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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 "memory/memRegion.hpp"
  30 #include "memory/virtualspace.hpp"
  31 #include "utilities/globalDefinitions.hpp"
  32 
  33 // The CollectedHeap type requires subtypes to implement a method
  34 // "block_start".  For some subtypes, notably generational
  35 // systems using card-table-based write barriers, the efficiency of this
  36 // operation may be important.  Implementations of the "BlockOffsetArray"
  37 // class may be useful in providing such efficient implementations.
  38 //
  39 // While generally mirroring the structure of the BOT for GenCollectedHeap,
  40 // the following types are tailored more towards G1's uses; these should,
  41 // however, be merged back into a common BOT to avoid code duplication
  42 // and reduce maintenance overhead.
  43 //
  44 //    G1BlockOffsetTable (abstract)
  45 //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)
  46 //       -- G1BlockOffsetArrayContigSpace
  47 //
  48 // A main impediment to the consolidation of this code might be the
  49 // effect of making some of the block_start*() calls non-const as
  50 // below. Whether that might adversely affect performance optimizations
  51 // that compilers might normally perform in the case of non-G1
  52 // collectors needs to be carefully investigated prior to any such
  53 // consolidation.
  54 
  55 // Forward declarations
  56 class G1BlockOffsetSharedArray;
  57 class G1OffsetTableContigSpace;
  58 
  59 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
  60   friend class VMStructs;
  61 protected:
  62   // These members describe the region covered by the table.
  63 
  64   // The space this table is covering.
  65   HeapWord* _bottom;    // == reserved.start
  66   HeapWord* _end;       // End of currently allocated region.
  67 
  68 public:
  69   // Initialize the table to cover the given space.
  70   // The contents of the initial table are undefined.
  71   G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
  72     _bottom(bottom), _end(end)
  73     {
  74       assert(_bottom <= _end, "arguments out of order");
  75     }
  76 
  77   // Note that the committed size of the covered space may have changed,
  78   // so the table size might also wish to change.
  79   virtual void resize(size_t new_word_size) = 0;
  80 
  81   virtual void set_bottom(HeapWord* new_bottom) {
  82     assert(new_bottom <= _end,
  83            "new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",
  84            p2i(new_bottom), p2i(_end));
  85     _bottom = new_bottom;
  86     resize(pointer_delta(_end, _bottom));
  87   }
  88 
  89   // Requires "addr" to be contained by a block, and returns the address of
  90   // the start of that block.  (May have side effects, namely updating of
  91   // shared array entries that "point" too far backwards.  This can occur,
  92   // for example, when LAB allocation is used in a space covered by the
  93   // table.)
  94   virtual HeapWord* block_start_unsafe(const void* addr) = 0;
  95   // Same as above, but does not have any of the possible side effects
  96   // discussed above.
  97   virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
  98 
  99   // Returns the address of the start of the block containing "addr", or
 100   // else "null" if it is covered by no block.  (May have side effects,
 101   // namely updating of shared array entries that "point" too far
 102   // backwards.  This can occur, for example, when lab allocation is used
 103   // in a space covered by the table.)
 104   inline HeapWord* block_start(const void* addr);
 105   // Same as above, but does not have any of the possible side effects
 106   // discussed above.
 107   inline HeapWord* block_start_const(const void* addr) const;
 108 };
 109 
 110 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {
 111  public:
 112   virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
 113     // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot
 114     // retrieve it here since this would cause firing of several asserts. The code
 115     // executed after commit of a region already needs to do some re-initialization of
 116     // the HeapRegion, so we combine that.
 117   }
 118 };
 119 
 120 // This implementation of "G1BlockOffsetTable" divides the covered region
 121 // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
 122 // for each such subregion indicates how far back one must go to find the
 123 // start of the chunk that includes the first word of the subregion.
 124 //
 125 // Each BlockOffsetArray is owned by a Space.  However, the actual array
 126 // may be shared by several BlockOffsetArrays; this is useful
 127 // when a single resizable area (such as a generation) is divided up into
 128 // several spaces in which contiguous allocation takes place,
 129 // such as, for example, in G1 or in the train generation.)
 130 
 131 // Here is the shared array type.
 132 
 133 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {
 134   friend class G1BlockOffsetArray;
 135   friend class G1BlockOffsetArrayContigSpace;
 136   friend class VMStructs;
 137 
 138 private:
 139   G1BlockOffsetSharedArrayMappingChangedListener _listener;
 140   // The reserved region covered by the shared array.
 141   MemRegion _reserved;
 142 
 143   // End of the current committed region.
 144   HeapWord* _end;
 145 
 146   // Array for keeping offsets for retrieving object start fast given an
 147   // address.
 148   u_char* _offset_array;          // byte array keeping backwards offsets
 149 
 150   void check_offset(size_t offset, const char* msg) const {
 151     assert(offset <= N_words,
 152            "%s - "
 153            "offset: " SIZE_FORMAT ", N_words: %u",
 154            msg, offset, (uint)N_words);
 155   }
 156 
 157   // Bounds checking accessors:
 158   // For performance these have to devolve to array accesses in product builds.
 159   inline u_char offset_array(size_t index) const;
 160 
 161   void set_offset_array_raw(size_t index, u_char offset) {
 162     _offset_array[index] = offset;
 163   }
 164 
 165   inline void set_offset_array(size_t index, u_char offset);
 166 
 167   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
 168 
 169   inline void set_offset_array(size_t left, size_t right, u_char offset);
 170 
 171   bool is_card_boundary(HeapWord* p) const;
 172 
 173   void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
 174 
 175 public:
 176 
 177   // Return the number of slots needed for an offset array
 178   // that covers mem_region_words words.
 179   static size_t compute_size(size_t mem_region_words) {
 180     size_t number_of_slots = (mem_region_words / N_words);
 181     return ReservedSpace::allocation_align_size_up(number_of_slots);
 182   }
 183 
 184   // Returns how many bytes of the heap a single byte of the BOT corresponds to.
 185   static size_t heap_map_factor() {
 186     return N_bytes;
 187   }
 188 
 189   enum SomePublicConstants {
 190     LogN = 9,
 191     LogN_words = LogN - LogHeapWordSize,
 192     N_bytes = 1 << LogN,
 193     N_words = 1 << LogN_words
 194   };
 195 
 196   // Initialize the table to cover from "base" to (at least)
 197   // "base + init_word_size".  In the future, the table may be expanded
 198   // (see "resize" below) up to the size of "_reserved" (which must be at
 199   // least "init_word_size".) The contents of the initial table are
 200   // undefined; it is the responsibility of the constituent
 201   // G1BlockOffsetTable(s) to initialize cards.
 202   G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);
 203 
 204   // Return the appropriate index into "_offset_array" for "p".
 205   inline size_t index_for(const void* p) const;
 206   inline size_t index_for_raw(const void* p) const;
 207 
 208   // Return the address indicating the start of the region corresponding to
 209   // "index" in "_offset_array".
 210   inline HeapWord* address_for_index(size_t index) const;
 211   // Variant of address_for_index that does not check the index for validity.
 212   inline HeapWord* address_for_index_raw(size_t index) const {
 213     return _reserved.start() + (index << LogN_words);
 214   }
 215 };
 216 
 217 // And here is the G1BlockOffsetTable subtype that uses the array.
 218 
 219 class G1BlockOffsetArray: public G1BlockOffsetTable {
 220   friend class G1BlockOffsetSharedArray;
 221   friend class G1BlockOffsetArrayContigSpace;
 222   friend class VMStructs;
 223 private:
 224   enum SomePrivateConstants {
 225     N_words = G1BlockOffsetSharedArray::N_words,
 226     LogN    = G1BlockOffsetSharedArray::LogN
 227   };
 228 
 229   // This is the array, which can be shared by several BlockOffsetArray's
 230   // servicing different
 231   G1BlockOffsetSharedArray* _array;
 232 
 233   // The space that owns this subregion.
 234   G1OffsetTableContigSpace* _gsp;
 235 
 236   // The portion [_unallocated_block, _sp.end()) of the space that
 237   // is a single block known not to contain any objects.
 238   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
 239   HeapWord* _unallocated_block;
 240 
 241   // Sets the entries
 242   // corresponding to the cards starting at "start" and ending at "end"
 243   // to point back to the card before "start": the interval [start, end)
 244   // is right-open.
 245   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
 246   // Same as above, except that the args here are a card _index_ interval
 247   // that is closed: [start_index, end_index]
 248   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
 249 
 250 protected:
 251 
 252   G1OffsetTableContigSpace* gsp() const { return _gsp; }
 253 
 254   inline size_t block_size(const HeapWord* p) const;
 255 
 256   // Returns the address of a block whose start is at most "addr".
 257   // If "has_max_index" is true, "assumes "max_index" is the last valid one
 258   // in the array.
 259   inline HeapWord* block_at_or_preceding(const void* addr,
 260                                          bool has_max_index,
 261                                          size_t max_index) const;
 262 
 263   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 264   // next block (or the end of the space.)  Return the address of the
 265   // beginning of the block that contains "addr".  Does so without side
 266   // effects (see, e.g., spec of  block_start.)
 267   inline HeapWord*
 268   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
 269                                          const void* addr) const;
 270 
 271   // "q" is a block boundary that is <= "addr"; return the address of the
 272   // beginning of the block that contains "addr".  May have side effects
 273   // on "this", by updating imprecise entries.
 274   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
 275                                                     const void* addr);
 276 
 277   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 278   // next block (or the end of the space.)  Return the address of the
 279   // beginning of the block that contains "addr".  May have side effects
 280   // on "this", by updating imprecise entries.
 281   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
 282                                                   HeapWord* n,
 283                                                   const void* addr);
 284 
 285   // Requires that "*threshold_" be the first array entry boundary at or
 286   // above "blk_start", and that "*index_" be the corresponding array
 287   // index.  If the block starts at or crosses "*threshold_", records
 288   // "blk_start" as the appropriate block start for the array index
 289   // starting at "*threshold_", and for any other indices crossed by the
 290   // block.  Updates "*threshold_" and "*index_" to correspond to the first
 291   // index after the block end.
 292   void alloc_block_work2(HeapWord** threshold_, size_t* index_,
 293                          HeapWord* blk_start, HeapWord* blk_end);
 294 
 295 public:
 296   // The space may not have it's bottom and top set yet, which is why the
 297   // region is passed as a parameter. The elements of the array are
 298   // initialized to zero.
 299   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr);
 300 
 301   // Note: this ought to be part of the constructor, but that would require
 302   // "this" to be passed as a parameter to a member constructor for
 303   // the containing concrete subtype of Space.
 304   // This would be legal C++, but MS VC++ doesn't allow it.
 305   void set_space(G1OffsetTableContigSpace* sp);
 306 
 307   // Resets the covered region to one with the same _bottom as before but
 308   // the "new_word_size".
 309   void resize(size_t new_word_size);
 310 
 311   virtual HeapWord* block_start_unsafe(const void* addr);
 312   virtual HeapWord* block_start_unsafe_const(const void* addr) const;
 313 
 314   void check_all_cards(size_t left_card, size_t right_card) const;
 315 
 316   void verify() const;
 317 
 318   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 319 };
 320 
 321 // A subtype of BlockOffsetArray that takes advantage of the fact
 322 // that its underlying space is a ContiguousSpace, so that its "active"
 323 // region can be more efficiently tracked (than for a non-contiguous space).
 324 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
 325   friend class VMStructs;
 326 
 327   // allocation boundary at which offset array must be updated
 328   HeapWord* _next_offset_threshold;
 329   size_t    _next_offset_index;      // index corresponding to that boundary
 330 
 331   // Work function to be called when allocation start crosses the next
 332   // threshold in the contig space.
 333   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
 334     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
 335                       blk_start, blk_end);
 336   }
 337 
 338   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
 339   // memory first.
 340   void zero_bottom_entry_raw();
 341   // Variant of initialize_threshold that does not check for availability of the
 342   // memory first.
 343   HeapWord* initialize_threshold_raw();
 344  public:
 345   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
 346 
 347   // Initialize the threshold to reflect the first boundary after the
 348   // bottom of the covered region.
 349   HeapWord* initialize_threshold();
 350 
 351   void reset_bot() {
 352     zero_bottom_entry_raw();
 353     initialize_threshold_raw();
 354   }
 355 
 356   // Return the next threshold, the point at which the table should be
 357   // updated.
 358   HeapWord* threshold() const { return _next_offset_threshold; }
 359 
 360   // These must be guaranteed to work properly (i.e., do nothing)
 361   // when "blk_start" ("blk" for second version) is "NULL".  In this
 362   // implementation, that's true because NULL is represented as 0, and thus
 363   // never exceeds the "_next_offset_threshold".
 364   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 365     if (blk_end > _next_offset_threshold)
 366       alloc_block_work1(blk_start, blk_end);
 367   }
 368   void alloc_block(HeapWord* blk, size_t size) {
 369      alloc_block(blk, blk+size);
 370   }
 371 
 372   HeapWord* block_start_unsafe(const void* addr);
 373   HeapWord* block_start_unsafe_const(const void* addr) const;
 374 
 375   void set_for_starts_humongous(HeapWord* new_top);
 376 
 377   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 378 };
 379 
 380 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP