C++ eden函数代码示例

void DefNewGeneration::gc_epilogue(bool full) {
  // 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();
  clear_should_allocate_from_space();
  if (collection_attempt_is_safe()) {
    gch->clear_incremental_collection_will_fail();
  } else {
    gch->set_incremental_collection_will_fail();
    if (full) { // we seem to be running out of space
      set_should_allocate_from_space();
    }
  }

  if (ZapUnusedHeapArea) {
    eden()->check_mangled_unused_area_complete();
    from()->check_mangled_unused_area_complete();
    to()->check_mangled_unused_area_complete();
  }

  // update the generation and space performance counters
  update_counters();
  gch->collector_policy()->counters()->update_counters();
}

void DefNewGeneration::space_iterate(SpaceClosure* blk,
				     bool usedOnly) {
  blk->do_space(eden());
  blk->do_space(from());
  if (!usedOnly)
    blk->do_space(to());
}

HeapWord* DefNewGeneration::allocate(size_t word_size,
                                     bool is_large_noref,
                                     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) {
    // Tell the next generation we reached a limit.
    HeapWord* new_limit = 
      next_gen()->allocation_limit_reached(eden(), eden()->top(), word_size);
    if (new_limit != NULL) {
      eden()->set_soft_end(new_limit);
      result = eden()->par_allocate(word_size);
    } else {
      assert(eden()->soft_end() == eden()->end(),
	     "invalid state after allocation_limit_reached returned null")
    }

    // 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.
    if (result == NULL) {
      result = allocate_from_space(word_size);
    }
  }

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);
}

int DefNewGeneration::addr_to_arena_id(void* addr) {
  if (eden()->contains(addr)) return 0;
  if (from()->contains(addr)) {
    return (from()->bottom() < to()->bottom()) ? 1 : 2;
  }
  if (to()->contains(addr)) {
    return (from()->bottom() < to()->bottom()) ? 2 : 1;
  }
  // Otherwise...
  return -3;
}

void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size) {
  // All space sizes must be multiples of car size in order for the CarTable to work.
  // Note that the CarTable is used with and without train gc (for fast lookup).
  uintx alignment = CarSpace::car_size();

  // 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_size_up(minimum_eden_size, alignment);
    uintx maximum_survivor_size = (size - minimum_eden_size) / 2;
    uintx unaligned_survivor_size = 
      align_size_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((HeapWord*)eden_start), "checking alignment");
  assert(Space::is_aligned((HeapWord*)from_start), "checking alignment");
  assert(Space::is_aligned((HeapWord*)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);

  eden()->initialize(edenMR, (minimum_eden_size == 0));
  from()->initialize(fromMR, true);
    to()->initialize(toMR  , true);

  if (jvmpi::is_event_enabled(JVMPI_EVENT_ARENA_NEW)) {
    CollectedHeap* ch = Universe::heap();
    jvmpi::post_arena_new_event(ch->addr_to_arena_id(eden_start), "Eden");
    jvmpi::post_arena_new_event(ch->addr_to_arena_id(from_start), "Semi");
    jvmpi::post_arena_new_event(ch->addr_to_arena_id(to_start), "Semi");
  }
}

void DefNewGeneration::remove_forwarding_pointers() {
  RemoveForwardPointerClosure rspc;
  eden()->object_iterate(&rspc);
  from()->object_iterate(&rspc);

  // Now restore saved marks, if any.
  assert(_objs_with_preserved_marks.size() == _preserved_marks_of_objs.size(),
         "should be the same");
  while (!_objs_with_preserved_marks.is_empty()) {
    oop obj   = _objs_with_preserved_marks.pop();
    markOop m = _preserved_marks_of_objs.pop();
    obj->set_mark(m);
  }
  _objs_with_preserved_marks.clear(true);
  _preserved_marks_of_objs.clear(true);
}

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;
  }
}

int main()
{
    world odd;
    world even;
    int i;
    init(odd);
    init(even);
    eden(even);
// simulation
    for (i = 0; i < CYCLES; ++i) {
        if ((i % 2)) {
            update(even,odd);
            dele(odd);
        }
        else {
            update(odd,even);
            dele(even);
        }
    }
}

void DefNewGeneration::compute_new_size() {
  // This is called after a gc that includes the following generation
  // (which is required to exist.)  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;
  }

  int next_level = level() + 1;
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  assert(next_level < gch->_n_gens,
         "DefNewGeneration cannot be an oldest gen");

  Generation* next_gen = gch->_gens[next_level];
  size_t old_size = next_gen->capacity();
  size_t new_size_before = _virtual_space.committed_size();
  size_t min_new_size = spec()->init_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;

  // Compute desired new generation size based on NewRatio and
  // NewSizeThreadIncrease
  size_t desired_new_size = old_size/NewRatio;
  int threads_count = Threads::number_of_non_daemon_threads();
  size_t thread_increase_size = threads_count * NewSizeThreadIncrease;
  desired_new_size = align_size_up(desired_new_size + thread_increase_size, 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());
    Universe::heap()->barrier_set()->resize_covered_region(cmr);
    if (Verbose && PrintGC) {
      size_t new_size_after  = _virtual_space.committed_size();
      size_t eden_size_after = eden()->capacity();
      size_t survivor_size_after = from()->capacity();
      gclog_or_tty->print("New generation size " SIZE_FORMAT "K->"
        SIZE_FORMAT "K [eden="
        SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
        new_size_before/K, new_size_after/K,
        eden_size_after/K, survivor_size_after/K);
      if (WizardMode) {
        gclog_or_tty->print("[allowed " SIZE_FORMAT "K extra for %d threads]",
          thread_increase_size/K, threads_count);
      }
      gclog_or_tty->cr();
    }
  }
}

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_size_up(minimum_eden_size, alignment);
    uintx maximum_survivor_size = (size - minimum_eden_size) / 2;
    uintx unaligned_survivor_size =
      align_size_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((HeapWord*)eden_start), "checking alignment");
  assert(Space::is_aligned((HeapWord*)from_start), "checking alignment");
  assert(Space::is_aligned((HeapWord*)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::record_spaces_top() {
  assert(ZapUnusedHeapArea, "Not mangling unused space");
  eden()->set_top_for_allocations();
  to()->set_top_for_allocations();
  from()->set_top_for_allocations();
}