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// The CollectedHeap type requires subtypes to implement a method

// "block_start".  For some subtypes, notably generational

// systems using card-table-based write barriers, the efficiency of this

// operation may be important.  Implementations of the "BlockOffsetArray"

// class may be useful in providing such efficient implementations.

//

// BlockOffsetTable (abstract)

//   - BlockOffsetArray (abstract)

//     - BlockOffsetArrayNonContigSpace

//     - BlockOffsetArrayContigSpace

//

class ContiguousSpace;

class SerializeOopClosure;

//////////////////////////////////////////////////////////////////////////

// The BlockOffsetTable "interface"

//////////////////////////////////////////////////////////////////////////

class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {

  friend class VMStructs;

protected:

  // These members describe the region covered by the table.

  // The space this table is covering.

  HeapWord* _bottom;    // == reserved.start

  HeapWord* _end;       // End of currently allocated region.

public:

  // Initialize the table to cover the given space.

  // The contents of the initial table are undefined.

  BlockOffsetTable(HeapWord* bottom, HeapWord* end):

    _bottom(bottom), _end(end) {

    assert(_bottom <= _end, "arguments out of order");

  }

  // Note that the committed size of the covered space may have changed,

  // so the table size might also wish to change.

  virtual void resize(size_t new_word_size) = 0;

  virtual void set_bottom(HeapWord* new_bottom) {

    assert(new_bottom <= _end, "new_bottom > _end");

    _bottom = new_bottom;

    resize(pointer_delta(_end, _bottom));

  }

  // Requires "addr" to be contained by a block, and returns the address of

  // the start of that block.

  virtual HeapWord* block_start_unsafe(const void* addr) const = 0;

  // Returns the address of the start of the block containing "addr", or

  // else "null" if it is covered by no block.

  HeapWord* block_start(const void* addr) const;

};

//////////////////////////////////////////////////////////////////////////

// One implementation of "BlockOffsetTable," the BlockOffsetArray,

// divides the covered region into "N"-word subregions (where

// "N" = 2^"LogN".  An array with an entry for each such subregion

// indicates how far back one must go to find the start of the

// chunk that includes the first word of the subregion.

//

// Each BlockOffsetArray is owned by a Space.  However, the actual array

// may be shared by several BlockOffsetArrays; this is useful

// when a single resizable area (such as a generation) is divided up into

// several spaces in which contiguous allocation takes place.  (Consider,

// for example, the garbage-first generation.)

// Here is the shared array type.

//////////////////////////////////////////////////////////////////////////

// BlockOffsetSharedArray

//////////////////////////////////////////////////////////////////////////

class BlockOffsetSharedArray: public CHeapObj {

  friend class BlockOffsetArray;

  friend class BlockOffsetArrayNonContigSpace;

  friend class BlockOffsetArrayContigSpace;

  friend class VMStructs;

 private:

  enum SomePrivateConstants {

    LogN = 9,

    LogN_words = LogN - LogHeapWordSize,

    N_bytes = 1 << LogN,

    N_words = 1 << LogN_words

  };

  // The reserved region covered by the shared array.

  MemRegion _reserved;

  // End of the current committed region.

  HeapWord* _end;

  // Array for keeping offsets for retrieving object start fast given an

  // address.

  VirtualSpace _vs;

  u_char* _offset_array;          // byte array keeping backwards offsets

 protected:

  // Bounds checking accessors:

  // For performance these have to devolve to array accesses in product builds.

  u_char offset_array(size_t index) const {

    assert(index < _vs.committed_size(), "index out of range");

    return _offset_array[index];

  }

    assert(index < _vs.committed_size(), "index out of range");

    _offset_array[index] = offset;

  }

    assert(index < _vs.committed_size(), "index out of range");

    assert(high >= low, "addresses out of order");

    assert(pointer_delta(high, low) <= N_words, "offset too large");

    _offset_array[index] = (u_char)pointer_delta(high, low);

