1 /*
   2  * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  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).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc_interface/collectedHeap.inline.hpp"
  27 #include "memory/blockOffsetTable.inline.hpp"
  28 #include "memory/iterator.hpp"
  29 #include "memory/space.inline.hpp"
  30 #include "memory/universe.hpp"
  31 #include "oops/oop.inline.hpp"
  32 #include "runtime/java.hpp"
  33 #include "services/memTracker.hpp"
  34 
  35 //////////////////////////////////////////////////////////////////////
  36 // BlockOffsetSharedArray
  37 //////////////////////////////////////////////////////////////////////
  38 
  39 BlockOffsetSharedArray::BlockOffsetSharedArray(MemRegion reserved,
  40                                                size_t init_word_size):
  41   _reserved(reserved), _end(NULL)
  42 {
  43   size_t size = compute_size(reserved.word_size());
  44   ReservedSpace rs(size);
  45   if (!rs.is_reserved()) {
  46     vm_exit_during_initialization("Could not reserve enough space for heap offset array");
  47   }
  48 
  49   MemTracker::record_virtual_memory_type((address)rs.base(), mtGC);
  50 
  51   if (!_vs.initialize(rs, 0)) {
  52     vm_exit_during_initialization("Could not reserve enough space for heap offset array");
  53   }
  54   _offset_array = (u_char*)_vs.low_boundary();
  55   resize(init_word_size);
  56   if (TraceBlockOffsetTable) {
  57     gclog_or_tty->print_cr("BlockOffsetSharedArray::BlockOffsetSharedArray: ");
  58     gclog_or_tty->print_cr("  "
  59                   "  rs.base(): " INTPTR_FORMAT
  60                   "  rs.size(): " INTPTR_FORMAT
  61                   "  rs end(): " INTPTR_FORMAT,
  62                   p2i(rs.base()), rs.size(), p2i(rs.base() + rs.size()));
  63     gclog_or_tty->print_cr("  "
  64                   "  _vs.low_boundary(): " INTPTR_FORMAT
  65                   "  _vs.high_boundary(): " INTPTR_FORMAT,
  66                   p2i(_vs.low_boundary()),
  67                   p2i(_vs.high_boundary()));
  68   }
  69 }
  70 
  71 void BlockOffsetSharedArray::resize(size_t new_word_size) {
  72   assert(new_word_size <= _reserved.word_size(), "Resize larger than reserved");
  73   size_t new_size = compute_size(new_word_size);
  74   size_t old_size = _vs.committed_size();
  75   size_t delta;
  76   char* high = _vs.high();
  77   _end = _reserved.start() + new_word_size;
  78   if (new_size > old_size) {
  79     delta = ReservedSpace::page_align_size_up(new_size - old_size);
  80     assert(delta > 0, "just checking");
  81     if (!_vs.expand_by(delta)) {
  82       // Do better than this for Merlin
  83       vm_exit_out_of_memory(delta, OOM_MMAP_ERROR, "offset table expansion");
  84     }
  85     assert(_vs.high() == high + delta, "invalid expansion");
  86   } else {
  87     delta = ReservedSpace::page_align_size_down(old_size - new_size);
  88     if (delta == 0) return;
  89     _vs.shrink_by(delta);
  90     assert(_vs.high() == high - delta, "invalid expansion");
  91   }
  92 }
  93 
  94 bool BlockOffsetSharedArray::is_card_boundary(HeapWord* p) const {
  95   assert(p >= _reserved.start(), "just checking");
  96   size_t delta = pointer_delta(p, _reserved.start());
  97   return (delta & right_n_bits(LogN_words)) == (size_t)NoBits;
  98 }
  99 
 100 
 101 //////////////////////////////////////////////////////////////////////
 102 // BlockOffsetArray
 103 //////////////////////////////////////////////////////////////////////
 104 
 105 BlockOffsetArray::BlockOffsetArray(BlockOffsetSharedArray* array,
 106                                    MemRegion mr, bool init_to_zero_) :
 107   BlockOffsetTable(mr.start(), mr.end()),
 108   _array(array)
 109 {
 110   assert(_bottom <= _end, "arguments out of order");
 111   set_init_to_zero(init_to_zero_);
 112   if (!init_to_zero_) {
 113     // initialize cards to point back to mr.start()
 114     set_remainder_to_point_to_start(mr.start() + N_words, mr.end());
 115     _array->set_offset_array(0, 0);  // set first card to 0
 116   }
 117 }
 118 
 119 
 120 // The arguments follow the normal convention of denoting
 121 // a right-open interval: [start, end)
 122 void
 123 BlockOffsetArray::
 124 set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing) {
 125 
 126   check_reducing_assertion(reducing);
 127   if (start >= end) {
 128     // The start address is equal to the end address (or to
 129     // the right of the end address) so there are not cards
 130     // that need to be updated..
