ysr@777: /*
ysr@777:  * Copyright 2001-2007 Sun Microsystems, Inc.  All Rights Reserved.
ysr@777:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
ysr@777:  *
ysr@777:  * This code is free software; you can redistribute it and/or modify it
ysr@777:  * under the terms of the GNU General Public License version 2 only, as
ysr@777:  * published by the Free Software Foundation.
ysr@777:  *
ysr@777:  * This code is distributed in the hope that it will be useful, but WITHOUT
ysr@777:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
ysr@777:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
ysr@777:  * version 2 for more details (a copy is included in the LICENSE file that
ysr@777:  * accompanied this code).
ysr@777:  *
ysr@777:  * You should have received a copy of the GNU General Public License version
ysr@777:  * 2 along with this work; if not, write to the Free Software Foundation,
ysr@777:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
ysr@777:  *
ysr@777:  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
ysr@777:  * CA 95054 USA or visit www.sun.com if you need additional information or
ysr@777:  * have any questions.
ysr@777:  *
ysr@777:  */
ysr@777: 
ysr@777: // The CollectedHeap type requires subtypes to implement a method
ysr@777: // "block_start".  For some subtypes, notably generational
ysr@777: // systems using card-table-based write barriers, the efficiency of this
ysr@777: // operation may be important.  Implementations of the "BlockOffsetArray"
ysr@777: // class may be useful in providing such efficient implementations.
ysr@777: //
ysr@777: // While generally mirroring the structure of the BOT for GenCollectedHeap,
ysr@777: // the following types are tailored more towards G1's uses; these should,
ysr@777: // however, be merged back into a common BOT to avoid code duplication
ysr@777: // and reduce maintenance overhead.
ysr@777: //
ysr@777: //    G1BlockOffsetTable (abstract)
ysr@777: //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)
ysr@777: //       -- G1BlockOffsetArrayContigSpace
ysr@777: //
ysr@777: // A main impediment to the consolidation of this code might be the
ysr@777: // effect of making some of the block_start*() calls non-const as
ysr@777: // below. Whether that might adversely affect performance optimizations
ysr@777: // that compilers might normally perform in the case of non-G1
ysr@777: // collectors needs to be carefully investigated prior to any such
ysr@777: // consolidation.
ysr@777: 
ysr@777: // Forward declarations
ysr@777: class ContiguousSpace;
ysr@777: class G1BlockOffsetSharedArray;
ysr@777: 
ysr@777: class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
ysr@777:   friend class VMStructs;
ysr@777: protected:
ysr@777:   // These members describe the region covered by the table.
ysr@777: 
ysr@777:   // The space this table is covering.
ysr@777:   HeapWord* _bottom;    // == reserved.start
ysr@777:   HeapWord* _end;       // End of currently allocated region.
ysr@777: 
ysr@777: public:
ysr@777:   // Initialize the table to cover the given space.
ysr@777:   // The contents of the initial table are undefined.
ysr@777:   G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
ysr@777:     _bottom(bottom), _end(end)
ysr@777:     {
ysr@777:       assert(_bottom <= _end, "arguments out of order");
ysr@777:     }
ysr@777: 
ysr@777:   // Note that the committed size of the covered space may have changed,
ysr@777:   // so the table size might also wish to change.
ysr@777:   virtual void resize(size_t new_word_size) = 0;
ysr@777: 
ysr@777:   virtual void set_bottom(HeapWord* new_bottom) {
ysr@777:     assert(new_bottom <= _end, "new_bottom > _end");
ysr@777:     _bottom = new_bottom;
ysr@777:     resize(pointer_delta(_end, _bottom));
ysr@777:   }
ysr@777: 
ysr@777:   // Requires "addr" to be contained by a block, and returns the address of
ysr@777:   // the start of that block.  (May have side effects, namely updating of
ysr@777:   // shared array entries that "point" too far backwards.  This can occur,
ysr@777:   // for example, when LAB allocation is used in a space covered by the
ysr@777:   // table.)
