C++ GenCollectedHeap::barrier_set方法代码示例

DefNewGeneration::DefNewGeneration(ReservedSpace rs,
                                   size_t initial_size,
                                   const char* policy)
  : Generation(rs, initial_size),
    _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->barrier_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_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;

  // 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());
    gch->barrier_set()->resize_covered_region(cmr);

    log_debug(gc, heap, ergo)(
        "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, heap, ergo)(
        "  [allowed " SIZE_FORMAT "K extra for %d threads]",
          thread_increase_size/K, threads_count);
      }
}