1// Bitmap Allocator. -*- C++ -*- 2 3// Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 4// Free Software Foundation, Inc. 5// 6// This file is part of the GNU ISO C++ Library. This library is free 7// software; you can redistribute it and/or modify it under the 8// terms of the GNU General Public License as published by the 9// Free Software Foundation; either version 3, or (at your option) 10// any later version. 11 12// This library is distributed in the hope that it will be useful, 13// but WITHOUT ANY WARRANTY; without even the implied warranty of 14// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15// GNU General Public License for more details. 16 17// Under Section 7 of GPL version 3, you are granted additional 18// permissions described in the GCC Runtime Library Exception, version 19// 3.1, as published by the Free Software Foundation. 20 21// You should have received a copy of the GNU General Public License and 22// a copy of the GCC Runtime Library Exception along with this program; 23// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 24// <http://www.gnu.org/licenses/>. 25 26/** @file ext/bitmap_allocator.h 27 * This file is a GNU extension to the Standard C++ Library. 28 */ 29 30#ifndef _BITMAP_ALLOCATOR_H 31#define _BITMAP_ALLOCATOR_H 1 32 33#include <utility> // For std::pair. 34#include <bits/functexcept.h> // For __throw_bad_alloc(). 35#include <functional> // For greater_equal, and less_equal. 36#include <new> // For operator new. 37#include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT 38#include <ext/concurrence.h> 39#include <bits/move.h> 40 41/** @brief The constant in the expression below is the alignment 42 * required in bytes. 43 */ 44#define _BALLOC_ALIGN_BYTES 8 45 46namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) 47{ 48 using std::size_t; 49 using std::ptrdiff_t; 50 51 namespace __detail 52 { 53 _GLIBCXX_BEGIN_NAMESPACE_VERSION 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 } 505 506 _GLIBCXX_END_NAMESPACE_VERSION 507 } // namespace __detail 508 509_GLIBCXX_BEGIN_NAMESPACE_VERSION 510 511 /** @brief Generic Version of the bsf instruction. 512 */ 513 inline size_t 514 _Bit_scan_forward(size_t __num) 515 { return static_cast<size_t>(__builtin_ctzl(__num)); } 516 517 /** @class free_list bitmap_allocator.h bitmap_allocator.h 518 * 519 * @brief The free list class for managing chunks of memory to be 520 * given to and returned by the bitmap_allocator. 521 */ 522 class free_list 523 { 524 public: 525 typedef size_t* value_type; 526 typedef __detail::__mini_vector<value_type> vector_type; 527 typedef vector_type::iterator iterator; 528 typedef __mutex __mutex_type; 529 530 private: 531 struct _LT_pointer_compare 532 { 533 bool 534 operator()(const size_t* __pui, 535 const size_t __cui) const throw() 536 { return *__pui < __cui; } 537 }; 538 539#if defined __GTHREADS 540 __mutex_type& 541 _M_get_mutex() 542 { 543 static __mutex_type _S_mutex; 544 return _S_mutex; 545 } 546#endif 547 548 vector_type& 549 _M_get_free_list() 550 { 551 static vector_type _S_free_list; 552 return _S_free_list; 553 } 554 555 /** @brief Performs validation of memory based on their size. 556 * 557 * @param __addr The pointer to the memory block to be 558 * validated. 559 * 560 * Validates the memory block passed to this function and 561 * appropriately performs the action of managing the free list of 562 * blocks by adding this block to the free list or deleting this 563 * or larger blocks from the free list. 564 */ 565 void 566 _M_validate(size_t* __addr) throw() 567 { 568 vector_type& __free_list = _M_get_free_list(); 569 const vector_type::size_type __max_size = 64; 570 if (__free_list.size() >= __max_size) 571 { 572 // Ok, the threshold value has been reached. We determine 573 // which block to remove from the list of free blocks. 574 if (*__addr >= *__free_list.back()) 575 { 576 // Ok, the new block is greater than or equal to the 577 // last block in the list of free blocks. We just free 578 // the new block. 579 ::operator delete(static_cast<void*>(__addr)); 580 return; 581 } 582 else 583 { 584 // Deallocate the last block in the list of free lists, 585 // and insert the new one in its correct position. 586 ::operator delete(static_cast<void*>(__free_list.back())); 587 __free_list.pop_back(); 588 } 589 } 590 591 // Just add the block to the list of free lists unconditionally. 592 iterator __temp = __detail::__lower_bound 593 (__free_list.begin(), __free_list.end(), 594 *__addr, _LT_pointer_compare()); 595 596 // We may insert the new free list before _temp; 597 __free_list.insert(__temp, __addr); 598 } 599 600 /** @brief Decides whether the wastage of memory is acceptable for 601 * the current memory request and returns accordingly. 602 * 603 * @param __block_size The size of the block available in the free 604 * list. 605 * 606 * @param __required_size The required size of the memory block. 607 * 608 * @return true if the wastage incurred is acceptable, else returns 609 * false. 610 */ 611 bool 612 _M_should_i_give(size_t __block_size, 613 size_t __required_size) throw() 614 { 615 const size_t __max_wastage_percentage = 36; 616 if (__block_size >= __required_size && 617 (((__block_size - __required_size) * 100 / __block_size) 618 < __max_wastage_percentage)) 619 return true; 620 else 621 return false; 622 } 623 624 public: 625 /** @brief This function returns the block of memory to the 626 * internal free list. 627 * 628 * @param __addr The pointer to the memory block that was given 629 * by a call to the _M_get function. 630 */ 631 inline void 632 _M_insert(size_t* __addr) throw() 633 { 634#if defined __GTHREADS 635 __scoped_lock __bfl_lock(_M_get_mutex()); 636#endif 637 // Call _M_validate to decide what should be done with 638 // this particular free list. 639 this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1); 640 // See discussion as to why this is 1! 641 } 642 643 /** @brief This function gets a block of memory of the specified 644 * size from the free list. 645 * 646 * @param __sz The size in bytes of the memory required. 647 * 648 * @return A pointer to the new memory block of size at least 649 * equal to that requested. 650 */ 651 size_t* 652 _M_get(size_t __sz) throw(std::bad_alloc); 653 654 /** @brief This function just clears the internal Free List, and 655 * gives back all the memory to the OS. 656 */ 657 void 658 _M_clear(); 659 }; 660 661 662 // Forward declare the class. 663 template<typename _Tp> 664 class bitmap_allocator; 665 666 // Specialize for void: 667 template<> 668 class bitmap_allocator<void> 669 { 670 public: 671 typedef void* pointer; 672 typedef const void* const_pointer; 673 674 // Reference-to-void members are impossible. 675 typedef void value_type; 676 template<typename _Tp1> 677 struct rebind 678 { 679 typedef bitmap_allocator<_Tp1> other; 680 }; 681 }; 682 683 /** 684 * @brief Bitmap Allocator, primary template. 685 * @ingroup allocators 686 */ 687 template<typename _Tp> 688 class bitmap_allocator : private free_list 689 { 690 public: 691 typedef size_t size_type; 692 typedef ptrdiff_t difference_type; 693 typedef _Tp* pointer; 694 typedef const _Tp* const_pointer; 695 typedef _Tp& reference; 696 typedef const _Tp& const_reference; 697 typedef _Tp value_type; 698 typedef free_list::__mutex_type __mutex_type; 699 700 template<typename _Tp1> 701 struct rebind 702 { 703 typedef bitmap_allocator<_Tp1> other; 704 }; 705 706 private: 707 template<size_t _BSize, size_t _AlignSize> 708 struct aligned_size 709 { 710 enum 711 { 712 modulus = _BSize % _AlignSize, 713 value = _BSize + (modulus ? _AlignSize - (modulus) : 0) 714 }; 715 }; 716 717 struct _Alloc_block 718 { 719 char __M_unused[aligned_size<sizeof(value_type), 720 _BALLOC_ALIGN_BYTES>::value]; 721 }; 722 723 724 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair; 725 726 typedef typename __detail::__mini_vector<_Block_pair> _BPVector; 727 typedef typename _BPVector::iterator _BPiter; 728 729 template<typename _Predicate> 730 static _BPiter 731 _S_find(_Predicate __p) 732 { 733 _BPiter __first = _S_mem_blocks.begin(); 734 while (__first != _S_mem_blocks.end() && !