1 // Bitmap Allocator. -*- C++ -*- 2 3 // Copyright (C) 2004-2018 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the 7 // terms of the GNU General Public License as published by the 8 // Free Software Foundation; either version 3, or (at your option) 9 // any later version. 10 11 // This library is distributed in the hope that it will be useful, 12 // but WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 // GNU General Public License for more details. 15 16 // Under Section 7 of GPL version 3, you are granted additional 17 // permissions described in the GCC Runtime Library Exception, version 18 // 3.1, as published by the Free Software Foundation. 19 20 // You should have received a copy of the GNU General Public License and 21 // a copy of the GCC Runtime Library Exception along with this program; 22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 // <http://www.gnu.org/licenses/>. 24 25 /** @file ext/bitmap_allocator.h 26 * This file is a GNU extension to the Standard C++ Library. 27 */ 28 29 #ifndef _BITMAP_ALLOCATOR_H 30 #define _BITMAP_ALLOCATOR_H 1 31 32 #include <utility> // For std::pair. 33 #include <bits/functexcept.h> // For __throw_bad_alloc(). 34 #include <functional> // For greater_equal, and less_equal. 35 #include <new> // For operator new. 36 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT 37 #include <ext/concurrence.h> 38 #include <bits/move.h> 39 40 /** @brief The constant in the expression below is the alignment 41 * required in bytes. 42 */ 43 #define _BALLOC_ALIGN_BYTES 8 44 45 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) 46 { 47 _GLIBCXX_BEGIN_NAMESPACE_VERSION 48 49 using std::size_t; 50 using std::ptrdiff_t; 51 52 namespace __detail 53 { 54 /** @class __mini_vector bitmap_allocator.h bitmap_allocator.h 55 * 56 * @brief __mini_vector<> is a stripped down version of the 57 * full-fledged std::vector<>. 58 * 59 * It is to be used only for built-in types or PODs. Notable 60 * differences are: 61 * 62 * 1. Not all accessor functions are present. 63 * 2. Used ONLY for PODs. 64 * 3. No Allocator template argument. Uses ::operator new() to get 65 * memory, and ::operator delete() to free it. 66 * Caveat: The dtor does NOT free the memory allocated, so this a 67 * memory-leaking vector! 68 */ 69 template<typename _Tp> 70 class __mini_vector 71 { 72 __mini_vector(const __mini_vector&); 73 __mini_vector& operator=(const __mini_vector&); 74 75 public: 76 typedef _Tp value_type; 77 typedef _Tp* pointer; 78 typedef _Tp& reference; 79 typedef const _Tp& const_reference; 80 typedef size_t size_type; 81 typedef ptrdiff_t difference_type; 82 typedef pointer iterator; 83 84 private: 85 pointer _M_start; 86 pointer _M_finish; 87 pointer _M_end_of_storage; 88 89 size_type 90 _M_space_left() const throw() 91 { return _M_end_of_storage - _M_finish; } 92 93 pointer 94 allocate(size_type __n) 95 { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); } 96 97 void 98 deallocate(pointer __p, size_type) 99 { ::operator delete(__p); } 100 101 public: 102 // Members used: size(), push_back(), pop_back(), 103 // insert(iterator, const_reference), erase(iterator), 104 // begin(), end(), back(), operator[]. 105 106 __mini_vector() 107 : _M_start(0), _M_finish(0), _M_end_of_storage(0) { } 108 109 size_type 110 size() const throw() 111 { return _M_finish - _M_start; } 112 113 iterator 114 begin() const throw() 115 { return this->_M_start; } 116 117 iterator 118 end() const throw() 119 { return this->_M_finish; } 120 121 reference 122 back() const throw() 123 { return *(this->end() - 1); } 124 125 reference 126 operator[](const size_type __pos) const throw() 127 { return this->_M_start[__pos]; } 128 129 void 130 insert(iterator __pos, const_reference __x); 131 132 void 133 push_back(const_reference __x) 134 { 135 if (this->_M_space_left()) 136 { 137 *this->end() = __x; 138 ++this->_M_finish; 139 } 140 else 141 this->insert(this->end(), __x); 142 } 143 144 void 145 pop_back() throw() 146 { --this->_M_finish; } 147 148 void 149 erase(iterator __pos) throw(); 150 151 void 152 clear() throw() 153 { this->_M_finish = this->_M_start; } 154 }; 155 156 // Out of line function definitions. 