ysr@777:   virtual HeapWord* block_start_unsafe(const void* addr) = 0;
ysr@777:   // Same as above, but does not have any of the possible side effects
ysr@777:   // discussed above.
ysr@777:   virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
ysr@777: 
ysr@777:   // Returns the address of the start of the block containing "addr", or
ysr@777:   // else "null" if it is covered by no block.  (May have side effects,
ysr@777:   // namely updating of shared array entries that "point" too far
ysr@777:   // backwards.  This can occur, for example, when lab allocation is used
ysr@777:   // in a space covered by the table.)
ysr@777:   inline HeapWord* block_start(const void* addr);
ysr@777:   // Same as above, but does not have any of the possible side effects
ysr@777:   // discussed above.
ysr@777:   inline HeapWord* block_start_const(const void* addr) const;
ysr@777: };
ysr@777: 
ysr@777: // This implementation of "G1BlockOffsetTable" divides the covered region
ysr@777: // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
ysr@777: // for each such subregion indicates how far back one must go to find the
ysr@777: // start of the chunk that includes the first word of the subregion.
ysr@777: //
ysr@777: // Each BlockOffsetArray is owned by a Space.  However, the actual array
ysr@777: // may be shared by several BlockOffsetArrays; this is useful
ysr@777: // when a single resizable area (such as a generation) is divided up into
ysr@777: // several spaces in which contiguous allocation takes place,
ysr@777: // such as, for example, in G1 or in the train generation.)
ysr@777: 
ysr@777: // Here is the shared array type.
ysr@777: 
ysr@777: class G1BlockOffsetSharedArray: public CHeapObj {
ysr@777:   friend class G1BlockOffsetArray;
ysr@777:   friend class G1BlockOffsetArrayContigSpace;
ysr@777:   friend class VMStructs;
ysr@777: 
ysr@777: private:
ysr@777:   // The reserved region covered by the shared array.
ysr@777:   MemRegion _reserved;
ysr@777: 
ysr@777:   // End of the current committed region.
ysr@777:   HeapWord* _end;
ysr@777: 
ysr@777:   // Array for keeping offsets for retrieving object start fast given an
ysr@777:   // address.
ysr@777:   VirtualSpace _vs;
ysr@777:   u_char* _offset_array;          // byte array keeping backwards offsets
ysr@777: 
ysr@777:   // Bounds checking accessors:
ysr@777:   // For performance these have to devolve to array accesses in product builds.
ysr@777:   u_char offset_array(size_t index) const {
ysr@777:     assert(index < _vs.committed_size(), "index out of range");
ysr@777:     return _offset_array[index];
ysr@777:   }
ysr@777: 
ysr@777:   void set_offset_array(size_t index, u_char offset) {
ysr@777:     assert(index < _vs.committed_size(), "index out of range");
ysr@777:     assert(offset <= N_words, "offset too large");
ysr@777:     _offset_array[index] = offset;
ysr@777:   }
ysr@777: 
ysr@777:   void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
ysr@777:     assert(index < _vs.committed_size(), "index out of range");
ysr@777:     assert(high >= low, "addresses out of order");
ysr@777:     assert(pointer_delta(high, low) <= N_words, "offset too large");
ysr@777:     _offset_array[index] = (u_char) pointer_delta(high, low);
ysr@777:   }
ysr@777: 
ysr@777:   void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
ysr@777:     assert(index_for(right - 1) < _vs.committed_size(),
ysr@777:            "right address out of range");
ysr@777:     assert(left  < right, "Heap addresses out of order");
ysr@777:     size_t num_cards = pointer_delta(right, left) >> LogN_words;
ysr@777:     memset(&_offset_array[index_for(left)], offset, num_cards);
ysr@777:   }
ysr@777: 
ysr@777:   void set_offset_array(size_t left, size_t right, u_char offset) {
ysr@777:     assert(right < _vs.committed_size(), "right address out of range");
ysr@777:     assert(left  <= right, "indexes out of order");
ysr@777:     size_t num_cards = right - left + 1;
ysr@777:     memset(&_offset_array[left], offset, num_cards);
ysr@777:   }
ysr@777: 
ysr@777:   void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
ysr@777:     assert(index < _vs.committed_size(), "index out of range");
ysr@777:     assert(high >= low, "addresses out of order");
ysr@777:     assert(pointer_delta(high, low) <= N_words, "offset too large");
ysr@777:     assert(_offset_array[index] == pointer_delta(high, low),
ysr@777:            "Wrong offset");
ysr@777:   }
ysr@777: 
ysr@777:   bool is_card_boundary(HeapWord* p) const;
ysr@777: 
ysr@777:   // Return the number of slots needed for an offset array
ysr@777:   // that covers mem_region_words words.
ysr@777:   // We always add an extra slot because if an object
ysr@777:   // ends on a card boundary we put a 0 in the next
ysr@777:   // offset array slot, so we want that slot always
ysr@777:   // to be reserved.
ysr@777: 
ysr@777:   size_t compute_size(size_t mem_region_words) {
ysr@777:     size_t number_of_slots = (mem_region_words / N_words) + 1;
ysr@777:     return ReservedSpace::page_align_size_up(number_of_slots);
ysr@777:   }
ysr@777: 
ysr@777: public:
ysr@777:   enum SomePublicConstants {
ysr@777:     LogN = 9,
ysr@777:     LogN_words = LogN - LogHeapWordSize,
ysr@777:     N_bytes = 1 << LogN,
ysr@777:     N_words = 1 << LogN_words
ysr@777:   };
ysr@777: 
ysr@777:   // Initialize the table to cover from "base" to (at least)
ysr@777:   // "base + init_word_size".  In the future, the table may be expanded
ysr@777:   // (see "resize" below) up to the size of "_reserved" (which must be at
ysr@777:   // least "init_word_size".) The contents of the initial table are
ysr@777:   // undefined; it is the responsibility of the constituent
ysr@777:   // G1BlockOffsetTable(s) to initialize cards.
ysr@777:   G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
ysr@777: 
ysr@777:   // Notes a change in the committed size of the region covered by the
ysr@777:   // table.  The "new_word_size" may not be larger than the size of the
ysr@777:   // reserved region this table covers.
ysr@777:   void resize(size_t new_word_size);
ysr@777: 
ysr@777:   void set_bottom(HeapWord* new_bottom);
ysr@777: 
ysr@777:   // Updates all the BlockOffsetArray's sharing this shared array to
ysr@777:   // reflect the current "top"'s of their spaces.
ysr@777:   void update_offset_arrays();
ysr@777: 
ysr@777:   // Return the appropriate index into "_offset_array" for "p".
ysr@777:   inline size_t index_for(const void* p) const;
ysr@777: 
ysr@777:   // Return the address indicating the start of the region corresponding to
ysr@777:   // "index" in "_offset_array".
ysr@777:   inline HeapWord* address_for_index(size_t index) const;
ysr@777: };
ysr@777: 
ysr@777: // And here is the G1BlockOffsetTable subtype that uses the array.
ysr@777: 
ysr@777: class G1BlockOffsetArray: public G1BlockOffsetTable {
ysr@777:   friend class G1BlockOffsetSharedArray;
ysr@777:   friend class G1BlockOffsetArrayContigSpace;
ysr@777:   friend class VMStructs;
ysr@777: private:
ysr@777:   enum SomePrivateConstants {
ysr@777:     N_words = G1BlockOffsetSharedArray::N_words,
ysr@777:     LogN    = G1BlockOffsetSharedArray::LogN
ysr@777:   };
ysr@777: 
ysr@777:   // The following enums are used by do_block_helper
ysr@777:   enum Action {
ysr@777:     Action_single,      // BOT records a single block (see single_block())
ysr@777:     Action_mark,        // BOT marks the start of a block (see mark_block())
ysr@777:     Action_check        // Check that BOT records block correctly
ysr@777:                         // (see verify_single_block()).
ysr@777:   };
ysr@777: 
ysr@777:   // This is the array, which can be shared by several BlockOffsetArray's
ysr@777:   // servicing different
ysr@777:   G1BlockOffsetSharedArray* _array;
ysr@777: 
ysr@777:   // The space that owns this subregion.
ysr@777:   Space* _sp;
ysr@777: 
ysr@777:   // If "_sp" is a contiguous space, the field below is the view of "_sp"
ysr@777:   // as a contiguous space, else NULL.
ysr@777:   ContiguousSpace* _csp;
ysr@777: 
ysr@777:   // If true, array entries are initialized to 0; otherwise, they are
ysr@777:   // initialized to point backwards to the beginning of the covered region.
ysr@777:   bool _init_to_zero;
ysr@777: 
ysr@777:   // The portion [_unallocated_block, _sp.end()) of the space that
ysr@777:   // is a single block known not to contain any objects.
ysr@777:   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
ysr@777:   HeapWord* _unallocated_block;
ysr@777: 
ysr@777:   // Sets the entries
ysr@777:   // corresponding to the cards starting at "start" and ending at "end"
ysr@777:   // to point back to the card before "start": the interval [start, end)
ysr@777:   // is right-open.
ysr@777:   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
ysr@777:   // Same as above, except that the args here are a card _index_ interval
ysr@777:   // that is closed: [start_index, end_index]
ysr@777:   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
ysr@777: 
ysr@777:   // A helper function for BOT adjustment/verification work
ysr@777:   void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
ysr@777: 
ysr@777: protected:
ysr@777: 
ysr@777:   ContiguousSpace* csp() const { return _csp; }
ysr@777: 
ysr@777:   // Returns the address of a block whose start is at most "addr".
ysr@777:   // If "has_max_index" is true, "assumes "max_index" is the last valid one
ysr@777:   // in the array.
ysr@777:   inline HeapWord* block_at_or_preceding(const void* addr,
ysr@777:                                          bool has_max_index,
ysr@777:                                          size_t max_index) const;
ysr@777: 
ysr@777:   // "q" is a block boundary that is <= "addr"; "n" is the address of the
ysr@777:   // next block (or the end of the space.)  Return the address of the
ysr@777:   // beginning of the block that contains "addr".  Does so without side
ysr@777:   // effects (see, e.g., spec of  block_start.)
ysr@777:   inline HeapWord*
ysr@777:   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
ysr@777:                                          const void* addr) const;
ysr@777: 
ysr@777:   // "q" is a block boundary that is <= "addr"; return the address of the
ysr@777:   // beginning of the block that contains "addr".  May have side effects
ysr@777:   // on "this", by updating imprecise entries.
ysr@777:   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
ysr@777:                                                     const void* addr);
ysr@777: 
ysr@777:   // "q" is a block boundary that is <= "addr"; "n" is the address of the
ysr@777:   // next block (or the end of the space.)  Return the address of the
ysr@777:   // beginning of the block that contains "addr".  May have side effects
ysr@777:   // on "this", by updating imprecise entries.
ysr@777:   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
ysr@777:                                                   HeapWord* n,
ysr@777:                                                   const void* addr);
ysr@777: 
ysr@777:   // Requires that "*threshold_" be the first array entry boundary at or
ysr@777:   // above "blk_start", and that "*index_" be the corresponding array
ysr@777:   // index.  If the block starts at or crosses "*threshold_", records
ysr@777:   // "blk_start" as the appropriate block start for the array index
ysr@777:   // starting at "*threshold_", and for any other indices crossed by the
ysr@777:   // block.  Updates "*threshold_" and "*index_" to correspond to the first
ysr@777:   // index after the block end.
ysr@777:   void alloc_block_work2(HeapWord** threshold_, size_t* index_,
ysr@777:                          HeapWord* blk_start, HeapWord* blk_end);
ysr@777: 
ysr@777: public:
ysr@777:   // The space may not have it's bottom and top set yet, which is why the
ysr@777:   // region is passed as a parameter.  If "init_to_zero" is true, the
ysr@777:   // elements of the array are initialized to zero.  Otherwise, they are
ysr@777:   // initialized to point backwards to the beginning.
