/*

 * Copyright 2001-2006 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 *

 */

# include "incls/_precompiled.incl"

# include "incls/_cardTableRS.cpp.incl"

CardTableRS::CardTableRS(MemRegion whole_heap,

                         int max_covered_regions) :

  GenRemSet(&_ct_bs),

  _ct_bs(whole_heap, max_covered_regions),

  _cur_youngergen_card_val(youngergenP1_card)

{

  _last_cur_val_in_gen = new jbyte[GenCollectedHeap::max_gens + 1];

  if (_last_cur_val_in_gen == NULL) {

    vm_exit_during_initialization("Could not last_cur_val_in_gen array.");

  }

  for (int i = 0; i < GenCollectedHeap::max_gens + 1; i++) {

    _last_cur_val_in_gen[i] = clean_card_val();

  }

  _ct_bs.set_CTRS(this);

}

void CardTableRS::resize_covered_region(MemRegion new_region) {

  _ct_bs.resize_covered_region(new_region);

}

jbyte CardTableRS::find_unused_youngergenP_card_value() {

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  for (jbyte v = youngergenP1_card;

       v < cur_youngergen_and_prev_nonclean_card;

       v++) {

    bool seen = false;

    for (int g = 0; g < gch->n_gens()+1; g++) {

      if (_last_cur_val_in_gen[g] == v) {

        seen = true;

        break;

      }

    }

    if (!seen) return v;

  }

  ShouldNotReachHere();

  return 0;

}

void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {

  // Parallel or sequential, we must always set the prev to equal the

  // last one written.

  if (parallel) {

    // Find a parallel value to be used next.

    jbyte next_val = find_unused_youngergenP_card_value();

    set_cur_youngergen_card_val(next_val);

  } else {

    // In an sequential traversal we will always write youngergen, so that

    // the inline barrier is  correct.

    set_cur_youngergen_card_val(youngergen_card);

  }

}

void CardTableRS::younger_refs_iterate(Generation* g,

                                       OopsInGenClosure* blk) {

  _last_cur_val_in_gen[g->level()+1] = cur_youngergen_card_val();

  g->younger_refs_iterate(blk);

}

class ClearNoncleanCardWrapper: public MemRegionClosure {

  MemRegionClosure* _dirty_card_closure;

  CardTableRS* _ct;

  bool _is_par;

private:

  // Clears the given card, return true if the corresponding card should be

  // processed.

  bool clear_card(jbyte* entry) {

    if (_is_par) {

      while (true) {

        // In the parallel case, we may have to do this several times.

        jbyte entry_val = *entry;

        assert(entry_val != CardTableRS::clean_card_val(),

               "We shouldn't be looking at clean cards, and this should "

               "be the only place they get cleaned.");

        if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)

            || _ct->is_prev_youngergen_card_val(entry_val)) {

          jbyte res =

            Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);

          if (res == entry_val) {

            break;

          } else {

            assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,

                   "The CAS above should only fail if another thread did "

                   "a GC write barrier.");

          }

        } else if (entry_val ==

                   CardTableRS::cur_youngergen_and_prev_nonclean_card) {

          // Parallelism shouldn't matter in this case.  Only the thread

          // assigned to scan the card should change this value.

          *entry = _ct->cur_youngergen_card_val();

          break;

        } else {

          assert(entry_val == _ct->cur_youngergen_card_val(),

                 "Should be the only possibility.");

          // In this case, the card was clean before, and become

          // cur_youngergen only because of processing of a promoted object.

          // We don't have to look at the card.

          return false;

        }

      }

      return true;

    } else {

      jbyte entry_val = *entry;

      assert(entry_val != CardTableRS::clean_card_val(),

             "We shouldn't be looking at clean cards, and this should "

             "be the only place they get cleaned.");

      assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,

             "This should be possible in the sequential case.");

      *entry = CardTableRS::clean_card_val();

      return true;

    }

  }

public:

  ClearNoncleanCardWrapper(MemRegionClosure* dirty_card_closure,

                           CardTableRS* ct) :

    _dirty_card_closure(dirty_card_closure), _ct(ct) {

    _is_par = (SharedHeap::heap()->n_par_threads() > 0);

  }

  void do_MemRegion(MemRegion mr) {

    // We start at the high end of "mr", walking backwards

    // while accumulating a contiguous dirty range of cards in

    // [start_of_non_clean, end_of_non_clean) which we then

    // process en masse.