157 template<typename _Tp> 158 void __mini_vector<_Tp>:: 159 insert(iterator __pos, const_reference __x) 160 { 161 if (this->_M_space_left()) 162 { 163 size_type __to_move = this->_M_finish - __pos; 164 iterator __dest = this->end(); 165 iterator __src = this->end() - 1; 166 167 ++this->_M_finish; 168 while (__to_move) 169 { 170 *__dest = *__src; 171 --__dest; --__src; --__to_move; 172 } 173 *__pos = __x; 174 } 175 else 176 { 177 size_type __new_size = this->size() ? this->size() * 2 : 1; 178 iterator __new_start = this->allocate(__new_size); 179 iterator __first = this->begin(); 180 iterator __start = __new_start; 181 while (__first != __pos) 182 { 183 *__start = *__first; 184 ++__start; ++__first; 185 } 186 *__start = __x; 187 ++__start; 188 while (__first != this->end()) 189 { 190 *__start = *__first; 191 ++__start; ++__first; 192 } 193 if (this->_M_start) 194 this->deallocate(this->_M_start, this->size()); 195 196 this->_M_start = __new_start; 197 this->_M_finish = __start; 198 this->_M_end_of_storage = this->_M_start + __new_size; 199 } 200 } 201 202 template<typename _Tp> 203 void __mini_vector<_Tp>:: 204 erase(iterator __pos) throw() 205 { 206 while (__pos + 1 != this->end()) 207 { 208 *__pos = __pos[1]; 209 ++__pos; 210 } 211 --this->_M_finish; 212 } 213 214 215 template<typename _Tp> 216 struct __mv_iter_traits 217 { 218 typedef typename _Tp::value_type value_type; 219 typedef typename _Tp::difference_type difference_type; 220 }; 221 222 template<typename _Tp> 223 struct __mv_iter_traits<_Tp*> 224 { 225 typedef _Tp value_type; 226 typedef ptrdiff_t difference_type; 227 }; 228 229 enum 230 { 231 bits_per_byte = 8, 232 bits_per_block = sizeof(size_t) * size_t(bits_per_byte) 233 }; 234 235 template<typename _ForwardIterator, typename _Tp, typename _Compare> 236 _ForwardIterator 237 __lower_bound(_ForwardIterator __first, _ForwardIterator __last, 238 const _Tp& __val, _Compare __comp) 239 { 240 typedef typename __mv_iter_traits<_ForwardIterator>::difference_type 241 _DistanceType; 242 243 _DistanceType __len = __last - __first; 244 _DistanceType __half; 245 _ForwardIterator __middle; 246 247 while (__len > 0) 248 { 249 __half = __len >> 1; 250 __middle = __first; 251 __middle += __half; 252 if (__comp(*__middle, __val)) 253 { 254 __first = __middle; 255 ++__first; 256 __len = __len - __half - 1; 257 } 258 else 259 __len = __half; 260 } 261 return __first; 262 } 263 264 /** @brief The number of Blocks pointed to by the address pair 265 * passed to the function. 266 */ 267 template<typename _AddrPair> 268 inline size_t 269 __num_blocks(_AddrPair __ap) 270 { return (__ap.second - __ap.first) + 1; } 271 272 /** @brief The number of Bit-maps pointed to by the address pair 273 * passed to the function. 274 */ 275 template<typename _AddrPair> 276 inline size_t 277 __num_bitmaps(_AddrPair __ap) 278 { return __num_blocks(__ap) / size_t(bits_per_block); } 279 280 // _Tp should be a pointer type. 281 template<typename _Tp> 282 class _Inclusive_between 283 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool> 284 { 285 typedef _Tp pointer; 286 pointer _M_ptr_value; 287 typedef typename std::pair<_Tp, _Tp> _Block_pair; 288 289 public: 290 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr) 291 { } 292 293 bool 294 operator()(_Block_pair __bp) const throw() 295 { 296 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second) 297 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first)) 298 return true; 299 else 300 return false; 301 } 302 }; 303 304 // Used to pass a Functor to functions by reference. 