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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 - offset: " SIZE_FORMAT ", N_words: %u",
 153            msg, offset, (uint)N_words);
 154   }
 155 
 156   // Bounds checking accessors:
 157   // For performance these have to devolve to array accesses in product builds.
 158   inline u_char offset_array(size_t index) const;
 159 
 160   void set_offset_array_raw(size_t index, u_char offset) {
 161     _offset_array[index] = offset;
 162   }
 163 
 164   inline void set_offset_array(size_t index, u_char offset);
 165 
 166   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
 167 
 168   inline void set_offset_array(size_t left, size_t right, u_char offset);
 169 
 170   bool is_card_boundary(HeapWord* p) const;
 171 
 172   void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
 173 
 174 public:
 175 
 176   // Return the number of slots needed for an offset array
 177   // that covers mem_region_words words.
 178   static size_t compute_size(size_t mem_region_words) {
 179     size_t number_of_slots = (mem_region_words / N_words);
 180     return ReservedSpace::allocation_align_size_up(number_of_slots);
 181   }
 182 
 183   // Returns how many bytes of the heap a single byte of the BOT corresponds to.
 184   static size_t heap_map_factor() {
 185     return N_bytes;
 186   }
 187 
 188   enum SomePublicConstants {
 189     LogN = 9,
 190     LogN_words = LogN - LogHeapWordSize,
 191     N_bytes = 1 << LogN,
 192     N_words = 1 << LogN_words
 193   };
 194 
 195   // Initialize the table to cover from "base" to (at least)
 196   // "base + init_word_size".  In the future, the table may be expanded
 197   // (see "resize" below) up to the size of "_reserved" (which must be at
 198   // least "init_word_size".) The contents of the initial table are
 199   // undefined; it is the responsibility of the constituent
 200   // G1BlockOffsetTable(s) to initialize cards.
 201   G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);
 202 
 203   // Return the appropriate index into "_offset_array" for "p".
 204   inline size_t index_for(const void* p) const;
 205   inline size_t index_for_raw(const void* p) const;
 206 
 207   // Return the address indicating the start of the region corresponding to
 208   // "index" in "_offset_array".
 209   inline HeapWord* address_for_index(size_t index) const;
 210   // Variant of address_for_index that does not check the index for validity.
 211   inline HeapWord* address_for_index_raw(size_t index) const {
 212     return _reserved.start() + (index << LogN_words);
 213   }
 214 };
 215 
 216 // And here is the G1BlockOffsetTable subtype that uses the array.
 217 
 218 class G1BlockOffsetArray: public G1BlockOffsetTable {
 219   friend class G1BlockOffsetSharedArray;
 220   friend class G1BlockOffsetArrayContigSpace;
 221   friend class VMStructs;
 222 private:
 223   enum SomePrivateConstants {
 224     N_words = G1BlockOffsetSharedArray::N_words,
 225     LogN    = G1BlockOffsetSharedArray::LogN
 226   };
 227 
 228   // This is the array, which can be shared by several BlockOffsetArray's
 229   // servicing different
 230   G1BlockOffsetSharedArray* _array;
 231 
 232   // The space that owns this subregion.
 233   G1OffsetTableContigSpace* _gsp;
 234 
 235   // The portion [_unallocated_block, _sp.end()) of the space that
 236   // is a single block known not to contain any objects.
 237   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
 238   HeapWord* _unallocated_block;
 239 
 240   // Sets the entries
 241   // corresponding to the cards starting at "start" and ending at "end"
 242   // to point back to the card before "start": the interval [start, end)
 243   // is right-open.
 244   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
 245   // Same as above, except that the args here are a card _index_ interval
 246   // that is closed: [start_index, end_index]
 247   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
 248 
 249 protected:
 250 
 251   G1OffsetTableContigSpace* gsp() const { return _gsp; }
 252 
 253   inline size_t block_size(const HeapWord* p) const;
 254 
 255   // Returns the address of a block whose start is at most "addr".
 256   // If "has_max_index" is true, "assumes "max_index" is the last valid one
 257   // in the array.
 258   inline HeapWord* block_at_or_preceding(const void* addr,
 259                                          bool has_max_index,
 260                                          size_t max_index) const;
 261 
 262   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 263   // next block (or the end of the space.)  Return the address of the
 264   // beginning of the block that contains "addr".  Does so without side
 265   // effects (see, e.g., spec of  block_start.)
