text: /*
   * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   *
   */
  
  #include "precompiled.hpp"
  #include "gc/serial/defNewGeneration.inline.hpp"
  #include "gc/serial/serialHeap.inline.hpp"
  #include "gc/serial/tenuredGeneration.hpp"
  #include "gc/shared/adaptiveSizePolicy.hpp"
  #include "gc/shared/ageTable.inline.hpp"
  #include "gc/shared/cardTableRS.hpp"
  #include "gc/shared/collectorCounters.hpp"
  #include "gc/shared/gcHeapSummary.hpp"
  #include "gc/shared/gcLocker.hpp"
  #include "gc/shared/gcPolicyCounters.hpp"
  #include "gc/shared/gcTimer.hpp"
  #include "gc/shared/gcTrace.hpp"
  #include "gc/shared/gcTraceTime.inline.hpp"
  #include "gc/shared/genOopClosures.inline.hpp"
  #include "gc/shared/generationSpec.hpp"
  #include "gc/shared/preservedMarks.inline.hpp"
  #include "gc/shared/referencePolicy.hpp"
  #include "gc/shared/space.inline.hpp"
  #include "gc/shared/spaceDecorator.hpp"
  #include "gc/shared/strongRootsScope.hpp"
  #include "gc/shared/weakProcessor.hpp"
  #include "logging/log.hpp"
  #include "memory/iterator.hpp"
  #include "memory/resourceArea.hpp"
  #include "oops/instanceRefKlass.hpp"
  #include "oops/oop.inline.hpp"
  #include "runtime/atomic.hpp"
  #include "runtime/java.hpp"
  #include "runtime/prefetch.inline.hpp"
  #include "runtime/thread.inline.hpp"
  #include "utilities/align.hpp"
  #include "utilities/copy.hpp"
  #include "utilities/globalDefinitions.hpp"
  #include "utilities/stack.inline.hpp"
  
  //
  // DefNewGeneration functions.
  
  // Methods of protected closure types.
  
  DefNewGeneration::IsAliveClosure::IsAliveClosure(Generation* young_gen) : _young_gen(young_gen) {
    assert(_young_gen->kind() == Generation::ParNew ||
           _young_gen->kind() == Generation::DefNew, "Expected the young generation here");
  }
  
  bool DefNewGeneration::IsAliveClosure::do_object_b(oop p) {
    return (HeapWord*)p >= _young_gen->reserved().end() || p->is_forwarded();
  }
  
  DefNewGeneration::KeepAliveClosure::
  KeepAliveClosure(ScanWeakRefClosure* cl) : _cl(cl) {
    _rs = GenCollectedHeap::heap()->rem_set();
  }
  
  void DefNewGeneration::KeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }
  void DefNewGeneration::KeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }
  
  
  DefNewGeneration::FastKeepAliveClosure::
  FastKeepAliveClosure(DefNewGeneration* g, ScanWeakRefClosure* cl) :
    DefNewGeneration::KeepAliveClosure(cl) {
    _boundary = g->reserved().end();
  }
  
  void DefNewGeneration::FastKeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
  void DefNewGeneration::FastKeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
  
  DefNewGeneration::FastEvacuateFollowersClosure::
  FastEvacuateFollowersClosure(SerialHeap* heap,
                               FastScanClosure* cur,
                               FastScanClosure* older) :
    _heap(heap), _scan_cur_or_nonheap(cur), _scan_older(older)
  {
  }
  
  void DefNewGeneration::FastEvacuateFollowersClosure::do_void() {
    do {
      _heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap, _scan_older);
    } while (!_heap->no_allocs_since_save_marks());
    guarantee(_heap->young_gen()->promo_failure_scan_is_complete(), "Failed to finish scan");
  }
  
  ScanClosure::ScanClosure(DefNewGeneration* g, bool gc_barrier) :
      OopsInClassLoaderDataOrGenClosure(g), _g(g), _gc_barrier(gc_barrier)
  {
    _boundary = _g->reserved().end();
  }
  
  void ScanClosure::do_oop(oop* p)       { ScanClosure::do_oop_work(p); }
  void ScanClosure::do_oop(narrowOop* p) { ScanClosure::do_oop_work(p); }
  
  FastScanClosure::FastScanClosure(DefNewGeneration* g, bool gc_barrier) :
      OopsInClassLoaderDataOrGenClosure(g), _g(g), _gc_barrier(gc_barrier)
  {
    _boundary = _g->reserved().end();
  }
  
  void FastScanClosure::do_oop(oop* p)       { FastScanClosure::do_oop_work(p); }
  void FastScanClosure::do_oop(narrowOop* p) { FastScanClosure::do_oop_work(p); }
  
  void CLDScanClosure::do_cld(ClassLoaderData* cld) {
    NOT_PRODUCT(ResourceMark rm);
    log_develop_trace(gc, scavenge)("CLDScanClosure::do_cld " PTR_FORMAT ", %s, dirty: %s",
                                    p2i(cld),
                                    cld->loader_name(),
                                    cld->has_modified_oops() ? "true" : "false");
  
    // If the cld has not been dirtied we know that there's
    // no references into  the young gen and we can skip it.
    if (cld->has_modified_oops()) {
      if (_accumulate_modified_oops) {
        cld->accumulate_modified_oops();
      }
  
      // Tell the closure which CLD is being scanned so that it can be dirtied
      // if oops are left pointing into the young gen.
      _scavenge_closure->set_scanned_cld(cld);
  
      // Clean the cld since we're going to scavenge all the metadata.
      cld->oops_do(_scavenge_closure, false, /*clear_modified_oops*/true);
  
      _scavenge_closure->set_scanned_cld(NULL);
    }
  }
  
  ScanWeakRefClosure::ScanWeakRefClosure(DefNewGeneration* g) :
    _g(g)
  {
    _boundary = _g->reserved().end();
  }
  
  void ScanWeakRefClosure::do_oop(oop* p)       { ScanWeakRefClosure::do_oop_work(p); }
  void ScanWeakRefClosure::do_oop(narrowOop* p) { ScanWeakRefClosure::do_oop_work(p); }
  
  DefNewGeneration::DefNewGeneration(ReservedSpace rs,
                                     size_t initial_size,
                                     const char* policy)
    : Generation(rs, initial_size),
      _preserved_marks_set(false /* in_c_heap */),
      _promo_failure_drain_in_progress(false),
      _should_allocate_from_space(false)
  {
    MemRegion cmr((HeapWord*)_virtual_space.low(),
                  (HeapWord*)_virtual_space.high());
    GenCollectedHeap* gch = GenCollectedHeap::heap();
  
    gch->rem_set()->resize_covered_region(cmr);
  
    _eden_space = new ContiguousSpace();
    _from_space = new ContiguousSpace();
    _to_space   = new ContiguousSpace();
  
    if (_eden_space == NULL || _from_space == NULL || _to_space == NULL) {
      vm_exit_during_initialization("Could not allocate a new gen space");
    }
  
    // Compute the maximum eden and survivor space sizes. These sizes
    // are computed assuming the entire reserved space is committed.
    // These values are exported as performance counters.
    uintx alignment = gch->collector_policy()->space_alignment();
    uintx size = _virtual_space.reserved_size();
    _max_survivor_size = compute_survivor_size(size, alignment);
    _max_eden_size = size - (2*_max_survivor_size);
  
    // allocate the performance counters
    GenCollectorPolicy* gcp = gch->gen_policy();
  
    // Generation counters -- generation 0, 3 subspaces
    _gen_counters = new GenerationCounters("new", 0, 3,
        gcp->min_young_size(), gcp->max_young_size(), &_virtual_space);
    _gc_counters = new CollectorCounters(policy, 0);
  
    _eden_counters = new CSpaceCounters("eden", 0, _max_eden_size, _eden_space,
                                        _gen_counters);
    _from_counters = new CSpaceCounters("s0", 1, _max_survivor_size, _from_space,
                                        _gen_counters);
    _to_counters = new CSpaceCounters("s1", 2, _max_survivor_size, _to_space,
                                      _gen_counters);
  
    compute_space_boundaries(0, SpaceDecorator::Clear, SpaceDecorator::Mangle);
    update_counters();
    _old_gen = NULL;
    _tenuring_threshold = MaxTenuringThreshold;
    _pretenure_size_threshold_words = PretenureSizeThreshold >> LogHeapWordSize;
  
    _gc_timer = new (ResourceObj::C_HEAP, mtGC) STWGCTimer();
  }
  
  void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size,
                                                  bool clear_space,
                                                  bool mangle_space) {
    uintx alignment =
      GenCollectedHeap::heap()->collector_policy()->space_alignment();
  
    // If the spaces are being cleared (only done at heap initialization
    // currently), the survivor spaces need not be empty.
    // Otherwise, no care is taken for used areas in the survivor spaces
    // so check.
    assert(clear_space || (to()->is_empty() && from()->is_empty()),
      "Initialization of the survivor spaces assumes these are empty");
  
