1 // Bitmap Allocator. -*- C++ -*- 2 3 // Copyright (C) 2004-2014 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 using std::size_t; 48 using std::ptrdiff_t; 49 50 namespace __detail 51 { 52 _GLIBCXX_BEGIN_NAMESPACE_VERSION 53 /** @class __mini_vector bitmap_allocator.h bitmap_allocator.h 54 * 55 * @brief __mini_vector<> is a stripped down version of the 56 * full-fledged std::vector<>. 57 * 58 * It is to be used only for built-in types or PODs. Notable 59 * differences are: 60 * 61 * 1. Not all accessor functions are present. 62 * 2. Used ONLY for PODs. 63 * 3. No Allocator template argument. Uses ::operator new() to get 64 * memory, and ::operator delete() to free it. 65 * Caveat: The dtor does NOT free the memory allocated, so this a 66 * memory-leaking vector! 67 */ 68 template<typename _Tp> 69 class __mini_vector 70 { 71 __mini_vector(const __mini_vector&); 72 __mini_vector& operator=(const __mini_vector&); 73 74 public: 75 typedef _Tp value_type; 76 typedef _Tp* pointer; 77 typedef _Tp& reference; 78 typedef const _Tp& const_reference; 79 typedef size_t size_type; 80 typedef ptrdiff_t difference_type; 81 typedef pointer iterator; 82 83 private: 84 pointer _M_start; 85 pointer _M_finish; 86 pointer _M_end_of_storage; 87 88 size_type 89 _M_space_left() const throw() 90 { return _M_end_of_storage - _M_finish; } 91 92 pointer 93 allocate(size_type __n) 94 { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); } 95 96 void 97 deallocate(pointer __p, size_type) 98 { ::operator delete(__p); } 99 100 public: 101 // Members used: size(), push_back(), pop_back(), 102 // insert(iterator, const_reference), erase(iterator), 103 // begin(), end(), back(), operator[]. 104 105 __mini_vector() 106 : _M_start(0), _M_finish(0), _M_end_of_storage(0) { } 107 108 size_type 109 size() const throw() 110 { return _M_finish - _M_start; } 111 112 iterator 113 begin() const throw() 114 { return this->_M_start; } 115 116 iterator 117 end() const throw() 118 { return this->_M_finish; } 119 120 reference 121 back() const throw() 122 { return *(this->end() - 1); } 123 124 reference 125 operator[](const size_type __pos) const throw() 126 { return this->_M_start[__pos]; } 127 128 void 129 insert(iterator __pos, const_reference __x); 130 131 void 132 push_back(const_reference __x) 133 { 134 if (this->_M_space_left()) 135 { 136 *this->end() = __x; 137 ++this->_M_finish; 138 } 139 else 140 this->insert(this->end(), __x); 141 } 142 143 void 144 pop_back() throw() 145 { --this->_M_finish; } 146 147 void 148 erase(iterator __pos) throw(); 149 150 void 151 clear() throw() 152 { this->_M_finish = this->_M_start; } 153 }; 154 155 // Out of line function definitions. 156 template<typename _Tp> 157 void __mini_vector<_Tp>:: 158 insert(iterator __pos, const_reference __x) 159 { 160 if (this->_M_space_left()) 161 { 162 size_type __to_move = this->_M_finish - __pos; 163 iterator __dest = this->end(); 164 iterator __src = this->end() - 1; 165 166 ++this->_M_finish; 167 while (__to_move) 168 { 169 *__dest = *__src; 170 --__dest; --__src; --__to_move; 171 } 172 *__pos = __x; 173 } 174 else 175 { 176 size_type __new_size = this->size() ? this->size() * 2 : 1; 177 iterator __new_start = this->allocate(__new_size); 178 iterator __first = this->begin(); 179 iterator __start = __new_start; 180 while (__first != __pos) 181 { 182 *__start = *__first; 183 ++__start; ++__first; 184 } 185 *__start = __x; 186 ++__start; 187 while (__first != this->end()) 188 { 189 *__start = *__first; 190 ++__start; ++__first; 191 } 192 if (this->_M_start) 193 this->deallocate(this->_M_start, this->size()); 194 195 this->_M_start = __new_start; 196 this->_M_finish = __start; 197 this->_M_end_of_storage = this->_M_start + __new_size; 198 } 199 } 200 201 template<typename _Tp> 202 void __mini_vector<_Tp>:: 203 erase(iterator __pos) throw() 204 { 205 while (__pos + 1 != this->end()) 206 { 207 *__pos = __pos[1]; 208 ++__pos; 209 } 210 --this->_M_finish; 211 } 212 213 214 template<typename _Tp> 215 struct __mv_iter_traits 216 { 217 typedef typename _Tp::value_type value_type; 218 typedef typename _Tp::difference_type difference_type; 219 }; 220 221 template<typename _Tp> 222 struct __mv_iter_traits<_Tp*> 223 { 224 typedef _Tp value_type; 225 typedef ptrdiff_t difference_type; 226 }; 227 228 enum 229 { 230 bits_per_byte = 8, 231 bits_per_block = sizeof(size_t) * size_t(bits_per_byte) 232 }; 233 234 template<typename _ForwardIterator, typename _Tp, typename _Compare> 235 _ForwardIterator 236 __lower_bound(_ForwardIterator __first, _ForwardIterator __last, 237 const _Tp& __val, _Compare __comp) 238 { 239 typedef typename __mv_iter_traits<_ForwardIterator>::difference_type 240 _DistanceType; 241 242 _DistanceType __len = __last - __first; 243 _DistanceType __half; 244 _ForwardIterator __middle; 245 246 while (__len > 0) 247 { 248 __half = __len >> 1; 249 __middle = __first; 250 __middle += __half; 251 if (__comp(*__middle, __val)) 252 { 253 __first = __middle; 254 ++__first; 255 __len = __len - __half - 1; 256 } 257 else 258 __len = __half; 259 } 260 return __first; 261 } 262 263 /** @brief The number of Blocks pointed to by the address pair 264 * passed to the function. 265 */ 266 template<typename _AddrPair> 267 inline size_t 268 __num_blocks(_AddrPair __ap) 269 { return (__ap.second - __ap.first) + 1; } 270 271 /** @brief The number of Bit-maps pointed to by the address pair 272 * passed to the function. 273 */ 274 template<typename _AddrPair> 275 inline size_t 276 __num_bitmaps(_AddrPair __ap) 277 { return __num_blocks(__ap) / size_t(bits_per_block); } 278 279 // _Tp should be a pointer type. 280 template<typename _Tp> 281 class _Inclusive_between 282 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool> 283 { 284 typedef _Tp pointer; 285 pointer _M_ptr_value; 286 typedef typename std::pair<_Tp, _Tp> _Block_pair; 287 288 public: 289 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr) 290 { } 291 292 bool 293 operator()(_Block_pair __bp) const throw() 294 { 295 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second) 296 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first)) 297 return true; 298 else 299 return false; 300 } 301 }; 302 303 // Used to pass a Functor to functions by reference. 304 template<typename _Functor> 305 class _Functor_Ref 306 : public std::unary_function<typename _Functor::argument_type, 307 typename _Functor::result_type> 308 { 309 _Functor& _M_fref; 310 311 public: 312 typedef typename _Functor::argument_type argument_type; 313 typedef typename _Functor::result_type result_type; 314 315 _Functor_Ref(_Functor& __fref) : _M_fref(__fref) 316 { } 317 318 result_type 319 operator()(argument_type __arg) 320 { return _M_fref(__arg); } 321 }; 322 323 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h 324 * 325 * @brief The class which acts as a predicate for applying the 326 * first-fit memory allocation policy for the bitmap allocator. 327 */ 328 // _Tp should be a pointer type, and _Alloc is the Allocator for 329 // the vector. 330 template<typename _Tp> 331 class _Ffit_finder 332 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool> 333 { 334 typedef typename std::pair<_Tp, _Tp> _Block_pair; 335 typedef typename __detail::__mini_vector<_Block_pair> _BPVector; 336 typedef typename _BPVector::difference_type _Counter_type; 337 338 size_t* _M_pbitmap; 339 _Counter_type _M_data_offset; 340 341 public: 342 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0) 343 { } 344 345 bool 346 operator()(_Block_pair __bp) throw() 347 { 348 // Set the _rover to the last physical location bitmap, 349 // which is the bitmap which belongs to the first free 350 // block. Thus, the bitmaps are in exact reverse order of 351 // the actual memory layout. So, we count down the bitmaps, 352 // which is the same as moving up the memory. 353 354 // If the used count stored at the start of the Bit Map headers 355 // is equal to the number of Objects that the current Block can 356 // store, then there is definitely no space for another single 357 // object, so just return false. 358 _Counter_type __diff = __detail::__num_bitmaps(__bp); 359 360 if (*(reinterpret_cast<size_t*> 361 (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp)) 362 return false; 363 364 size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1; 365 366 for (_Counter_type __i = 0; __i < __diff; ++__i) 367 { 368 _M_data_offset = __i; 369 if (*__rover) 370 { 371 _M_pbitmap = __rover; 372 return true; 373 } 374 --__rover; 375 } 376 return false; 377 } 378 379 size_t* 380 _M_get() const throw() 381 { return _M_pbitmap; } 382 383 _Counter_type 384 _M_offset() const throw() 385 { return _M_data_offset * size_t(bits_per_block); } 386 }; 387 388 /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h 389 * 390 * @brief The bitmap counter which acts as the bitmap 391 * manipulator, and manages the bit-manipulation functions and 392 * the searching and identification functions on the bit-map. 393 */ 394 // _Tp should be a pointer type. 395 template<typename _Tp> 396 class _Bitmap_counter 397 { 398 typedef typename 399 __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector; 400 typedef typename _BPVector::size_type _Index_type; 401 typedef _Tp pointer; 402 403 _BPVector& _M_vbp; 404 size_t* _M_curr_bmap; 405 size_t* _M_last_bmap_in_block; 406 _Index_type _M_curr_index; 407 408 public: 409 // Use the 2nd parameter with care. Make sure that such an 410 // entry exists in the vector before passing that particular 411 // index to this ctor. 412 _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp) 413 { this->_M_reset(__index); } 414 415 void 416 _M_reset(long __index = -1) throw() 417 { 418 if (__index == -1) 419 { 420 _M_curr_bmap = 0; 421 _M_curr_index = static_cast<_Index_type>(-1); 422 return; 423 } 424 425 _M_curr_index = __index; 426 _M_curr_bmap = reinterpret_cast<size_t*> 427 (_M_vbp[_M_curr_index].first) - 1; 428 429 _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1); 430 431 _M_last_bmap_in_block = _M_curr_bmap 432 - ((_M_vbp[_M_curr_index].second 433 - _M_vbp[_M_curr_index].first + 1) 434 / size_t(bits_per_block) - 1); 435 } 436 437 // Dangerous Function! Use with extreme care. Pass to this 438 // function ONLY those values that are known to be correct, 439 // otherwise this will mess up big time. 440 void 441 _M_set_internal_bitmap(size_t* __new_internal_marker) throw() 442 { _M_curr_bmap = __new_internal_marker; } 443 444 bool 445 _M_finished() const throw() 446 { return(_M_curr_bmap == 0); } 447 448 _Bitmap_counter& 449 operator++() throw() 450 { 451 if (_M_curr_bmap == _M_last_bmap_in_block) 452 { 453 if (++_M_curr_index == _M_vbp.size()) 454 _M_curr_bmap = 0; 455 else 456 this->_M_reset(_M_curr_index); 457 } 458 else 459 --_M_curr_bmap; 460 return *this; 461 } 462 463 size_t* 464 _M_get() const throw() 465 { return _M_curr_bmap; } 466 467 pointer 468 _M_base() const throw() 469 { return _M_vbp[_M_curr_index].first; } 470 471 _Index_type 472 _M_offset() const throw() 473 { 474 return size_t(bits_per_block) 475 * ((reinterpret_cast<size_t*>(this->_M_base()) 476 - _M_curr_bmap) - 1); 477 } 478 479 _Index_type 480 _M_where() const throw() 481 { return _M_curr_index; } 482 }; 483 484 /** @brief Mark a memory address as allocated by re-setting the 485 * corresponding bit in the bit-map. 486 */ 487 inline void 488 __bit_allocate(size_t* __pbmap, size_t __pos) throw() 489 { 490 size_t __mask = 1 << __pos; 491 __mask = ~__mask; 492 *__pbmap &= __mask; 493 } 494 495 /** @brief Mark a memory address as free by setting the 496 * corresponding bit in the bit-map. 497 */ 498 inline void 499 __bit_free(size_t* __pbmap, size_t __pos) throw() 500 { 501 size_t __mask = 1 << __pos; 502 *__pbmap |= __mask; 503 } 504 505 _GLIBCXX_END_NAMESPACE_VERSION 506 } // namespace __detail 507 508 _GLIBCXX_BEGIN_NAMESPACE_VERSION 509 510 /** @brief Generic Version of the bsf instruction. 511 */ 512 inline size_t 513 _Bit_scan_forward(size_t __num) 514 { return static_cast<size_t>(__builtin_ctzl(__num)); } 515 516 /** @class free_list bitmap_allocator.h bitmap_allocator.h 517 * 518 * @brief The free list class for managing chunks of memory to be 519 * given to and returned by the bitmap_allocator. 520 */ 521 class free_list 522 { 523 public: 524 typedef size_t* value_type; 525 typedef __detail::__mini_vector<value_type> vector_type; 526 typedef vector_type::iterator iterator; 527 typedef __mutex __mutex_type; 528 529 private: 530 struct _LT_pointer_compare 531 { 532 bool 533 operator()(const size_t* __pui, 534 const size_t __cui) const throw() 535 { return *__pui < __cui; } 536 }; 537 538 #if defined __GTHREADS 539 __mutex_type& 540 _M_get_mutex() 541 { 542 static __mutex_type _S_mutex; 543 return _S_mutex; 544 } 545 #endif 546 547 vector_type& 548 _M_get_free_list() 549 { 550 static vector_type _S_free_list; 551 return _S_free_list; 552 } 553 554 /** @brief Performs validation of memory based on their size. 555 * 556 * @param __addr The pointer to the memory block to be 557 * validated. 558 * 559 * Validates the memory block passed to this function and 560 * appropriately performs the action of managing the free list of 561 * blocks by adding this block to the free list or deleting this 562 * or larger blocks from the free list. 563 */ 564 void 565 _M_validate(size_t* __addr) throw() 566 { 567 vector_type& __free_list = _M_get_free_list(); 568 const vector_type::size_type __max_size = 64; 569 if (__free_list.size() >= __max_size) 570 { 571 // Ok, the threshold value has been reached. We determine 572 // which block to remove from the list of free blocks. 573 if (*__addr >= *__free_list.back()) 574 { 575 // Ok, the new block is greater than or equal to the 576 // last block in the list of free blocks. We just free 577 // the new block. 578 ::operator delete(static_cast<void*>(__addr)); 579 return; 580 } 581 else 582 { 583 // Deallocate the last block in the list of free lists, 584 // and insert the new one in its correct position. 585 ::operator delete(static_cast<void*>(__free_list.back())); 586 __free_list.pop_back(); 587 } 588 } 589 590 // Just add the block to the list of free lists unconditionally. 591 iterator __temp = __detail::__lower_bound 592 (__free_list.begin(), __free_list.end(), 593 *__addr, _LT_pointer_compare()); 594 595 // We may insert the new free list before _temp; 596 __free_list.insert(__temp, __addr); 597 } 598 599 /** @brief Decides whether the wastage of memory is acceptable for 600 * the current memory request and returns accordingly. 601 * 602 * @param __block_size The size of the block available in the free 603 * list. 604 * 605 * @param __required_size The required size of the memory block. 606 * 607 * @return true if the wastage incurred is acceptable, else returns 608 * false. 609 */ 610 bool 611 _M_should_i_give(size_t __block_size, 612 size_t __required_size) throw() 613 { 614 const size_t __max_wastage_percentage = 36; 615 if (__block_size >= __required_size && 616 (((__block_size - __required_size) * 100 / __block_size) 617 < __max_wastage_percentage)) 618 return true; 619 else 620 return false; 621 } 622 623 public: 624 /** @brief This function returns the block of memory to the 625 * internal free list. 626 * 627 * @param __addr The pointer to the memory block that was given 628 * by a call to the _M_get function. 629 */ 630 inline void 631 _M_insert(size_t* __addr) throw() 632 { 633 #if defined __GTHREADS 634 __scoped_lock __bfl_lock(_M_get_mutex()); 635 #endif 636 // Call _M_validate to decide what should be done with 637 // this particular free list. 638 this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1); 639 // See discussion as to why this is 1! 640 } 641 642 /** @brief This function gets a block of memory of the specified 643 * size from the free list. 644 * 645 * @param __sz The size in bytes of the memory required. 646 * 647 * @return A pointer to the new memory block of size at least 648 * equal to that requested. 649 */ 650 size_t* 651 _M_get(size_t __sz) throw(std::bad_alloc); 652 653 /** @brief This function just clears the internal Free List, and 654 * gives back all the memory to the OS. 655 */ 656 void 657 _M_clear(); 658 }; 659 660 661 // Forward declare the class. 662 template<typename _Tp> 663 class bitmap_allocator; 664 665 // Specialize for void: 666 template<> 667 class bitmap_allocator<void> 668 { 669 public: 670 typedef void* pointer; 671 typedef const void* const_pointer; 672 673 // Reference-to-void members are impossible. 674 typedef void value_type; 675 template<typename _Tp1> 676 struct rebind 677 { 678 typedef bitmap_allocator<_Tp1> other; 679 }; 680 }; 681 682 /** 683 * @brief Bitmap Allocator, primary template. 684 * @ingroup allocators 685 */ 686 template<typename _Tp> 687 class bitmap_allocator : private free_list 688 { 689 public: 690 typedef size_t size_type; 691 typedef ptrdiff_t difference_type; 692 typedef _Tp* pointer; 693 typedef const _Tp* const_pointer; 694 typedef _Tp& reference; 695 typedef const _Tp& const_reference; 696 typedef _Tp value_type; 697 typedef free_list::__mutex_type __mutex_type; 698 699 template<typename _Tp1> 700 struct rebind 701 { 702 typedef bitmap_allocator<_Tp1> other; 703 }; 704 705 #if __cplusplus >= 201103L 706 // _GLIBCXX_RESOLVE_LIB_DEFECTS 707 // 2103. propagate_on_container_move_assignment 708 typedef std::true_type propagate_on_container_move_assignment; 709 #endif 710 711 private: 712 template<size_t _BSize, size_t _AlignSize> 713 struct aligned_size 714 { 715 enum 716 { 717 modulus = _BSize % _AlignSize, 718 value = _BSize + (modulus ? _AlignSize - (modulus) : 0) 719 }; 720 }; 721 722 struct _Alloc_block 723 { 724 char __M_unused[aligned_size<sizeof(value_type), 725 _BALLOC_ALIGN_BYTES>::value]; 726 }; 727 728 729 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair; 730 731 typedef typename __detail::__mini_vector<_Block_pair> _BPVector; 732 typedef typename _BPVector::iterator _BPiter; 733 734 template<typename _Predicate> 735 static _BPiter 736 _S_find(_Predicate __p) 737 { 738 _BPiter __first = _S_mem_blocks.begin(); 739 while (__first != _S_mem_blocks.end() && !__p(*__first)) 740 ++__first; 741 return __first; 742 } 743 744 #if defined _GLIBCXX_DEBUG 745 // Complexity: O(lg(N)). Where, N is the number of block of size 746 // sizeof(value_type). 747 void 748 _S_check_for_free_blocks() throw() 749 { 750 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 751 _BPiter __bpi = _S_find(_FFF()); 752 753 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end()); 754 } 755 #endif 756 757 /** @brief Responsible for exponentially growing the internal 758 * memory pool. 759 * 760 * @throw std::bad_alloc. If memory can not be allocated. 