view src/share/vm/memory/space.cpp @ 3602:da91efe96a93

6964458: Reimplement class meta-data storage to use native memory Summary: Remove PermGen, allocate meta-data in metaspace linked to class loaders, rewrite GC walking, rewrite and rename metadata to be C++ classes Reviewed-by: jmasa, stefank, never, coleenp, kvn, brutisso, mgerdin, dholmes, jrose, twisti, roland Contributed-by: jmasa <jon.masamitsu@oracle.com>, stefank <stefan.karlsson@oracle.com>, mgerdin <mikael.gerdin@oracle.com>, never <tom.rodriguez@oracle.com>
author coleenp
date Sat, 01 Sep 2012 13:25:18 -0400
parents b632e80fc9dc
children 2fc0334f613a
line wrap: on
line source
/*
 * Copyright (c) 1997, 2012, 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 "classfile/systemDictionary.hpp"
#include "classfile/vmSymbols.hpp"
#include "gc_implementation/shared/liveRange.hpp"
#include "gc_implementation/shared/markSweep.hpp"
#include "gc_implementation/shared/spaceDecorator.hpp"
#include "memory/blockOffsetTable.inline.hpp"
#include "memory/defNewGeneration.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/space.hpp"
#include "memory/space.inline.hpp"
#include "memory/universe.inline.hpp"
#include "oops/oop.inline.hpp"
#include "oops/oop.inline2.hpp"
#include "runtime/java.hpp"
#include "runtime/safepoint.hpp"
#include "utilities/copy.hpp"
#include "utilities/globalDefinitions.hpp"

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

HeapWord* DirtyCardToOopClosure::get_actual_top(HeapWord* top,
                                                HeapWord* top_obj) {
  if (top_obj != NULL) {
    if (_sp->block_is_obj(top_obj)) {
      if (_precision == CardTableModRefBS::ObjHeadPreciseArray) {
        if (oop(top_obj)->is_objArray() || oop(top_obj)->is_typeArray()) {
          // An arrayOop is starting on the dirty card - since we do exact
          // store checks for objArrays we are done.
        } else {
          // Otherwise, it is possible that the object starting on the dirty
          // card spans the entire card, and that the store happened on a
          // later card.  Figure out where the object ends.
          // Use the block_size() method of the space over which
          // the iteration is being done.  That space (e.g. CMS) may have
          // specific requirements on object sizes which will
          // be reflected in the block_size() method.
          top = top_obj + oop(top_obj)->size();
        }
      }
    } else {
      top = top_obj;
    }
  } else {
    assert(top == _sp->end(), "only case where top_obj == NULL");
  }
  return top;
}

void DirtyCardToOopClosure::walk_mem_region(MemRegion mr,
                                            HeapWord* bottom,
                                            HeapWord* top) {
  // 1. Blocks may or may not be objects.
  // 2. Even when a block_is_obj(), it may not entirely
  //    occupy the block if the block quantum is larger than
  //    the object size.
  // We can and should try to optimize by calling the non-MemRegion
  // version of oop_iterate() for all but the extremal objects
  // (for which we need to call the MemRegion version of
  // oop_iterate()) To be done post-beta XXX
  for (; bottom < top; bottom += _sp->block_size(bottom)) {
    // As in the case of contiguous space above, we'd like to
    // just use the value returned by oop_iterate to increment the
    // current pointer; unfortunately, that won't work in CMS because
    // we'd need an interface change (it seems) to have the space
    // "adjust the object size" (for instance pad it up to its
    // block alignment or minimum block size restrictions. XXX
    if (_sp->block_is_obj(bottom) &&
        !_sp->obj_allocated_since_save_marks(oop(bottom))) {
      oop(bottom)->oop_iterate(_cl, mr);
    }
  }
}

// We get called with "mr" representing the dirty region
// that we want to process. Because of imprecise marking,
// we may need to extend the incoming "mr" to the right,
// and scan more. However, because we may already have
// scanned some of that extended region, we may need to
// trim its right-end back some so we do not scan what
// we (or another worker thread) may already have scanned
// or planning to scan.
void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {

  // Some collectors need to do special things whenever their dirty
  // cards are processed. For instance, CMS must remember mutator updates
  // (i.e. dirty cards) so as to re-scan mutated objects.
  // Such work can be piggy-backed here on dirty card scanning, so as to make
  // it slightly more efficient than doing a complete non-detructive pre-scan
  // of the card table.
  MemRegionClosure* pCl = _sp->preconsumptionDirtyCardClosure();
  if (pCl != NULL) {
    pCl->do_MemRegion(mr);
  }

  HeapWord* bottom = mr.start();
  HeapWord* last = mr.last();
  HeapWord* top = mr.end();
  HeapWord* bottom_obj;
  HeapWord* top_obj;

  assert(_precision == CardTableModRefBS::ObjHeadPreciseArray ||
         _precision == CardTableModRefBS::Precise,
         "Only ones we deal with for now.");

  assert(_precision != CardTableModRefBS::ObjHeadPreciseArray ||
         _cl->idempotent() || _last_bottom == NULL ||
         top <= _last_bottom,
         "Not decreasing");
  NOT_PRODUCT(_last_bottom = mr.start());

  bottom_obj = _sp->block_start(bottom);
  top_obj    = _sp->block_start(last);

  assert(bottom_obj <= bottom, "just checking");
  assert(top_obj    <= top,    "just checking");

  // Given what we think is the top of the memory region and
  // the start of the object at the top, get the actual
  // value of the top.
  top = get_actual_top(top, top_obj);

  // If the previous call did some part of this region, don't redo.
  if (_precision == CardTableModRefBS::ObjHeadPreciseArray &&
      _min_done != NULL &&
      _min_done < top) {
    top = _min_done;
  }

  // Top may have been reset, and in fact may be below bottom,
  // e.g. the dirty card region is entirely in a now free object
  // -- something that could happen with a concurrent sweeper.
  bottom = MIN2(bottom, top);
  MemRegion extended_mr = MemRegion(bottom, top);
  assert(bottom <= top &&
         (_precision != CardTableModRefBS::ObjHeadPreciseArray ||
          _min_done == NULL ||
          top <= _min_done),
         "overlap!");

  // Walk the region if it is not empty; otherwise there is nothing to do.
  if (!extended_mr.is_empty()) {
    walk_mem_region(extended_mr, bottom_obj, top);
  }

  // An idempotent closure might be applied in any order, so we don't
  // record a _min_done for it.
  if (!_cl->idempotent()) {
    _min_done = bottom;
  } else {
    assert(_min_done == _last_explicit_min_done,
           "Don't update _min_done for idempotent cl");
  }
}

DirtyCardToOopClosure* Space::new_dcto_cl(ExtendedOopClosure* cl,
                                          CardTableModRefBS::PrecisionStyle precision,
                                          HeapWord* boundary) {
  return new DirtyCardToOopClosure(this, cl, precision, boundary);
}

HeapWord* ContiguousSpaceDCTOC::get_actual_top(HeapWord* top,
                                               HeapWord* top_obj) {
  if (top_obj != NULL && top_obj < (_sp->toContiguousSpace())->top()) {
    if (_precision == CardTableModRefBS::ObjHeadPreciseArray) {
      if (oop(top_obj)->is_objArray() || oop(top_obj)->is_typeArray()) {
        // An arrayOop is starting on the dirty card - since we do exact
        // store checks for objArrays we are done.
      } else {
        // Otherwise, it is possible that the object starting on the dirty
        // card spans the entire card, and that the store happened on a
        // later card.  Figure out where the object ends.
        assert(_sp->block_size(top_obj) == (size_t) oop(top_obj)->size(),
          "Block size and object size mismatch");
        top = top_obj + oop(top_obj)->size();
      }
    }
  } else {
    top = (_sp->toContiguousSpace())->top();
  }
  return top;
}

void Filtering_DCTOC::walk_mem_region(MemRegion mr,
                                      HeapWord* bottom,
                                      HeapWord* top) {
  // Note that this assumption won't hold if we have a concurrent
  // collector in this space, which may have freed up objects after
  // they were dirtied and before the stop-the-world GC that is
  // examining cards here.
  assert(bottom < top, "ought to be at least one obj on a dirty card.");

  if (_boundary != NULL) {
    // We have a boundary outside of which we don't want to look
    // at objects, so create a filtering closure around the
    // oop closure before walking the region.
    FilteringClosure filter(_boundary, _cl);
    walk_mem_region_with_cl(mr, bottom, top, &filter);
  } else {
    // No boundary, simply walk the heap with the oop closure.
    walk_mem_region_with_cl(mr, bottom, top, _cl);
  }