    // Compute sizes
    uintx size = _virtual_space.committed_size();
    uintx survivor_size = compute_survivor_size(size, alignment);
    uintx eden_size = size - (2*survivor_size);
    assert(eden_size > 0 && survivor_size <= eden_size, "just checking");
  
    if (eden_size < minimum_eden_size) {
      // May happen due to 64Kb rounding, if so adjust eden size back up
      minimum_eden_size = align_up(minimum_eden_size, alignment);
      uintx maximum_survivor_size = (size - minimum_eden_size) / 2;
      uintx unaligned_survivor_size =
        align_down(maximum_survivor_size, alignment);
      survivor_size = MAX2(unaligned_survivor_size, alignment);
      eden_size = size - (2*survivor_size);
      assert(eden_size > 0 && survivor_size <= eden_size, "just checking");
      assert(eden_size >= minimum_eden_size, "just checking");
    }
  
    char *eden_start = _virtual_space.low();
    char *from_start = eden_start + eden_size;
    char *to_start   = from_start + survivor_size;
    char *to_end     = to_start   + survivor_size;
  
    assert(to_end == _virtual_space.high(), "just checking");
    assert(Space::is_aligned(eden_start), "checking alignment");
    assert(Space::is_aligned(from_start), "checking alignment");
    assert(Space::is_aligned(to_start),   "checking alignment");
  
    MemRegion edenMR((HeapWord*)eden_start, (HeapWord*)from_start);
    MemRegion fromMR((HeapWord*)from_start, (HeapWord*)to_start);
    MemRegion toMR  ((HeapWord*)to_start, (HeapWord*)to_end);
  
    // A minimum eden size implies that there is a part of eden that
    // is being used and that affects the initialization of any
    // newly formed eden.
    bool live_in_eden = minimum_eden_size > 0;
  
    // If not clearing the spaces, do some checking to verify that
    // the space are already mangled.
    if (!clear_space) {
      // Must check mangling before the spaces are reshaped.  Otherwise,
      // the bottom or end of one space may have moved into another
      // a failure of the check may not correctly indicate which space
      // is not properly mangled.
      if (ZapUnusedHeapArea) {
        HeapWord* limit = (HeapWord*) _virtual_space.high();
        eden()->check_mangled_unused_area(limit);
        from()->check_mangled_unused_area(limit);
          to()->check_mangled_unused_area(limit);
      }
    }
  
    // Reset the spaces for their new regions.
    eden()->initialize(edenMR,
                       clear_space && !live_in_eden,
                       SpaceDecorator::Mangle);
    // If clear_space and live_in_eden, we will not have cleared any
    // portion of eden above its top. This can cause newly
    // expanded space not to be mangled if using ZapUnusedHeapArea.
    // We explicitly do such mangling here.
    if (ZapUnusedHeapArea && clear_space && live_in_eden && mangle_space) {
      eden()->mangle_unused_area();
    }
    from()->initialize(fromMR, clear_space, mangle_space);
    to()->initialize(toMR, clear_space, mangle_space);
  
    // Set next compaction spaces.
    eden()->set_next_compaction_space(from());
    // The to-space is normally empty before a compaction so need
    // not be considered.  The exception is during promotion
    // failure handling when to-space can contain live objects.
    from()->set_next_compaction_space(NULL);
  }
  
  void DefNewGeneration::swap_spaces() {
    ContiguousSpace* s = from();
    _from_space        = to();
    _to_space          = s;
    eden()->set_next_compaction_space(from());
    // The to-space is normally empty before a compaction so need
    // not be considered.  The exception is during promotion
    // failure handling when to-space can contain live objects.
    from()->set_next_compaction_space(NULL);
  
    if (UsePerfData) {
      CSpaceCounters* c = _from_counters;
      _from_counters = _to_counters;
      _to_counters = c;
    }
  }
  
  bool DefNewGeneration::expand(size_t bytes) {
    MutexLocker x(ExpandHeap_lock);
    HeapWord* prev_high = (HeapWord*) _virtual_space.high();
    bool success = _virtual_space.expand_by(bytes);
    if (success && ZapUnusedHeapArea) {
      // Mangle newly committed space immediately because it
      // can be done here more simply that after the new
      // spaces have been computed.
      HeapWord* new_high = (HeapWord*) _virtual_space.high();
      MemRegion mangle_region(prev_high, new_high);
      SpaceMangler::mangle_region(mangle_region);
    }
  
    // Do not attempt an expand-to-the reserve size.  The
    // request should properly observe the maximum size of
    // the generation so an expand-to-reserve should be
    // unnecessary.  Also a second call to expand-to-reserve
    // value potentially can cause an undue expansion.
    // For example if the first expand fail for unknown reasons,
    // but the second succeeds and expands the heap to its maximum
    // value.
    if (GCLocker::is_active()) {
      log_debug(gc)("Garbage collection disabled, expanded heap instead");
    }
  
    return success;
  }
  
  size_t DefNewGeneration::adjust_for_thread_increase(size_t new_size_candidate,
                                                      size_t new_size_before,
                                                      size_t alignment) const {
    size_t desired_new_size = new_size_before;
  
    if (NewSizeThreadIncrease > 0) {
      int threads_count;
      size_t thread_increase_size = 0;
  
      // 1. Check an overflow at 'threads_count * NewSizeThreadIncrease'.
      threads_count = Threads::number_of_non_daemon_threads();
      if (threads_count > 0 && NewSizeThreadIncrease <= max_uintx / threads_count) {
        thread_increase_size = threads_count * NewSizeThreadIncrease;
  
        // 2. Check an overflow at 'new_size_candidate + thread_increase_size'.
        if (new_size_candidate <= max_uintx - thread_increase_size) {
          new_size_candidate += thread_increase_size;
  
          // 3. Check an overflow at 'align_up'.
          size_t aligned_max = ((max_uintx - alignment) & ~(alignment-1));
          if (new_size_candidate <= aligned_max) {
            desired_new_size = align_up(new_size_candidate, alignment);
          }
        }
      }
    }
  
    return desired_new_size;
  }
  
  void DefNewGeneration::compute_new_size() {
    // This is called after a GC that includes the old generation, so from-space
    // will normally be empty.
    // Note that we check both spaces, since if scavenge failed they revert roles.
    // If not we bail out (otherwise we would have to relocate the objects).
    if (!from()->is_empty() || !to()->is_empty()) {
      return;
    }
  
    GenCollectedHeap* gch = GenCollectedHeap::heap();
  
    size_t old_size = gch->old_gen()->capacity();
    size_t new_size_before = _virtual_space.committed_size();
    size_t min_new_size = initial_size();
    size_t max_new_size = reserved().byte_size();
    assert(min_new_size <= new_size_before &&
           new_size_before <= max_new_size,
           "just checking");
    // All space sizes must be multiples of Generation::GenGrain.
    size_t alignment = Generation::GenGrain;
  
    int threads_count = 0;
    size_t thread_increase_size = 0;
  
    size_t new_size_candidate = old_size / NewRatio;
    // Compute desired new generation size based on NewRatio and NewSizeThreadIncrease
    // and reverts to previous value if any overflow happens
    size_t desired_new_size = adjust_for_thread_increase(new_size_candidate, new_size_before, alignment);
  
    // Adjust new generation size
    desired_new_size = MAX2(MIN2(desired_new_size, max_new_size), min_new_size);
    assert(desired_new_size <= max_new_size, "just checking");
  
    bool changed = false;
    if (desired_new_size > new_size_before) {
      size_t change = desired_new_size - new_size_before;
      assert(change % alignment == 0, "just checking");
      if (expand(change)) {
         changed = true;
      }
      // If the heap failed to expand to the desired size,
      // "changed" will be false.  If the expansion failed
      // (and at this point it was expected to succeed),
      // ignore the failure (leaving "changed" as false).
    }
    if (desired_new_size < new_size_before && eden()->is_empty()) {
      // bail out of shrinking if objects in eden
      size_t change = new_size_before - desired_new_size;
      assert(change % alignment == 0, "just checking");
      _virtual_space.shrink_by(change);
      changed = true;
    }
    if (changed) {
      // The spaces have already been mangled at this point but
      // may not have been cleared (set top = bottom) and should be.
      // Mangling was done when the heap was being expanded.
      compute_space_boundaries(eden()->used(),
                               SpaceDecorator::Clear,
                               SpaceDecorator::DontMangle);
      MemRegion cmr((HeapWord*)_virtual_space.low(),
                    (HeapWord*)_virtual_space.high());
      gch->rem_set()->resize_covered_region(cmr);
  
      log_debug(gc, ergo, heap)(
          "New generation size " SIZE_FORMAT "K->" SIZE_FORMAT "K [eden=" SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
          new_size_before/K, _virtual_space.committed_size()/K,
          eden()->capacity()/K, from()->capacity()/K);
      log_trace(gc, ergo, heap)(
          "  [allowed " SIZE_FORMAT "K extra for %d threads]",
            thread_increase_size/K, threads_count);
        }
  }
  
  void DefNewGeneration::younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) {
    assert(false, "NYI -- are you sure you want to call this?");
  }
  
  
  size_t DefNewGeneration::capacity() const {
    return eden()->capacity()
         + from()->capacity();  // to() is only used during scavenge
  }
  
  
  size_t DefNewGeneration::used() const {
    return eden()->used()
         + from()->used();      // to() is only used during scavenge
  }
  
  
  size_t DefNewGeneration::free() const {
    return eden()->free()
         + from()->free();      // to() is only used during scavenge
  }
  
  size_t DefNewGeneration::max_capacity() const {
    const size_t alignment = GenCollectedHeap::heap()->collector_policy()->space_alignment();
    const size_t reserved_bytes = reserved().byte_size();
    return reserved_bytes - compute_survivor_size(reserved_bytes, alignment);
  }
  
  size_t DefNewGeneration::unsafe_max_alloc_nogc() const {
    return eden()->free();
  }
  
  size_t DefNewGeneration::capacity_before_gc() const {
    return eden()->capacity();
  }
  
  size_t DefNewGeneration::contiguous_available() const {
    return eden()->free();
  }
  
  
  HeapWord* volatile* DefNewGeneration::top_addr() const { return eden()->top_addr(); }
  HeapWord** DefNewGeneration::end_addr() const { return eden()->end_addr(); }
  
  void DefNewGeneration::object_iterate(ObjectClosure* blk) {
    eden()->object_iterate(blk);
    from()->object_iterate(blk);
  }
  
  
  void DefNewGeneration::space_iterate(SpaceClosure* blk,
                                       bool usedOnly) {
    blk->do_space(eden());
    blk->do_space(from());
    blk->do_space(to());
  }
  
  // The last collection bailed out, we are running out of heap space,
  // so we try to allocate the from-space, too.
  HeapWord* DefNewGeneration::allocate_from_space(size_t size) {
    bool should_try_alloc = should_allocate_from_space() || GCLocker::is_active_and_needs_gc();
  
    // If the Heap_lock is not locked by this thread, this will be called
    // again later with the Heap_lock held.
    bool do_alloc = should_try_alloc && (Heap_lock->owned_by_self() || (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()));
  
    HeapWord* result = NULL;
    if (do_alloc) {
      result = from()->allocate(size);
    }
  
    log_trace(gc, alloc)("DefNewGeneration::allocate_from_space(" SIZE_FORMAT "):  will_fail: %s  heap_lock: %s  free: " SIZE_FORMAT "%s%s returns %s",
                          size,
                          GenCollectedHeap::heap()->incremental_collection_will_fail(false /* don't consult_young */) ?
                            "true" : "false",
                          Heap_lock->is_locked() ? "locked" : "unlocked",
                          from()->free(),
                          should_try_alloc ? "" : "  should_allocate_from_space: NOT",
                          do_alloc ? "  Heap_lock is not owned by self" : "",
                          result == NULL ? "NULL" : "object");
  
    return result;
  }
  
  HeapWord* DefNewGeneration::expand_and_allocate(size_t size,
                                                  bool   is_tlab,
                                                  bool   parallel) {
    // We don't attempt to expand the young generation (but perhaps we should.)
    return allocate(size, is_tlab);
  }
  
  void DefNewGeneration::adjust_desired_tenuring_threshold() {
    // Set the desired survivor size to half the real survivor space
    size_t const survivor_capacity = to()->capacity() / HeapWordSize;
    size_t const desired_survivor_size = (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
  
    _tenuring_threshold = age_table()->compute_tenuring_threshold(desired_survivor_size);
  
    if (UsePerfData) {
      GCPolicyCounters* gc_counters = GenCollectedHeap::heap()->counters();
      gc_counters->tenuring_threshold()->set_value(_tenuring_threshold);
      gc_counters->desired_survivor_size()->set_value(desired_survivor_size * oopSize);
    }
  
    age_table()->print_age_table(_tenuring_threshold);
  }
  
  void DefNewGeneration::collect(bool   full,
                                 bool   clear_all_soft_refs,
                                 size_t size,
                                 bool   is_tlab) {
    assert(full || size > 0, "otherwise we don't want to collect");
  
    SerialHeap* heap = SerialHeap::heap();
  
    _gc_timer->register_gc_start();
    DefNewTracer gc_tracer;
    gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer->gc_start());
  
    _old_gen = heap->old_gen();
  
    // If the next generation is too full to accommodate promotion
    // from this generation, pass on collection; let the next generation
    // do it.
    if (!collection_attempt_is_safe()) {
      log_trace(gc)(":: Collection attempt not safe ::");
      heap->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
      return;
    }
    assert(to()->is_empty(), "Else not collection_attempt_is_safe");
  
    init_assuming_no_promotion_failure();
  
    GCTraceTime(Trace, gc, phases) tm("DefNew", NULL, heap->gc_cause());
  
    heap->trace_heap_before_gc(&gc_tracer);
  
    // These can be shared for all code paths
    IsAliveClosure is_alive(this);
    ScanWeakRefClosure scan_weak_ref(this);
  
    age_table()->clear();
    to()->clear(SpaceDecorator::Mangle);
    // The preserved marks should be empty at the start of the GC.
    _preserved_marks_set.init(1);
  
    heap->rem_set()->prepare_for_younger_refs_iterate(false);
  
    assert(heap->no_allocs_since_save_marks(),
           "save marks have not been newly set.");
  
    FastScanClosure fsc_with_no_gc_barrier(this, false);
    FastScanClosure fsc_with_gc_barrier(this, true);
  