305 template<typename _Functor> 306 class _Functor_Ref 307 : public std::unary_function<typename _Functor::argument_type, 308 typename _Functor::result_type> 309 { 310 _Functor& _M_fref; 311 312 public: 313 typedef typename _Functor::argument_type argument_type; 314 typedef typename _Functor::result_type result_type; 315 316 _Functor_Ref(_Functor& __fref) : _M_fref(__fref) 317 { } 318 319 result_type 320 operator()(argument_type __arg) 321 { return _M_fref(__arg); } 322 }; 323 324 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h 325 * 326 * @brief The class which acts as a predicate for applying the 327 * first-fit memory allocation policy for the bitmap allocator. 328 */ 329 // _Tp should be a pointer type, and _Alloc is the Allocator for 330 // the vector. 331 template<typename _Tp> 332 class _Ffit_finder 333 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool> 334 { 335 typedef typename std::pair<_Tp, _Tp> _Block_pair; 336 typedef typename __detail::__mini_vector<_Block_pair> _BPVector; 337 typedef typename _BPVector::difference_type _Counter_type; 338 339 size_t* _M_pbitmap; 340 _Counter_type _M_data_offset; 341 342 public: 343 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0) 344 { } 345 346 bool 347 operator()(_Block_pair __bp) throw() 348 { 349 // Set the _rover to the last physical location bitmap, 350 // which is the bitmap which belongs to the first free 351 // block. Thus, the bitmaps are in exact reverse order of 352 // the actual memory layout. So, we count down the bitmaps, 353 // which is the same as moving up the memory. 354 355 // If the used count stored at the start of the Bit Map headers 356 // is equal to the number of Objects that the current Block can 357 // store, then there is definitely no space for another single 358 // object, so just return false. 359 _Counter_type __diff = __detail::__num_bitmaps(__bp); 360 361 if (*(reinterpret_cast<size_t*> 362 (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp)) 363 return false; 364 365 size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1; 366 367 for (_Counter_type __i = 0; __i < __diff; ++__i) 368 { 369 _M_data_offset = __i; 370 if (*__rover) 371 { 372 _M_pbitmap = __rover; 373 return true; 374 } 375 --__rover; 376 } 377 return false; 378 } 379 380 size_t* 381 _M_get() const throw() 382 { return _M_pbitmap; } 383 384 _Counter_type 385 _M_offset() const throw() 386 { return _M_data_offset * size_t(bits_per_block); } 387 }; 388 389 /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h 390 * 391 * @brief The bitmap counter which acts as the bitmap 392 * manipulator, and manages the bit-manipulation functions and 393 * the searching and identification functions on the bit-map. 394 */ 395 // _Tp should be a pointer type. 396 template<typename _Tp> 397 class _Bitmap_counter 398 { 399 typedef typename 400 __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector; 401 typedef typename _BPVector::size_type _Index_type; 402 typedef _Tp pointer; 403 404 _BPVector& _M_vbp; 405 size_t* _M_curr_bmap; 406 size_t* _M_last_bmap_in_block; 407 _Index_type _M_curr_index; 408 409 public: 410 // Use the 2nd parameter with care. Make sure that such an 411 // entry exists in the vector before passing that particular 412 // index to this ctor. 413 _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp) 414 { this->_M_reset(__index); } 415 416 void 417 _M_reset(long __index = -1) throw() 418 { 419 if (__index == -1) 420 { 421 _M_curr_bmap = 0; 422 _M_curr_index = static_cast<_Index_type>(-1); 423 return; 424 } 425 426 _M_curr_index = __index; 427 _M_curr_bmap = reinterpret_cast<size_t*> 428 (_M_vbp[_M_curr_index].first) - 1; 429 430 _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1); 431 432 _M_last_bmap_in_block = _M_curr_bmap 433 - ((_M_vbp[_M_curr_index].second 434 - _M_vbp[_M_curr_index].first + 1) 435 / size_t(bits_per_block) - 1); 436 } 437 438 // Dangerous Function! Use with extreme care. Pass to this 439 // function ONLY those values that are known to be correct, 440 // otherwise this will mess up big time. 441 void 442 _M_set_internal_bitmap(size_t* __new_internal_marker) throw() 443 { _M_curr_bmap = __new_internal_marker; } 444 445 bool 446 _M_finished() const throw() 447 { return(_M_curr_bmap == 0); } 448 449 _Bitmap_counter& 450 operator++() throw() 451 { 452 if (_M_curr_bmap == _M_last_bmap_in_block) 453 { 454 if (++_M_curr_index == _M_vbp.size()) 455 _M_curr_bmap = 0; 456 else 457 this->_M_reset(_M_curr_index); 458 } 459 else 460 --_M_curr_bmap; 461 return *this; 462 } 463 464 size_t* 465 _M_get() const throw() 466 { return _M_curr_bmap; } 467 468 pointer 469 _M_base() const throw() 470 { return _M_vbp[_M_curr_index].first; } 471 472 _Index_type 473 _M_offset() const throw() 474 { 475 return size_t(bits_per_block) 476 * ((reinterpret_cast<size_t*>(this->_M_base()) 477 - _M_curr_bmap) - 1); 478 } 479 480 _Index_type 481 _M_where() const throw() 482 { return _M_curr_index; } 483 }; 484 485 /** @brief Mark a memory address as allocated by re-setting the 486 * corresponding bit in the bit-map. 487 */ 488 inline void 489 __bit_allocate(size_t* __pbmap, size_t __pos) throw() 490 { 491 size_t __mask = 1 << __pos; 492 __mask = ~__mask; 493 *__pbmap &= __mask; 494 } 495 496 /** @brief Mark a memory address as free by setting the 497 * corresponding bit in the bit-map. 498 */ 499 inline void 500 __bit_free(size_t* __pbmap, size_t __pos) throw() 501 { 502 size_t __mask = 1 << __pos; 503 *__pbmap |= __mask; 504 } 505 } // namespace __detail 506 507 /** @brief Generic Version of the bsf instruction. 508 */ 509 inline size_t 510 _Bit_scan_forward(size_t __num) 511 { return static_cast<size_t>(__builtin_ctzl(__num)); } 512 513 /** @class free_list bitmap_allocator.h bitmap_allocator.h 514 * 515 * @brief The free list class for managing chunks of memory to be 516 * given to and returned by the bitmap_allocator. 517 */ 518 class free_list 519 { 520 public: 521 typedef size_t* value_type; 522 typedef __detail::__mini_vector<value_type> vector_type; 523 typedef vector_type::iterator iterator; 524 typedef __mutex __mutex_type; 525 526 private: 527 struct _LT_pointer_compare 528 { 529 bool 530 operator()(const size_t* __pui, 531 const size_t __cui) const throw() 532 { return *__pui < __cui; } 533 }; 534 535 #if defined __GTHREADS 536 __mutex_type& 537 _M_get_mutex() 538 { 539 static __mutex_type _S_mutex; 540 return _S_mutex; 541 } 542 #endif 543 544 vector_type& 545 _M_get_free_list() 546 { 547 static vector_type _S_free_list; 548 return _S_free_list; 549 } 550 551 /** @brief Performs validation of memory based on their size. 552 * 553 * @param __addr The pointer to the memory block to be 554 * validated. 555 * 556 * Validates the memory block passed to this function and 557 * appropriately performs the action of managing the free list of 558 * blocks by adding this block to the free list or deleting this 559 * or larger blocks from the free list. 560 */ 561 void 562 _M_validate(size_t* __addr) throw() 563 { 564 vector_type& __free_list = _M_get_free_list(); 565 const vector_type::size_type __max_size = 64; 566 if (__free_list.size() >= __max_size) 567 { 568 // Ok, the threshold value has been reached. We determine 569 // which block to remove from the list of free blocks. 570 if (*__addr >= *__free_list.back()) 571 { 572 // Ok, the new block is greater than or equal to the 573 // last block in the list of free blocks. We just free 574 // the new block. 575 ::operator delete(static_cast<void*>(__addr)); 576 return; 577 } 578 else 579 { 580 // Deallocate the last block in the list of free lists, 581 // and insert the new one in its correct position. 582 ::operator delete(static_cast<void*>(__free_list.back())); 583 __free_list.pop_back(); 584 } 585 } 586 587 // Just add the block to the list of free lists unconditionally. 588 iterator __temp = __detail::__lower_bound 589 (__free_list.begin(), __free_list.end(), 590 *__addr, _LT_pointer_compare()); 591 592 // We may insert the new free list before _temp; 593 __free_list.insert(__temp, __addr); 594 } 595 596 /** @brief Decides whether the wastage of memory is acceptable for 597 * the current memory request and returns accordingly. 598 * 599 * @param __block_size The size of the block available in the free 600 * list. 601 * 602 * @param __required_size The required size of the memory block. 603 * 604 * @return true if the wastage incurred is acceptable, else returns 605 * false. 606 */ 607 bool 608 _M_should_i_give(size_t __block_size, 609 size_t __required_size) throw() 610 { 611 const size_t __max_wastage_percentage = 36; 612 if (__block_size >= __required_size && 613 (((__block_size - __required_size) * 100 / __block_size) 614 < __max_wastage_percentage)) 615 return true; 616 else 617 return false; 618 } 619 620 public: 621 /** @brief This function returns the block of memory to the 622 * internal free list. 623 * 624 * @param __addr The pointer to the memory block that was given 625 * by a call to the _M_get function. 626 */ 627 inline void 628 _M_insert(size_t* __addr) throw() 629 { 630 #if defined __GTHREADS 631 __scoped_lock __bfl_lock(_M_get_mutex()); 632 #endif 633 // Call _M_validate to decide what should be done with 634 // this particular free list. 635 this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1); 636 // See discussion as to why this is 1! 637 } 638 639 /** @brief This function gets a block of memory of the specified 640 * size from the free list. 641 * 642 * @param __sz The size in bytes of the memory required. 643 * 644 * @return A pointer to the new memory block of size at least 645 * equal to that requested. 646 */ 647 size_t* 648 _M_get(size_t __sz) _GLIBCXX_THROW(std::bad_alloc); 649 650 /** @brief This function just clears the internal Free List, and 651 * gives back all the memory to the OS. 652 */ 653 void 654 _M_clear(); 655 }; 656 657 658 // Forward declare the class. 659 template<typename _Tp> 660 class bitmap_allocator; 661 662 // Specialize for void: 663 template<> 664 class bitmap_allocator<void> 665 { 666 public: 667 typedef void* pointer; 668 typedef const void* const_pointer; 669 670 // Reference-to-void members are impossible. 671 typedef void value_type; 672 template<typename _Tp1> 673 struct rebind 674 { 675 typedef bitmap_allocator<_Tp1> other; 676 }; 677 }; 678 679 /** 680 * @brief Bitmap Allocator, primary template. 681 * @ingroup allocators 682 */ 683 template<typename _Tp> 684 class bitmap_allocator : private free_list 685 { 686 public: 687 typedef size_t size_type; 688 typedef ptrdiff_t difference_type; 689 typedef _Tp* pointer; 690 typedef const _Tp* const_pointer; 691 typedef _Tp& reference; 692 typedef const _Tp& const_reference; 693 typedef _Tp value_type; 694 typedef free_list::__mutex_type __mutex_type; 695 696 template<typename _Tp1> 697 struct rebind 698 { 699 typedef bitmap_allocator<_Tp1> other; 700 }; 701 702 #if __cplusplus >= 201103L 703 // _GLIBCXX_RESOLVE_LIB_DEFECTS 704 // 2103. propagate_on_container_move_assignment 705 typedef std::true_type propagate_on_container_move_assignment; 706 #endif 707 708 private: 709 template<size_t _BSize, size_t _AlignSize> 710 struct aligned_size 711 { 712 enum 713 { 714 modulus = _BSize % _AlignSize, 715 value = _BSize + (modulus ? _AlignSize - (modulus) : 0) 716 }; 717 }; 718 719 struct _Alloc_block 720 { 721 char __M_unused[aligned_size<sizeof(value_type), 722 _BALLOC_ALIGN_BYTES>::value]; 723 }; 724 725 726 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair; 727 728 typedef typename __detail::__mini_vector<_Block_pair> _BPVector; 729 typedef typename _BPVector::iterator _BPiter; 730 731 template<typename _Predicate> 732 static _BPiter 733 _S_find(_Predicate __p) 734 { 735 _BPiter __first = _S_mem_blocks.begin(); 736 while (__first != _S_mem_blocks.end() && !__p(*__first)) 737 ++__first; 738 return __first; 739 } 740 741 #if defined _GLIBCXX_DEBUG 742 // Complexity: O(lg(N)). Where, N is the number of block of size 743 // sizeof(value_type). 744 void 745 _S_check_for_free_blocks() throw() 746 { 747 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 748 _BPiter __bpi = _S_find(_FFF()); 749 750 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end()); 751 } 752 #endif 753 754 /** @brief Responsible for exponentially growing the internal 755 * memory pool. 756 * 757 * @throw std::bad_alloc. If memory can not be allocated. 758 * 759 * Complexity: O(1), but internally depends upon the 760 * complexity of the function free_list::_M_get. The part where 761 * the bitmap headers are written has complexity: O(X),where X 762 * is the number of blocks of size sizeof(value_type) within 763 * the newly acquired block. Having a tight bound. 764 */ 765 void 766 _S_refill_pool() _GLIBCXX_THROW(std::bad_alloc) 767 { 768 #if defined _GLIBCXX_DEBUG 769 _S_check_for_free_blocks(); 770 #endif 771 772 const size_t __num_bitmaps = (_S_block_size 773 / size_t(__detail::bits_per_block)); 774 const size_t __size_to_allocate = sizeof(size_t) 775 + _S_block_size * sizeof(_Alloc_block) 776 + __num_bitmaps * sizeof(size_t); 777 778 size_t* __temp = 779 reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate)); 780 *__temp = 0; 781 ++__temp; 782 783 // The Header information goes at the Beginning of the Block. 784 _Block_pair __bp = 785 std::make_pair(reinterpret_cast<_Alloc_block*> 786 (__temp + __num_bitmaps), 787 reinterpret_cast<_Alloc_block*> 788 (__temp + __num_bitmaps) 789 + _S_block_size - 1); 790 791 // Fill the Vector with this information. 792 _S_mem_blocks.push_back(__bp); 793 794 for (size_t __i = 0; __i < __num_bitmaps; ++__i) 795 __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free. 796 797 _S_block_size *= 2; 798 } 799 800 static _BPVector _S_mem_blocks; 801 static size_t _S_block_size; 802 static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request; 803 static typename _BPVector::size_type _S_last_dealloc_index; 804 #if defined __GTHREADS 805 static __mutex_type _S_mut; 806 #endif 807 808 public: 809 810 /** @brief Allocates memory for a single object of size 811 * sizeof(_Tp). 812 * 813 * @throw std::bad_alloc. If memory can not be allocated. 814 * 815 * Complexity: Worst case complexity is O(N), but that 816 * is hardly ever hit. If and when this particular case is 817 * encountered, the next few cases are guaranteed to have a 818 * worst case complexity of O(1)! That's why this function 819 * performs very well on average. You can consider this 820 * function to have a complexity referred to commonly as: 821 * Amortized Constant time. 822 */ 823 pointer 824 _M_allocate_single_object() _GLIBCXX_THROW(std::bad_alloc) 825 { 826 #if defined __GTHREADS 827 __scoped_lock __bit_lock(_S_mut); 828 #endif 829 830 // The algorithm is something like this: The last_request 831 // variable points to the last accessed Bit Map. When such a 832 // condition occurs, we try to find a free block in the 833 // current bitmap, or succeeding bitmaps until the last bitmap 834 // is reached. If no free block turns up, we resort to First 835 // Fit method. 836 837 // WARNING: Do not re-order the condition in the while 838 // statement below, because it relies on C++'s short-circuit 839 // evaluation. The return from _S_last_request->_M_get() will 840 // NOT be dereference able if _S_last_request->_M_finished() 841 // returns true. This would inevitably lead to a NULL pointer 842 // dereference if tinkered with. 843 while (_S_last_request._M_finished() == false 844 && (*(_S_last_request._M_get()) == 0)) 845 _S_last_request.operator++(); 846 847 if (__builtin_expect(_S_last_request._M_finished() == true, false)) 848 { 849 // Fall Back to First Fit algorithm. 850 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 851 _FFF __fff; 852 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff)); 853 854 if (__bpi != _S_mem_blocks.end()) 855 { 856 // Search was successful. Ok, now mark the first bit from 857 // the right as 0, meaning Allocated. This bit is obtained 858 // by calling _M_get() on __fff. 859 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get()); 860 __detail::__bit_allocate(__fff._M_get(), __nz_bit); 861 862 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin()); 863 864 // Now, get the address of the bit we marked as allocated. 