}

// We must replicate this so that the static type of "FilteringClosure"
// (see above) is apparent at the oop_iterate calls.
#define ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(ClosureType) \
void ContiguousSpaceDCTOC::walk_mem_region_with_cl(MemRegion mr,        \
                                                   HeapWord* bottom,    \
                                                   HeapWord* top,       \
                                                   ClosureType* cl) {   \
  bottom += oop(bottom)->oop_iterate(cl, mr);                           \
  if (bottom < top) {                                                   \
    HeapWord* next_obj = bottom + oop(bottom)->size();                  \
    while (next_obj < top) {                                            \
      /* Bottom lies entirely below top, so we can call the */          \
      /* non-memRegion version of oop_iterate below. */                 \
      oop(bottom)->oop_iterate(cl);                                     \
      bottom = next_obj;                                                \
      next_obj = bottom + oop(bottom)->size();                          \
    }                                                                   \
    /* Last object. */                                                  \
    oop(bottom)->oop_iterate(cl, mr);                                   \
  }                                                                     \
}

// (There are only two of these, rather than N, because the split is due
// only to the introduction of the FilteringClosure, a local part of the
// impl of this abstraction.)
ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(ExtendedOopClosure)
ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(FilteringClosure)

DirtyCardToOopClosure*
ContiguousSpace::new_dcto_cl(ExtendedOopClosure* cl,
                             CardTableModRefBS::PrecisionStyle precision,
                             HeapWord* boundary) {
  return new ContiguousSpaceDCTOC(this, cl, precision, boundary);
}

void Space::initialize(MemRegion mr,
                       bool clear_space,
                       bool mangle_space) {
  HeapWord* bottom = mr.start();
  HeapWord* end    = mr.end();
  assert(Universe::on_page_boundary(bottom) && Universe::on_page_boundary(end),
         "invalid space boundaries");
  set_bottom(bottom);
  set_end(end);
  if (clear_space) clear(mangle_space);
}

void Space::clear(bool mangle_space) {
  if (ZapUnusedHeapArea && mangle_space) {
    mangle_unused_area();
  }
}

ContiguousSpace::ContiguousSpace(): CompactibleSpace(), _top(NULL),
    _concurrent_iteration_safe_limit(NULL) {
  _mangler = new GenSpaceMangler(this);
}

ContiguousSpace::~ContiguousSpace() {
  delete _mangler;
}

void ContiguousSpace::initialize(MemRegion mr,
                                 bool clear_space,
                                 bool mangle_space)
{
  CompactibleSpace::initialize(mr, clear_space, mangle_space);
  set_concurrent_iteration_safe_limit(top());
}

void ContiguousSpace::clear(bool mangle_space) {
  set_top(bottom());
  set_saved_mark();
  CompactibleSpace::clear(mangle_space);
}

bool ContiguousSpace::is_in(const void* p) const {
  return _bottom <= p && p < _top;
}

bool ContiguousSpace::is_free_block(const HeapWord* p) const {
  return p >= _top;
}

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

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

void OffsetTableContigSpace::set_end(HeapWord* new_end) {
  // Space should not advertize an increase in size
  // until after the underlying offest table has been enlarged.
  _offsets.resize(pointer_delta(new_end, bottom()));
  Space::set_end(new_end);
}

#ifndef PRODUCT

void ContiguousSpace::set_top_for_allocations(HeapWord* v) {
  mangler()->set_top_for_allocations(v);
}
void ContiguousSpace::set_top_for_allocations() {
  mangler()->set_top_for_allocations(top());
}
void ContiguousSpace::check_mangled_unused_area(HeapWord* limit) {
  mangler()->check_mangled_unused_area(limit);
}

void ContiguousSpace::check_mangled_unused_area_complete() {
  mangler()->check_mangled_unused_area_complete();
}

// Mangled only the unused space that has not previously
// been mangled and that has not been allocated since being
// mangled.
void ContiguousSpace::mangle_unused_area() {
  mangler()->mangle_unused_area();
}
void ContiguousSpace::mangle_unused_area_complete() {
  mangler()->mangle_unused_area_complete();
}
void ContiguousSpace::mangle_region(MemRegion mr) {
  // Although this method uses SpaceMangler::mangle_region() which
  // is not specific to a space, the when the ContiguousSpace version
  // is called, it is always with regard to a space and this
  // bounds checking is appropriate.
  MemRegion space_mr(bottom(), end());
  assert(space_mr.contains(mr), "Mangling outside space");
  SpaceMangler::mangle_region(mr);
}
#endif  // NOT_PRODUCT

void CompactibleSpace::initialize(MemRegion mr,
                                  bool clear_space,
                                  bool mangle_space) {
  Space::initialize(mr, clear_space, mangle_space);
  set_compaction_top(bottom());
  _next_compaction_space = NULL;
}

void CompactibleSpace::clear(bool mangle_space) {
  Space::clear(mangle_space);
  _compaction_top = bottom();
}

HeapWord* CompactibleSpace::forward(oop q, size_t size,
                                    CompactPoint* cp, HeapWord* compact_top) {
  // q is alive
  // First check if we should switch compaction space
  assert(this == cp->space, "'this' should be current compaction space.");
  size_t compaction_max_size = pointer_delta(end(), compact_top);
  while (size > compaction_max_size) {
    // switch to next compaction space
    cp->space->set_compaction_top(compact_top);
    cp->space = cp->space->next_compaction_space();
    if (cp->space == NULL) {
      cp->gen = GenCollectedHeap::heap()->prev_gen(cp->gen);
      assert(cp->gen != NULL, "compaction must succeed");
      cp->space = cp->gen->first_compaction_space();
      assert(cp->space != NULL, "generation must have a first compaction space");
    }
    compact_top = cp->space->bottom();
    cp->space->set_compaction_top(compact_top);
    cp->threshold = cp->space->initialize_threshold();
    compaction_max_size = pointer_delta(cp->space->end(), compact_top);
  }

  // store the forwarding pointer into the mark word
  if ((HeapWord*)q != compact_top) {
    q->forward_to(oop(compact_top));
    assert(q->is_gc_marked(), "encoding the pointer should preserve the mark");
  } else {
    // if the object isn't moving we can just set the mark to the default
    // mark and handle it specially later on.
    q->init_mark();
    assert(q->forwardee() == NULL, "should be forwarded to NULL");
  }

  VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(q, size));
  compact_top += size;

  // we need to update the offset table so that the beginnings of objects can be
  // found during scavenge.  Note that we are updating the offset table based on
  // where the object will be once the compaction phase finishes.
  if (compact_top > cp->threshold)
    cp->threshold =
      cp->space->cross_threshold(compact_top - size, compact_top);
  return compact_top;
}


bool CompactibleSpace::insert_deadspace(size_t& allowed_deadspace_words,
                                        HeapWord* q, size_t deadlength) {
  if (allowed_deadspace_words >= deadlength) {
    allowed_deadspace_words -= deadlength;
    CollectedHeap::fill_with_object(q, deadlength);
    oop(q)->set_mark(oop(q)->mark()->set_marked());
    assert((int) deadlength == oop(q)->size(), "bad filler object size");
    // Recall that we required "q == compaction_top".
    return true;
  } else {
    allowed_deadspace_words = 0;
    return false;
  }
}

#define block_is_always_obj(q) true
#define obj_size(q) oop(q)->size()
#define adjust_obj_size(s) s

void CompactibleSpace::prepare_for_compaction(CompactPoint* cp) {
  SCAN_AND_FORWARD(cp, end, block_is_obj, block_size);
}

// Faster object search.
void ContiguousSpace::prepare_for_compaction(CompactPoint* cp) {
  SCAN_AND_FORWARD(cp, top, block_is_always_obj, obj_size);
}

void Space::adjust_pointers() {
  // adjust all the interior pointers to point at the new locations of objects
  // Used by MarkSweep::mark_sweep_phase3()

  // First check to see if there is any work to be done.
  if (used() == 0) {
    return;  // Nothing to do.
  }

  // Otherwise...
  HeapWord* q = bottom();
  HeapWord* t = end();

  debug_only(HeapWord* prev_q = NULL);
  while (q < t) {
    if (oop(q)->is_gc_marked()) {
      // q is alive