    CLDScanClosure cld_scan_closure(&fsc_with_no_gc_barrier,
                                    heap->rem_set()->cld_rem_set()->accumulate_modified_oops());
  
    set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
    FastEvacuateFollowersClosure evacuate_followers(heap,
                                                    &fsc_with_no_gc_barrier,
                                                    &fsc_with_gc_barrier);
  
    assert(heap->no_allocs_since_save_marks(),
           "save marks have not been newly set.");
  
    {
      // DefNew needs to run with n_threads == 0, to make sure the serial
      // version of the card table scanning code is used.
      // See: CardTableRS::non_clean_card_iterate_possibly_parallel.
      StrongRootsScope srs(0);
  
      heap->young_process_roots(&srs,
                                &fsc_with_no_gc_barrier,
                                &fsc_with_gc_barrier,
                                &cld_scan_closure);
    }
  
    // "evacuate followers".
    evacuate_followers.do_void();
  
    FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
    ReferenceProcessor* rp = ref_processor();
    rp->setup_policy(clear_all_soft_refs);
    ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());
    const ReferenceProcessorStats& stats =
    rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
                                      NULL, &pt);
    gc_tracer.report_gc_reference_stats(stats);
    gc_tracer.report_tenuring_threshold(tenuring_threshold());
    pt.print_all_references();
  
    assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
  
    WeakProcessor::weak_oops_do(&is_alive, &keep_alive);
  
    // Verify that the usage of keep_alive didn't copy any objects.
    assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
  
    if (!_promotion_failed) {
      // Swap the survivor spaces.
      eden()->clear(SpaceDecorator::Mangle);
      from()->clear(SpaceDecorator::Mangle);
      if (ZapUnusedHeapArea) {
        // This is now done here because of the piece-meal mangling which
        // can check for valid mangling at intermediate points in the
        // collection(s).  When a young collection fails to collect
        // sufficient space resizing of the young generation can occur
        // an redistribute the spaces in the young generation.  Mangle
        // here so that unzapped regions don't get distributed to
        // other spaces.
        to()->mangle_unused_area();
      }
      swap_spaces();
  
      assert(to()->is_empty(), "to space should be empty now");
  
      adjust_desired_tenuring_threshold();
  
      // A successful scavenge should restart the GC time limit count which is
      // for full GC's.
      AdaptiveSizePolicy* size_policy = heap->size_policy();
      size_policy->reset_gc_overhead_limit_count();
      assert(!heap->incremental_collection_failed(), "Should be clear");
    } else {
      assert(_promo_failure_scan_stack.is_empty(), "post condition");
      _promo_failure_scan_stack.clear(true); // Clear cached segments.
  
      remove_forwarding_pointers();
      log_info(gc, promotion)("Promotion failed");
      // Add to-space to the list of space to compact
      // when a promotion failure has occurred.  In that
      // case there can be live objects in to-space
      // as a result of a partial evacuation of eden
      // and from-space.
      swap_spaces();   // For uniformity wrt ParNewGeneration.
      from()->set_next_compaction_space(to());
      heap->set_incremental_collection_failed();
  
      // Inform the next generation that a promotion failure occurred.
      _old_gen->promotion_failure_occurred();
      gc_tracer.report_promotion_failed(_promotion_failed_info);
  
      // Reset the PromotionFailureALot counters.
      NOT_PRODUCT(heap->reset_promotion_should_fail();)
    }
    // We should have processed and cleared all the preserved marks.
    _preserved_marks_set.reclaim();
    // set new iteration safe limit for the survivor spaces
    from()->set_concurrent_iteration_safe_limit(from()->top());
    to()->set_concurrent_iteration_safe_limit(to()->top());
  
    // We need to use a monotonically non-decreasing time in ms
    // or we will see time-warp warnings and os::javaTimeMillis()
    // does not guarantee monotonicity.
    jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
    update_time_of_last_gc(now);
  
    heap->trace_heap_after_gc(&gc_tracer);
  
    _gc_timer->register_gc_end();
  
    gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
  }
  
  void DefNewGeneration::init_assuming_no_promotion_failure() {
    _promotion_failed = false;
    _promotion_failed_info.reset();
    from()->set_next_compaction_space(NULL);
  }
  
  void DefNewGeneration::remove_forwarding_pointers() {
    RemoveForwardedPointerClosure rspc;
    eden()->object_iterate(&rspc);
    from()->object_iterate(&rspc);
    restore_preserved_marks();
  }
  
  void DefNewGeneration::restore_preserved_marks() {
    SharedRestorePreservedMarksTaskExecutor task_executor(NULL);
    _preserved_marks_set.restore(&task_executor);
  }
  
  void DefNewGeneration::handle_promotion_failure(oop old) {
    log_debug(gc, promotion)("Promotion failure size = %d) ", old->size());
  
    _promotion_failed = true;
    _promotion_failed_info.register_copy_failure(old->size());
    _preserved_marks_set.get()->push_if_necessary(old, old->mark_raw());
    // forward to self
    old->forward_to(old);
  
    _promo_failure_scan_stack.push(old);
  
    if (!_promo_failure_drain_in_progress) {
      // prevent recursion in copy_to_survivor_space()
      _promo_failure_drain_in_progress = true;
      drain_promo_failure_scan_stack();
      _promo_failure_drain_in_progress = false;
    }
  }
  
  oop DefNewGeneration::copy_to_survivor_space(oop old) {
    assert(is_in_reserved(old) && !old->is_forwarded(),
           "shouldn't be scavenging this oop");
    size_t s = old->size();
    oop obj = NULL;
  
    // Try allocating obj in to-space (unless too old)
    if (old->age() < tenuring_threshold()) {
      obj = (oop) to()->allocate_aligned(s);
    }
  
    // Otherwise try allocating obj tenured
    if (obj == NULL) {
      obj = _old_gen->promote(old, s);
      if (obj == NULL) {
        handle_promotion_failure(old);
        return old;
      }
    } else {
      // Prefetch beyond obj
      const intx interval = PrefetchCopyIntervalInBytes;
      Prefetch::write(obj, interval);
  
      // Copy obj
      Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)obj, s);
  
      // Increment age if obj still in new generation
      obj->incr_age();
      age_table()->add(obj, s);
    }
  
    // Done, insert forward pointer to obj in this header
    old->forward_to(obj);
  
    return obj;
  }
  
  void DefNewGeneration::drain_promo_failure_scan_stack() {
    while (!_promo_failure_scan_stack.is_empty()) {
       oop obj = _promo_failure_scan_stack.pop();
       obj->oop_iterate(_promo_failure_scan_stack_closure);
    }
  }
  
  void DefNewGeneration::save_marks() {
    eden()->set_saved_mark();
    to()->set_saved_mark();
    from()->set_saved_mark();
  }
  
  
  void DefNewGeneration::reset_saved_marks() {
    eden()->reset_saved_mark();
    to()->reset_saved_mark();
    from()->reset_saved_mark();
  }
  
  
  bool DefNewGeneration::no_allocs_since_save_marks() {
    assert(eden()->saved_mark_at_top(), "Violated spec - alloc in eden");
    assert(from()->saved_mark_at_top(), "Violated spec - alloc in from");
    return to()->saved_mark_at_top();
  }
  
  void DefNewGeneration::contribute_scratch(ScratchBlock*& list, Generation* requestor,
                                           size_t max_alloc_words) {
    if (requestor == this || _promotion_failed) {
      return;
    }
    assert(GenCollectedHeap::heap()->is_old_gen(requestor), "We should not call our own generation");
  
    /* $$$ Assert this?  "trace" is a "MarkSweep" function so that's not appropriate.
    if (to_space->top() > to_space->bottom()) {
      trace("to_space not empty when contribute_scratch called");
    }
    */
  
    ContiguousSpace* to_space = to();
    assert(to_space->end() >= to_space->top(), "pointers out of order");
    size_t free_words = pointer_delta(to_space->end(), to_space->top());
    if (free_words >= MinFreeScratchWords) {
      ScratchBlock* sb = (ScratchBlock*)to_space->top();
      sb->num_words = free_words;
      sb->next = list;
      list = sb;
    }
  }
  
  void DefNewGeneration::reset_scratch() {
    // If contributing scratch in to_space, mangle all of
    // to_space if ZapUnusedHeapArea.  This is needed because
    // top is not maintained while using to-space as scratch.
    if (ZapUnusedHeapArea) {
      to()->mangle_unused_area_complete();
    }
  }
  
  bool DefNewGeneration::collection_attempt_is_safe() {
    if (!to()->is_empty()) {
      log_trace(gc)(":: to is not empty ::");
      return false;
    }
    if (_old_gen == NULL) {
      GenCollectedHeap* gch = GenCollectedHeap::heap();
      _old_gen = gch->old_gen();
    }
    return _old_gen->promotion_attempt_is_safe(used());
  }
  
  void DefNewGeneration::gc_epilogue(bool full) {
    DEBUG_ONLY(static bool seen_incremental_collection_failed = false;)
  
    assert(!GCLocker::is_active(), "We should not be executing here");
    // Check if the heap is approaching full after a collection has
    // been done.  Generally the young generation is empty at
    // a minimum at the end of a collection.  If it is not, then
    // the heap is approaching full.
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    if (full) {
      DEBUG_ONLY(seen_incremental_collection_failed = false;)
      if (!collection_attempt_is_safe() && !_eden_space->is_empty()) {
        log_trace(gc)("DefNewEpilogue: cause(%s), full, not safe, set_failed, set_alloc_from, clear_seen",
                              GCCause::to_string(gch->gc_cause()));
        gch->set_incremental_collection_failed(); // Slight lie: a full gc left us in that state
        set_should_allocate_from_space(); // we seem to be running out of space
      } else {
        log_trace(gc)("DefNewEpilogue: cause(%s), full, safe, clear_failed, clear_alloc_from, clear_seen",
                              GCCause::to_string(gch->gc_cause()));
        gch->clear_incremental_collection_failed(); // We just did a full collection
        clear_should_allocate_from_space(); // if set
      }
    } else {
  #ifdef ASSERT
      // It is possible that incremental_collection_failed() == true
      // here, because an attempted scavenge did not succeed. The policy
      // is normally expected to cause a full collection which should
      // clear that condition, so we should not be here twice in a row
      // with incremental_collection_failed() == true without having done
      // a full collection in between.
      if (!seen_incremental_collection_failed &&
          gch->incremental_collection_failed()) {
        log_trace(gc)("DefNewEpilogue: cause(%s), not full, not_seen_failed, failed, set_seen_failed",
                              GCCause::to_string(gch->gc_cause()));
        seen_incremental_collection_failed = true;
      } else if (seen_incremental_collection_failed) {
        log_trace(gc)("DefNewEpilogue: cause(%s), not full, seen_failed, will_clear_seen_failed",
                              GCCause::to_string(gch->gc_cause()));
        assert(gch->gc_cause() == GCCause::_scavenge_alot ||
               (GCCause::is_user_requested_gc(gch->gc_cause()) && UseConcMarkSweepGC && ExplicitGCInvokesConcurrent) ||
               !gch->incremental_collection_failed(),
               "Twice in a row");
        seen_incremental_collection_failed = false;
      }
  #endif // ASSERT
    }
  
    if (ZapUnusedHeapArea) {
      eden()->check_mangled_unused_area_complete();
      from()->check_mangled_unused_area_complete();
      to()->check_mangled_unused_area_complete();
    }
  
    if (!CleanChunkPoolAsync) {
      Chunk::clean_chunk_pool();
    }
  
    // update the generation and space performance counters
    update_counters();
    gch->counters()->update_counters();
  }
  
  void DefNewGeneration::record_spaces_top() {
    assert(ZapUnusedHeapArea, "Not mangling unused space");
    eden()->set_top_for_allocations();
    to()->set_top_for_allocations();
    from()->set_top_for_allocations();
  }
  
  void DefNewGeneration::ref_processor_init() {
    Generation::ref_processor_init();
  }
  
  
  void DefNewGeneration::update_counters() {
    if (UsePerfData) {
      _eden_counters->update_all();
      _from_counters->update_all();
      _to_counters->update_all();
      _gen_counters->update_all();
    }
  }
  
  void DefNewGeneration::verify() {
    eden()->verify();
    from()->verify();
      to()->verify();
  }
  
  void DefNewGeneration::print_on(outputStream* st) const {
    Generation::print_on(st);
    st->print("  eden");
    eden()->print_on(st);
    st->print("  from");
    from()->print_on(st);
    st->print("  to  ");
    to()->print_on(st);
  }
  
  
  const char* DefNewGeneration::name() const {
    return "def new generation";
  }
  
  // Moved from inline file as they are not called inline
  CompactibleSpace* DefNewGeneration::first_compaction_space() const {
    return eden();
  }
  
  HeapWord* DefNewGeneration::allocate(size_t word_size, bool is_tlab) {
    // This is the slow-path allocation for the DefNewGeneration.
    // Most allocations are fast-path in compiled code.
    // We try to allocate from the eden.  If that works, we are happy.
    // Note that since DefNewGeneration supports lock-free allocation, we
    // have to use it here, as well.
    HeapWord* result = eden()->par_allocate(word_size);
    if (result != NULL) {
      if (_old_gen != NULL) {
        _old_gen->sample_eden_chunk();
      }
    } else {
      // If the eden is full and the last collection bailed out, we are running
      // out of heap space, and we try to allocate the from-space, too.
      // allocate_from_space can't be inlined because that would introduce a
      // circular dependency at compile time.
      result = allocate_from_space(word_size);
    }
    return result;
  }
  
  HeapWord* DefNewGeneration::par_allocate(size_t word_size,
                                           bool is_tlab) {
    HeapWord* res = eden()->par_allocate(word_size);
    if (_old_gen != NULL) {
      _old_gen->sample_eden_chunk();
    }
    return res;
  }
  
  size_t DefNewGeneration::tlab_capacity() const {
    return eden()->capacity();
  }
  
  size_t DefNewGeneration::tlab_used() const {
    return eden()->used();
  }
  
  size_t DefNewGeneration::unsafe_max_tlab_alloc() const {
    return unsafe_max_alloc_nogc();
  }
  