865 pointer __ret = reinterpret_cast<pointer> 866 (__bpi->first + __fff._M_offset() + __nz_bit); 867 size_t* __puse_count = 868 reinterpret_cast<size_t*> 869 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1); 870 871 ++(*__puse_count); 872 return __ret; 873 } 874 else 875 { 876 // Search was unsuccessful. We Add more memory to the 877 // pool by calling _S_refill_pool(). 878 _S_refill_pool(); 879 880 // _M_Reset the _S_last_request structure to the first 881 // free block's bit map. 882 _S_last_request._M_reset(_S_mem_blocks.size() - 1); 883 884 // Now, mark that bit as allocated. 885 } 886 } 887 888 // _S_last_request holds a pointer to a valid bit map, that 889 // points to a free block in memory. 890 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get()); 891 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit); 892 893 pointer __ret = reinterpret_cast<pointer> 894 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit); 895 896 size_t* __puse_count = reinterpret_cast<size_t*> 897 (_S_mem_blocks[_S_last_request._M_where()].first) 898 - (__detail:: 899 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1); 900 901 ++(*__puse_count); 902 return __ret; 903 } 904 905 /** @brief Deallocates memory that belongs to a single object of 906 * size sizeof(_Tp). 907 * 908 * Complexity: O(lg(N)), but the worst case is not hit 909 * often! This is because containers usually deallocate memory 910 * close to each other and this case is handled in O(1) time by 911 * the deallocate function. 912 */ 913 void 914 _M_deallocate_single_object(pointer __p) throw() 915 { 916 #if defined __GTHREADS 917 __scoped_lock __bit_lock(_S_mut); 918 #endif 919 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p); 920 921 typedef typename _BPVector::iterator _Iterator; 922 typedef typename _BPVector::difference_type _Difference_type; 923 924 _Difference_type __diff; 925 long __displacement; 926 927 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 928 929 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p); 930 if (__ibt(_S_mem_blocks[_S_last_dealloc_index])) 931 { 932 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index 933 <= _S_mem_blocks.size() - 1); 934 935 // Initial Assumption was correct! 936 __diff = _S_last_dealloc_index; 937 __displacement = __real_p - _S_mem_blocks[__diff].first; 938 } 939 else 940 { 941 _Iterator _iter = _S_find(__ibt); 942 943 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end()); 944 945 __diff = _iter - _S_mem_blocks.begin(); 946 __displacement = __real_p - _S_mem_blocks[__diff].first; 947 _S_last_dealloc_index = __diff; 948 } 949 950 // Get the position of the iterator that has been found. 951 const size_t __rotate = (__displacement 952 % size_t(__detail::bits_per_block)); 953 size_t* __bitmapC = 954 reinterpret_cast<size_t*> 955 (_S_mem_blocks[__diff].first) - 1; 956 __bitmapC -= (__displacement / size_t(__detail::bits_per_block)); 957 958 __detail::__bit_free(__bitmapC, __rotate); 959 size_t* __puse_count = reinterpret_cast<size_t*> 960 (_S_mem_blocks[__diff].first) 961 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1); 962 963 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0); 964 965 --(*__puse_count); 966 967 if (__builtin_expect(*__puse_count == 0, false)) 968 { 969 _S_block_size /= 2; 970 971 // We can safely remove this block. 972 // _Block_pair __bp = _S_mem_blocks[__diff]; 973 this->_M_insert(__puse_count); 974 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff); 975 976 // Reset the _S_last_request variable to reflect the 977 // erased block. We do this to protect future requests 978 // after the last block has been removed from a particular 979 // memory Chunk, which in turn has been returned to the 980 // free list, and hence had been erased from the vector, 981 // so the size of the vector gets reduced by 1. 