__p(*__first)) 735 ++__first; 736 return __first; 737 } 738 739#if defined _GLIBCXX_DEBUG 740 // Complexity: O(lg(N)). Where, N is the number of block of size 741 // sizeof(value_type). 742 void 743 _S_check_for_free_blocks() throw() 744 { 745 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 746 _BPiter __bpi = _S_find(_FFF()); 747 748 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end()); 749 } 750#endif 751 752 /** @brief Responsible for exponentially growing the internal 753 * memory pool. 754 * 755 * @throw std::bad_alloc. If memory can not be allocated. 756 * 757 * Complexity: O(1), but internally depends upon the 758 * complexity of the function free_list::_M_get. The part where 759 * the bitmap headers are written has complexity: O(X),where X 760 * is the number of blocks of size sizeof(value_type) within 761 * the newly acquired block. Having a tight bound. 762 */ 763 void 764 _S_refill_pool() throw(std::bad_alloc) 765 { 766#if defined _GLIBCXX_DEBUG 767 _S_check_for_free_blocks(); 768#endif 769 770 const size_t __num_bitmaps = (_S_block_size 771 / size_t(__detail::bits_per_block)); 772 const size_t __size_to_allocate = sizeof(size_t) 773 + _S_block_size * sizeof(_Alloc_block) 774 + __num_bitmaps * sizeof(size_t); 775 776 size_t* __temp = 777 reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate)); 778 *__temp = 0; 779 ++__temp; 780 781 // The Header information goes at the Beginning of the Block. 782 _Block_pair __bp = 783 std::make_pair(reinterpret_cast<_Alloc_block*> 784 (__temp + __num_bitmaps), 785 reinterpret_cast<_Alloc_block*> 786 (__temp + __num_bitmaps) 787 + _S_block_size - 1); 788 789 // Fill the Vector with this information. 790 _S_mem_blocks.push_back(__bp); 791 792 for (size_t __i = 0; __i < __num_bitmaps; ++__i) 793 __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free. 794 795 _S_block_size *= 2; 796 } 797 798 static _BPVector _S_mem_blocks; 799 static size_t _S_block_size; 800 static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request; 801 static typename _BPVector::size_type _S_last_dealloc_index; 802#if defined __GTHREADS 803 static __mutex_type _S_mut; 804#endif 805 806 public: 807 808 /** @brief Allocates memory for a single object of size 809 * sizeof(_Tp). 810 * 811 * @throw std::bad_alloc. If memory can not be allocated. 812 * 813 * Complexity: Worst case complexity is O(N), but that 814 * is hardly ever hit. If and when this particular case is 815 * encountered, the next few cases are guaranteed to have a 816 * worst case complexity of O(1)! That's why this function 817 * performs very well on average. You can consider this 818 * function to have a complexity referred to commonly as: 819 * Amortized Constant time. 820 */ 821 pointer 822 _M_allocate_single_object() throw(std::bad_alloc) 823 { 824#if defined __GTHREADS 825 __scoped_lock __bit_lock(_S_mut); 826#endif 827 828 // The algorithm is something like this: The last_request 829 // variable points to the last accessed Bit Map. When such a 830 // condition occurs, we try to find a free block in the 831 // current bitmap, or succeeding bitmaps until the last bitmap 832 // is reached. If no free block turns up, we resort to First 833 // Fit method. 834 835 // WARNING: Do not re-order the condition in the while 836 // statement below, because it relies on C++'s short-circuit 837 // evaluation. The return from _S_last_request->_M_get() will 838 // NOT be dereference able if _S_last_request->_M_finished() 839 // returns true. This would inevitably lead to a NULL pointer 840 // dereference if tinkered with. 841 while (_S_last_request._M_finished() == false 842 && (*(_S_last_request._M_get()) == 0)) 843 _S_last_request.operator++(); 844 845 if (__builtin_expect(_S_last_request._M_finished() == true, false)) 846 { 847 // Fall Back to First Fit algorithm. 848 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF; 849 _FFF __fff; 850 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff)); 851 852 if (__bpi != _S_mem_blocks.end()) 853 { 854 // Search was successful. Ok, now mark the first bit from 855 // the right as 0, meaning Allocated. This bit is obtained 856 // by calling _M_get() on __fff. 857 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get()); 858 __detail::__bit_allocate(__fff._M_get(), __nz_bit); 859 860 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin()); 861 862 // Now, get the address of the bit we marked as allocated. 863 pointer __ret = reinterpret_cast<pointer> 864 (__bpi->first + __fff._M_offset() + __nz_bit); 865 size_t* __puse_count = 866 reinterpret_cast<size_t*> 867 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1); 868 869 ++(*__puse_count); 870 return __ret; 871 } 872 else 873 { 874 // Search was unsuccessful. We Add more memory to the 875 // pool by calling _S_refill_pool(). 876 _S_refill_pool(); 877 878 // _M_Reset the _S_last_request structure to the first 879 // free block's bit map. 880 _S_last_request._M_reset(_S_mem_blocks.size() - 1); 881 882 // Now, mark that bit as allocated. 883 } 884 } 885 886 // _S_last_request holds a pointer to a valid bit map, that 887 // points to a free block in memory. 888 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get()); 889 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit); 890 891 pointer __ret = reinterpret_cast<pointer> 892 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit); 893 894 size_t* __puse_count = reinterpret_cast<size_t*> 895 (_S_mem_blocks[_S_last_request._M_where()].first) 896 - (__detail:: 897 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1); 898 899 ++(*__puse_count); 900 return __ret; 901 } 902 903 /** @brief Deallocates memory that belongs to a single object of 904 * size sizeof(_Tp). 905 * 906 * Complexity: O(lg(N)), but the worst case is not hit 907 * often! This is because containers usually deallocate memory 908 * close to each other and this case is handled in O(1) time by 909 * the deallocate function. 910 */ 911 void 912 _M_deallocate_single_object(pointer __p) throw() 913 { 914#if defined __GTHREADS 915 __scoped_lock __bit_lock(_S_mut); 916#endif 917 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p); 918 919 typedef typename _BPVector::iterator _Iterator; 920 typedef typename _BPVector::difference_type _Difference_type; 921 922 _Difference_type __diff; 923 long __displacement; 924 925 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 926 927 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p); 928 if (__ibt(_S_mem_blocks[_S_last_dealloc_index])) 929 { 930 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index 931 <= _S_mem_blocks.size() - 1); 932 933 // Initial Assumption was correct! 934 __diff = _S_last_dealloc_index; 935 __displacement = __real_p - _S_mem_blocks[__diff].first; 936 } 937 else 938 { 939 _Iterator _iter = _S_find(__ibt); 940 941 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end()); 942 943 __diff = _iter - _S_mem_blocks.begin(); 944 __displacement = __real_p - _S_mem_blocks[__diff].first; 945 _S_last_dealloc_index = __diff; 946 } 947 948 // Get the position of the iterator that has been found. 949 const size_t __rotate = (__displacement 950 % size_t(__detail::bits_per_block)); 951 size_t* __bitmapC = 952 reinterpret_cast<size_t*> 953 (_S_mem_blocks[__diff].first) - 1; 954 __bitmapC -= (__displacement / size_t(__detail::bits_per_block)); 955 956 __detail::__bit_free(__bitmapC, __rotate); 957 size_t* __puse_count = reinterpret_cast<size_t*> 958 (_S_mem_blocks[__diff].first) 959 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1); 960 961 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0); 962 963 --(*__puse_count); 964 965 if (__builtin_expect(*__puse_count == 0, false)) 966 { 967 _S_block_size /= 2; 968 969 // We can safely remove this block. 970 // _Block_pair __bp = _S_mem_blocks[__diff]; 971 this->_M_insert(__puse_count); 972 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff); 973 974 // Reset the _S_last_request variable to reflect the 975 // erased block. We do this to protect future requests 976 // after the last block has been removed from a particular 977 // memory Chunk, which in turn has been returned to the 978 // free list, and hence had been erased from the vector, 979 // so the size of the vector gets reduced by 1. 980 if ((_Difference_type)_S_last_request._M_where() >= __diff--) 981 _S_last_request._M_reset(__diff); 982 983 // If the Index into the vector of the region of memory 984 // that might hold the next address that will be passed to 985 // deallocated may have been invalidated due to the above 986 // erase procedure being called on the vector, hence we 987 // try to restore this invariant too. 988 if (_S_last_dealloc_index >= _S_mem_blocks.size()) 989 { 990 _S_last_dealloc_index =(__diff != -1 ? __diff : 0); 991 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0); 992 } 993 } 994 } 995 996 public: 997 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 998 { } 999 1000 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT 1001 { } 1002 1003 template<typename _Tp1> 1004 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT 1005 { } 1006 1007 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT 1008 { } 1009 1010 pointer 1011 allocate(size_type __n) 1012 { 1013 if (__n > this->max_size()) 1014 std::__throw_bad_alloc(); 1015 1016 if (__builtin_expect(__n == 1, true)) 1017 return this->_M_allocate_single_object(); 1018 else 1019 { 1020 const size_type __b = __n * sizeof(value_type); 1021 return reinterpret_cast<pointer>(::operator new(__b)); 1022 } 1023 } 1024 1025 pointer 1026 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer) 1027 { return allocate(__n); } 1028 1029 void 1030 deallocate(pointer __p, size_type __n) throw() 1031 { 1032 if (__builtin_expect(__p != 0, true)) 1033 { 1034 if (__builtin_expect(__n == 1, true)) 1035 this->_M_deallocate_single_object(__p); 1036 else 1037 ::operator delete(__p); 1038 } 1039 } 1040 1041 pointer 1042 address(reference __r) const _GLIBCXX_NOEXCEPT 1043 { return std::__addressof(__r); } 1044 1045 const_pointer 1046 address(const_reference __r) const _GLIBCXX_NOEXCEPT 1047 { return std::__addressof(__r); } 1048 1049 size_type 1050 max_size() const _GLIBCXX_USE_NOEXCEPT 1051 { return size_type(-1) / sizeof(value_type); } 1052 1053#ifdef __GXX_EXPERIMENTAL_CXX0X__ 1054 template<typename _Up, typename... _Args> 1055 void 1056 construct(_Up* __p, _Args&&... __args) 1057 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); } 1058 1059 template<typename _Up> 1060 void 1061 destroy(_Up* __p) 1062 { __p->~_Up(); } 1063#else 1064 void 1065 construct(pointer __p, const_reference __data) 1066 { ::new((void *)__p) value_type(__data); } 1067 1068 void 1069 destroy(pointer __p) 1070 { __p->~value_type(); } 1071#endif 1072 }; 1073 1074 template<typename _Tp1, typename _Tp2> 1075 bool 1076 operator==(const bitmap_allocator<_Tp1>&, 1077 const bitmap_allocator<_Tp2>&) throw() 1078 { return true; } 1079 1080 template<typename _Tp1, typename _Tp2> 1081 bool 1082 operator!=(const bitmap_allocator<_Tp1>&, 1083 const bitmap_allocator<_Tp2>&) throw() 1084 { return false; } 1085 1086 // Static member definitions. 1087 template<typename _Tp> 1088 typename bitmap_allocator<_Tp>::_BPVector 1089 bitmap_allocator<_Tp>::_S_mem_blocks; 1090 1091 template<typename _Tp> 1092 size_t bitmap_allocator<_Tp>::_S_block_size = 1093 2 * size_t(__detail::bits_per_block); 1094 1095 template<typename _Tp> 1096 typename bitmap_allocator<_Tp>::_BPVector::size_type 1097 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0; 1098 1099 template<typename _Tp> 1100 __detail::_Bitmap_counter 1101 <typename bitmap_allocator<_Tp>::_Alloc_block*> 1102 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks); 1103 1104#if defined __GTHREADS 1105 template<typename _Tp> 1106 typename bitmap_allocator<_Tp>::__mutex_type 1107 bitmap_allocator<_Tp>::_S_mut; 1108#endif 1109 1110_GLIBCXX_END_NAMESPACE_VERSION 1111} // namespace __gnu_cxx 1112 1113#endif 1114 1115