// This method currently does not expect to expand into eden (i.e.,
// the virtual space boundaries is expected to be consistent
// with the eden boundaries..
void PSYoungGen::post_resize() {
  assert_locked_or_safepoint(Heap_lock);
  assert((eden_space()->bottom() < to_space()->bottom()) &&
         (eden_space()->bottom() < from_space()->bottom()),
         "Eden is assumed to be below the survivor spaces");

  MemRegion cmr((HeapWord*)virtual_space()->low(),
                (HeapWord*)virtual_space()->high());
  Universe::heap()->barrier_set()->resize_covered_region(cmr);
  space_invariants();
}

void PSYoungGen::space_invariants() {
  ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  const size_t alignment = heap->intra_heap_alignment();

  // Currently, our eden size cannot shrink to zero
  guarantee(eden_space()->capacity_in_bytes() >= alignment, "eden too small");
  guarantee(from_space()->capacity_in_bytes() >= alignment, "from too small");
  guarantee(to_space()->capacity_in_bytes() >= alignment, "to too small");

  // Relationship of spaces to each other
  char* eden_start = (char*)eden_space()->bottom();
  char* eden_end   = (char*)eden_space()->end();
  char* from_start = (char*)from_space()->bottom();
  char* from_end   = (char*)from_space()->end();
  char* to_start   = (char*)to_space()->bottom();
  char* to_end     = (char*)to_space()->end();

  guarantee(eden_start >= virtual_space()->low(), "eden bottom");
  guarantee(eden_start < eden_end, "eden space consistency");
  guarantee(from_start < from_end, "from space consistency");
  guarantee(to_start < to_end, "to space consistency");

  // Check whether from space is below to space
  if (from_start < to_start) {
    // Eden, from, to
    guarantee(eden_end <= from_start, "eden/from boundary");
    guarantee(from_end <= to_start,   "from/to boundary");
    guarantee(to_end <= virtual_space()->high(), "to end");
  } else {
    // Eden, to, from
    guarantee(eden_end <= to_start, "eden/to boundary");
    guarantee(to_end <= from_start, "to/from boundary");
    guarantee(from_end <= virtual_space()->high(), "from end");
  }

  // More checks that the virtual space is consistent with the spaces
  assert(virtual_space()->committed_size() >=
    (eden_space()->capacity_in_bytes() +
     to_space()->capacity_in_bytes() +
     from_space()->capacity_in_bytes()), "Committed size is inconsistent");
  assert(virtual_space()->committed_size() <= virtual_space()->reserved_size(),
    "Space invariant");
  char* eden_top = (char*)eden_space()->top();
  char* from_top = (char*)from_space()->top();
  char* to_top = (char*)to_space()->top();
  assert(eden_top <= virtual_space()->high(), "eden top");
  assert(from_top <= virtual_space()->high(), "from top");
  assert(to_top <= virtual_space()->high(), "to top");

  virtual_space()->verify();
}

// The current implementation only considers to the end of eden.
// If to_space is below from_space, to_space is not considered.
// to_space can be.
size_t ASPSYoungGen::available_to_live() {
  ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  const size_t alignment = heap->intra_heap_alignment();

  // Include any space that is committed but is not in eden.
  size_t available = pointer_delta(eden_space()->bottom(),
                                   virtual_space()->low(),
                                   sizeof(char));

  const size_t eden_capacity = eden_space()->capacity_in_bytes();
  if (eden_space()->is_empty() && eden_capacity > alignment) {
    available += eden_capacity - alignment;
  }
  return available;
}

void PSYoungGen::set_space_boundaries(size_t eden_size, size_t survivor_size) {
  assert(eden_size < virtual_space()->committed_size(), "just checking");
  assert(eden_size > 0  && survivor_size > 0, "just checking");

  // Initial layout is Eden, to, from. After swapping survivor spaces,
  // that leaves us with Eden, from, to, which is step one in our two
  // step resize-with-live-data procedure.
  char *eden_start = virtual_space()->low();
  char *to_start   = eden_start + eden_size;
  char *from_start = to_start   + survivor_size;
  char *from_end   = from_start + survivor_size;

  assert(from_end == virtual_space()->high(), "just checking");
  assert(is_object_aligned((intptr_t)eden_start), "checking alignment");
  assert(is_object_aligned((intptr_t)to_start),   "checking alignment");
  assert(is_object_aligned((intptr_t)from_start), "checking alignment");