982 if ((_Difference_type)_S_last_request._M_where() >= __diff--) 983 _S_last_request._M_reset(__diff); 984 985 // If the Index into the vector of the region of memory 986 // that might hold the next address that will be passed to 987 // deallocated may have been invalidated due to the above 988 // erase procedure being called on the vector, hence we 989 // try to restore this invariant too. 990 if (_S_last_dealloc_index >= _S_mem_blocks.size()) 991 { 992 _S_last_dealloc_index =(__diff != -1 ? __diff : 0); 993 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 994 } 995 } 996 } 997 998 public: 999 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 1000 { } 1001 1002 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT 1003 { } 1004 1005 template<typename _Tp1> 1006 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT 1007 { } 1008 1009 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 1010 { } 1011 1012 pointer 1013 allocate(size_type __n) 1014 { 1015 if (__n > this->max_size()) 1016 std::__throw_bad_alloc(); 1017 1018 #if __cpp_aligned_new 1019 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__) 1020 { 1021 const size_type __b = __n * sizeof(value_type); 1022 std::align_val_t __al = std::align_val_t(alignof(value_type)); 1023 return static_cast<pointer>(::operator new(__b, __al)); 1024 } 1025 #endif 1026 1027 if (__builtin_expect(__n == 1, true)) 1028 return this->_M_allocate_single_object(); 1029 else 1030 { 1031 const size_type __b = __n * sizeof(value_type); 1032 return reinterpret_cast<pointer>(::operator new(__b)); 1033 } 1034 } 1035 1036 pointer 1037 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer) 1038 { return allocate(__n); } 1039 1040 void 1041 deallocate(pointer __p, size_type __n) throw() 1042 { 1043 if (__builtin_expect(__p != 0, true)) 1044 { 1045 #if __cpp_aligned_new 1046 // Types with extended alignment are handled by operator delete. 1047 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__) 1048 { 1049 ::operator delete(__p, std::align_val_t(alignof(value_type))); 1050 return; 1051 } 1052 #endif 1053 1054 if (__builtin_expect(__n == 1, true)) 1055 this->_M_deallocate_single_object(__p); 1056 else 1057 ::operator delete(__p); 1058 } 1059 } 1060 1061 pointer 1062 address(reference __r) const _GLIBCXX_NOEXCEPT 1063 { return std::__addressof(__r); } 1064 1065 const_pointer 1066 address(const_reference __r) const _GLIBCXX_NOEXCEPT 1067 { return std::__addressof(__r); } 1068 1069 size_type 1070 max_size() const _GLIBCXX_USE_NOEXCEPT 1071 { return size_type(-1) / sizeof(value_type); } 1072 1073 #if __cplusplus >= 201103L 1074 template<typename _Up, typename... _Args> 1075 void 1076 construct(_Up* __p, _Args&&... __args) 1077 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); } 1078 1079 template<typename _Up> 1080 void 1081 destroy(_Up* __p) 1082 { __p->~_Up(); } 1083 #else 1084 void 1085 construct(pointer __p, const_reference __data) 1086 { ::new((void *)__p) value_type(__data); } 1087 1088 void 1089 destroy(pointer __p) 1090 { __p->~value_type(); } 1091 #endif 1092 }; 1093 1094 template<typename _Tp1, typename _Tp2> 1095 bool 1096 operator==(const bitmap_allocator<_Tp1>&, 1097 const bitmap_allocator<_Tp2>&) throw() 1098 { return true; } 1099 1100 template<typename _Tp1, typename _Tp2> 1101 bool 1102 operator!=(const bitmap_allocator<_Tp1>&, 1103 const bitmap_allocator<_Tp2>&) throw() 1104 { return false; } 1105 1106 // Static member definitions. 1107 template<typename _Tp> 1108 typename bitmap_allocator<_Tp>::_BPVector 1109 bitmap_allocator<_Tp>::_S_mem_blocks; 1110 1111 template<typename _Tp> 1112 size_t bitmap_allocator<_Tp>::_S_block_size = 1113 2 * size_t(__detail::bits_per_block); 1114 1115 template<typename _Tp> 1116 typename bitmap_allocator<_Tp>::_BPVector::size_type 1117 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0; 1118 1119 template<typename _Tp> 1120 __detail::_Bitmap_counter 1121 <typename bitmap_allocator<_Tp>::_Alloc_block*> 1122 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks); 1123 1124 #if defined __GTHREADS 1125 template<typename _Tp> 1126 typename bitmap_allocator<_Tp>::__mutex_type 1127 bitmap_allocator<_Tp>::_S_mut; 1128 #endif 1129 1130 _GLIBCXX_END_NAMESPACE_VERSION 1131 } // namespace __gnu_cxx 1132 1133 #endif 1134