1 /* 2 * Copyright (c) 2000, 2015, 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 #ifndef SHARE_VM_MEMORY_BLOCKOFFSETTABLE_HPP 26 #define SHARE_VM_MEMORY_BLOCKOFFSETTABLE_HPP 27 28 #include "memory/memRegion.hpp" 29 #include "memory/virtualspace.hpp" 30 #include "utilities/globalDefinitions.hpp" 31 32 // The CollectedHeap type requires subtypes to implement a method 33 // "block_start". For some subtypes, notably generational 34 // systems using card-table-based write barriers, the efficiency of this 35 // operation may be important. Implementations of the "BlockOffsetArray" 36 // class may be useful in providing such efficient implementations. 37 // 38 // BlockOffsetTable (abstract) 39 // - BlockOffsetArray (abstract) 40 // - BlockOffsetArrayNonContigSpace 41 // - BlockOffsetArrayContigSpace 42 // 43 44 class ContiguousSpace; 45 46 ////////////////////////////////////////////////////////////////////////// 47 // The BlockOffsetTable "interface" 48 ////////////////////////////////////////////////////////////////////////// 49 class BlockOffsetTable VALUE_OBJ_CLASS_SPEC { 50 friend class VMStructs; 51 protected: 52 // These members describe the region covered by the table. 53 54 // The space this table is covering. 55 HeapWord* _bottom; // == reserved.start 56 HeapWord* _end; // End of currently allocated region. 57 58 public: 59 // Initialize the table to cover the given space. 60 // The contents of the initial table are undefined. 61 BlockOffsetTable(HeapWord* bottom, HeapWord* end): 62 _bottom(bottom), _end(end) { 63 assert(_bottom <= _end, "arguments out of order"); 64 } 65 66 // Note that the committed size of the covered space may have changed, 67 // so the table size might also wish to change. 68 virtual void resize(size_t new_word_size) = 0; 69 70 virtual void set_bottom(HeapWord* new_bottom) { 71 assert(new_bottom <= _end, "new_bottom > _end"); 72 _bottom = new_bottom; 73 resize(pointer_delta(_end, _bottom)); 74 } 75 76 // Requires "addr" to be contained by a block, and returns the address of 77 // the start of that block. 78 virtual HeapWord* block_start_unsafe(const void* addr) const = 0; 79 80 // Returns the address of the start of the block containing "addr", or 81 // else "null" if it is covered by no block. 82 HeapWord* block_start(const void* addr) const; 83 }; 84 85 ////////////////////////////////////////////////////////////////////////// 86 // One implementation of "BlockOffsetTable," the BlockOffsetArray, 87 // divides the covered region into "N"-word subregions (where 88 // "N" = 2^"LogN". An array with an entry for each such subregion 89 // indicates how far back one must go to find the start of the 90 // chunk that includes the first word of the subregion. 91 // 92 // Each BlockOffsetArray is owned by a Space. However, the actual array 93 // may be shared by several BlockOffsetArrays; this is useful 94 // when a single resizable area (such as a generation) is divided up into 95 // several spaces in which contiguous allocation takes place. (Consider, 96 // for example, the garbage-first generation.) 97 98 // Here is the shared array type. 99 ////////////////////////////////////////////////////////////////////////// 100 // BlockOffsetSharedArray 101 ////////////////////////////////////////////////////////////////////////// 102 class BlockOffsetSharedArray: public CHeapObj<mtGC> { 103 friend class BlockOffsetArray; 104 friend class BlockOffsetArrayNonContigSpace; 105 friend class BlockOffsetArrayContigSpace; 106 friend class VMStructs; 107 108 private: 109 enum SomePrivateConstants { 110 LogN = 9, 111 LogN_words = LogN - LogHeapWordSize, 112 N_bytes = 1 << LogN, 113 N_words = 1 << LogN_words 114 }; 115 116 bool _init_to_zero; 117 118 // The reserved region covered by the shared array. 119 MemRegion _reserved; 120 121 // End of the current committed region. 122 HeapWord* _end; 123 124 // Array for keeping offsets for retrieving object start fast given an 125 // address. 126 VirtualSpace _vs; 127 u_char* _offset_array; // byte array keeping backwards offsets 128 129 protected: 130 // Bounds checking accessors: 131 // For performance these have to devolve to array accesses in product builds. 132 u_char offset_array(size_t index) const { 133 assert(index < _vs.committed_size(), "index out of range"); 134 return _offset_array[index]; 135 } 136 // An assertion-checking helper method for the set_offset_array() methods below. 137 void check_reducing_assertion(bool reducing); 138 139 void set_offset_array(size_t index, u_char offset, bool reducing = false) { 140 check_reducing_assertion(reducing); 141 assert(index < _vs.committed_size(), "index out of range"); 142 assert(!reducing || _offset_array[index] >= offset, "Not reducing"); 143 _offset_array[index] = offset; 144 } 145 146 void set_offset_array(size_t index, HeapWord* high, HeapWord* low, bool reducing = false) { 147 check_reducing_assertion(reducing); 148 assert(index < _vs.committed_size(), "index out of range"); 149 assert(high >= low, "addresses out of order"); 150 assert(pointer_delta(high, low) <= N_words, "offset too large"); 151 assert(!reducing || _offset_array[index] >= (u_char)pointer_delta(high, low), 152 "Not reducing"); 153 _offset_array[index] = (u_char)pointer_delta(high, low); 154 } 155 156 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset, bool reducing = false) { 157 check_reducing_assertion(reducing); 158 assert(index_for(right - 1) < _vs.committed_size(), 159 "right address out of range"); 160 assert(left < right, "Heap addresses out of order"); 161 size_t num_cards = pointer_delta(right, left) >> LogN_words; 162 163 // Below, we may use an explicit loop instead of memset() 164 // because on certain platforms memset() can give concurrent 165 // readers "out-of-thin-air," phantom zeros; see 6948537. 166 if (UseMemSetInBOT) { 167 memset(&_offset_array[index_for(left)], offset, num_cards); 168 } else { 169 size_t i = index_for(left); 170 const size_t end = i + num_cards; 171 for (; i < end; i++) { 172 // Elided until CR 6977974 is fixed properly. 173 // assert(!reducing || _offset_array[i] >= offset, "Not reducing"); 174 _offset_array[i] = offset; 175 } 176 } 177 } 178 179 void set_offset_array(size_t left, size_t right, u_char offset, bool reducing = false) { 180 check_reducing_assertion(reducing); 181 assert(right < _vs.committed_size(), "right address out of range"); 182 assert(left <= right, "indexes out of order"); 183 size_t num_cards = right - left + 1; 184 185 // Below, we may use an explicit loop instead of memset 186 // because on certain platforms memset() can give concurrent 187 // readers "out-of-thin-air," phantom zeros; see 6948537. 188 if (UseMemSetInBOT) { 189 memset(&_offset_array[left], offset, num_cards); 190 } else { 191 size_t i = left; 192 const size_t end = i + num_cards; 193 for (; i < end; i++) { 194 // Elided until CR 6977974 is fixed properly. 195 // assert(!reducing || _offset_array[i] >= offset, "Not reducing"); 196 _offset_array[i] = offset; 197 } 198 } 199 } 200 201 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const { 202 assert(index < _vs.committed_size(), "index out of range"); 203 assert(high >= low, "addresses out of order"); 204 assert(pointer_delta(high, low) <= N_words, "offset too large"); 205 assert(_offset_array[index] == pointer_delta(high, low), 206 "Wrong offset"); 207 } 208 209 bool is_card_boundary(HeapWord* p) const; 210 211 // Return the number of slots needed for an offset array 212 // that covers mem_region_words words. 213 // We always add an extra slot because if an object 214 // ends on a card boundary we put a 0 in the next 215 // offset array slot, so we want that slot always 216 // to be reserved. 217 218 size_t compute_size(size_t mem_region_words) { 219 size_t number_of_slots = (mem_region_words / N_words) + 1; 220 return ReservedSpace::allocation_align_size_up(number_of_slots); 221 } 222 223 public: 224 // Initialize the table to cover from "base" to (at least) 225 // "base + init_word_size". In the future, the table may be expanded 226 // (see "resize" below) up to the size of "_reserved" (which must be at 227 // least "init_word_size".) The contents of the initial table are 228 // undefined; it is the responsibility of the constituent 229 // BlockOffsetTable(s) to initialize cards. 230 BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size); 231 232 // Notes a change in the committed size of the region covered by the 233 // table. The "new_word_size" may not be larger than the size of the 234 // reserved region this table covers. 235 void resize(size_t new_word_size); 236 237 void set_bottom(HeapWord* new_bottom); 238 239 // Whether entries should be initialized to zero. Used currently only for 240 // error checking. 241 void set_init_to_zero(bool val) { _init_to_zero = val; } 242 bool init_to_zero() { return _init_to_zero; } 243 244 // Updates all the BlockOffsetArray's sharing this shared array to 245 // reflect the current "top"'s of their spaces. 246 void update_offset_arrays(); // Not yet implemented! 247 248 // Return the appropriate index into "_offset_array" for "p". 249 size_t index_for(const void* p) const; 250 251 // Return the address indicating the start of the region corresponding to 252 // "index" in "_offset_array". 253 HeapWord* address_for_index(size_t index) const; 254 }; 255 256 ////////////////////////////////////////////////////////////////////////// 257 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray. 258 ////////////////////////////////////////////////////////////////////////// 259 class BlockOffsetArray: public BlockOffsetTable { 260 friend class VMStructs; 261 friend class G1BlockOffsetArray; // temp. until we restructure and cleanup 262 protected: 263 // The following enums are used by do_block_internal() below 264 enum Action { 265 Action_single, // BOT records a single block (see single_block()) 266 Action_mark, // BOT marks the start of a block (see mark_block()) 267 Action_check // Check that BOT records block correctly 268 // (see verify_single_block()). 269 }; 270 271 enum SomePrivateConstants { 272 N_words = BlockOffsetSharedArray::N_words, 273 LogN = BlockOffsetSharedArray::LogN, 274 // entries "e" of at least N_words mean "go back by Base^(e-N_words)." 275 // All entries are less than "N_words + N_powers". 276 LogBase = 4, 277 Base = (1 << LogBase), 278 N_powers = 14 279 }; 280 281 static size_t power_to_cards_back(uint i) { 282 return (size_t)1 << (LogBase * i); 283 } 284 static size_t power_to_words_back(uint i) { 285 return power_to_cards_back(i) * N_words; 286 } 287 static size_t entry_to_cards_back(u_char entry) { 288 assert(entry >= N_words, "Precondition"); 289 return power_to_cards_back(entry - N_words); 290 } 291 static size_t entry_to_words_back(u_char entry) { 292 assert(entry >= N_words, "Precondition"); 293 return power_to_words_back(entry - N_words); 294 } 295 296 // The shared array, which is shared with other BlockOffsetArray's 297 // corresponding to different spaces within a generation or span of 298 // memory. 299 BlockOffsetSharedArray* _array; 300 301 // The space that owns this subregion. 302 Space* _sp; 303 304 // If true, array entries are initialized to 0; otherwise, they are 305 // initialized to point backwards to the beginning of the covered region. 306 bool _init_to_zero; 307 308 // An assertion-checking helper method for the set_remainder*() methods below. 309 void check_reducing_assertion(bool reducing) { _array->check_reducing_assertion(reducing); } 310 311 // Sets the entries 312 // corresponding to the cards starting at "start" and ending at "end" 313 // to point back to the card before "start": the interval [start, end) 314 // is right-open. The last parameter, reducing, indicates whether the 315 // updates to individual entries always reduce the entry from a higher 316 // to a lower value. (For example this would hold true during a temporal 317 // regime during which only block splits were updating the BOT. 318 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing = false); 319 // Same as above, except that the args here are a card _index_ interval 320 // that is closed: [start_index, end_index] 321 void set_remainder_to_point_to_start_incl(size_t start, size_t end, bool reducing = false); 322 323 // A helper function for BOT adjustment/verification work 324 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action, bool reducing = false); 325 326 public: 327 // The space may not have its bottom and top set yet, which is why the 328 // region is passed as a parameter. If "init_to_zero" is true, the 329 // elements of the array are initialized to zero. Otherwise, they are 330 // initialized to point backwards to the beginning. 331 BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr, 332 bool init_to_zero_); 333 334 // Note: this ought to be part of the constructor, but that would require 335 // "this" to be passed as a parameter to a member constructor for 336 // the containing concrete subtype of Space. 337 // This would be legal C++, but MS VC++ doesn't allow it. 338 void set_space(Space* sp) { _sp = sp; } 339 340 // Resets the covered region to the given "mr". 341 void set_region(MemRegion mr) { 342 _bottom = mr.start(); 343 _end = mr.end(); 344 } 345 346 // Note that the committed size of the covered space may have changed, 347 // so the table size might also wish to change. 348 virtual void resize(size_t new_word_size) { 349 HeapWord* new_end = _bottom + new_word_size; 350 if (_end < new_end && !init_to_zero()) { 351 // verify that the old and new boundaries are also card boundaries 352 assert(_array->is_card_boundary(_end), 353 "_end not a card boundary"); 354 assert(_array->is_card_boundary(new_end), 355 "new _end would not be a card boundary"); 356 // set all the newly added cards 357 _array->set_offset_array(_end, new_end, N_words); 358 } 359 _end = new_end; // update _end 360 } 361 362 // Adjust the BOT to show that it has a single block in the 363 // range [blk_start, blk_start + size). All necessary BOT 364 // cards are adjusted, but _unallocated_block isn't. 365 void single_block(HeapWord* blk_start, HeapWord* blk_end); 366 void single_block(HeapWord* blk, size_t size) { 367 single_block(blk, blk + size); 368 } 369 370 // When the alloc_block() call returns, the block offset table should 371 // have enough information such that any subsequent block_start() call 372 // with an argument equal to an address that is within the range 373 // [blk_start, blk_end) would return the value blk_start, provided 374 // there have been no calls in between that reset this information 375 // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call 376 // for an appropriate range covering the said interval). 377 // These methods expect to be called with [blk_start, blk_end) 378 // representing a block of memory in the heap. 379 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end); 380 void alloc_block(HeapWord* blk, size_t size) { 381 alloc_block(blk, blk + size); 382 } 383 384 // If true, initialize array slots with no allocated blocks to zero. 385 // Otherwise, make them point back to the front. 386 bool init_to_zero() { return _init_to_zero; } 387 // Corresponding setter 388 void set_init_to_zero(bool val) { 389 _init_to_zero = val; 390 assert(_array != NULL, "_array should be non-NULL"); 391 _array->set_init_to_zero(val); 392 } 393 394 // Debugging 395 // Return the index of the last entry in the "active" region. 396 virtual size_t last_active_index() const = 0; 397 // Verify the block offset table 398 void verify() const; 399 void check_all_cards(size_t left_card, size_t right_card) const; 400 }; 401 402 //////////////////////////////////////////////////////////////////////////// 403 // A subtype of BlockOffsetArray that takes advantage of the fact 404 // that its underlying space is a NonContiguousSpace, so that some 405 // specialized interfaces can be made available for spaces that 406 // manipulate the table. 407 //////////////////////////////////////////////////////////////////////////// 408 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray { 409 friend class VMStructs; 410 private: 411 // The portion [_unallocated_block, _sp.end()) of the space that 412 // is a single block known not to contain any objects. 413 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag. 414 HeapWord* _unallocated_block; 415 416 public: 417 BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr): 418 BlockOffsetArray(array, mr, false), 419 _unallocated_block(_bottom) { } 420 421 // Accessor 422 HeapWord* unallocated_block() const { 423 assert(BlockOffsetArrayUseUnallocatedBlock, 424 "_unallocated_block is not being maintained"); 425 return _unallocated_block; 426 } 427 428 void set_unallocated_block(HeapWord* block) { 429 assert(BlockOffsetArrayUseUnallocatedBlock, 430 "_unallocated_block is not being maintained"); 431 assert(block >= _bottom && block <= _end, "out of range"); 432 _unallocated_block = block; 433 } 434 435 // These methods expect to be called with [blk_start, blk_end) 436 // representing a block of memory in the heap. 437 void alloc_block(HeapWord* blk_start, HeapWord* blk_end); 438 void alloc_block(HeapWord* blk, size_t size) { 439 alloc_block(blk, blk + size); 440 } 441 442 // The following methods are useful and optimized for a 443 // non-contiguous space. 444 445 // Given a block [blk_start, blk_start + full_blk_size), and 446 // a left_blk_size < full_blk_size, adjust the BOT to show two 447 // blocks [blk_start, blk_start + left_blk_size) and 448 // [blk_start + left_blk_size, blk_start + full_blk_size). 449 // It is assumed (and verified in the non-product VM) that the 450 // BOT was correct for the original block. 