ysr@777:   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
ysr@777:                      bool init_to_zero);
ysr@777: 
ysr@777:   // Note: this ought to be part of the constructor, but that would require
ysr@777:   // "this" to be passed as a parameter to a member constructor for
ysr@777:   // the containing concrete subtype of Space.
ysr@777:   // This would be legal C++, but MS VC++ doesn't allow it.
ysr@777:   void set_space(Space* sp);
ysr@777: 
ysr@777:   // Resets the covered region to the given "mr".
ysr@777:   void set_region(MemRegion mr);
ysr@777: 
ysr@777:   // Resets the covered region to one with the same _bottom as before but
ysr@777:   // the "new_word_size".
ysr@777:   void resize(size_t new_word_size);
ysr@777: 
ysr@777:   // These must be guaranteed to work properly (i.e., do nothing)
ysr@777:   // when "blk_start" ("blk" for second version) is "NULL".
ysr@777:   virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
ysr@777:   virtual void alloc_block(HeapWord* blk, size_t size) {
ysr@777:     alloc_block(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   // The following methods are useful and optimized for a
ysr@777:   // general, non-contiguous space.
ysr@777: 
ysr@777:   // The given arguments are required to be the starts of adjacent ("blk1"
ysr@777:   // before "blk2") well-formed blocks covered by "this".  After this call,
ysr@777:   // they should be considered to form one block.
ysr@777:   virtual void join_blocks(HeapWord* blk1, HeapWord* blk2);
ysr@777: 
ysr@777:   // Given a block [blk_start, blk_start + full_blk_size), and
ysr@777:   // a left_blk_size < full_blk_size, adjust the BOT to show two
ysr@777:   // blocks [blk_start, blk_start + left_blk_size) and
ysr@777:   // [blk_start + left_blk_size, blk_start + full_blk_size).
ysr@777:   // It is assumed (and verified in the non-product VM) that the
ysr@777:   // BOT was correct for the original block.
ysr@777:   void split_block(HeapWord* blk_start, size_t full_blk_size,
ysr@777:                            size_t left_blk_size);
ysr@777: 
ysr@777:   // Adjust the BOT to show that it has a single block in the
ysr@777:   // range [blk_start, blk_start + size). All necessary BOT
ysr@777:   // cards are adjusted, but _unallocated_block isn't.
ysr@777:   void single_block(HeapWord* blk_start, HeapWord* blk_end);
ysr@777:   void single_block(HeapWord* blk, size_t size) {
ysr@777:     single_block(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   // Adjust BOT to show that it has a block in the range
ysr@777:   // [blk_start, blk_start + size). Only the first card
ysr@777:   // of BOT is touched. It is assumed (and verified in the
ysr@777:   // non-product VM) that the remaining cards of the block
ysr@777:   // are correct.
ysr@777:   void mark_block(HeapWord* blk_start, HeapWord* blk_end);
ysr@777:   void mark_block(HeapWord* blk, size_t size) {
ysr@777:     mark_block(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   // Adjust _unallocated_block to indicate that a particular
ysr@777:   // block has been newly allocated or freed. It is assumed (and
ysr@777:   // verified in the non-product VM) that the BOT is correct for
ysr@777:   // the given block.
ysr@777:   inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
ysr@777:     // Verify that the BOT shows [blk, blk + blk_size) to be one block.
ysr@777:     verify_single_block(blk_start, blk_end);
ysr@777:     if (BlockOffsetArrayUseUnallocatedBlock) {
ysr@777:       _unallocated_block = MAX2(_unallocated_block, blk_end);
ysr@777:     }
ysr@777:   }
ysr@777: 
ysr@777:   inline void allocated(HeapWord* blk, size_t size) {
ysr@777:     allocated(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   inline void freed(HeapWord* blk_start, HeapWord* blk_end);
ysr@777: 
ysr@777:   inline void freed(HeapWord* blk, size_t size);
ysr@777: 
ysr@777:   virtual HeapWord* block_start_unsafe(const void* addr);
ysr@777:   virtual HeapWord* block_start_unsafe_const(const void* addr) const;
ysr@777: 
ysr@777:   // Requires "addr" to be the start of a card and returns the
ysr@777:   // start of the block that contains the given address.