761 * 762 * Complexity: O(1), but internally depends upon the 763 * complexity of the function free_list::_M_get. The part where 764 * the bitmap headers are written has complexity: O(X),where X 765 * is the number of blocks of size sizeof(value_type) within 766 * the newly acquired block. Having a tight bound. 767 */ 768 void 769 _S_refill_pool() throw(std::bad_alloc) 770 { 771 #if defined _GLIBCXX_DEBUG 772 _S_check_for_free_blocks(); 773 #endif 774 775 const size_t __num_bitmaps = (_S_block_size 776 / size_t(__detail::bits_per_block)); 777 const size_t __size_to_allocate = sizeof(size_t) 778 + _S_block_size * sizeof(_Alloc_block) 779 + __num_bitmaps * sizeof(size_t); 780 781 size_t* __temp = 782 reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate)); 783 *__temp = 0; 784 ++__temp; 785 786 // The Header information goes at the Beginning of the Block. 787 _Block_pair __bp = 788 std::make_pair(reinterpret_cast<_Alloc_block*> 789 (__temp + __num_bitmaps), 790 reinterpret_cast<_Alloc_block*> 791 (__temp + __num_bitmaps) 792 + _S_block_size - 1); 793 794 // Fill the Vector with this information. 795 _S_mem_blocks.push_back(__bp); 796 797 for (size_t __i = 0; __i < __num_bitmaps; ++__i) 798 __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free. 799 800 _S_block_size *= 2; 801 } 802 803 static _BPVector _S_mem_blocks; 804 static size_t _S_block_size; 805 static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request; 806 static typename _BPVector::size_type _S_last_dealloc_index; 807 #if defined __GTHREADS 808 static __mutex_type _S_mut; 809 #endif 810 811 public: 812 813 /** @brief Allocates memory for a single object of size 814 * sizeof(_Tp). 815 * 816 * @throw std::bad_alloc. If memory can not be allocated. 817 * 818 * Complexity: Worst case complexity is O(N), but that 819 * is hardly ever hit. If and when this particular case is 820 * encountered, the next few cases are guaranteed to have a 821 * worst case complexity of O(1)! That's why this function 822 * performs very well on average. You can consider this 823 * function to have a complexity referred to commonly as: 824 * Amortized Constant time. 825 */ 826 pointer 827 _M_allocate_single_object() throw(std::bad_alloc) 828 { 829 #if defined __GTHREADS 830 __scoped_lock __bit_lock(_S_mut); 831 #endif 832 833 // The algorithm is something like this: The last_request 834 // variable points to the last accessed Bit Map. When such a 835 // condition occurs, we try to find a free block in the 836 // current bitmap, or succeeding bitmaps until the last bitmap 837 // is reached. If no free block turns up, we resort to First 838 // Fit method. 839 840 // WARNING: Do not re-order the condition in the while 841 // statement below, because it relies on C++'s short-circuit 842 // evaluation. The return from _S_last_request->_M_get() will 843 // NOT be dereference able if _S_last_request->_M_finished() 844 // returns true. This would inevitably lead to a NULL pointer 845 // dereference if tinkered with. 846 while (_S_last_request._M_finished() == false 847 && (*(_S_last_request._M_get()) == 0)) 848 _S_last_request.operator++(); 849 850 if (__builtin_expect(_S_last_request._M_finished() == true, false)) 851 { 852 // Fall Back to First Fit algorithm. 853 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 854 _FFF __fff; 855 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff)); 856 857 if (__bpi != _S_mem_blocks.end()) 858 { 859 // Search was successful. Ok, now mark the first bit from 860 // the right as 0, meaning Allocated. This bit is obtained 861 // by calling _M_get() on __fff. 862 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get()); 863 __detail::__bit_allocate(__fff._M_get(), __nz_bit); 864 865 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin()); 866 867 // Now, get the address of the bit we marked as allocated. 868 pointer __ret = reinterpret_cast<pointer> 869 (__bpi->first + __fff._M_offset() + __nz_bit); 870 size_t* __puse_count = 871 reinterpret_cast<size_t*> 872 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1); 873 874 ++(*__puse_count); 875 return __ret; 876 } 877 else 878 { 879 // Search was unsuccessful. We Add more memory to the 880 // pool by calling _S_refill_pool(). 881 _S_refill_pool(); 882 883 // _M_Reset the _S_last_request structure to the first 884 // free block's bit map. 885 _S_last_request._M_reset(_S_mem_blocks.size() - 1); 886 887 // Now, mark that bit as allocated. 888 } 889 } 890 891 // _S_last_request holds a pointer to a valid bit map, that 892 // points to a free block in memory. 893 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get()); 894 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit); 895 896 pointer __ret = reinterpret_cast<pointer> 897 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit); 898 899 size_t* __puse_count = reinterpret_cast<size_t*> 900 (_S_mem_blocks[_S_last_request._M_where()].first) 901 - (__detail:: 902 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1); 903 904 ++(*__puse_count); 905 return __ret; 906 } 907 908 /** @brief Deallocates memory that belongs to a single object of 909 * size sizeof(_Tp). 910 * 911 * Complexity: O(lg(N)), but the worst case is not hit 912 * often! This is because containers usually deallocate memory 913 * close to each other and this case is handled in O(1) time by 914 * the deallocate function. 915 */ 916 void 917 _M_deallocate_single_object(pointer __p) throw() 918 { 919 #if defined __GTHREADS 920 __scoped_lock __bit_lock(_S_mut); 921 #endif 922 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p); 923 924 typedef typename _BPVector::iterator _Iterator; 925 typedef typename _BPVector::difference_type _Difference_type; 926 927 _Difference_type __diff; 928 long __displacement; 929 930 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 931 932 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p); 933 if (__ibt(_S_mem_blocks[_S_last_dealloc_index])) 934 { 935 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index 936 <= _S_mem_blocks.size() - 1); 937 938 // Initial Assumption was correct! 939 __diff = _S_last_dealloc_index; 940 __displacement = __real_p - _S_mem_blocks[__diff].first; 941 } 942 else 943 { 944 _Iterator _iter = _S_find(__ibt); 945 946 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end()); 947 948 __diff = _iter - _S_mem_blocks.begin(); 949 __displacement = __real_p - _S_mem_blocks[__diff].first; 950 _S_last_dealloc_index = __diff; 951 } 952 953 // Get the position of the iterator that has been found. 954 const size_t __rotate = (__displacement 955 % size_t(__detail::bits_per_block)); 956 size_t* __bitmapC = 957 reinterpret_cast<size_t*> 958 (_S_mem_blocks[__diff].first) - 1; 959 __bitmapC -= (__displacement / size_t(__detail::bits_per_block)); 960 961 __detail::__bit_free(__bitmapC, __rotate); 962 size_t* __puse_count = reinterpret_cast<size_t*> 963 (_S_mem_blocks[__diff].first) 964 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1); 965 966 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0); 967 968 --(*__puse_count); 969 970 if (__builtin_expect(*__puse_count == 0, false)) 971 { 972 _S_block_size /= 2; 973 974 // We can safely remove this block. 975 // _Block_pair __bp = _S_mem_blocks[__diff]; 976 this->_M_insert(__puse_count); 977 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff); 978 979 // Reset the _S_last_request variable to reflect the 980 // erased block. We do this to protect future requests 981 // after the last block has been removed from a particular 982 // memory Chunk, which in turn has been returned to the 983 // free list, and hence had been erased from the vector, 984 // so the size of the vector gets reduced by 1. 