451 void split_block(HeapWord* blk_start, size_t full_blk_size, 452 size_t left_blk_size); 453 454 // Adjust BOT to show that it has a block in the range 455 // [blk_start, blk_start + size). Only the first card 456 // of BOT is touched. It is assumed (and verified in the 457 // non-product VM) that the remaining cards of the block 458 // are correct. 459 void mark_block(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false); 460 void mark_block(HeapWord* blk, size_t size, bool reducing = false) { 461 mark_block(blk, blk + size, reducing); 462 } 463 464 // Adjust _unallocated_block to indicate that a particular 465 // block has been newly allocated or freed. It is assumed (and 466 // verified in the non-product VM) that the BOT is correct for 467 // the given block. 468 void allocated(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false) { 469 // Verify that the BOT shows [blk, blk + blk_size) to be one block. 470 verify_single_block(blk_start, blk_end); 471 if (BlockOffsetArrayUseUnallocatedBlock) { 472 _unallocated_block = MAX2(_unallocated_block, blk_end); 473 } 474 } 475 476 void allocated(HeapWord* blk, size_t size, bool reducing = false) { 477 allocated(blk, blk + size, reducing); 478 } 479 480 void freed(HeapWord* blk_start, HeapWord* blk_end); 481 void freed(HeapWord* blk, size_t size); 482 483 HeapWord* block_start_unsafe(const void* addr) const; 484 485 // Requires "addr" to be the start of a card and returns the 486 // start of the block that contains the given address. 487 HeapWord* block_start_careful(const void* addr) const; 488 489 // Verification & debugging: ensure that the offset table reflects 490 // the fact that the block [blk_start, blk_end) or [blk, blk + size) 491 // is a single block of storage. NOTE: can't const this because of 492 // call to non-const do_block_internal() below. 493 void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) 494 PRODUCT_RETURN; 495 void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN; 496 497 // Verify that the given block is before _unallocated_block 498 void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end) 499 const PRODUCT_RETURN; 500 void verify_not_unallocated(HeapWord* blk, size_t size) 501 const PRODUCT_RETURN; 502 503 // Debugging support 504 virtual size_t last_active_index() const; 505 }; 506 507 //////////////////////////////////////////////////////////////////////////// 508 // A subtype of BlockOffsetArray that takes advantage of the fact 509 // that its underlying space is a ContiguousSpace, so that its "active" 510 // region can be more efficiently tracked (than for a non-contiguous space). 511 //////////////////////////////////////////////////////////////////////////// 512 class BlockOffsetArrayContigSpace: public BlockOffsetArray { 513 friend class VMStructs; 514 private: 515 // allocation boundary at which offset array must be updated 516 HeapWord* _next_offset_threshold; 517 size_t _next_offset_index; // index corresponding to that boundary 518 519 // Work function when allocation start crosses threshold. 520 void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end); 521 522 public: 523 BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr): 524 BlockOffsetArray(array, mr, true) { 525 _next_offset_threshold = NULL; 526 _next_offset_index = 0; 527 } 528 529 void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); } 530 531 // Initialize the threshold for an empty heap. 532 HeapWord* initialize_threshold(); 533 // Zero out the entry for _bottom (offset will be zero) 534 void zero_bottom_entry(); 535 536 // Return the next threshold, the point at which the table should be 537 // updated. 538 HeapWord* threshold() const { return _next_offset_threshold; } 539 540 // In general, these methods expect to be called with 541 // [blk_start, blk_end) representing a block of memory in the heap. 542 // In this implementation, however, we are OK even if blk_start and/or 543 // blk_end are NULL because NULL is represented as 0, and thus 544 // never exceeds the "_next_offset_threshold". 545 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) { 546 if (blk_end > _next_offset_threshold) { 547 alloc_block_work(blk_start, blk_end); 548 } 549 } 550 void alloc_block(HeapWord* blk, size_t size) { 551 alloc_block(blk, blk + size); 552 } 553 554 HeapWord* block_start_unsafe(const void* addr) const; 555 556 // Debugging support 557 virtual size_t last_active_index() const; 558 }; 559 560 #endif // SHARE_VM_MEMORY_BLOCKOFFSETTABLE_HPP