 131     return;
 132   }
 133 
 134   // Write the backskip value for each region.
 135   //
 136   //    offset
 137   //    card             2nd                       3rd
 138   //     | +- 1st        |                         |
 139   //     v v             v                         v
 140   //    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+-+-+-
 141   //    |x|0|0|0|0|0|0|0|1|1|1|1|1|1| ... |1|1|1|1|2|2|2|2|2|2| ...
 142   //    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+-+-+-
 143   //    11              19                        75
 144   //      12
 145   //
 146   //    offset card is the card that points to the start of an object
 147   //      x - offset value of offset card
 148   //    1st - start of first logarithmic region
 149   //      0 corresponds to logarithmic value N_words + 0 and 2**(3 * 0) = 1
 150   //    2nd - start of second logarithmic region
 151   //      1 corresponds to logarithmic value N_words + 1 and 2**(3 * 1) = 8
 152   //    3rd - start of third logarithmic region
 153   //      2 corresponds to logarithmic value N_words + 2 and 2**(3 * 2) = 64
 154   //
 155   //    integer below the block offset entry is an example of
 156   //    the index of the entry
 157   //
 158   //    Given an address,
 159   //      Find the index for the address
 160   //      Find the block offset table entry
 161   //      Convert the entry to a back slide
 162   //        (e.g., with today's, offset = 0x81 =>
 163   //          back slip = 2**(3*(0x81 - N_words)) = 2**3) = 8
 164   //      Move back N (e.g., 8) entries and repeat with the
 165   //        value of the new entry
 166   //
 167   size_t start_card = _array->index_for(start);
 168   size_t end_card = _array->index_for(end-1);
 169   assert(start ==_array->address_for_index(start_card), "Precondition");
 170   assert(end ==_array->address_for_index(end_card)+N_words, "Precondition");
 171   set_remainder_to_point_to_start_incl(start_card, end_card, reducing); // closed interval
 172 }
 173 
 174 
 175 // Unlike the normal convention in this code, the argument here denotes
 176 // a closed, inclusive interval: [start_card, end_card], cf set_remainder_to_point_to_start()
 177 // above.
 178 void
 179 BlockOffsetArray::set_remainder_to_point_to_start_incl(size_t start_card, size_t end_card, bool reducing) {
 180 
 181   check_reducing_assertion(reducing);
 182   if (start_card > end_card) {
 183     return;
 184   }
 185   assert(start_card > _array->index_for(_bottom), "Cannot be first card");
 186   assert(_array->offset_array(start_card-1) <= N_words,
 187     "Offset card has an unexpected value");
 188   size_t start_card_for_region = start_card;
 189   u_char offset = max_jubyte;
 190   for (int i = 0; i < N_powers; i++) {
 191     // -1 so that the the card with the actual offset is counted.  Another -1
 192     // so that the reach ends in this region and not at the start
 193     // of the next.
 194     size_t reach = start_card - 1 + (power_to_cards_back(i+1) - 1);
 195     offset = N_words + i;
 196     if (reach >= end_card) {
 197       _array->set_offset_array(start_card_for_region, end_card, offset, reducing);
 198       start_card_for_region = reach + 1;
 199       break;
 200     }
 201     _array->set_offset_array(start_card_for_region, reach, offset, reducing);
 202     start_card_for_region = reach + 1;
 203   }
 204   assert(start_card_for_region > end_card, "Sanity check");
 205   DEBUG_ONLY(check_all_cards(start_card, end_card);)
 206 }
 207 
 208 // The card-interval [start_card, end_card] is a closed interval; this
 209 // is an expensive check -- use with care and only under protection of
 210 // suitable flag.
 211 void BlockOffsetArray::check_all_cards(size_t start_card, size_t end_card) const {
 212 
 213   if (end_card < start_card) {
 214     return;
 215   }
 216   guarantee(_array->offset_array(start_card) == N_words, "Wrong value in second card");
 217   u_char last_entry = N_words;
 218   for (size_t c = start_card + 1; c <= end_card; c++ /* yeah! */) {
 219     u_char entry = _array->offset_array(c);
 220     guarantee(entry >= last_entry, "Monotonicity");
 221     if (c - start_card > power_to_cards_back(1)) {
 222       guarantee(entry > N_words, "Should be in logarithmic region");
 223     }
 224     size_t backskip = entry_to_cards_back(entry);
 225     size_t landing_card = c - backskip;
 226     guarantee(landing_card >= (start_card - 1), "Inv");
 227     if (landing_card >= start_card) {
 228       guarantee(_array->offset_array(landing_card) <= entry, "Monotonicity");
 229     } else {
 230       guarantee(landing_card == (start_card - 1), "Tautology");
 231       // Note that N_words is the maximum offset value
 232       guarantee(_array->offset_array(landing_card) <= N_words, "Offset value");
 233     }
 234     last_entry = entry;  // remember for monotonicity test
 235   }
 236 }
 237 
 238 
 239 void
 240 BlockOffsetArray::alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 241   assert(blk_start != NULL && blk_end > blk_start,
 242          "phantom block");
 243   single_block(blk_start, blk_end);
 244 }
 245 
 246 // Action_mark - update the BOT for the block [blk_start, blk_end).
 247 //               Current typical use is for splitting a block.
 248 // Action_single - udpate the BOT for an allocation.
 249 // Action_verify - BOT verification.
 250 void
 251 BlockOffsetArray::do_block_internal(HeapWord* blk_start,
 252                                     HeapWord* blk_end,
 253                                     Action action, bool reducing) {
 254   assert(Universe::heap()->is_in_reserved(blk_start),
 255          "reference must be into the heap");
 256   assert(Universe::heap()->is_in_reserved(blk_end-1),
 257          "limit must be within the heap");
 258   // This is optimized to make the test fast, assuming we only rarely
 259   // cross boundaries.
 260   uintptr_t end_ui = (uintptr_t)(blk_end - 1);
 261   uintptr_t start_ui = (uintptr_t)blk_start;
 262   // Calculate the last card boundary preceding end of blk
 263   intptr_t boundary_before_end = (intptr_t)end_ui;
 264   clear_bits(boundary_before_end, right_n_bits(LogN));
 265   if (start_ui <= (uintptr_t)boundary_before_end) {
 266     // blk starts at or crosses a boundary
 267     // Calculate index of card on which blk begins
 268     size_t    start_index = _array->index_for(blk_start);
 269     // Index of card on which blk ends
 270     size_t    end_index   = _array->index_for(blk_end - 1);
 271     // Start address of card on which blk begins
 272     HeapWord* boundary    = _array->address_for_index(start_index);
 273     assert(boundary <= blk_start, "blk should start at or after boundary");
 274     if (blk_start != boundary) {
 275       // blk starts strictly after boundary
 276       // adjust card boundary and start_index forward to next card
 277       boundary += N_words;
 278       start_index++;
 279     }
 280     assert(start_index <= end_index, "monotonicity of index_for()");
 281     assert(boundary <= (HeapWord*)boundary_before_end, "tautology");
 282     switch (action) {
 283       case Action_mark: {
 284         if (init_to_zero()) {
 285           _array->set_offset_array(start_index, boundary, blk_start, reducing);
 286           break;
 287         } // Else fall through to the next case
 288       }
 289       case Action_single: {
 290         _array->set_offset_array(start_index, boundary, blk_start, reducing);
 291         // We have finished marking the "offset card". We need to now
 292         // mark the subsequent cards that this blk spans.
 293         if (start_index < end_index) {
 294           HeapWord* rem_st = _array->address_for_index(start_index) + N_words;
 295           HeapWord* rem_end = _array->address_for_index(end_index) + N_words;
 296           set_remainder_to_point_to_start(rem_st, rem_end, reducing);
 297         }
 298         break;
 299       }
 300       case Action_check: {
 301         _array->check_offset_array(start_index, boundary, blk_start);
 302         // We have finished checking the "offset card". We need to now
 303         // check the subsequent cards that this blk spans.
 304         check_all_cards(start_index + 1, end_index);
 305         break;
 306       }
 307       default:
 308         ShouldNotReachHere();
 309     }
 310   }
 311 }
 312 
 313 // The range [blk_start, blk_end) represents a single contiguous block
 314 // of storage; modify the block offset table to represent this
 315 // information; Right-open interval: [blk_start, blk_end)
 316 // NOTE: this method does _not_ adjust _unallocated_block.
 317 void
 318 BlockOffsetArray::single_block(HeapWord* blk_start,
 319                                HeapWord* blk_end) {
 320   do_block_internal(blk_start, blk_end, Action_single);
 321 }
 322 
 323 void BlockOffsetArray::verify() const {
 324   // For each entry in the block offset table, verify that
 325   // the entry correctly finds the start of an object at the
 326   // first address covered by the block or to the left of that
 327   // first address.
 328 
 329   size_t next_index = 1;
 330   size_t last_index = last_active_index();
 331 
 332   // Use for debugging.  Initialize to NULL to distinguish the
 333   // first iteration through the while loop.
 334   HeapWord* last_p = NULL;
 335   HeapWord* last_start = NULL;
 336   oop last_o = NULL;
 337 
 338   while (next_index <= last_index) {
 339     // Use an address past the start of the address for
 340     // the entry.
 341     HeapWord* p = _array->address_for_index(next_index) + 1;
 342     if (p >= _end) {
 343       // That's all of the allocated block table.
 344       return;
 345     }
 346     // block_start() asserts that start <= p.
 347     HeapWord* start = block_start(p);
 348     // First check if the start is an allocated block and only
 349     // then if it is a valid object.
 350     oop o = oop(start);
 351     assert(!Universe::is_fully_initialized() ||
 352            _sp->is_free_block(start) ||
 353            o->is_oop_or_null(), "Bad object was found");
 354     next_index++;
 355     last_p = p;
 356     last_start = start;
 357     last_o = o;
 358   }
 359 }
 360 
 361 //////////////////////////////////////////////////////////////////////
 362 // BlockOffsetArrayNonContigSpace
 363 //////////////////////////////////////////////////////////////////////
 364 
 365 // The block [blk_start, blk_end) has been allocated;
 366 // adjust the block offset table to represent this information;
 367 // NOTE: Clients of BlockOffsetArrayNonContigSpace: consider using
 368 // the somewhat more lightweight split_block() or
 369 // (when init_to_zero()) mark_block() wherever possible.
 370 // right-open interval: [blk_start, blk_end)
 371 void
 372 BlockOffsetArrayNonContigSpace::alloc_block(HeapWord* blk_start,
 373                                             HeapWord* blk_end) {
 374   assert(blk_start != NULL && blk_end > blk_start,
 375          "phantom block");
 376   single_block(blk_start, blk_end);
 377   allocated(blk_start, blk_end);
 378 }
 379 
 380 // Adjust BOT to show that a previously whole block has been split
 381 // into two.  We verify the BOT for the first part (prefix) and
 382 // update the  BOT for the second part (suffix).
 383 //      blk is the start of the block
 384 //      blk_size is the size of the original block
 385 //      left_blk_size is the size of the first part of the split
 386 void BlockOffsetArrayNonContigSpace::split_block(HeapWord* blk,
 387                                                  size_t blk_size,
 388                                                  size_t left_blk_size) {
 389   // Verify that the BOT shows [blk, blk + blk_size) to be one block.
 390   verify_single_block(blk, blk_size);
 391   // Update the BOT to indicate that [blk + left_blk_size, blk + blk_size)
 392   // is one single block.
 393   assert(blk_size > 0, "Should be positive");
 394   assert(left_blk_size > 0, "Should be positive");
 395   assert(left_blk_size < blk_size, "Not a split");
 396 
 397   // Start addresses of prefix block and suffix block.
 398   HeapWord* pref_addr = blk;
 399   HeapWord* suff_addr = blk + left_blk_size;
 400   HeapWord* end_addr  = blk + blk_size;
 401 
 402   // Indices for starts of prefix block and suffix block.
 403   size_t pref_index = _array->index_for(pref_addr);
 404   if (_array->address_for_index(pref_index) != pref_addr) {
 405     // pref_addr does not begin pref_index
 406     pref_index++;
 407   }
 408 
 409   size_t suff_index = _array->index_for(suff_addr);
 410   if (_array->address_for_index(suff_index) != suff_addr) {
 411     // suff_addr does not begin suff_index
 412     suff_index++;
 413   }
 414 
 415   // Definition: A block B, denoted [B_start, B_end) __starts__
 416   //     a card C, denoted [C_start, C_end), where C_start and C_end
 417   //     are the heap addresses that card C covers, iff
 418   //     B_start <= C_start < B_end.
 419   //
 420   //     We say that a card C "is started by" a block B, iff
 421   //     B "starts" C.
 422   //
 423   //     Note that the cardinality of the set of cards {C}
 424   //     started by a block B can be 0, 1, or more.
 425   //
 426   // Below, pref_index and suff_index are, respectively, the
 427   // first (least) card indices that the prefix and suffix of
 428   // the split start; end_index is one more than the index of
 429   // the last (greatest) card that blk starts.
 430   size_t end_index  = _array->index_for(end_addr - 1) + 1;
 431 
 432   // Calculate the # cards that the prefix and suffix affect.
 433   size_t num_pref_cards = suff_index - pref_index;
 434 
 435   size_t num_suff_cards = end_index  - suff_index;
 436   // Change the cards that need changing
 437   if (num_suff_cards > 0) {
 438     HeapWord* boundary = _array->address_for_index(suff_index);
 439     // Set the offset card for suffix block
 440     _array->set_offset_array(suff_index, boundary, suff_addr, true /* reducing */);
 441     // Change any further cards that need changing in the suffix
 442     if (num_pref_cards > 0) {
 443       if (num_pref_cards >= num_suff_cards) {
 444         // Unilaterally fix all of the suffix cards: closed card
 445         // index interval in args below.
 446         set_remainder_to_point_to_start_incl(suff_index + 1, end_index - 1, true /* reducing */);
 447       } else {
 448         // Unilaterally fix the first (num_pref_cards - 1) following
 449         // the "offset card" in the suffix block.
 450         set_remainder_to_point_to_start_incl(suff_index + 1,
 451           suff_index + num_pref_cards - 1, true /* reducing */);
 452         // Fix the appropriate cards in the remainder of the
 453         // suffix block -- these are the last num_pref_cards
 454         // cards in each power block of the "new" range plumbed
 455         // from suff_addr.
 456         bool more = true;
 457         uint i = 1;
 458         while (more && (i < N_powers)) {
 459           size_t back_by = power_to_cards_back(i);
 460           size_t right_index = suff_index + back_by - 1;
 461           size_t left_index  = right_index - num_pref_cards + 1;
 462           if (right_index >= end_index - 1) { // last iteration
 463             right_index = end_index - 1;
 464             more = false;
 465           }
 466           if (back_by > num_pref_cards) {
 467             // Fill in the remainder of this "power block", if it
 468             // is non-null.
 469             if (left_index <= right_index) {
 470               _array->set_offset_array(left_index, right_index,
 471                                      N_words + i - 1, true /* reducing */);
 472             } else {
 473               more = false; // we are done
 474             }
 475             i++;
 476             break;
 477           }
 478           i++;
 479         }
 480         while (more && (i < N_powers)) {
 481           size_t back_by = power_to_cards_back(i);
 482           size_t right_index = suff_index + back_by - 1;
 483           size_t left_index  = right_index - num_pref_cards + 1;
 484           if (right_index >= end_index - 1) { // last iteration
 485             right_index = end_index - 1;
 486             if (left_index > right_index) {
 487               break;
 488             }
 489             more  = false;
 490           }
 491           assert(left_index <= right_index, "Error");
 492           _array->set_offset_array(left_index, right_index, N_words + i - 1, true /* reducing */);
 493           i++;
 494         }
 495       }
 496     } // else no more cards to fix in suffix
 497   } // else nothing needs to be done
 498   // Verify that we did the right thing
 499   verify_single_block(pref_addr, left_blk_size);
 500   verify_single_block(suff_addr, blk_size - left_blk_size);
 501 }
 502 
 503 
 504 // Mark the BOT such that if [blk_start, blk_end) straddles a card
 505 // boundary, the card following the first such boundary is marked
 506 // with the appropriate offset.
 507 // NOTE: this method does _not_ adjust _unallocated_block or
 508 // any cards subsequent to the first one.
 509 void
 510 BlockOffsetArrayNonContigSpace::mark_block(HeapWord* blk_start,
 511                                            HeapWord* blk_end, bool reducing) {
 512   do_block_internal(blk_start, blk_end, Action_mark, reducing);
 513 }
 514 
 515 HeapWord* BlockOffsetArrayNonContigSpace::block_start_unsafe(
 516   const void* addr) const {
 517   assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
 518   assert(_bottom <= addr && addr < _end,
 519          "addr must be covered by this Array");
 520   // Must read this exactly once because it can be modified by parallel
 521   // allocation.
 522   HeapWord* ub = _unallocated_block;
 523   if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
 524     assert(ub < _end, "tautology (see above)");
 525     return ub;
 526   }
 527 
 528   // Otherwise, find the block start using the table.
 529   size_t index = _array->index_for(addr);
 530   HeapWord* q = _array->address_for_index(index);
 531 
 532   uint offset = _array->offset_array(index);    // Extend u_char to uint.
 533   while (offset >= N_words) {
 534     // The excess of the offset from N_words indicates a power of Base
 535     // to go back by.
 536     size_t n_cards_back = entry_to_cards_back(offset);
 537     q -= (N_words * n_cards_back);
 538     assert(q >= _sp->bottom(),
 539            err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
 540                    p2i(q), p2i(_sp->bottom())));
 541     assert(q < _sp->end(),
 542            err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
 543                    p2i(q), p2i(_sp->end())));
 544     index -= n_cards_back;
 545     offset = _array->offset_array(index);
 546   }
 547   assert(offset < N_words, "offset too large");
 548   index--;
 549   q -= offset;
 550   assert(q >= _sp->bottom(),
 551          err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
 552                  p2i(q), p2i(_sp->bottom())));
 553   assert(q < _sp->end(),
 554          err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
 555                  p2i(q), p2i(_sp->end())));
 556   HeapWord* n = q;
 557 
 558   while (n <= addr) {
 559     debug_only(HeapWord* last = q);   // for debugging
 560     q = n;
 561     n += _sp->block_size(n);
 562     assert(n > q,
 563            err_msg("Looping at n = " PTR_FORMAT " with last = " PTR_FORMAT","
 564                    " while querying blk_start(" PTR_FORMAT ")"
 565                    " on _sp = [" PTR_FORMAT "," PTR_FORMAT ")",
 566                    p2i(n), p2i(last), p2i(addr), p2i(_sp->bottom()), p2i(_sp->end())));
 567   }
 568   assert(q <= addr,
 569          err_msg("wrong order for current (" INTPTR_FORMAT ")" " <= arg (" INTPTR_FORMAT ")",
 570                  p2i(q), p2i(addr)));
 571   assert(addr <= n,
 572          err_msg("wrong order for arg (" INTPTR_FORMAT ") <= next (" INTPTR_FORMAT ")",
 573                  p2i(addr), p2i(n)));
 574   return q;
 575 }
 576 
 577 HeapWord* BlockOffsetArrayNonContigSpace::block_start_careful(
 578   const void* addr) const {
 579   assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
 580 
 581   assert(_bottom <= addr && addr < _end,
 582          "addr must be covered by this Array");
 583   // Must read this exactly once because it can be modified by parallel
 584   // allocation.
 585   HeapWord* ub = _unallocated_block;
 586   if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
 587     assert(ub < _end, "tautology (see above)");
 588     return ub;
 589   }
 590 
 591   // Otherwise, find the block start using the table, but taking
 592   // care (cf block_start_unsafe() above) not to parse any objects/blocks
 593   // on the cards themselves.
 594   size_t index = _array->index_for(addr);
 595   assert(_array->address_for_index(index) == addr,
 596          "arg should be start of card");
 597 
 598   HeapWord* q = (HeapWord*)addr;
 599   uint offset;
 600   do {
 601     offset = _array->offset_array(index);
 602     if (offset < N_words) {
 603       q -= offset;
 604     } else {
 605       size_t n_cards_back = entry_to_cards_back(offset);
 606       q -= (n_cards_back * N_words);
 607       index -= n_cards_back;
 608     }
 609   } while (offset >= N_words);
 610   assert(q <= addr, "block start should be to left of arg");
 611   return q;
 612 }
 613 
 614 #ifndef PRODUCT
 615 // Verification & debugging - ensure that the offset table reflects the fact
 616 // that the block [blk_start, blk_end) or [blk, blk + size) is a
 617 // single block of storage. NOTE: can't const this because of
 618 // call to non-const do_block_internal() below.
 619 void BlockOffsetArrayNonContigSpace::verify_single_block(
 620   HeapWord* blk_start, HeapWord* blk_end) {
 621   if (VerifyBlockOffsetArray) {
 622     do_block_internal(blk_start, blk_end, Action_check);
 623   }
 624 }
 625 
 626 void BlockOffsetArrayNonContigSpace::verify_single_block(
 627   HeapWord* blk, size_t size) {
 628   verify_single_block(blk, blk + size);
 629 }
 630 
 631 // Verify that the given block is before _unallocated_block
 632 void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
 633   HeapWord* blk_start, HeapWord* blk_end) const {
 634   if (BlockOffsetArrayUseUnallocatedBlock) {
 635     assert(blk_start < blk_end, "Block inconsistency?");
 636     assert(blk_end <= _unallocated_block, "_unallocated_block problem");
 637   }
 638 }
 639 
 640 void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
 641   HeapWord* blk, size_t size) const {
 642   verify_not_unallocated(blk, blk + size);
 643 }
 644 #endif // PRODUCT
 645 
 646 size_t BlockOffsetArrayNonContigSpace::last_active_index() const {
 647   if (_unallocated_block == _bottom) {
 648     return 0;
 649   } else {
 650     return _array->index_for(_unallocated_block - 1);
 651   }
 652 }
 653 
 654 //////////////////////////////////////////////////////////////////////
 655 // BlockOffsetArrayContigSpace
 656 //////////////////////////////////////////////////////////////////////
 657 
 658 HeapWord* BlockOffsetArrayContigSpace::block_start_unsafe(const void* addr) const {
 659   assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
 660 
 661   // Otherwise, find the block start using the table.
 662   assert(_bottom <= addr && addr < _end,
 663          "addr must be covered by this Array");
 664   size_t index = _array->index_for(addr);
 665   // We must make sure that the offset table entry we use is valid.  If
 666   // "addr" is past the end, start at the last known one and go forward.
 667   index = MIN2(index, _next_offset_index-1);
 668   HeapWord* q = _array->address_for_index(index);
 669 
 670   uint offset = _array->offset_array(index);    // Extend u_char to uint.
 671   while (offset > N_words) {
 672     // The excess of the offset from N_words indicates a power of Base
 673     // to go back by.
 674     size_t n_cards_back = entry_to_cards_back(offset);
 675     q -= (N_words * n_cards_back);
 676     assert(q >= _sp->bottom(), "Went below bottom!");
 677     index -= n_cards_back;
 678     offset = _array->offset_array(index);
 679   }
 680   while (offset == N_words) {
 681     assert(q >= _sp->bottom(), "Went below bottom!");
 682     q -= N_words;
 683     index--;
 684     offset = _array->offset_array(index);
 685   }
 686   assert(offset < N_words, "offset too large");
 687   q -= offset;
 688   HeapWord* n = q;
 689 
 690   while (n <= addr) {
 691     debug_only(HeapWord* last = q);   // for debugging
 692     q = n;
 693     n += _sp->block_size(n);
 694   }
 695   assert(q <= addr, "wrong order for current and arg");
 696   assert(addr <= n, "wrong order for arg and next");
 697   return q;
 698 }
 699 
 700 //
 701 //              _next_offset_threshold
 702 //              |   _next_offset_index
 703 //              v   v
 704 //      +-------+-------+-------+-------+-------+
 705 //      | i-1   |   i   | i+1   | i+2   | i+3   |
 706 //      +-------+-------+-------+-------+-------+
 707 //       ( ^    ]
 708 //         block-start
 709 //
 710 
 711 void BlockOffsetArrayContigSpace::alloc_block_work(HeapWord* blk_start,
 712                                         HeapWord* blk_end) {
 713   assert(blk_start != NULL && blk_end > blk_start,
 714          "phantom block");
 715   assert(blk_end > _next_offset_threshold,
 716          "should be past threshold");
 717   assert(blk_start <= _next_offset_threshold,
 718          "blk_start should be at or before threshold");
 719   assert(pointer_delta(_next_offset_threshold, blk_start) <= N_words,
 720          "offset should be <= BlockOffsetSharedArray::N");
 721   assert(Universe::heap()->is_in_reserved(blk_start),
 722          "reference must be into the heap");
 723   assert(Universe::heap()->is_in_reserved(blk_end-1),
 724          "limit must be within the heap");
 725   assert(_next_offset_threshold ==
 726          _array->_reserved.start() + _next_offset_index*N_words,
 727          "index must agree with threshold");
 728 
 729   debug_only(size_t orig_next_offset_index = _next_offset_index;)
 730 
 731   // Mark the card that holds the offset into the block.  Note
 732   // that _next_offset_index and _next_offset_threshold are not
 733   // updated until the end of this method.
 734   _array->set_offset_array(_next_offset_index,
 735                            _next_offset_threshold,
 736                            blk_start);
 737 
 738   // We need to now mark the subsequent cards that this blk spans.
 739 
 740   // Index of card on which blk ends.
 741   size_t end_index   = _array->index_for(blk_end - 1);
 742 
 743   // Are there more cards left to be updated?
 744   if (_next_offset_index + 1 <= end_index) {
 745     HeapWord* rem_st  = _array->address_for_index(_next_offset_index + 1);
 746     // Calculate rem_end this way because end_index
 747     // may be the last valid index in the covered region.
 748     HeapWord* rem_end = _array->address_for_index(end_index) +  N_words;
 749     set_remainder_to_point_to_start(rem_st, rem_end);
 750   }
 751 
 752   // _next_offset_index and _next_offset_threshold updated here.
 753   _next_offset_index = end_index + 1;
 754   // Calculate _next_offset_threshold this way because end_index
 755   // may be the last valid index in the covered region.
 756   _next_offset_threshold = _array->address_for_index(end_index) + N_words;
 757   assert(_next_offset_threshold >= blk_end, "Incorrect offset threshold");
 758 
 759 #ifdef ASSERT
 760   // The offset can be 0 if the block starts on a boundary.  That
 761   // is checked by an assertion above.
 762   size_t start_index = _array->index_for(blk_start);
 763   HeapWord* boundary    = _array->address_for_index(start_index);
 764   assert((_array->offset_array(orig_next_offset_index) == 0 &&
 765           blk_start == boundary) ||
 766           (_array->offset_array(orig_next_offset_index) > 0 &&
 767          _array->offset_array(orig_next_offset_index) <= N_words),
 768          "offset array should have been set");
 769   for (size_t j = orig_next_offset_index + 1; j <= end_index; j++) {
 770     assert(_array->offset_array(j) > 0 &&
 771            _array->offset_array(j) <= (u_char) (N_words+N_powers-1),
 772            "offset array should have been set");
 773   }
 774 #endif
 775 }
 776 
 777 HeapWord* BlockOffsetArrayContigSpace::initialize_threshold() {
 778   assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
 779          "just checking");
 780   _next_offset_index = _array->index_for(_bottom);
 781   _next_offset_index++;
 782   _next_offset_threshold =
 783     _array->address_for_index(_next_offset_index);
 784   return _next_offset_threshold;
 785 }
 786 
 787 void BlockOffsetArrayContigSpace::zero_bottom_entry() {
 788   assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
 789          "just checking");
 790   size_t bottom_index = _array->index_for(_bottom);
 791   _array->set_offset_array(bottom_index, 0);
 792 }
 793 
 794 size_t BlockOffsetArrayContigSpace::last_active_index() const {
 795   size_t result = _next_offset_index - 1;
 796   return ((intptr_t)result) >= 0 ? result : 0;
 797 }