      VALIDATE_MARK_SWEEP_ONLY(MarkSweep::track_interior_pointers(oop(q)));
      // point all the oops to the new location
      size_t size = oop(q)->adjust_pointers();
      VALIDATE_MARK_SWEEP_ONLY(MarkSweep::check_interior_pointers());

      debug_only(prev_q = q);
      VALIDATE_MARK_SWEEP_ONLY(MarkSweep::validate_live_oop(oop(q), size));

      q += size;
    } else {
      // q is not a live object.  But we're not in a compactible space,
      // So we don't have live ranges.
      debug_only(prev_q = q);
      q += block_size(q);
      assert(q > prev_q, "we should be moving forward through memory");
    }
  }
  assert(q == t, "just checking");
}

void CompactibleSpace::adjust_pointers() {
  // Check first is there is any work to do.
  if (used() == 0) {
    return;   // Nothing to do.
  }

  SCAN_AND_ADJUST_POINTERS(adjust_obj_size);
}

void CompactibleSpace::compact() {
  SCAN_AND_COMPACT(obj_size);
}

void Space::print_short() const { print_short_on(tty); }

void Space::print_short_on(outputStream* st) const {
  st->print(" space " SIZE_FORMAT "K, %3d%% used", capacity() / K,
              (int) ((double) used() * 100 / capacity()));
}

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

void Space::print_on(outputStream* st) const {
  print_short_on(st);
  st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ")",
                bottom(), end());
}

void ContiguousSpace::print_on(outputStream* st) const {
  print_short_on(st);
  st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", " INTPTR_FORMAT ")",
                bottom(), top(), end());
}

void OffsetTableContigSpace::print_on(outputStream* st) const {
  print_short_on(st);
  st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", "
                INTPTR_FORMAT ", " INTPTR_FORMAT ")",
              bottom(), top(), _offsets.threshold(), end());
}

void ContiguousSpace::verify() const {
  HeapWord* p = bottom();
  HeapWord* t = top();
  HeapWord* prev_p = NULL;
  while (p < t) {
    oop(p)->verify();
    prev_p = p;
    p += oop(p)->size();
  }
  guarantee(p == top(), "end of last object must match end of space");
  if (top() != end()) {
    guarantee(top() == block_start_const(end()-1) &&
              top() == block_start_const(top()),
              "top should be start of unallocated block, if it exists");
  }
}

void Space::oop_iterate(ExtendedOopClosure* blk) {
  ObjectToOopClosure blk2(blk);
  object_iterate(&blk2);
}

HeapWord* Space::object_iterate_careful(ObjectClosureCareful* cl) {
  guarantee(false, "NYI");
  return bottom();
}

HeapWord* Space::object_iterate_careful_m(MemRegion mr,
                                          ObjectClosureCareful* cl) {
  guarantee(false, "NYI");
  return bottom();
}


void Space::object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl) {
  assert(!mr.is_empty(), "Should be non-empty");
  // We use MemRegion(bottom(), end()) rather than used_region() below
  // because the two are not necessarily equal for some kinds of
  // spaces, in particular, certain kinds of free list spaces.
  // We could use the more complicated but more precise:
  // MemRegion(used_region().start(), round_to(used_region().end(), CardSize))
  // but the slight imprecision seems acceptable in the assertion check.
  assert(MemRegion(bottom(), end()).contains(mr),
         "Should be within used space");
  HeapWord* prev = cl->previous();   // max address from last time
  if (prev >= mr.end()) { // nothing to do
    return;
  }
  // This assert will not work when we go from cms space to perm
  // space, and use same closure. Easy fix deferred for later. XXX YSR
  // assert(prev == NULL || contains(prev), "Should be within space");

  bool last_was_obj_array = false;
  HeapWord *blk_start_addr, *region_start_addr;
  if (prev > mr.start()) {
    region_start_addr = prev;
    blk_start_addr    = prev;
    // The previous invocation may have pushed "prev" beyond the
    // last allocated block yet there may be still be blocks
    // in this region due to a particular coalescing policy.
    // Relax the assertion so that the case where the unallocated
    // block is maintained and "prev" is beyond the unallocated
    // block does not cause the assertion to fire.
    assert((BlockOffsetArrayUseUnallocatedBlock &&
            (!is_in(prev))) ||
           (blk_start_addr == block_start(region_start_addr)), "invariant");
  } else {
    region_start_addr = mr.start();
    blk_start_addr    = block_start(region_start_addr);
  }
  HeapWord* region_end_addr = mr.end();
  MemRegion derived_mr(region_start_addr, region_end_addr);
  while (blk_start_addr < region_end_addr) {
    const size_t size = block_size(blk_start_addr);
    if (block_is_obj(blk_start_addr)) {
      last_was_obj_array = cl->do_object_bm(oop(blk_start_addr), derived_mr);
    } else {
      last_was_obj_array = false;
    }
    blk_start_addr += size;
  }
  if (!last_was_obj_array) {
    assert((bottom() <= blk_start_addr) && (blk_start_addr <= end()),
           "Should be within (closed) used space");
    assert(blk_start_addr > prev, "Invariant");
    cl->set_previous(blk_start_addr); // min address for next time
  }
}

bool Space::obj_is_alive(const HeapWord* p) const {
  assert (block_is_obj(p), "The address should point to an object");
  return true;
}

void ContiguousSpace::object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl) {
  assert(!mr.is_empty(), "Should be non-empty");
  assert(used_region().contains(mr), "Should be within used space");
  HeapWord* prev = cl->previous();   // max address from last time
  if (prev >= mr.end()) { // nothing to do
    return;
  }
  // See comment above (in more general method above) in case you
  // happen to use this method.
  assert(prev == NULL || is_in_reserved(prev), "Should be within space");

  bool last_was_obj_array = false;
  HeapWord *obj_start_addr, *region_start_addr;
  if (prev > mr.start()) {
    region_start_addr = prev;
    obj_start_addr    = prev;
    assert(obj_start_addr == block_start(region_start_addr), "invariant");
  } else {
    region_start_addr = mr.start();
    obj_start_addr    = block_start(region_start_addr);
  }
  HeapWord* region_end_addr = mr.end();
  MemRegion derived_mr(region_start_addr, region_end_addr);
  while (obj_start_addr < region_end_addr) {
    oop obj = oop(obj_start_addr);
    const size_t size = obj->size();
    last_was_obj_array = cl->do_object_bm(obj, derived_mr);
    obj_start_addr += size;
  }
  if (!last_was_obj_array) {
    assert((bottom() <= obj_start_addr)  && (obj_start_addr <= end()),
           "Should be within (closed) used space");
    assert(obj_start_addr > prev, "Invariant");
    cl->set_previous(obj_start_addr); // min address for next time
  }
}

#ifndef SERIALGC
#define ContigSpace_PAR_OOP_ITERATE_DEFN(OopClosureType, nv_suffix)         \
                                                                            \
  void ContiguousSpace::par_oop_iterate(MemRegion mr, OopClosureType* blk) {\
    HeapWord* obj_addr = mr.start();                                        \
    HeapWord* t = mr.end();                                                 \
    while (obj_addr < t) {                                                  \
      assert(oop(obj_addr)->is_oop(), "Should be an oop");                  \
      obj_addr += oop(obj_addr)->oop_iterate(blk);                          \
    }                                                                       \
  }

  ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DEFN)

#undef ContigSpace_PAR_OOP_ITERATE_DEFN
#endif // SERIALGC

void ContiguousSpace::oop_iterate(ExtendedOopClosure* blk) {
  if (is_empty()) return;
  HeapWord* obj_addr = bottom();
  HeapWord* t = top();
  // Could call objects iterate, but this is easier.
  while (obj_addr < t) {
    obj_addr += oop(obj_addr)->oop_iterate(blk);
  }
}

void ContiguousSpace::oop_iterate(MemRegion mr, ExtendedOopClosure* blk) {
  if (is_empty()) {
    return;
  }
  MemRegion cur = MemRegion(bottom(), top());
  mr = mr.intersection(cur);
  if (mr.is_empty()) {
    return;
  }
  if (mr.equals(cur)) {
    oop_iterate(blk);
    return;
  }
  assert(mr.end() <= top(), "just took an intersection above");
  HeapWord* obj_addr = block_start(mr.start());
  HeapWord* t = mr.end();