  MemRegion eden_mr((HeapWord*)eden_start, (HeapWord*)to_start);
  MemRegion to_mr  ((HeapWord*)to_start, (HeapWord*)from_start);
  MemRegion from_mr((HeapWord*)from_start, (HeapWord*)from_end);

  eden_space()->initialize(eden_mr, true, ZapUnusedHeapArea);
    to_space()->initialize(to_mr  , true, ZapUnusedHeapArea);
  from_space()->initialize(from_mr, true, ZapUnusedHeapArea);
}

// Return the number of bytes the young gen is willing give up.
//
// Future implementations could check the survivors and if to_space is in the
// right place (below from_space), take a chunk from to_space.
size_t ASPSYoungGen::available_for_contraction() {

  size_t uncommitted_bytes = virtual_space()->uncommitted_size();
  if (uncommitted_bytes != 0) {
    return uncommitted_bytes;
  }

  if (eden_space()->is_empty()) {
    // Respect the minimum size for eden and for the young gen as a whole.
    ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
    const size_t eden_alignment = heap->intra_heap_alignment();
    const size_t gen_alignment = heap->young_gen_alignment();

    assert(eden_space()->capacity_in_bytes() >= eden_alignment,
      "Alignment is wrong");
    size_t eden_avail = eden_space()->capacity_in_bytes() - eden_alignment;
    eden_avail = align_size_down(eden_avail, gen_alignment);

    assert(virtual_space()->committed_size() >= min_gen_size(),
      "minimum gen size is wrong");
    size_t gen_avail = virtual_space()->committed_size() - min_gen_size();
    assert(virtual_space()->is_aligned(gen_avail), "not aligned");

    const size_t max_contraction = MIN2(eden_avail, gen_avail);
    // See comment for ASPSOldGen::available_for_contraction()
    // for reasons the "increment" fraction is used.
    PSAdaptiveSizePolicy* policy = heap->size_policy();
    size_t result = policy->eden_increment_aligned_down(max_contraction);
    size_t result_aligned = align_size_down(result, gen_alignment);
    if (PrintAdaptiveSizePolicy && Verbose) {
      gclog_or_tty->print_cr("ASPSYoungGen::available_for_contraction: %d K",
        result_aligned/K);
      gclog_or_tty->print_cr("  max_contraction %d K", max_contraction/K);
      gclog_or_tty->print_cr("  eden_avail %d K", eden_avail/K);
      gclog_or_tty->print_cr("  gen_avail %d K", gen_avail/K);
    }
    return result_aligned;

  }

  return 0;
}

void PSYoungGen::print_on(outputStream* st) const {
  st->print(" %-15s", "PSYoungGen");
  if (PrintGCDetails && Verbose) {
    st->print(" total " SIZE_FORMAT ", used " SIZE_FORMAT,
               capacity_in_bytes(), used_in_bytes());
  } else {
    st->print(" total " SIZE_FORMAT "K, used " SIZE_FORMAT "K",
               capacity_in_bytes()/K, used_in_bytes()/K);
  }
  virtual_space()->print_space_boundaries_on(st);
  st->print("  eden"); eden_space()->print_on(st);
  st->print("  from"); from_space()->print_on(st);
  st->print("  to  "); to_space()->print_on(st);
}

PSHeapSummary ParallelScavengeHeap::create_ps_heap_summary() {
  PSOldGen* old = old_gen();
  HeapWord* old_committed_end = (HeapWord*)old->virtual_space()->committed_high_addr();
  VirtualSpaceSummary old_summary(old->reserved().start(), old_committed_end, old->reserved().end());
  SpaceSummary old_space(old->reserved().start(), old_committed_end, old->used_in_bytes());

  PSYoungGen* young = young_gen();
  VirtualSpaceSummary young_summary(young->reserved().start(),
    (HeapWord*)young->virtual_space()->committed_high_addr(), young->reserved().end());

  MutableSpace* eden = young_gen()->eden_space();
  SpaceSummary eden_space(eden->bottom(), eden->end(), eden->used_in_bytes());

  MutableSpace* from = young_gen()->from_space();
  SpaceSummary from_space(from->bottom(), from->end(), from->used_in_bytes());

  MutableSpace* to = young_gen()->to_space();
  SpaceSummary to_space(to->bottom(), to->end(), to->used_in_bytes());

  VirtualSpaceSummary heap_summary = create_heap_space_summary();
  return PSHeapSummary(heap_summary, used(), old_summary, old_space, young_summary, eden_space, from_space, to_space);
}