ysr@777:   HeapWord* block_start_careful(const void* addr) const;
ysr@777: 
ysr@777:   // If true, initialize array slots with no allocated blocks to zero.
ysr@777:   // Otherwise, make them point back to the front.
ysr@777:   bool init_to_zero() { return _init_to_zero; }
ysr@777: 
ysr@777:   // Verification & debugging - ensure that the offset table reflects the fact
ysr@777:   // that the block [blk_start, blk_end) or [blk, blk + size) is a
ysr@777:   // single block of storage. NOTE: can;t const this because of
ysr@777:   // call to non-const do_block_internal() below.
ysr@777:   inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
ysr@777:     if (VerifyBlockOffsetArray) {
ysr@777:       do_block_internal(blk_start, blk_end, Action_check);
ysr@777:     }
ysr@777:   }
ysr@777: 
ysr@777:   inline void verify_single_block(HeapWord* blk, size_t size) {
ysr@777:     verify_single_block(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   // Verify that the given block is before _unallocated_block
ysr@777:   inline void verify_not_unallocated(HeapWord* blk_start,
ysr@777:                                      HeapWord* blk_end) const {
ysr@777:     if (BlockOffsetArrayUseUnallocatedBlock) {
ysr@777:       assert(blk_start < blk_end, "Block inconsistency?");
ysr@777:       assert(blk_end <= _unallocated_block, "_unallocated_block problem");
ysr@777:     }
ysr@777:   }
ysr@777: 
ysr@777:   inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
ysr@777:     verify_not_unallocated(blk, blk + size);
ysr@777:   }
ysr@777: 
ysr@777:   void check_all_cards(size_t left_card, size_t right_card) const;
ysr@777: };
ysr@777: 
ysr@777: // A subtype of BlockOffsetArray that takes advantage of the fact
ysr@777: // that its underlying space is a ContiguousSpace, so that its "active"
ysr@777: // region can be more efficiently tracked (than for a non-contiguous space).
ysr@777: class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
ysr@777:   friend class VMStructs;
ysr@777: 
ysr@777:   // allocation boundary at which offset array must be updated
ysr@777:   HeapWord* _next_offset_threshold;
ysr@777:   size_t    _next_offset_index;      // index corresponding to that boundary
ysr@777: 
ysr@777:   // Work function to be called when allocation start crosses the next
ysr@777:   // threshold in the contig space.
ysr@777:   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
ysr@777:     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
ysr@777:                       blk_start, blk_end);
ysr@777:   }
ysr@777: 
ysr@777: 
ysr@777:  public:
ysr@777:   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
ysr@777: 
ysr@777:   // Initialize the threshold to reflect the first boundary after the
ysr@777:   // bottom of the covered region.
ysr@777:   HeapWord* initialize_threshold();
ysr@777: 
ysr@777:   // Zero out the entry for _bottom (offset will be zero).
ysr@777:   void      zero_bottom_entry();
ysr@777: 
ysr@777:   // Return the next threshold, the point at which the table should be
ysr@777:   // updated.
ysr@777:   HeapWord* threshold() const { return _next_offset_threshold; }
ysr@777: 
ysr@777:   // These must be guaranteed to work properly (i.e., do nothing)
ysr@777:   // when "blk_start" ("blk" for second version) is "NULL".  In this
ysr@777:   // implementation, that's true because NULL is represented as 0, and thus
ysr@777:   // never exceeds the "_next_offset_threshold".
ysr@777:   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
ysr@777:     if (blk_end > _next_offset_threshold)
ysr@777:       alloc_block_work1(blk_start, blk_end);
ysr@777:   }
ysr@777:   void alloc_block(HeapWord* blk, size_t size) {
ysr@777:      alloc_block(blk, blk+size);
ysr@777:   }
ysr@777: 
ysr@777:   HeapWord* block_start_unsafe(const void* addr);
ysr@777:   HeapWord* block_start_unsafe_const(const void* addr) const;
ysr@777: };