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  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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  * accompanied this code).

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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];

   }

   void set_offset_array(size_t index, u_char offset) {

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

     _offset_array[index] = offset;

   }

   void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {

     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);

   }

   void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {

     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;

       }

     }

   }

   void set_offset_array(size_t left, size_t right, u_char 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)

   // is right-open.

   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);

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

   // that is closed: [start_index, end_index]

   void set_remainder_to_point_to_start_incl(size_t start, size_t end);

   // A helper function for BOT adjustment/verification work

   void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);

  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,

                    bool init_to_zero);

   // 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.

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

   void mark_block(HeapWord* blk, size_t size) {

     mark_block(blk, blk + size);

   }

   // 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.

   void allocated(HeapWord* blk_start, HeapWord* blk_end) {

     // 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 allocated(HeapWord* blk, size_t size) {

     allocated(blk, blk + size);

   }

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

   void freed(HeapWord* blk, size_t size) {

     freed(blk, blk + size);

   }

   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

   // Work function when allocation start crosses threshold.

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

  public:

   BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):

     BlockOffsetArray(array, mr, true) {

     _next_offset_threshold = NULL;

     _next_offset_index = 0;

   }

   void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }

   // Initialize the threshold for an empty heap.

   HeapWord* initialize_threshold();

   // Zero out the entry for _bottom (offset will be zero)

   void      zero_bottom_entry();

   // Return the next threshold, the point at which the table should be

   // updated.

   HeapWord* threshold() const { return _next_offset_threshold; }

   // In general, these methods expect to be called with

   // [blk_start, blk_end) representing a block of memory in the heap.

   // In this implementation, however, we are OK even if blk_start and/or

   // blk_end are NULL because NULL is represented as 0, and thus

   // never exceeds the "_next_offset_threshold".

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

     if (blk_end > _next_offset_threshold) {

       alloc_block_work(blk_start, blk_end);

     }

   }

   void alloc_block(HeapWord* blk, size_t size) {

     alloc_block(blk, blk + size);

   }

   HeapWord* block_start_unsafe(const void* addr) const;

   void serialize(SerializeOopClosure* soc);

   // Debugging support

   virtual size_t last_active_index() const;

 };