    HeapWord* end_of_non_clean = mr.end();

    HeapWord* start_of_non_clean = end_of_non_clean;

    jbyte*       entry = _ct->byte_for(mr.last());

    const jbyte* first_entry = _ct->byte_for(mr.start());

    while (entry >= first_entry) {

      HeapWord* cur = _ct->addr_for(entry);

      if (!clear_card(entry)) {

        // We hit a clean card; process any non-empty

        // dirty range accumulated so far.

        if (start_of_non_clean < end_of_non_clean) {

          MemRegion mr2(start_of_non_clean, end_of_non_clean);

          _dirty_card_closure->do_MemRegion(mr2);

        }

        // Reset the dirty window while continuing to

        // look for the next dirty window to process.

        end_of_non_clean = cur;

        start_of_non_clean = end_of_non_clean;

      }

      // Open the left end of the window one card to the left.

      start_of_non_clean = cur;

      // Note that "entry" leads "start_of_non_clean" in

      // its leftward excursion after this point

      // in the loop and, when we hit the left end of "mr",

      // will point off of the left end of the card-table

      // for "mr".

      entry--;

    }

    // If the first card of "mr" was dirty, we will have

    // been left with a dirty window, co-initial with "mr",

    // which we now process.

    if (start_of_non_clean < end_of_non_clean) {

      MemRegion mr2(start_of_non_clean, end_of_non_clean);

      _dirty_card_closure->do_MemRegion(mr2);

    }

  }

};

// clean (by dirty->clean before) ==> cur_younger_gen

// dirty                          ==> cur_youngergen_and_prev_nonclean_card

// precleaned                     ==> cur_youngergen_and_prev_nonclean_card

// prev-younger-gen               ==> cur_youngergen_and_prev_nonclean_card

// cur-younger-gen                ==> cur_younger_gen

// cur_youngergen_and_prev_nonclean_card ==> no change.

void CardTableRS::write_ref_field_gc_par(oop* field, oop new_val) {

  jbyte* entry = ct_bs()->byte_for(field);

  do {

    jbyte entry_val = *entry;

    // We put this first because it's probably the most common case.

    if (entry_val == clean_card_val()) {

      // No threat of contention with cleaning threads.

      *entry = cur_youngergen_card_val();

      return;

    } else if (card_is_dirty_wrt_gen_iter(entry_val)

               || is_prev_youngergen_card_val(entry_val)) {

      // Mark it as both cur and prev youngergen; card cleaning thread will

      // eventually remove the previous stuff.

      jbyte new_val = cur_youngergen_and_prev_nonclean_card;

      jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);

      // Did the CAS succeed?

      if (res == entry_val) return;

      // Otherwise, retry, to see the new value.

      continue;

    } else {

      assert(entry_val == cur_youngergen_and_prev_nonclean_card

             || entry_val == cur_youngergen_card_val(),

             "should be only possibilities.");

      return;

    }

  } while (true);

}

void CardTableRS::younger_refs_in_space_iterate(Space* sp,

                                                OopsInGenClosure* cl) {

  DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, _ct_bs.precision(),

                                                   cl->gen_boundary());

  ClearNoncleanCardWrapper clear_cl(dcto_cl, this);

  _ct_bs.non_clean_card_iterate(sp, sp->used_region_at_save_marks(),

                                dcto_cl, &clear_cl, false);

}

void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Generations younger than gen have been evacuated. We can clear

  // card table entries for gen (we know that it has no pointers

  // to younger gens) and for those below. The card tables for

  // the youngest gen need never be cleared, and those for perm gen

  // will be cleared based on the parameter clear_perm.

  // There's a bit of subtlety in the clear() and invalidate()

  // methods that we exploit here and in invalidate_or_clear()

  // below to avoid missing cards at the fringes. If clear() or

  // invalidate() are changed in the future, this code should

  // be revisited. 20040107.ysr

  Generation* g = gen;

  for(Generation* prev_gen = gch->prev_gen(g);

      prev_gen != NULL;

      g = prev_gen, prev_gen = gch->prev_gen(g)) {

    MemRegion to_be_cleared_mr = g->prev_used_region();

    clear(to_be_cleared_mr);

  }

  // Clear perm gen cards if asked to do so.

  if (clear_perm) {

    MemRegion to_be_cleared_mr = gch->perm_gen()->prev_used_region();

    clear(to_be_cleared_mr);

  }

}

void CardTableRS::invalidate_or_clear(Generation* gen, bool younger,

                                      bool perm) {

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // For each generation gen (and younger and/or perm)

  // invalidate the cards for the currently occupied part

  // of that generation and clear the cards for the

  // unoccupied part of the generation (if any, making use

  // of that generation's prev_used_region to determine that

  // region). No need to do anything for the youngest

  // generation. Also see note#20040107.ysr above.

  Generation* g = gen;

  for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;

      g = prev_gen, prev_gen = gch->prev_gen(g))  {

    MemRegion used_mr = g->used_region();

    MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);

    if (!to_be_cleared_mr.is_empty()) {

      clear(to_be_cleared_mr);

    }

    invalidate(used_mr);

    if (!younger) break;

  }

  // Clear perm gen cards if asked to do so.

  if (perm) {

    g = gch->perm_gen();

    MemRegion used_mr = g->used_region();

    MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);

    if (!to_be_cleared_mr.is_empty()) {

      clear(to_be_cleared_mr);

    }

    invalidate(used_mr);

  }

}

class VerifyCleanCardClosure: public OopClosure {

  HeapWord* boundary;

  HeapWord* begin; HeapWord* end;

public:

  void do_oop(oop* p) {

    HeapWord* jp = (HeapWord*)p;

    if (jp >= begin && jp < end) {

      guarantee(*p == NULL || (HeapWord*)p < boundary

                || (HeapWord*)(*p) >= boundary,

                "pointer on clean card crosses boundary");

    }

  }

  VerifyCleanCardClosure(HeapWord* b, HeapWord* _begin, HeapWord* _end) :

    boundary(b), begin(_begin), end(_end) {}

};

class VerifyCTSpaceClosure: public SpaceClosure {

  CardTableRS* _ct;

  HeapWord* _boundary;

public:

  VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :

    _ct(ct), _boundary(boundary) {}

  void do_space(Space* s) { _ct->verify_space(s, _boundary); }

};

class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {

  CardTableRS* _ct;

public:

  VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}

  void do_generation(Generation* gen) {

    // Skip the youngest generation.

    if (gen->level() == 0) return;

    // Normally, we're interested in pointers to younger generations.

    VerifyCTSpaceClosure blk(_ct, gen->reserved().start());

    gen->space_iterate(&blk, true);

  }

};

void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {

  // We don't need to do young-gen spaces.

  if (s->end() <= gen_boundary) return;

  MemRegion used = s->used_region();

  jbyte* cur_entry = byte_for(used.start());

  jbyte* limit = byte_after(used.last());

  while (cur_entry < limit) {

    if (*cur_entry == CardTableModRefBS::clean_card) {

      jbyte* first_dirty = cur_entry+1;

      while (first_dirty < limit &&

             *first_dirty == CardTableModRefBS::clean_card) {

        first_dirty++;

      }

      // If the first object is a regular object, and it has a

      // young-to-old field, that would mark the previous card.

      HeapWord* boundary = addr_for(cur_entry);

      HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);

      HeapWord* boundary_block = s->block_start(boundary);

      HeapWord* begin = boundary;             // Until proven otherwise.

      HeapWord* start_block = boundary_block; // Until proven otherwise.

      if (boundary_block < boundary) {

        if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {

          oop boundary_obj = oop(boundary_block);

          if (!boundary_obj->is_objArray() &&

              !boundary_obj->is_typeArray()) {

            guarantee(cur_entry > byte_for(used.start()),

                      "else boundary would be boundary_block");

            if (*byte_for(boundary_block) != CardTableModRefBS::clean_card) {

              begin = boundary_block + s->block_size(boundary_block);

              start_block = begin;

            }

          }

        }

      }

      // Now traverse objects until end.

      HeapWord* cur = start_block;

      VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);

      while (cur < end) {

        if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {

          oop(cur)->oop_iterate(&verify_blk);

        }

        cur += s->block_size(cur);

      }

      cur_entry = first_dirty;

    } else {

      // We'd normally expect that cur_youngergen_and_prev_nonclean_card

      // is a transient value, that cannot be in the card table

      // except during GC, and thus assert that:

      // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,

      //        "Illegal CT value");

      // That however, need not hold, as will become clear in the

      // following...

      // We'd normally expect that if we are in the parallel case,

      // we can't have left a prev value (which would be different

      // from the current value) in the card table, and so we'd like to

      // assert that:

      // guarantee(cur_youngergen_card_val() == youngergen_card

      //           || !is_prev_youngergen_card_val(*cur_entry),

      //           "Illegal CT value");

      // That, however, may not hold occasionally, because of

      // CMS or MSC in the old gen. To wit, consider the

      // following two simple illustrative scenarios:

      // (a) CMS: Consider the case where a large object L

      //     spanning several cards is allocated in the old

      //     gen, and has a young gen reference stored in it, dirtying

      //     some interior cards. A young collection scans the card,

      //     finds a young ref and installs a youngergenP_n value.

      //     L then goes dead. Now a CMS collection starts,

      //     finds L dead and sweeps it up. Assume that L is

      //     abutting _unallocated_blk, so _unallocated_blk is

      //     adjusted down to (below) L. Assume further that

      //     no young collection intervenes during this CMS cycle.

      //     The next young gen cycle will not get to look at this

      //     youngergenP_n card since it lies in the unoccupied

      //     part of the space.

      //     Some young collections later the blocks on this

      //     card can be re-allocated either due to direct allocation

      //     or due to absorbing promotions. At this time, the

      //     before-gc verification will fail the above assert.

      // (b) MSC: In this case, an object L with a young reference

      //     is on a card that (therefore) holds a youngergen_n value.

      //     Suppose also that L lies towards the end of the used

      //     the used space before GC. An MSC collection

      //     occurs that compacts to such an extent that this

      //     card is no longer in the occupied part of the space.

      //     Since current code in MSC does not always clear cards

      //     in the unused part of old gen, this stale youngergen_n

      //     value is left behind and can later be covered by

      //     an object when promotion or direct allocation

      //     re-allocates that part of the heap.

      //

      // Fortunately, the presence of such stale card values is

      // "only" a minor annoyance in that subsequent young collections

      // might needlessly scan such cards, but would still never corrupt

      // the heap as a result. However, it's likely not to be a significant

      // performance inhibitor in practice. For instance,

      // some recent measurements with unoccupied cards eagerly cleared

      // out to maintain this invariant, showed next to no

      // change in young collection times; of course one can construct

      // degenerate examples where the cost can be significant.)

      // Note, in particular, that if the "stale" card is modified

      // after re-allocation, it would be dirty, not "stale". Thus,

      // we can never have a younger ref in such a card and it is

      // safe not to scan that card in any collection. [As we see

      // below, we do some unnecessary scanning

      // in some cases in the current parallel scanning algorithm.]

      //

      // The main point below is that the parallel card scanning code

      // deals correctly with these stale card values. There are two main

      // cases to consider where we have a stale "younger gen" value and a

      // "derivative" case to consider, where we have a stale

      // "cur_younger_gen_and_prev_non_clean" value, as will become

      // apparent in the case analysis below.

      // o Case 1. If the stale value corresponds to a younger_gen_n

      //   value other than the cur_younger_gen value then the code

      //   treats this as being tantamount to a prev_younger_gen

      //   card. This means that the card may be unnecessarily scanned.

      //   There are two sub-cases to consider:

      //   o Case 1a. Let us say that the card is in the occupied part

      //     of the generation at the time the collection begins. In

      //     that case the card will be either cleared when it is scanned

      //     for young pointers, or will be set to cur_younger_gen as a

      //     result of promotion. (We have elided the normal case where

      //     the scanning thread and the promoting thread interleave

      //     possibly resulting in a transient

      //     cur_younger_gen_and_prev_non_clean value before settling

      //     to cur_younger_gen. [End Case 1a.]

      //   o Case 1b. Consider now the case when the card is in the unoccupied

      //     part of the space which becomes occupied because of promotions

      //     into it during the current young GC. In this case the card

      //     will never be scanned for young references. The current

      //     code will set the card value to either

      //     cur_younger_gen_and_prev_non_clean or leave

      //     it with its stale value -- because the promotions didn't

      //     result in any younger refs on that card. Of these two

      //     cases, the latter will be covered in Case 1a during

      //     a subsequent scan. To deal with the former case, we need

      //     to further consider how we deal with a stale value of

      //     cur_younger_gen_and_prev_non_clean in our case analysis

      //     below. This we do in Case 3 below. [End Case 1b]

      //   [End Case 1]

      // o Case 2. If the stale value corresponds to cur_younger_gen being

      //   a value not necessarily written by a current promotion, the

      //   card will not be scanned by the younger refs scanning code.

      //   (This is OK since as we argued above such cards cannot contain

      //   any younger refs.) The result is that this value will be

      //   treated as a prev_younger_gen value in a subsequent collection,

      //   which is addressed in Case 1 above. [End Case 2]

      // o Case 3. We here consider the "derivative" case from Case 1b. above

      //   because of which we may find a stale

      //   cur_younger_gen_and_prev_non_clean card value in the table.

      //   Once again, as in Case 1, we consider two subcases, depending

      //   on whether the card lies in the occupied or unoccupied part

      //   of the space at the start of the young collection.

      //   o Case 3a. Let us say the card is in the occupied part of

      //     the old gen at the start of the young collection. In that

      //     case, the card will be scanned by the younger refs scanning

      //     code which will set it to cur_younger_gen. In a subsequent

      //     scan, the card will be considered again and get its final

      //     correct value. [End Case 3a]

      //   o Case 3b. Now consider the case where the card is in the

      //     unoccupied part of the old gen, and is occupied as a result

      //     of promotions during thus young gc. In that case,

      //     the card will not be scanned for younger refs. The presence

      //     of newly promoted objects on the card will then result in

      //     its keeping the value cur_younger_gen_and_prev_non_clean

      //     value, which we have dealt with in Case 3 here. [End Case 3b]

      //   [End Case 3]

      //

      // (Please refer to the code in the helper class

      // ClearNonCleanCardWrapper and in CardTableModRefBS for details.)

      //

      // The informal arguments above can be tightened into a formal

      // correctness proof and it behooves us to write up such a proof,

      // or to use model checking to prove that there are no lingering

      // concerns.

      //

      // Clearly because of Case 3b one cannot bound the time for

      // which a card will retain what we have called a "stale" value.

      // However, one can obtain a Loose upper bound on the redundant

      // work as a result of such stale values. Note first that any

      // time a stale card lies in the occupied part of the space at

      // the start of the collection, it is scanned by younger refs

      // code and we can define a rank function on card values that

      // declines when this is so. Note also that when a card does not

      // lie in the occupied part of the space at the beginning of a

      // young collection, its rank can either decline or stay unchanged.

      // In this case, no extra work is done in terms of redundant

      // younger refs scanning of that card.

      // Then, the case analysis above reveals that, in the worst case,

      // any such stale card will be scanned unnecessarily at most twice.

      //

      // It is nonethelss advisable to try and get rid of some of this

      // redundant work in a subsequent (low priority) re-design of

      // the card-scanning code, if only to simplify the underlying

      // state machine analysis/proof. ysr 1/28/2002. XXX

      cur_entry++;

    }