 // Allocation
 HeapWord* allocate(size_t word_size) {
   HeapWord* result = eden_space()->cas_allocate(word_size);
   return result;
 }

void PSYoungGen::verify() {
  eden_space()->verify();
  from_space()->verify();
  to_space()->verify();
}

void PSYoungGen::verify(bool allow_dirty) {
  eden_space()->verify(allow_dirty);
  from_space()->verify(allow_dirty);
  to_space()->verify(allow_dirty);
}

void ASPSYoungGen::resize_spaces(size_t requested_eden_size,
                                 size_t requested_survivor_size) {
  assert(UseAdaptiveSizePolicy, "sanity check");
  assert(requested_eden_size > 0 && requested_survivor_size > 0,
         "just checking");

  space_invariants();

  // We require eden and to space to be empty
  if ((!eden_space()->is_empty()) || (!to_space()->is_empty())) {
    return;
  }

  if (PrintAdaptiveSizePolicy && Verbose) {
    gclog_or_tty->print_cr("PSYoungGen::resize_spaces(requested_eden_size: "
                  SIZE_FORMAT
                  ", requested_survivor_size: " SIZE_FORMAT ")",
                  requested_eden_size, requested_survivor_size);
    gclog_or_tty->print_cr("    eden: [" PTR_FORMAT ".." PTR_FORMAT ") "
                  SIZE_FORMAT,
                  eden_space()->bottom(),
                  eden_space()->end(),
                  pointer_delta(eden_space()->end(),
                                eden_space()->bottom(),
                                sizeof(char)));
    gclog_or_tty->print_cr("    from: [" PTR_FORMAT ".." PTR_FORMAT ") "
                  SIZE_FORMAT,
                  from_space()->bottom(),
                  from_space()->end(),
                  pointer_delta(from_space()->end(),
                                from_space()->bottom(),
                                sizeof(char)));
    gclog_or_tty->print_cr("      to: [" PTR_FORMAT ".." PTR_FORMAT ") "
                  SIZE_FORMAT,
                  to_space()->bottom(),
                  to_space()->end(),
                  pointer_delta(  to_space()->end(),
                                  to_space()->bottom(),
                                  sizeof(char)));
  }

  // There's nothing to do if the new sizes are the same as the current
  if (requested_survivor_size == to_space()->capacity_in_bytes() &&
      requested_survivor_size == from_space()->capacity_in_bytes() &&
      requested_eden_size == eden_space()->capacity_in_bytes()) {
    if (PrintAdaptiveSizePolicy && Verbose) {
      gclog_or_tty->print_cr("    capacities are the right sizes, returning");
    }
    return;
  }

  char* eden_start = (char*)virtual_space()->low();
  char* eden_end   = (char*)eden_space()->end();
  char* from_start = (char*)from_space()->bottom();
  char* from_end   = (char*)from_space()->end();
  char* to_start   = (char*)to_space()->bottom();
  char* to_end     = (char*)to_space()->end();

  assert(eden_start < from_start, "Cannot push into from_space");

  ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  const size_t alignment = heap->intra_heap_alignment();
  const bool maintain_minimum =
    (requested_eden_size + 2 * requested_survivor_size) <= min_gen_size();

  bool eden_from_to_order = from_start < to_start;
  // Check whether from space is below to space
  if (eden_from_to_order) {
    // Eden, from, to

    if (PrintAdaptiveSizePolicy && Verbose) {
      gclog_or_tty->print_cr("  Eden, from, to:");
    }

    // Set eden
    // "requested_eden_size" is a goal for the size of eden
    // and may not be attainable.  "eden_size" below is
    // calculated based on the location of from-space and
    // the goal for the size of eden.  from-space is
    // fixed in place because it contains live data.
    // The calculation is done this way to avoid 32bit
    // overflow (i.e., eden_start + requested_eden_size
    // may too large for representation in 32bits).
    size_t eden_size;
    if (maintain_minimum) {
      // Only make eden larger than the requested size if
      // the minimum size of the generation has to be maintained.
      // This could be done in general but policy at a higher
      // level is determining a requested size for eden and that
      // should be honored unless there is a fundamental reason.
      eden_size = pointer_delta(from_start,
                                eden_start,
                                sizeof(char));
    } else {
      eden_size = MIN2(requested_eden_size,
                       pointer_delta(from_start, eden_start, sizeof(char)));
    }

    eden_end = eden_start + eden_size;
    assert(eden_end >= eden_start, "addition overflowed")
//.........这里部分代码省略.........