  }

    assert(index_for(right - 1) < _vs.committed_size(),

           "right address out of range");

    assert(left  < right, "Heap addresses out of order");

    size_t num_cards = pointer_delta(right, left) >> LogN_words;

    // Below, we may use an explicit loop instead of memset()

    // because on certain platforms memset() can give concurrent

    // readers "out-of-thin-air," phantom zeros; see 6948537.

    if (UseMemSetInBOT) {

      memset(&_offset_array[index_for(left)], offset, num_cards);

    } else {

      size_t i = index_for(left);

      const size_t end = i + num_cards;

      for (; i < end; i++) {

        _offset_array[i] = offset;

      }

    }

  }

    assert(right < _vs.committed_size(), "right address out of range");

    assert(left  <= right, "indexes out of order");

    size_t num_cards = right - left + 1;

    // Below, we may use an explicit loop instead of memset

    // because on certain platforms memset() can give concurrent

    // readers "out-of-thin-air," phantom zeros; see 6948537.

    if (UseMemSetInBOT) {

      memset(&_offset_array[left], offset, num_cards);

    } else {

      size_t i = left;

      const size_t end = i + num_cards;

      for (; i < end; i++) {

        _offset_array[i] = offset;

      }

    }

  }

  void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {

    assert(index < _vs.committed_size(), "index out of range");

    assert(high >= low, "addresses out of order");

    assert(pointer_delta(high, low) <= N_words, "offset too large");

    assert(_offset_array[index] == pointer_delta(high, low),

           "Wrong offset");

  }

  bool is_card_boundary(HeapWord* p) const;

  // Return the number of slots needed for an offset array

  // that covers mem_region_words words.

  // We always add an extra slot because if an object

  // ends on a card boundary we put a 0 in the next

  // offset array slot, so we want that slot always

  // to be reserved.

  size_t compute_size(size_t mem_region_words) {

    size_t number_of_slots = (mem_region_words / N_words) + 1;

    return ReservedSpace::allocation_align_size_up(number_of_slots);

  }

public:

  // Initialize the table to cover from "base" to (at least)

  // "base + init_word_size".  In the future, the table may be expanded

  // (see "resize" below) up to the size of "_reserved" (which must be at

  // least "init_word_size".)  The contents of the initial table are

  // undefined; it is the responsibility of the constituent

  // BlockOffsetTable(s) to initialize cards.

  BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);

  // Notes a change in the committed size of the region covered by the

  // table.  The "new_word_size" may not be larger than the size of the

  // reserved region this table covers.

  void resize(size_t new_word_size);

  void set_bottom(HeapWord* new_bottom);

  // Updates all the BlockOffsetArray's sharing this shared array to

  // reflect the current "top"'s of their spaces.

  void update_offset_arrays();   // Not yet implemented!

  // Return the appropriate index into "_offset_array" for "p".

  size_t index_for(const void* p) const;

  // Return the address indicating the start of the region corresponding to

  // "index" in "_offset_array".

  HeapWord* address_for_index(size_t index) const;

  // Return the address "p" incremented by the size of

  // a region.  This method does not align the address

  // returned to the start of a region.  It is a simple

  // primitive.

  HeapWord* inc_by_region_size(HeapWord* p) const { return p + N_words; }

  // Shared space support

  void serialize(SerializeOopClosure* soc, HeapWord* start, HeapWord* end);

};

//////////////////////////////////////////////////////////////////////////

// The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.

//////////////////////////////////////////////////////////////////////////

class BlockOffsetArray: public BlockOffsetTable {

  friend class VMStructs;

  friend class G1BlockOffsetArray; // temp. until we restructure and cleanup

 protected:

  // The following enums are used by do_block_internal() below

  enum Action {

    Action_single,      // BOT records a single block (see single_block())

    Action_mark,        // BOT marks the start of a block (see mark_block())

    Action_check        // Check that BOT records block correctly

                        // (see verify_single_block()).

  };

  enum SomePrivateConstants {

    N_words = BlockOffsetSharedArray::N_words,

    LogN    = BlockOffsetSharedArray::LogN,

    // entries "e" of at least N_words mean "go back by Base^(e-N_words)."

    // All entries are less than "N_words + N_powers".

    LogBase = 4,

    Base = (1 << LogBase),

    N_powers = 14

  };

  static size_t power_to_cards_back(uint i) {

    return (size_t)(1 << (LogBase * i));

  }

  static size_t power_to_words_back(uint i) {

    return power_to_cards_back(i) * N_words;

  }

  static size_t entry_to_cards_back(u_char entry) {

    assert(entry >= N_words, "Precondition");

    return power_to_cards_back(entry - N_words);

  }

  static size_t entry_to_words_back(u_char entry) {

    assert(entry >= N_words, "Precondition");

    return power_to_words_back(entry - N_words);

  }

  // The shared array, which is shared with other BlockOffsetArray's

  // corresponding to different spaces within a generation or span of

  // memory.

  BlockOffsetSharedArray* _array;

  // The space that owns this subregion.

  Space* _sp;

  // If true, array entries are initialized to 0; otherwise, they are

  // initialized to point backwards to the beginning of the covered region.

  bool _init_to_zero;

  // Sets the entries

  // corresponding to the cards starting at "start" and ending at "end"

  // to point back to the card before "start": the interval [start, end)

  // Same as above, except that the args here are a card _index_ interval

  // that is closed: [start_index, end_index]

  // A helper function for BOT adjustment/verification work

 public:

  // The space may not have its bottom and top set yet, which is why the

  // region is passed as a parameter.  If "init_to_zero" is true, the

  // elements of the array are initialized to zero.  Otherwise, they are

  // initialized to point backwards to the beginning.

  BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,

  // Note: this ought to be part of the constructor, but that would require

  // "this" to be passed as a parameter to a member constructor for

  // the containing concrete subtype of Space.

  // This would be legal C++, but MS VC++ doesn't allow it.

  void set_space(Space* sp) { _sp = sp; }

  // Resets the covered region to the given "mr".

  void set_region(MemRegion mr) {

    _bottom = mr.start();

    _end = mr.end();

  }

  // Note that the committed size of the covered space may have changed,

  // so the table size might also wish to change.

  virtual void resize(size_t new_word_size) {

    HeapWord* new_end = _bottom + new_word_size;

    if (_end < new_end && !init_to_zero()) {

      // verify that the old and new boundaries are also card boundaries

      assert(_array->is_card_boundary(_end),

             "_end not a card boundary");

      assert(_array->is_card_boundary(new_end),

             "new _end would not be a card boundary");

      // set all the newly added cards

      _array->set_offset_array(_end, new_end, N_words);

    }

    _end = new_end;  // update _end

  }

  // Adjust the BOT to show that it has a single block in the

  // range [blk_start, blk_start + size). All necessary BOT

  // cards are adjusted, but _unallocated_block isn't.

  void single_block(HeapWord* blk_start, HeapWord* blk_end);

  void single_block(HeapWord* blk, size_t size) {

    single_block(blk, blk + size);

  }

  // When the alloc_block() call returns, the block offset table should

  // have enough information such that any subsequent block_start() call

  // with an argument equal to an address that is within the range

  // [blk_start, blk_end) would return the value blk_start, provided

  // there have been no calls in between that reset this information

  // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call

  // for an appropriate range covering the said interval).

  // These methods expect to be called with [blk_start, blk_end)

  // representing a block of memory in the heap.

  virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);

  void alloc_block(HeapWord* blk, size_t size) {

    alloc_block(blk, blk + size);

  }

  // If true, initialize array slots with no allocated blocks to zero.

  // Otherwise, make them point back to the front.

  bool init_to_zero() { return _init_to_zero; }

  // Debugging

  // Return the index of the last entry in the "active" region.

  virtual size_t last_active_index() const = 0;

  // Verify the block offset table

  void verify() const;

  void check_all_cards(size_t left_card, size_t right_card) const;

};

////////////////////////////////////////////////////////////////////////////

// A subtype of BlockOffsetArray that takes advantage of the fact

// that its underlying space is a NonContiguousSpace, so that some

// specialized interfaces can be made available for spaces that

// manipulate the table.

////////////////////////////////////////////////////////////////////////////

class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {

  friend class VMStructs;

 private:

  // The portion [_unallocated_block, _sp.end()) of the space that

  // is a single block known not to contain any objects.

  // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.

  HeapWord* _unallocated_block;

 public:

  BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):

    BlockOffsetArray(array, mr, false),

    _unallocated_block(_bottom) { }

  // accessor

  HeapWord* unallocated_block() const {

    assert(BlockOffsetArrayUseUnallocatedBlock,

           "_unallocated_block is not being maintained");

    return _unallocated_block;

  }

  void set_unallocated_block(HeapWord* block) {

    assert(BlockOffsetArrayUseUnallocatedBlock,

           "_unallocated_block is not being maintained");

    assert(block >= _bottom && block <= _end, "out of range");

    _unallocated_block = block;

  }

  // These methods expect to be called with [blk_start, blk_end)

  // representing a block of memory in the heap.

  void alloc_block(HeapWord* blk_start, HeapWord* blk_end);

  void alloc_block(HeapWord* blk, size_t size) {

    alloc_block(blk, blk + size);

  }

  // The following methods are useful and optimized for a

  // non-contiguous space.

  // Given a block [blk_start, blk_start + full_blk_size), and

  // a left_blk_size < full_blk_size, adjust the BOT to show two

  // blocks [blk_start, blk_start + left_blk_size) and

  // [blk_start + left_blk_size, blk_start + full_blk_size).

  // It is assumed (and verified in the non-product VM) that the

  // BOT was correct for the original block.

  void split_block(HeapWord* blk_start, size_t full_blk_size,

                           size_t left_blk_size);

  // Adjust BOT to show that it has a block in the range

  // [blk_start, blk_start + size). Only the first card

  // of BOT is touched. It is assumed (and verified in the

  // non-product VM) that the remaining cards of the block

  // are correct.

  }

  // Adjust _unallocated_block to indicate that a particular

  // block has been newly allocated or freed. It is assumed (and

  // verified in the non-product VM) that the BOT is correct for

  // the given block.

    // Verify that the BOT shows [blk, blk + blk_size) to be one block.

    verify_single_block(blk_start, blk_end);

    if (BlockOffsetArrayUseUnallocatedBlock) {

      _unallocated_block = MAX2(_unallocated_block, blk_end);

    }

  }

  }

  void freed(HeapWord* blk_start, HeapWord* blk_end);

  HeapWord* block_start_unsafe(const void* addr) const;

  // Requires "addr" to be the start of a card and returns the

  // start of the block that contains the given address.

  HeapWord* block_start_careful(const void* addr) const;

  // Verification & debugging: ensure that the offset table reflects

  // the fact that the block [blk_start, blk_end) or [blk, blk + size)

  // is a single block of storage. NOTE: can't const this because of

  // call to non-const do_block_internal() below.

  void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)

    PRODUCT_RETURN;

  void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;

  // Verify that the given block is before _unallocated_block

  void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)

    const PRODUCT_RETURN;

  void verify_not_unallocated(HeapWord* blk, size_t size)

    const PRODUCT_RETURN;

  // Debugging support

  virtual size_t last_active_index() const;

};

////////////////////////////////////////////////////////////////////////////

// A subtype of BlockOffsetArray that takes advantage of the fact

// that its underlying space is a ContiguousSpace, so that its "active"

// region can be more efficiently tracked (than for a non-contiguous space).

////////////////////////////////////////////////////////////////////////////

class BlockOffsetArrayContigSpace: public BlockOffsetArray {

  friend class VMStructs;

 private:

  // allocation boundary at which offset array must be updated

  HeapWord* _next_offset_threshold;

  size_t    _next_offset_index;      // index corresponding to that boundary