  // Handle first object specially.
  oop obj = oop(obj_addr);
  SpaceMemRegionOopsIterClosure smr_blk(blk, mr);
  obj_addr += obj->oop_iterate(&smr_blk);
  while (obj_addr < t) {
    oop obj = oop(obj_addr);
    assert(obj->is_oop(), "expected an oop");
    obj_addr += obj->size();
    // If "obj_addr" is not greater than top, then the
    // entire object "obj" is within the region.
    if (obj_addr <= t) {
      obj->oop_iterate(blk);
    } else {
      // "obj" extends beyond end of region
      obj->oop_iterate(&smr_blk);
      break;
    }
  };
}

void ContiguousSpace::object_iterate(ObjectClosure* blk) {
  if (is_empty()) return;
  WaterMark bm = bottom_mark();
  object_iterate_from(bm, blk);
}

// For a continguous space object_iterate() and safe_object_iterate()
// are the same.
void ContiguousSpace::safe_object_iterate(ObjectClosure* blk) {
  object_iterate(blk);
}

void ContiguousSpace::object_iterate_from(WaterMark mark, ObjectClosure* blk) {
  assert(mark.space() == this, "Mark does not match space");
  HeapWord* p = mark.point();
  while (p < top()) {
    blk->do_object(oop(p));
    p += oop(p)->size();
  }
}

HeapWord*
ContiguousSpace::object_iterate_careful(ObjectClosureCareful* blk) {
  HeapWord * limit = concurrent_iteration_safe_limit();
  assert(limit <= top(), "sanity check");
  for (HeapWord* p = bottom(); p < limit;) {
    size_t size = blk->do_object_careful(oop(p));
    if (size == 0) {
      return p;  // failed at p
    } else {
      p += size;
    }
  }
  return NULL; // all done
}

#define ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)  \
                                                                          \
void ContiguousSpace::                                                    \
oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk) {            \
  HeapWord* t;                                                            \
  HeapWord* p = saved_mark_word();                                        \
  assert(p != NULL, "expected saved mark");                               \
                                                                          \
  const intx interval = PrefetchScanIntervalInBytes;                      \
  do {                                                                    \
    t = top();                                                            \
    while (p < t) {                                                       \
      Prefetch::write(p, interval);                                       \
      debug_only(HeapWord* prev = p);                                     \
      oop m = oop(p);                                                     \
      p += m->oop_iterate(blk);                                           \
    }                                                                     \
  } while (t < top());                                                    \
                                                                          \
  set_saved_mark_word(p);                                                 \
}

ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN)

#undef ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN

// Very general, slow implementation.
HeapWord* ContiguousSpace::block_start_const(const void* p) const {
  assert(MemRegion(bottom(), end()).contains(p), "p not in space");
  if (p >= top()) {
    return top();
  } else {
    HeapWord* last = bottom();
    HeapWord* cur = last;
    while (cur <= p) {
      last = cur;
      cur += oop(cur)->size();
    }
    assert(oop(last)->is_oop(), "Should be an object start");
    return last;
  }
}

size_t ContiguousSpace::block_size(const HeapWord* p) const {
  assert(MemRegion(bottom(), end()).contains(p), "p not in space");
  HeapWord* current_top = top();
  assert(p <= current_top, "p is not a block start");
  assert(p == current_top || oop(p)->is_oop(), "p is not a block start");
  if (p < current_top)
    return oop(p)->size();
  else {
    assert(p == current_top, "just checking");
    return pointer_delta(end(), (HeapWord*) p);
  }
}

// This version requires locking.
inline HeapWord* ContiguousSpace::allocate_impl(size_t size,
                                                HeapWord* const end_value) {
  // In G1 there are places where a GC worker can allocates into a
  // region using this serial allocation code without being prone to a
  // race with other GC workers (we ensure that no other GC worker can
  // access the same region at the same time). So the assert below is
  // too strong in the case of G1.
  assert(Heap_lock->owned_by_self() ||
         (SafepointSynchronize::is_at_safepoint() &&
                               (Thread::current()->is_VM_thread() || UseG1GC)),
         "not locked");
  HeapWord* obj = top();
  if (pointer_delta(end_value, obj) >= size) {
    HeapWord* new_top = obj + size;
    set_top(new_top);
    assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
    return obj;
  } else {
    return NULL;
  }
}

// This version is lock-free.
inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size,
                                                    HeapWord* const end_value) {
  do {
    HeapWord* obj = top();
    if (pointer_delta(end_value, obj) >= size) {
      HeapWord* new_top = obj + size;
      HeapWord* result = (HeapWord*)Atomic::cmpxchg_ptr(new_top, top_addr(), obj);
      // result can be one of two:
      //  the old top value: the exchange succeeded
      //  otherwise: the new value of the top is returned.
      if (result == obj) {
        assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
        return obj;
      }
    } else {
      return NULL;
    }
  } while (true);
}

