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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.

 //

 // While generally mirroring the structure of the BOT for GenCollectedHeap,

 // the following types are tailored more towards G1's uses; these should,

 // however, be merged back into a common BOT to avoid code duplication

 // and reduce maintenance overhead.

 //

 //    G1BlockOffsetTable (abstract)

 //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)

 //       -- G1BlockOffsetArrayContigSpace

 //

 // A main impediment to the consolidation of this code might be the

 // effect of making some of the block_start*() calls non-const as

 // below. Whether that might adversely affect performance optimizations

 // that compilers might normally perform in the case of non-G1

 // collectors needs to be carefully investigated prior to any such

 // consolidation.

 // Forward declarations

 class ContiguousSpace;

 class G1BlockOffsetSharedArray;

 class G1BlockOffsetTable 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.

   G1BlockOffsetTable(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.  (May have side effects, namely updating of

   // shared array entries that "point" too far backwards.  This can occur,

   // for example, when LAB allocation is used in a space covered by the

   // table.)

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

   // Same as above, but does not have any of the possible side effects

   // discussed above.

   virtual HeapWord* block_start_unsafe_const(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.  (May have side effects,

   // namely updating of shared array entries that "point" too far

   // backwards.  This can occur, for example, when lab allocation is used

   // in a space covered by the table.)

   inline HeapWord* block_start(const void* addr);

   // Same as above, but does not have any of the possible side effects

   // discussed above.

   inline HeapWord* block_start_const(const void* addr) const;

 };

 // This implementation of "G1BlockOffsetTable" 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,

 // such as, for example, in G1 or in the train generation.)

 // Here is the shared array type.

 class G1BlockOffsetSharedArray: public CHeapObj {

   friend class G1BlockOffsetArray;

   friend class G1BlockOffsetArrayContigSpace;

   friend class VMStructs;

 private:

   // 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

   // 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");

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

     _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;

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

   }

   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;

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

   }

   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::page_align_size_up(number_of_slots);

   }

 public:

   enum SomePublicConstants {

     LogN = 9,

     LogN_words = LogN - LogHeapWordSize,

     N_bytes = 1 << LogN,

     N_words = 1 << LogN_words

   };

   // 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

   // G1BlockOffsetTable(s) to initialize cards.

   G1BlockOffsetSharedArray(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();

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

   inline size_t index_for(const void* p) const;

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

   // "index" in "_offset_array".

   inline HeapWord* address_for_index(size_t index) const;

 };

 // And here is the G1BlockOffsetTable subtype that uses the array.

 class G1BlockOffsetArray: public G1BlockOffsetTable {

   friend class G1BlockOffsetSharedArray;

   friend class G1BlockOffsetArrayContigSpace;

   friend class VMStructs;

 private:

   enum SomePrivateConstants {

     N_words = G1BlockOffsetSharedArray::N_words,

     LogN    = G1BlockOffsetSharedArray::LogN

   };

   // The following enums are used by do_block_helper

   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()).

   };

   // This is the array, which can be shared by several BlockOffsetArray's

   // servicing different

   G1BlockOffsetSharedArray* _array;

   // The space that owns this subregion.

   Space* _sp;

   // If "_sp" is a contiguous space, the field below is the view of "_sp"

   // as a contiguous space, else NULL.

   ContiguousSpace* _csp;

   // 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;

   // 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;

   // 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);

 protected:

   ContiguousSpace* csp() const { return _csp; }

   // Returns the address of a block whose start is at most "addr".

   // If "has_max_index" is true, "assumes "max_index" is the last valid one

   // in the array.

   inline HeapWord* block_at_or_preceding(const void* addr,

                                          bool has_max_index,

                                          size_t max_index) const;

   // "q" is a block boundary that is <= "addr"; "n" is the address of the

   // next block (or the end of the space.)  Return the address of the

   // beginning of the block that contains "addr".  Does so without side

   // effects (see, e.g., spec of  block_start.)

   inline HeapWord*

   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,

                                          const void* addr) const;

   // "q" is a block boundary that is <= "addr"; return the address of the

   // beginning of the block that contains "addr".  May have side effects

   // on "this", by updating imprecise entries.

   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,

                                                     const void* addr);

   // "q" is a block boundary that is <= "addr"; "n" is the address of the

   // next block (or the end of the space.)  Return the address of the

   // beginning of the block that contains "addr".  May have side effects

   // on "this", by updating imprecise entries.

   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,

                                                   HeapWord* n,

                                                   const void* addr);

   // Requires that "*threshold_" be the first array entry boundary at or

   // above "blk_start", and that "*index_" be the corresponding array

   // index.  If the block starts at or crosses "*threshold_", records

   // "blk_start" as the appropriate block start for the array index

   // starting at "*threshold_", and for any other indices crossed by the

   // block.  Updates "*threshold_" and "*index_" to correspond to the first

   // index after the block end.

   void alloc_block_work2(HeapWord** threshold_, size_t* index_,

                          HeapWord* blk_start, HeapWord* blk_end);

 public:

   // The space may not have it's 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.

   G1BlockOffsetArray(G1BlockOffsetSharedArray* 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);

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

   void set_region(MemRegion mr);

   // Resets the covered region to one with the same _bottom as before but

   // the "new_word_size".

   void resize(size_t new_word_size);

   // These must be guaranteed to work properly (i.e., do nothing)

   // when "blk_start" ("blk" for second version) is "NULL".

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

   virtual void alloc_block(HeapWord* blk, size_t size) {

     alloc_block(blk, blk + size);

   }

   // The following methods are useful and optimized for a

   // general, non-contiguous space.

   // The given arguments are required to be the starts of adjacent ("blk1"

   // before "blk2") well-formed blocks covered by "this".  After this call,

   // they should be considered to form one block.

   virtual void join_blocks(HeapWord* blk1, HeapWord* blk2);

   // 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 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);

   }

   // 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.

   inline 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);

     }

   }

   inline void allocated(HeapWord* blk, size_t size) {

     allocated(blk, blk + size);

   }

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

   inline void freed(HeapWord* blk, size_t size);

   virtual HeapWord* block_start_unsafe(const void* addr);

   virtual HeapWord* block_start_unsafe_const(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;

   // 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; }

   // 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.

   inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {

     if (VerifyBlockOffsetArray) {

       do_block_internal(blk_start, blk_end, Action_check);

     }

   }

   inline void verify_single_block(HeapWord* blk, size_t size) {

     verify_single_block(blk, blk + size);

   }

   // Verify that the given block is before _unallocated_block

   inline void verify_not_unallocated(HeapWord* blk_start,

                                      HeapWord* blk_end) const {

     if (BlockOffsetArrayUseUnallocatedBlock) {

       assert(blk_start < blk_end, "Block inconsistency?");

       assert(blk_end <= _unallocated_block, "_unallocated_block problem");

     }

   }

   inline void verify_not_unallocated(HeapWord* blk, size_t size) const {

     verify_not_unallocated(blk, blk + size);

   }

   void check_all_cards(size_t left_card, size_t right_card) const;

   virtual void set_for_starts_humongous(HeapWord* new_end);

 };

 // 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 G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {

   friend class VMStructs;

   // 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 to be called when allocation start crosses the next

   // threshold in the contig space.

   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {

     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,

                       blk_start, blk_end);

   }

  public:

   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);

   // Initialize the threshold to reflect the first boundary after the

   // bottom of the covered region.

   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; }

   // These must be guaranteed to work properly (i.e., do nothing)

   // when "blk_start" ("blk" for second version) is "NULL".  In this

   // implementation, that's true 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_work1(blk_start, blk_end);

   }

   void alloc_block(HeapWord* blk, size_t size) {

      alloc_block(blk, blk+size);

   }

   HeapWord* block_start_unsafe(const void* addr);

   HeapWord* block_start_unsafe_const(const void* addr) const;

   virtual void set_for_starts_humongous(HeapWord* new_end);

 };