985 if ((_Difference_type)_S_last_request._M_where() >= __diff--) 986 _S_last_request._M_reset(__diff); 987 988 // If the Index into the vector of the region of memory 989 // that might hold the next address that will be passed to 990 // deallocated may have been invalidated due to the above 991 // erase procedure being called on the vector, hence we 992 // try to restore this invariant too. 993 if (_S_last_dealloc_index >= _S_mem_blocks.size()) 994 { 995 _S_last_dealloc_index =(__diff != -1 ? __diff : 0); 996 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 997 } 998 } 999 } 1000 1001 public: 1002 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 1003 { } 1004 1005 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT 1006 { } 1007 1008 template<typename _Tp1> 1009 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT 1010 { } 1011 1012 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 1013 { } 1014 1015 pointer 1016 allocate(size_type __n) 1017 { 1018 if (__n > this->max_size()) 1019 std::__throw_bad_alloc(); 1020 1021 if (__builtin_expect(__n == 1, true)) 1022 return this->_M_allocate_single_object(); 1023 else 1024 { 1025 const size_type __b = __n * sizeof(value_type); 1026 return reinterpret_cast<pointer>(::operator new(__b)); 1027 } 1028 } 1029 1030 pointer 1031 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer) 1032 { return allocate(__n); } 1033 1034 void 1035 deallocate(pointer __p, size_type __n) throw() 1036 { 1037 if (__builtin_expect(__p != 0, true)) 1038 { 1039 if (__builtin_expect(__n == 1, true)) 1040 this->_M_deallocate_single_object(__p); 1041 else 1042 ::operator delete(__p); 1043 } 1044 } 1045 1046 pointer 1047 address(reference __r) const _GLIBCXX_NOEXCEPT 1048 { return std::__addressof(__r); } 1049 1050 const_pointer 1051 address(const_reference __r) const _GLIBCXX_NOEXCEPT 1052 { return std::__addressof(__r); } 1053 1054 size_type 1055 max_size() const _GLIBCXX_USE_NOEXCEPT 1056 { return size_type(-1) / sizeof(value_type); } 1057 1058 #if __cplusplus >= 201103L 1059 template<typename _Up, typename... _Args> 1060 void 1061 construct(_Up* __p, _Args&&... __args) 1062 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); } 1063 1064 template<typename _Up> 1065 void 1066 destroy(_Up* __p) 1067 { __p->~_Up(); } 1068 #else 1069 void 1070 construct(pointer __p, const_reference __data) 1071 { ::new((void *)__p) value_type(__data); } 1072 1073 void 1074 destroy(pointer __p) 1075 { __p->~value_type(); } 1076 #endif 1077 }; 1078 1079 template<typename _Tp1, typename _Tp2> 1080 bool 1081 operator==(const bitmap_allocator<_Tp1>&, 1082 const bitmap_allocator<_Tp2>&) throw() 1083 { return true; } 1084 1085 template<typename _Tp1, typename _Tp2> 1086 bool 1087 operator!=(const bitmap_allocator<_Tp1>&, 1088 const bitmap_allocator<_Tp2>&) throw() 1089 { return false; } 1090 1091 // Static member definitions. 1092 template<typename _Tp> 1093 typename bitmap_allocator<_Tp>::_BPVector 1094 bitmap_allocator<_Tp>::_S_mem_blocks; 1095 1096 template<typename _Tp> 1097 size_t bitmap_allocator<_Tp>::_S_block_size = 1098 2 * size_t(__detail::bits_per_block); 1099 1100 template<typename _Tp> 1101 typename bitmap_allocator<_Tp>::_BPVector::size_type 1102 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0; 1103 1104 template<typename _Tp> 1105 __detail::_Bitmap_counter 1106 <typename bitmap_allocator<_Tp>::_Alloc_block*> 1107 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks); 1108 1109 #if defined __GTHREADS 1110 template<typename _Tp> 1111 typename bitmap_allocator<_Tp>::__mutex_type 1112 bitmap_allocator<_Tp>::_S_mut; 1113 #endif 1114 1115 _GLIBCXX_END_NAMESPACE_VERSION 1116 } // namespace __gnu_cxx 1117 1118 #endif 1119 1120