1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  24 
  25 #ifndef SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP
  26 #define SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP
  27 
  28 #include "gc/g1/g1RegionToSpaceMapper.hpp"
  29 #include "gc/shared/blockOffsetTable.hpp"
  30 #include "memory/memRegion.hpp"
  31 #include "memory/virtualspace.hpp"
  32 #include "utilities/globalDefinitions.hpp"
  33 
  34 // Forward declarations
  35 class G1BlockOffsetTable;
  36 class G1ContiguousSpace;
  37 
  38 // This implementation of "G1BlockOffsetTable" divides the covered region
  39 // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
  40 // for each such subregion indicates how far back one must go to find the
  41 // start of the chunk that includes the first word of the subregion.
  42 //
  43 // Each G1BlockOffsetTablePart is owned by a G1ContiguousSpace.
  44 
  45 class G1BlockOffsetTable: public CHeapObj<mtGC> {
  46   friend class G1BlockOffsetTablePart;
  47   friend class VMStructs;
  48 
  49 private:
  50   // The reserved region covered by the table.
  51   MemRegion _reserved;
  52 
  53   // Array for keeping offsets for retrieving object start fast given an
  54   // address.
  55   u_char* _offset_array;          // byte array keeping backwards offsets
  56 
  57   void check_offset(size_t offset, const char* msg) const {
  58     assert(offset <= BOTConstants::N_words,
  59            "%s - offset: " SIZE_FORMAT ", N_words: %u",
  60            msg, offset, BOTConstants::N_words);
  61   }
  62 
  63   // Bounds checking accessors:
  64   // For performance these have to devolve to array accesses in product builds.
  65   inline u_char offset_array(size_t index) const;
  66 
  67   void set_offset_array_raw(size_t index, u_char offset) {
  68     _offset_array[index] = offset;
  69   }
  70 
  71   inline void set_offset_array(size_t index, u_char offset);
  72 
  73   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
  74 
  75   inline void set_offset_array(size_t left, size_t right, u_char offset);
  76 
  77   bool is_card_boundary(HeapWord* p) const;
  78 
  79   void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
  80 
  81 public:
  82 
  83   // Return the number of slots needed for an offset array
  84   // that covers mem_region_words words.
  85   static size_t compute_size(size_t mem_region_words) {
  86     size_t number_of_slots = (mem_region_words / BOTConstants::N_words);
  87     return ReservedSpace::allocation_align_size_up(number_of_slots);
  88   }
  89 
  90   // Returns how many bytes of the heap a single byte of the BOT corresponds to.
  91   static size_t heap_map_factor() {
  92     return BOTConstants::N_bytes;
  93   }
  94 
  95   // Initialize the Block Offset Table to cover the memory region passed
  96   // in the heap parameter.
  97   G1BlockOffsetTable(MemRegion heap, G1RegionToSpaceMapper* storage);
  98 
  99   // Return the appropriate index into "_offset_array" for "p".
 100   inline size_t index_for(const void* p) const;
 101   inline size_t index_for_raw(const void* p) const;
 102 
 103   // Return the address indicating the start of the region corresponding to
 104   // "index" in "_offset_array".
 105   inline HeapWord* address_for_index(size_t index) const;
 106   // Variant of address_for_index that does not check the index for validity.
 107   inline HeapWord* address_for_index_raw(size_t index) const {
 108     return _reserved.start() + (index << BOTConstants::LogN_words);
 109   }
 110 };
 111 
 112 class G1BlockOffsetTablePart VALUE_OBJ_CLASS_SPEC {
 113   friend class G1BlockOffsetTable;
 114   friend class VMStructs;
 115 private:
 116   // allocation boundary at which offset array must be updated
 117   HeapWord* _next_offset_threshold;
 118   size_t    _next_offset_index;      // index corresponding to that boundary
 119 
 120   // Indicates if an object can span into this G1BlockOffsetTablePart.
 121   debug_only(bool _object_can_span;)
 122 
 123   // This is the global BlockOffsetTable.
 124   G1BlockOffsetTable* _bot;
 125 
 126   // The space that owns this subregion.
 127   G1ContiguousSpace* _space;
 128 
 129   // Sets the entries
 130   // corresponding to the cards starting at "start" and ending at "end"
 131   // to point back to the card before "start": the interval [start, end)
 132   // is right-open.
 133   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
 134   // Same as above, except that the args here are a card _index_ interval
 135   // that is closed: [start_index, end_index]
 136   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
 137 
 138   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
 139   // memory first.
 140   void zero_bottom_entry_raw();
 141   // Variant of initialize_threshold that does not check for availability of the
 142   // memory first.
 143   HeapWord* initialize_threshold_raw();
 144 
 145   inline size_t block_size(const HeapWord* p) const;
 146 
 147   // Returns the address of a block whose start is at most "addr".
 148   // If "has_max_index" is true, "assumes "max_index" is the last valid one
 149   // in the array.
 150   inline HeapWord* block_at_or_preceding(const void* addr,
 151                                          bool has_max_index,
 152                                          size_t max_index) const;
 153 
 154   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 155   // next block (or the end of the space.)  Return the address of the
 156   // beginning of the block that contains "addr".  Does so without side
 157   // effects (see, e.g., spec of  block_start.)
 158   inline HeapWord* forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
 159                                                           const void* addr) const;
 160 
 161   // "q" is a block boundary that is <= "addr"; return the address of the
 162   // beginning of the block that contains "addr".  May have side effects
 163   // on "this", by updating imprecise entries.
 164   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
 165                                                     const void* addr);
 166 
 167   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 168   // next block (or the end of the space.)  Return the address of the
 169   // beginning of the block that contains "addr".  May have side effects
 170   // on "this", by updating imprecise entries.
 171   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
 172                                                   HeapWord* n,
 173                                                   const void* addr);
 174 
 175   // Requires that "*threshold_" be the first array entry boundary at or
 176   // above "blk_start", and that "*index_" be the corresponding array
 177   // index.  If the block starts at or crosses "*threshold_", records
 178   // "blk_start" as the appropriate block start for the array index
 179   // starting at "*threshold_", and for any other indices crossed by the
 180   // block.  Updates "*threshold_" and "*index_" to correspond to the first
 181   // index after the block end.
 182   void alloc_block_work(HeapWord** threshold_, size_t* index_,
 183                         HeapWord* blk_start, HeapWord* blk_end);
 184 
 185   void check_all_cards(size_t left_card, size_t right_card) const;
 186 
 187 public:
 188   //  The elements of the array are initialized to zero.
 189   G1BlockOffsetTablePart(G1BlockOffsetTable* array, G1ContiguousSpace* gsp);
 190 
 191   void verify() const;
 192 
 193   // Returns the address of the start of the block containing "addr", or
 194   // else "null" if it is covered by no block.  (May have side effects,
 195   // namely updating of shared array entries that "point" too far
 196   // backwards.  This can occur, for example, when lab allocation is used
 197   // in a space covered by the table.)
 198   inline HeapWord* block_start(const void* addr);
 199   // Same as above, but does not have any of the possible side effects
 200   // discussed above.
 201   inline HeapWord* block_start_const(const void* addr) const;
 202 
 203   // Initialize the threshold to reflect the first boundary after the
 204   // bottom of the covered region.
 205   HeapWord* initialize_threshold();
 206 
 207   void reset_bot() {
 208     zero_bottom_entry_raw();
 209     initialize_threshold_raw();
 210   }
 211 
 212   // Return the next threshold, the point at which the table should be
 213   // updated.
 214   HeapWord* threshold() const { return _next_offset_threshold; }
 215 
 216   // These must be guaranteed to work properly (i.e., do nothing)
 217   // when "blk_start" ("blk" for second version) is "NULL".  In this
 218   // implementation, that's true because NULL is represented as 0, and thus
 219   // never exceeds the "_next_offset_threshold".
 220   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 221     if (blk_end > _next_offset_threshold) {
 222       alloc_block_work(&_next_offset_threshold, &_next_offset_index, blk_start, blk_end);
 223     }
 224   }
 225   void alloc_block(HeapWord* blk, size_t size) {
 226     alloc_block(blk, blk+size);
 227   }
 228 
 229   void set_for_starts_humongous(HeapWord* obj_top, size_t fill_size);
 230   void set_object_can_span(bool can_span) NOT_DEBUG_RETURN;
 231 
 232   void print_on(outputStream* out) PRODUCT_RETURN;
 233 };
 234 
 235 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP