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  24 
  25 #ifndef SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP
  26 #define SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP
  27 
  28 #include "gc/shared/memset_with_concurrent_readers.hpp"
  29 #include "memory/memRegion.hpp"
  30 #include "memory/virtualspace.hpp"
  31 #include "runtime/globals.hpp"
  32 #include "utilities/globalDefinitions.hpp"
  33 #include "utilities/macros.hpp"
  34 
  35 // The CollectedHeap type requires subtypes to implement a method
  36 // "block_start".  For some subtypes, notably generational
  37 // systems using card-table-based write barriers, the efficiency of this
  38 // operation may be important.  Implementations of the "BlockOffsetArray"
  39 // class may be useful in providing such efficient implementations.
  40 //
  41 // BlockOffsetTable (abstract)
  42 //   - BlockOffsetArray (abstract)
  43 //     - BlockOffsetArrayNonContigSpace
  44 //     - BlockOffsetArrayContigSpace
  45 //
  46 
  47 class ContiguousSpace;
  48 
  49 class BOTConstants : public AllStatic {
  50 public:
  51   static const uint LogN = 9;
  52   static const uint LogN_words = LogN - LogHeapWordSize;
  53   static const uint N_bytes = 1 << LogN;
  54   static const uint N_words = 1 << LogN_words;
  55   // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
  56   // All entries are less than "N_words + N_powers".
  57   static const uint LogBase = 4;
  58   static const uint Base = (1 << LogBase);
  59   static const uint N_powers = 14;
  60 
  61   static size_t power_to_cards_back(uint i) {
  62     return (size_t)1 << (LogBase * i);
  63   }
  64   static size_t power_to_words_back(uint i) {
  65     return power_to_cards_back(i) * N_words;
  66   }
  67   static size_t entry_to_cards_back(u_char entry) {
  68     assert(entry >= N_words, "Precondition");
  69     return power_to_cards_back(entry - N_words);
  70   }
  71   static size_t entry_to_words_back(u_char entry) {
  72     assert(entry >= N_words, "Precondition");
  73     return power_to_words_back(entry - N_words);
  74   }
  75 };
  76 
  77 //////////////////////////////////////////////////////////////////////////
  78 // The BlockOffsetTable "interface"
  79 //////////////////////////////////////////////////////////////////////////
  80 class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
  81   friend class VMStructs;
  82 protected:
  83   // These members describe the region covered by the table.
  84 
  85   // The space this table is covering.
  86   HeapWord* _bottom;    // == reserved.start
  87   HeapWord* _end;       // End of currently allocated region.
  88 
  89 public:
  90   // Initialize the table to cover the given space.
  91   // The contents of the initial table are undefined.
  92   BlockOffsetTable(HeapWord* bottom, HeapWord* end):
  93     _bottom(bottom), _end(end) {
  94     assert(_bottom <= _end, "arguments out of order");
  95   }
  96 
  97   // Note that the committed size of the covered space may have changed,
  98   // so the table size might also wish to change.
  99   virtual void resize(size_t new_word_size) = 0;
 100 
 101   virtual void set_bottom(HeapWord* new_bottom) {
 102     assert(new_bottom <= _end, "new_bottom > _end");
 103     _bottom = new_bottom;
 104     resize(pointer_delta(_end, _bottom));
 105   }
 106 
 107   // Requires "addr" to be contained by a block, and returns the address of
 108   // the start of that block.
 109   virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
 110 
 111   // Returns the address of the start of the block containing "addr", or
 112   // else "null" if it is covered by no block.
 113   HeapWord* block_start(const void* addr) const;
 114 };
 115 
 116 //////////////////////////////////////////////////////////////////////////
 117 // One implementation of "BlockOffsetTable," the BlockOffsetArray,
 118 // divides the covered region into "N"-word subregions (where
 119 // "N" = 2^"LogN".  An array with an entry for each such subregion
 120 // indicates how far back one must go to find the start of the
 121 // chunk that includes the first word of the subregion.
 122 //
 123 // Each BlockOffsetArray is owned by a Space.  However, the actual array
 124 // may be shared by several BlockOffsetArrays; this is useful
 125 // when a single resizable area (such as a generation) is divided up into
 126 // several spaces in which contiguous allocation takes place.  (Consider,
 127 // for example, the garbage-first generation.)
 128 
 129 // Here is the shared array type.
 130 //////////////////////////////////////////////////////////////////////////
 131 // BlockOffsetSharedArray
 132 //////////////////////////////////////////////////////////////////////////
 133 class BlockOffsetSharedArray: public CHeapObj<mtGC> {
 134   friend class BlockOffsetArray;
 135   friend class BlockOffsetArrayNonContigSpace;
 136   friend class BlockOffsetArrayContigSpace;
 137   friend class VMStructs;
 138 
 139  private:
 140   bool _init_to_zero;
 141 
 142   // The reserved region covered by the shared array.
 143   MemRegion _reserved;
 144 
 145   // End of the current committed region.
 146   HeapWord* _end;
 147 
 148   // Array for keeping offsets for retrieving object start fast given an
 149   // address.
 150   VirtualSpace _vs;
 151   u_char* _offset_array;          // byte array keeping backwards offsets
 152 
 153   void fill_range(size_t start, size_t num_cards, u_char offset) {
 154     void* start_ptr = &_offset_array[start];
 155 #if INCLUDE_ALL_GCS
 156     // If collector is concurrent, special handling may be needed.
 157     assert(!UseG1GC, "Shouldn't be here when using G1");
 158     if (UseConcMarkSweepGC) {
 159       memset_with_concurrent_readers(start_ptr, offset, num_cards);
 160       return;
 161     }
 162 #endif // INCLUDE_ALL_GCS
 163     memset(start_ptr, offset, num_cards);
 164   }
 165 
 166  protected:
 167   // Bounds checking accessors:
 168   // For performance these have to devolve to array accesses in product builds.
 169   u_char offset_array(size_t index) const {
 170     assert(index < _vs.committed_size(), "index out of range");
 171     return _offset_array[index];
 172   }
 173   // An assertion-checking helper method for the set_offset_array() methods below.
 174   void check_reducing_assertion(bool reducing);
 175 
 176   void set_offset_array(size_t index, u_char offset, bool reducing = false) {
 177     check_reducing_assertion(reducing);
 178     assert(index < _vs.committed_size(), "index out of range");
 179     assert(!reducing || _offset_array[index] >= offset, "Not reducing");
 180     _offset_array[index] = offset;
 181   }
 182 
 183   void set_offset_array(size_t index, HeapWord* high, HeapWord* low, bool reducing = false) {
 184     check_reducing_assertion(reducing);
 185     assert(index < _vs.committed_size(), "index out of range");
 186     assert(high >= low, "addresses out of order");
 187     assert(pointer_delta(high, low) <= BOTConstants::N_words, "offset too large");
 188     assert(!reducing || _offset_array[index] >=  (u_char)pointer_delta(high, low),
 189            "Not reducing");
 190     _offset_array[index] = (u_char)pointer_delta(high, low);
 191   }
 192 
 193   void set_offset_array(HeapWord* left, HeapWord* right, u_char offset, bool reducing = false) {
 194     check_reducing_assertion(reducing);
 195     assert(index_for(right - 1) < _vs.committed_size(),
 196            "right address out of range");
 197     assert(left  < right, "Heap addresses out of order");
 198     size_t num_cards = pointer_delta(right, left) >> BOTConstants::LogN_words;
 199 
 200     fill_range(index_for(left), num_cards, offset);
 201   }
 202 
 203   void set_offset_array(size_t left, size_t right, u_char offset, bool reducing = false) {
 204     check_reducing_assertion(reducing);
 205     assert(right < _vs.committed_size(), "right address out of range");
 206     assert(left  <= right, "indexes out of order");
 207     size_t num_cards = right - left + 1;
 208 
 209     fill_range(left, num_cards, offset);
 210   }
 211 
 212   void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
 213     assert(index < _vs.committed_size(), "index out of range");
 214     assert(high >= low, "addresses out of order");
 215     assert(pointer_delta(high, low) <= BOTConstants::N_words, "offset too large");
 216     assert(_offset_array[index] == pointer_delta(high, low),
 217            "Wrong offset");
 218   }
 219 
 220   bool is_card_boundary(HeapWord* p) const;
 221 
 222   // Return the number of slots needed for an offset array
 223   // that covers mem_region_words words.
 224   // We always add an extra slot because if an object
 225   // ends on a card boundary we put a 0 in the next
 226   // offset array slot, so we want that slot always
 227   // to be reserved.
