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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP

 #include "gc_implementation/g1/g1RegionToSpaceMapper.hpp"

 #include "memory/memRegion.hpp"

 #include "runtime/virtualspace.hpp"

 #include "utilities/globalDefinitions.hpp"

 // 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 G1BlockOffsetSharedArray;

 class G1OffsetTableContigSpace;

 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,

            err_msg("new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",

                    p2i(new_bottom), p2i(_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;

 };

 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {

  public:

   virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) {

     // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot

     // retrieve it here since this would cause firing of several asserts. The code

     // executed after commit of a region already needs to do some re-initialization of

     // the HeapRegion, so we combine that.

   }

 };

 // 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<mtGC> {

   friend class G1BlockOffsetArray;

   friend class G1BlockOffsetArrayContigSpace;

   friend class VMStructs;

 private:

   G1BlockOffsetSharedArrayMappingChangedListener _listener;

   // 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.

   volatile u_char* _offset_array;          // byte array keeping backwards offsets

   void check_offset(size_t offset, const char* msg) const {

     assert(offset <= N_words,

            err_msg("%s - "

                    "offset: " SIZE_FORMAT ", N_words: " UINT32_FORMAT,

                    msg, offset, N_words));

   }

   // Bounds checking accessors:

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

   inline u_char offset_array(size_t index) const;

   inline void set_offset_array_raw(size_t index, u_char offset);

   inline void set_offset_array(size_t index, u_char offset);

   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);

   inline void set_offset_array(size_t left, size_t right, u_char offset);

   bool is_card_boundary(HeapWord* p) const;

 public:

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

   // that covers mem_region_words words.

   static size_t compute_size(size_t mem_region_words) {

     size_t number_of_slots = (mem_region_words / N_words);

     return ReservedSpace::allocation_align_size_up(number_of_slots);

   }

   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 heap, G1RegionToSpaceMapper* storage);

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

   inline size_t index_for(const void* p) const;

   inline size_t index_for_raw(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;

   // Variant of address_for_index that does not check the index for validity.

   inline HeapWord* address_for_index_raw(size_t index) const {

     return _reserved.start() + (index << LogN_words);

   }

 };

 // 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

   };

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

   // servicing different

   G1BlockOffsetSharedArray* _array;

   // The space that owns this subregion.

   G1OffsetTableContigSpace* _gsp;

   // 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);

 protected:

   G1OffsetTableContigSpace* gsp() const { return _gsp; }

   inline size_t block_size(const HeapWord* p) const;

   // 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. The elements of the array are

   // initialized to zero.

   G1BlockOffsetArray(G1BlockOffsetSharedArray* 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(G1OffsetTableContigSpace* sp);

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

   // the "new_word_size".

   void resize(size_t new_word_size);

   virtual HeapWord* block_start_unsafe(const void* addr);

   virtual HeapWord* block_start_unsafe_const(const void* addr) const;

   // Used by region verification. Checks that the contents of the

   // BOT reflect that there's a single object that spans the address

   // range [obj_start, obj_start + word_size); returns true if this is

   // the case, returns false if it's not.

   bool verify_for_object(HeapWord* obj_start, size_t word_size) const;

   void check_all_cards(size_t left_card, size_t right_card) const;

   virtual void print_on(outputStream* out) PRODUCT_RETURN;

 };

 // 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);

   }

   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the

   // memory first.

   void zero_bottom_entry_raw();

   // Variant of initialize_threshold that does not check for availability of the

   // memory first.

   HeapWord* initialize_threshold_raw();

  public:

   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);

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

   // bottom of the covered region.

   HeapWord* initialize_threshold();

   void reset_bot() {

     zero_bottom_entry_raw();

     initialize_threshold_raw();

   }

   // 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;

   void set_for_starts_humongous(HeapWord* new_top);

   virtual void print_on(outputStream* out) PRODUCT_RETURN;

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP