src/hotspot/share/gc/parallel/psPromotionLAB.cpp

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#include "gc/parallel/mutableSpace.hpp"
#include "gc/parallel/parallelScavengeHeap.hpp"
#include "gc/parallel/psPromotionLAB.hpp"
#include "memory/universe.hpp"
#include "oops/oop.inline.hpp"

// This is the shared initialization code. It sets up the basic pointers,
// and allows enough extra space for a filler object. We call a virtual
// method, "lab_is_valid()" to handle the different asserts the old/young
// labs require.
void PSPromotionLAB::initialize(MemRegion lab) {
  assert(lab_is_valid(lab), "Sanity");

  HeapWord* bottom = lab.start();
  HeapWord* end    = lab.end();

  set_bottom(bottom);
  set_end(end);
  set_top(bottom);

  // We can be initialized to a zero size!
  if (free() > 0) {
    if (ZapUnusedHeapArea) {
      DEBUG_ONLY(Copy::fill_to_words(top(), free()/HeapWordSize, badHeapWord));
    }

    // NOTE! We need to allow space for a filler object.
    assert(lab.word_size() >= CollectedHeap::min_dummy_object_size(), "lab is too small");
    end = end - CollectedHeap::min_dummy_object_size();
    set_end(end);

    _state = needs_flush;
  } else {
    _state = zero_size;
  }

  assert(this->top() <= this->end(), "pointers out of order");
}

// Fill all remaining lab space with an unreachable object.
// The goal is to leave a contiguous parseable span of objects.
void PSPromotionLAB::flush() {
  assert(_state != flushed, "Attempt to flush PLAB twice");
  assert(top() <= end(), "pointers out of order");

  // If we were initialized to a zero sized lab, there is
  // nothing to flush
  if (_state == zero_size)
    return;

  // PLAB's never allocate the last aligned_header_size
  // so they can always fill with an array.
  HeapWord* tlab_end = end() + CollectedHeap::min_dummy_object_size();
  CollectedHeap::fill_with_object(top(), tlab_end, trueInDebug);

  set_bottom(nullptr);
  set_end(nullptr);
  set_top(nullptr);

  _state = flushed;
}

void PSPromotionLAB::unallocate_object(HeapWord* obj, size_t obj_size) {
  assert(ParallelScavengeHeap::heap()->is_in(obj), "Object outside heap");

  // If the object is inside this LAB, we just bump-down the `top` pointer.
  // Otherwise, we overwrite it with a filler object.
  if (contains(obj)) {
    HeapWord* object_end = obj + obj_size;
    assert(object_end == top(), "Not matching last allocation");

    set_top(obj);
  } else {
    CollectedHeap::fill_with_object(obj, obj_size);
  }
}

// Fill all remaining lab space with an unreachable object.
// The goal is to leave a contiguous parseable span of objects.
void PSOldPromotionLAB::flush() {
  assert(_state != flushed, "Attempt to flush PLAB twice");
  assert(top() <= end(), "pointers out of order");

  if (_state == zero_size)
    return;

  HeapWord* obj = top();

  PSPromotionLAB::flush();

  assert(_start_array != nullptr, "Sanity");

  // filler obj
  _start_array->update_for_block(obj, obj + cast_to_oop(obj)->size());
}

#ifdef ASSERT

bool PSYoungPromotionLAB::lab_is_valid(MemRegion lab) {
  ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  MutableSpace* to_space = heap->young_gen()->to_space();
  MemRegion used = to_space->used_region();
  if (used.contains(lab)) {
    return true;
  }

  return false;
}

bool PSOldPromotionLAB::lab_is_valid(MemRegion lab) {
  ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  PSOldGen* old_gen = heap->old_gen();
  MemRegion used = old_gen->object_space()->used_region();

  return used.contains(lab);
}

#endif /* ASSERT */