 228 
 229   size_t compute_size(size_t mem_region_words) {
 230     size_t number_of_slots = (mem_region_words / BOTConstants::N_words) + 1;
 231     return ReservedSpace::allocation_align_up(number_of_slots);
 232   }
 233 
 234 public:
 235   // Initialize the table to cover from "base" to (at least)
 236   // "base + init_word_size".  In the future, the table may be expanded
 237   // (see "resize" below) up to the size of "_reserved" (which must be at
 238   // least "init_word_size".)  The contents of the initial table are
 239   // undefined; it is the responsibility of the constituent
 240   // BlockOffsetTable(s) to initialize cards.
 241   BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
 242 
 243   // Notes a change in the committed size of the region covered by the
 244   // table.  The "new_word_size" may not be larger than the size of the
 245   // reserved region this table covers.
 246   void resize(size_t new_word_size);
 247 
 248   void set_bottom(HeapWord* new_bottom);
 249 
 250   // Whether entries should be initialized to zero. Used currently only for
 251   // error checking.
 252   void set_init_to_zero(bool val) { _init_to_zero = val; }
 253   bool init_to_zero() { return _init_to_zero; }
 254 
 255   // Updates all the BlockOffsetArray's sharing this shared array to
 256   // reflect the current "top"'s of their spaces.
 257   void update_offset_arrays();   // Not yet implemented!
 258 
 259   // Return the appropriate index into "_offset_array" for "p".
 260   size_t index_for(const void* p) const;
 261 
 262   // Return the address indicating the start of the region corresponding to
 263   // "index" in "_offset_array".
 264   HeapWord* address_for_index(size_t index) const;
 265 };
 266 
 267 //////////////////////////////////////////////////////////////////////////
 268 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
 269 //////////////////////////////////////////////////////////////////////////
 270 class BlockOffsetArray: public BlockOffsetTable {
 271   friend class VMStructs;
 272  protected:
 273   // The following enums are used by do_block_internal() below
 274   enum Action {
 275     Action_single,      // BOT records a single block (see single_block())
 276     Action_mark,        // BOT marks the start of a block (see mark_block())
 277     Action_check        // Check that BOT records block correctly
 278                         // (see verify_single_block()).
 279   };
 280 
 281   // The shared array, which is shared with other BlockOffsetArray's
 282   // corresponding to different spaces within a generation or span of
 283   // memory.
 284   BlockOffsetSharedArray* _array;
 285 
 286   // The space that owns this subregion.
 287   Space* _sp;
 288 
 289   // If true, array entries are initialized to 0; otherwise, they are
 290   // initialized to point backwards to the beginning of the covered region.
 291   bool _init_to_zero;
 292 
 293   // An assertion-checking helper method for the set_remainder*() methods below.
 294   void check_reducing_assertion(bool reducing) { _array->check_reducing_assertion(reducing); }
 295 
 296   // Sets the entries
 297   // corresponding to the cards starting at "start" and ending at "end"
 298   // to point back to the card before "start": the interval [start, end)
 299   // is right-open. The last parameter, reducing, indicates whether the
 300   // updates to individual entries always reduce the entry from a higher
 301   // to a lower value. (For example this would hold true during a temporal
 302   // regime during which only block splits were updating the BOT.
 303   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing = false);
 304   // Same as above, except that the args here are a card _index_ interval
 305   // that is closed: [start_index, end_index]
 306   void set_remainder_to_point_to_start_incl(size_t start, size_t end, bool reducing = false);
 307 
 308   // A helper function for BOT adjustment/verification work
 309   void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action, bool reducing = false);
 310 
 311  public:
 312   // The space may not have its bottom and top set yet, which is why the
 313   // region is passed as a parameter.  If "init_to_zero" is true, the
 314   // elements of the array are initialized to zero.  Otherwise, they are
 315   // initialized to point backwards to the beginning.
 316   BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
 317                    bool init_to_zero_);
 318 
 319   // Note: this ought to be part of the constructor, but that would require
 320   // "this" to be passed as a parameter to a member constructor for
 321   // the containing concrete subtype of Space.
 322   // This would be legal C++, but MS VC++ doesn't allow it.
 323   void set_space(Space* sp) { _sp = sp; }
 324 
 325   // Resets the covered region to the given "mr".
 326   void set_region(MemRegion mr) {
 327     _bottom = mr.start();
 328     _end = mr.end();
 329   }
 330 
 331   // Note that the committed size of the covered space may have changed,
 332   // so the table size might also wish to change.