// Requires locking.
HeapWord* ContiguousSpace::allocate(size_t size) {
  return allocate_impl(size, end());
}

// Lock-free.
HeapWord* ContiguousSpace::par_allocate(size_t size) {
  return par_allocate_impl(size, end());
}

void ContiguousSpace::allocate_temporary_filler(int factor) {
  // allocate temporary type array decreasing free size with factor 'factor'
  assert(factor >= 0, "just checking");
  size_t size = pointer_delta(end(), top());

  // if space is full, return
  if (size == 0) return;

  if (factor > 0) {
    size -= size/factor;
  }
  size = align_object_size(size);

  const size_t array_header_size = typeArrayOopDesc::header_size(T_INT);
  if (size >= (size_t)align_object_size(array_header_size)) {
    size_t length = (size - array_header_size) * (HeapWordSize / sizeof(jint));
    // allocate uninitialized int array
    typeArrayOop t = (typeArrayOop) allocate(size);
    assert(t != NULL, "allocation should succeed");
    t->set_mark(markOopDesc::prototype());
    t->set_klass(Universe::intArrayKlassObj());
    t->set_length((int)length);
  } else {
    assert(size == CollectedHeap::min_fill_size(),
           "size for smallest fake object doesn't match");
    instanceOop obj = (instanceOop) allocate(size);
    obj->set_mark(markOopDesc::prototype());
    obj->set_klass_gap(0);
    obj->set_klass(SystemDictionary::Object_klass());
  }
}

void EdenSpace::clear(bool mangle_space) {
  ContiguousSpace::clear(mangle_space);
  set_soft_end(end());
}

// Requires locking.
HeapWord* EdenSpace::allocate(size_t size) {
  return allocate_impl(size, soft_end());
}

// Lock-free.
HeapWord* EdenSpace::par_allocate(size_t size) {
  return par_allocate_impl(size, soft_end());
}

HeapWord* ConcEdenSpace::par_allocate(size_t size)
{
  do {
    // The invariant is top() should be read before end() because
    // top() can't be greater than end(), so if an update of _soft_end
    // occurs between 'end_val = end();' and 'top_val = top();' top()
    // also can grow up to the new end() and the condition
    // 'top_val > end_val' is true. To ensure the loading order
    // OrderAccess::loadload() is required after top() read.
    HeapWord* obj = top();
    OrderAccess::loadload();
    if (pointer_delta(*soft_end_addr(), obj) >= size) {
      HeapWord* new_top = obj + size;
      HeapWord* result = (HeapWord*)Atomic::cmpxchg_ptr(new_top, top_addr(), obj);
      // result can be one of two:
      //  the old top value: the exchange succeeded
      //  otherwise: the new value of the top is returned.
      if (result == obj) {
        assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
        return obj;
      }
    } else {
      return NULL;
    }
  } while (true);
}


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

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

OffsetTableContigSpace::OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
                                               MemRegion mr) :
  _offsets(sharedOffsetArray, mr),
  _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true)
{
  _offsets.set_contig_space(this);
  initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
}

#define OBJ_SAMPLE_INTERVAL 0
#define BLOCK_SAMPLE_INTERVAL 100

void OffsetTableContigSpace::verify() const {
  HeapWord* p = bottom();
  HeapWord* prev_p = NULL;
  int objs = 0;
  int blocks = 0;

  if (VerifyObjectStartArray) {
    _offsets.verify();
  }

  while (p < top()) {
    size_t size = oop(p)->size();
    // For a sampling of objects in the space, find it using the
    // block offset table.
    if (blocks == BLOCK_SAMPLE_INTERVAL) {
      guarantee(p == block_start_const(p + (size/2)),
                "check offset computation");
      blocks = 0;
    } else {
      blocks++;
    }

    if (objs == OBJ_SAMPLE_INTERVAL) {
      oop(p)->verify();
      objs = 0;
    } else {
      objs++;
    }
    prev_p = p;
    p += size;
  }
  guarantee(p == top(), "end of last object must match end of space");
}


size_t TenuredSpace::allowed_dead_ratio() const {
  return MarkSweepDeadRatio;
}