 266   inline HeapWord*
 267   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
 268                                          const void* addr) const;
 269 
 270   // "q" is a block boundary that is <= "addr"; return the address of the
 271   // beginning of the block that contains "addr".  May have side effects
 272   // on "this", by updating imprecise entries.
 273   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
 274                                                     const void* addr);
 275 
 276   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 277   // next block (or the end of the space.)  Return the address of the
 278   // beginning of the block that contains "addr".  May have side effects
 279   // on "this", by updating imprecise entries.
 280   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
 281                                                   HeapWord* n,
 282                                                   const void* addr);
 283 
 284   // Requires that "*threshold_" be the first array entry boundary at or
 285   // above "blk_start", and that "*index_" be the corresponding array
 286   // index.  If the block starts at or crosses "*threshold_", records
 287   // "blk_start" as the appropriate block start for the array index
 288   // starting at "*threshold_", and for any other indices crossed by the
 289   // block.  Updates "*threshold_" and "*index_" to correspond to the first
 290   // index after the block end.
 291   void alloc_block_work2(HeapWord** threshold_, size_t* index_,
 292                          HeapWord* blk_start, HeapWord* blk_end);
 293 
 294 public:
 295   // The space may not have it's bottom and top set yet, which is why the
 296   // region is passed as a parameter. The elements of the array are
 297   // initialized to zero.
 298   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr);
 299 
 300   // Note: this ought to be part of the constructor, but that would require
 301   // "this" to be passed as a parameter to a member constructor for
 302   // the containing concrete subtype of Space.
 303   // This would be legal C++, but MS VC++ doesn't allow it.
 304   void set_space(G1OffsetTableContigSpace* sp);
 305 
 306   // Resets the covered region to one with the same _bottom as before but
 307   // the "new_word_size".
 308   void resize(size_t new_word_size);
 309 
 310   virtual HeapWord* block_start_unsafe(const void* addr);
 311   virtual HeapWord* block_start_unsafe_const(const void* addr) const;
 312 
 313   void check_all_cards(size_t left_card, size_t right_card) const;
 314 
 315   void verify() const;
 316 
 317   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 318 };
 319 
 320 // A subtype of BlockOffsetArray that takes advantage of the fact
 321 // that its underlying space is a ContiguousSpace, so that its "active"
 322 // region can be more efficiently tracked (than for a non-contiguous space).
 323 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
 324   friend class VMStructs;
 325 
 326   // allocation boundary at which offset array must be updated
 327   HeapWord* _next_offset_threshold;
 328   size_t    _next_offset_index;      // index corresponding to that boundary
 329 
 330   // Work function to be called when allocation start crosses the next
 331   // threshold in the contig space.
 332   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
 333     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
 334                       blk_start, blk_end);
 335   }
 336 
 337   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
 338   // memory first.
 339   void zero_bottom_entry_raw();
 340   // Variant of initialize_threshold that does not check for availability of the
 341   // memory first.
 342   HeapWord* initialize_threshold_raw();
 343  public:
 344   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
 345 
 346   // Initialize the threshold to reflect the first boundary after the
 347   // bottom of the covered region.
 348   HeapWord* initialize_threshold();
 349 
 350   void reset_bot() {
 351     zero_bottom_entry_raw();
 352     initialize_threshold_raw();
 353   }
 354 
 355   // Return the next threshold, the point at which the table should be
 356   // updated.
 357   HeapWord* threshold() const { return _next_offset_threshold; }
 358 
 359   // These must be guaranteed to work properly (i.e., do nothing)
 360   // when "blk_start" ("blk" for second version) is "NULL".  In this
 361   // implementation, that's true because NULL is represented as 0, and thus
 362   // never exceeds the "_next_offset_threshold".
 363   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 364     if (blk_end > _next_offset_threshold)
 365       alloc_block_work1(blk_start, blk_end);
 366   }
 367   void alloc_block(HeapWord* blk, size_t size) {
 368      alloc_block(blk, blk+size);
 369   }
 370 
 371   HeapWord* block_start_unsafe(const void* addr);
 372   HeapWord* block_start_unsafe_const(const void* addr) const;
 373 
 374   void set_for_starts_humongous(HeapWord* new_top);
 375 
 376   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 377 };
 378 
 379 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP