G1CollectedHeap::retire_mutator_alloc_region(HeapRegion* alloc_region,
                                                  size_t allocated_bytes) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);
  assert(alloc_region->is_young(), "all mutator alloc regions should be young");

  g1_policy()->add_region_to_incremental_cset_lhs(alloc_region);
  _summary_bytes_used += allocated_bytes;
  _hr_printer.retire(alloc_region);
}

HeapRegion* MutatorAllocRegion::allocate_new_region(size_t word_size,
                                                    bool force) {
  return _g1h->new_mutator_alloc_region(word_size, force);
}

void MutatorAllocRegion::retire_region(HeapRegion* alloc_region,
                                       size_t allocated_bytes) {
  _g1h->retire_mutator_alloc_region(alloc_region, allocated_bytes);
}

// Methods for the GC alloc regions

HeapRegion* G1CollectedHeap::new_gc_alloc_region(size_t word_size,
                                                 size_t count,
                                                 GCAllocPurpose ap) {
  assert(FreeList_lock->owned_by_self(), "pre-condition");

  if (count < g1_policy()->max_regions(ap)) {
    HeapRegion* new_alloc_region = new_region(word_size,
                                              true /* do_expand */);
    if (new_alloc_region != NULL) {
      // We really only need to do this for old regions given that we
      // should never scan survivors. But it doesn't hurt to do it
      // for survivors too.
      new_alloc_region->set_saved_mark();
      if (ap == GCAllocForSurvived) {
        new_alloc_region->set_survivor();
        _hr_printer.alloc(new_alloc_region, G1HRPrinter::Survivor);
      } else {
        _hr_printer.alloc(new_alloc_region, G1HRPrinter::Old);
      }
      return new_alloc_region;
    } else {
      g1_policy()->note_alloc_region_limit_reached(ap);
    }
  }
  return NULL;
}

void G1CollectedHeap::retire_gc_alloc_region(HeapRegion* alloc_region,
                                             size_t allocated_bytes,
                                             GCAllocPurpose ap) {
  alloc_region->note_end_of_copying();
  g1_policy()->record_bytes_copied_during_gc(allocated_bytes);
  if (ap == GCAllocForSurvived) {
    young_list()->add_survivor_region(alloc_region);
  }
  _hr_printer.retire(alloc_region);
}

HeapRegion* SurvivorGCAllocRegion::allocate_new_region(size_t word_size,
                                                       bool force) {
  assert(!force, "not supported for GC alloc regions");
  return _g1h->new_gc_alloc_region(word_size, count(), GCAllocForSurvived);
}

void SurvivorGCAllocRegion::retire_region(HeapRegion* alloc_region,
                                          size_t allocated_bytes) {
  _g1h->retire_gc_alloc_region(alloc_region, allocated_bytes,
                               GCAllocForSurvived);
}

HeapRegion* OldGCAllocRegion::allocate_new_region(size_t word_size,
                                                  bool force) {
  assert(!force, "not supported for GC alloc regions");
  return _g1h->new_gc_alloc_region(word_size, count(), GCAllocForTenured);
}

void OldGCAllocRegion::retire_region(HeapRegion* alloc_region,
                                     size_t allocated_bytes) {
  _g1h->retire_gc_alloc_region(alloc_region, allocated_bytes,
                               GCAllocForTenured);
}
// Heap region set verification

class VerifyRegionListsClosure : public HeapRegionClosure {
private:
  HumongousRegionSet* _humongous_set;
  FreeRegionList*     _free_list;
  size_t              _region_count;

public:
  VerifyRegionListsClosure(HumongousRegionSet* humongous_set,
                           FreeRegionList* free_list) :
    _humongous_set(humongous_set), _free_list(free_list),
    _region_count(0) { }

  size_t region_count()      { return _region_count;      }

  bool doHeapRegion(HeapRegion* hr) {
    _region_count += 1;

    if (hr->continuesHumongous()) {
      return false;
    }

    if (hr->is_young()) {
      // TODO
    } else if (hr->startsHumongous()) {
      _humongous_set->verify_next_region(hr);
    } else if (hr->is_empty()) {
      _free_list->verify_next_region(hr);
    }
    return false;
  }
};

HeapRegion* G1CollectedHeap::new_heap_region(size_t hrs_index,
                                             HeapWord* bottom) {
  HeapWord* end = bottom + HeapRegion::GrainWords;
  MemRegion mr(bottom, end);
  assert(_g1_reserved.contains(mr), "invariant");
  // This might return NULL if the allocation fails
  return new HeapRegion(hrs_index, _bot_shared, mr, true /* is_zeroed */);
}

void G1CollectedHeap::verify_region_sets() {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);

  // First, check the explicit lists.
  _free_list.verify();
  {
    // Given that a concurrent operation might be adding regions to
    // the secondary free list we have to take the lock before
    // verifying it.
    MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
    _secondary_free_list.verify();
  }
  _humongous_set.verify();

  // If a concurrent region freeing operation is in progress it will
  // be difficult to correctly attributed any free regions we come
  // across to the correct free list given that they might belong to
  // one of several (free_list, secondary_free_list, any local lists,
  // etc.). So, if that's the case we will skip the rest of the
  // verification operation. Alternatively, waiting for the concurrent
  // operation to complete will have a non-trivial effect on the GC's
  // operation (no concurrent operation will last longer than the
  // interval between two calls to verification) and it might hide
  // any issues that we would like to catch during testing.
  if (free_regions_coming()) {
    return;
  }

  // Make sure we append the secondary_free_list on the free_list so
  // that all free regions we will come across can be safely
  // attributed to the free_list.
  append_secondary_free_list_if_not_empty_with_lock();

  // Finally, make sure that the region accounting in the lists is
  // consistent with what we see in the heap.
  _humongous_set.verify_start();
  _free_list.verify_start();

  VerifyRegionListsClosure cl(&_humongous_set, &_free_list);
  heap_region_iterate(&cl);

  _humongous_set.verify_end();
  _free_list.verify_end();
}