 333   virtual void resize(size_t new_word_size) {
 334     HeapWord* new_end = _bottom + new_word_size;
 335     if (_end < new_end && !init_to_zero()) {
 336       // verify that the old and new boundaries are also card boundaries
 337       assert(_array->is_card_boundary(_end),
 338              "_end not a card boundary");
 339       assert(_array->is_card_boundary(new_end),
 340              "new _end would not be a card boundary");
 341       // set all the newly added cards
 342       _array->set_offset_array(_end, new_end, BOTConstants::N_words);
 343     }
 344     _end = new_end;  // update _end
 345   }
 346 
 347   // Adjust the BOT to show that it has a single block in the
 348   // range [blk_start, blk_start + size). All necessary BOT
 349   // cards are adjusted, but _unallocated_block isn't.
 350   void single_block(HeapWord* blk_start, HeapWord* blk_end);
 351   void single_block(HeapWord* blk, size_t size) {
 352     single_block(blk, blk + size);
 353   }
 354 
 355   // When the alloc_block() call returns, the block offset table should
 356   // have enough information such that any subsequent block_start() call
 357   // with an argument equal to an address that is within the range
 358   // [blk_start, blk_end) would return the value blk_start, provided
 359   // there have been no calls in between that reset this information
 360   // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
 361   // for an appropriate range covering the said interval).
 362   // These methods expect to be called with [blk_start, blk_end)
 363   // representing a block of memory in the heap.
 364   virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
 365   void alloc_block(HeapWord* blk, size_t size) {
 366     alloc_block(blk, blk + size);
 367   }
 368 
 369   // If true, initialize array slots with no allocated blocks to zero.
 370   // Otherwise, make them point back to the front.
 371   bool init_to_zero() { return _init_to_zero; }
 372   // Corresponding setter
 373   void set_init_to_zero(bool val) {
 374     _init_to_zero = val;
 375     assert(_array != NULL, "_array should be non-NULL");
 376     _array->set_init_to_zero(val);
 377   }
 378 
 379   // Debugging
 380   // Return the index of the last entry in the "active" region.
 381   virtual size_t last_active_index() const = 0;
 382   // Verify the block offset table
 383   void verify() const;
 384   void check_all_cards(size_t left_card, size_t right_card) const;
 385 };
 386 
 387 ////////////////////////////////////////////////////////////////////////////
 388 // A subtype of BlockOffsetArray that takes advantage of the fact
 389 // that its underlying space is a NonContiguousSpace, so that some
 390 // specialized interfaces can be made available for spaces that
 391 // manipulate the table.
 392 ////////////////////////////////////////////////////////////////////////////
 393 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
 394   friend class VMStructs;
 395  private:
 396   // The portion [_unallocated_block, _sp.end()) of the space that
 397   // is a single block known not to contain any objects.
 398   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
 399   HeapWord* _unallocated_block;
 400 
 401  public:
 402   BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
 403     BlockOffsetArray(array, mr, false),
 404     _unallocated_block(_bottom) { }
 405 
 406   // Accessor
 407   HeapWord* unallocated_block() const {
 408     assert(BlockOffsetArrayUseUnallocatedBlock,
 409            "_unallocated_block is not being maintained");
 410     return _unallocated_block;
 411   }
 412 
 413   void set_unallocated_block(HeapWord* block) {
 414     assert(BlockOffsetArrayUseUnallocatedBlock,
 415            "_unallocated_block is not being maintained");
 416     assert(block >= _bottom && block <= _end, "out of range");
 417     _unallocated_block = block;
 418   }
 419 
 420   // These methods expect to be called with [blk_start, blk_end)
 421   // representing a block of memory in the heap.
 422   void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
 423   void alloc_block(HeapWord* blk, size_t size) {
 424     alloc_block(blk, blk + size);
 425   }
 426 
 427   // The following methods are useful and optimized for a
 428   // non-contiguous space.
 429 
 430   // Given a block [blk_start, blk_start + full_blk_size), and
 431   // a left_blk_size < full_blk_size, adjust the BOT to show two
 432   // blocks [blk_start, blk_start + left_blk_size) and
 433   // [blk_start + left_blk_size, blk_start + full_blk_size).
 434   // It is assumed (and verified in the non-product VM) that the
 435   // BOT was correct for the original block.
 436   void split_block(HeapWord* blk_start, size_t full_blk_size,
 437                            size_t left_blk_size);
 438 
 439   // Adjust BOT to show that it has a block in the range
 440   // [blk_start, blk_start + size). Only the first card
 441   // of BOT is touched. It is assumed (and verified in the
 442   // non-product VM) that the remaining cards of the block
 443   // are correct.
 444   void mark_block(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false);
 445   void mark_block(HeapWord* blk, size_t size, bool reducing = false) {
 446     mark_block(blk, blk + size, reducing);
 447   }
 448 
 449   // Adjust _unallocated_block to indicate that a particular
 450   // block has been newly allocated or freed. It is assumed (and
 451   // verified in the non-product VM) that the BOT is correct for
 452   // the given block.
 453   void allocated(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false) {
 454     // Verify that the BOT shows [blk, blk + blk_size) to be one block.
 455     verify_single_block(blk_start, blk_end);
 456     if (BlockOffsetArrayUseUnallocatedBlock) {
 457       _unallocated_block = MAX2(_unallocated_block, blk_end);
 458     }
 459   }
 460 
 461   void allocated(HeapWord* blk, size_t size, bool reducing = false) {
 462     allocated(blk, blk + size, reducing);
 463   }
 464 
 465   void freed(HeapWord* blk_start, HeapWord* blk_end);
 466   void freed(HeapWord* blk, size_t size);
 467 
 468   HeapWord* block_start_unsafe(const void* addr) const;
 469 
 470   // Requires "addr" to be the start of a card and returns the
 471   // start of the block that contains the given address.
 472   HeapWord* block_start_careful(const void* addr) const;
 473 
 474   // Verification & debugging: ensure that the offset table reflects
 475   // the fact that the block [blk_start, blk_end) or [blk, blk + size)
 476   // is a single block of storage. NOTE: can't const this because of
 477   // call to non-const do_block_internal() below.
 478   void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
 479     PRODUCT_RETURN;
 480   void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
 481 
 482   // Verify that the given block is before _unallocated_block
 483   void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
 484     const PRODUCT_RETURN;
 485   void verify_not_unallocated(HeapWord* blk, size_t size)
 486     const PRODUCT_RETURN;
 487 
 488   // Debugging support
 489   virtual size_t last_active_index() const;
 490 };
 491 
 492 ////////////////////////////////////////////////////////////////////////////
 493 // A subtype of BlockOffsetArray that takes advantage of the fact
 494 // that its underlying space is a ContiguousSpace, so that its "active"
 495 // region can be more efficiently tracked (than for a non-contiguous space).
 496 ////////////////////////////////////////////////////////////////////////////
 497 class BlockOffsetArrayContigSpace: public BlockOffsetArray {
 498   friend class VMStructs;
 499  private:
 500   // allocation boundary at which offset array must be updated
 501   HeapWord* _next_offset_threshold;
 502   size_t    _next_offset_index;      // index corresponding to that boundary
 503 
 504   // Work function when allocation start crosses threshold.
 505   void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
 506 
 507  public:
 508   BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
 509     BlockOffsetArray(array, mr, true) {
 510     _next_offset_threshold = NULL;
 511     _next_offset_index = 0;
 512   }
 513 
 514   void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
 515 
 516   // Initialize the threshold for an empty heap.
 517   HeapWord* initialize_threshold();
 518   // Zero out the entry for _bottom (offset will be zero)
 519   void      zero_bottom_entry();
 520 
 521   // Return the next threshold, the point at which the table should be
 522   // updated.
 523   HeapWord* threshold() const { return _next_offset_threshold; }
 524 
 525   // In general, these methods expect to be called with
 526   // [blk_start, blk_end) representing a block of memory in the heap.
 527   // In this implementation, however, we are OK even if blk_start and/or
 528   // blk_end are NULL because NULL is represented as 0, and thus
 529   // never exceeds the "_next_offset_threshold".
 530   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 531     if (blk_end > _next_offset_threshold) {
 532       alloc_block_work(blk_start, blk_end);
 533     }
 534   }
 535   void alloc_block(HeapWord* blk, size_t size) {
 536     alloc_block(blk, blk + size);
 537   }
 538 
 539   HeapWord* block_start_unsafe(const void* addr) const;
 540 
 541   // Debugging support
 542   virtual size_t last_active_index() const;
 543 };
 544 
 545 #endif // SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP