1 // Bitmap Allocator. -*- C++ -*-
2
3 // Copyright (C) 2004-2023 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 <bits/requires_hosted.h> // GNU extensions are currently omitted
33
34 #include <utility> // For std::pair.
35 #include <bits/functexcept.h> // For __throw_bad_alloc().
36 #include <bits/stl_function.h> // For greater_equal, and less_equal.
37 #include <new> // For operator new.
38 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
39 #include <ext/concurrence.h>
40 #include <bits/move.h>
41
42 /** @brief The constant in the expression below is the alignment
43 * required in bytes.
44 */
45 #define _BALLOC_ALIGN_BYTES 8
46
47 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
48 {
49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51 namespace __detail
52 {
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 std::size_t size_type;
80 typedef std::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 _GLIBCXX_NODISCARD 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 std::ptrdiff_t difference_type;
226 };
227
228 enum
229 {
230 bits_per_byte = 8,
231 bits_per_block = sizeof(std::size_t) * std::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 std::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 std::size_t
276 __num_bitmaps(_AddrPair __ap)
277 { return __num_blocks(__ap) / std::size_t(bits_per_block); }
278
279 // _Tp should be a pointer type.
280 template<typename _Tp>
281 class _Inclusive_between
282 {
283 typedef _Tp pointer;
284 pointer _M_ptr_value;
285 typedef typename std::pair<_Tp, _Tp> _Block_pair;
286
287 public:
288 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
289 { }
290
291 bool
292 operator()(_Block_pair __bp) const throw()
293 {
294 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
295 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
296 return true;
297 else
298 return false;
299 }
300 };
301
302 // Used to pass a Functor to functions by reference.
303 template<typename _Functor>
304 class _Functor_Ref
305 {
306 _Functor& _M_fref;
307
308 public:
309 typedef typename _Functor::argument_type argument_type;
310 typedef typename _Functor::result_type result_type;
311
312 _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
313 { }
314
315 result_type
316 operator()(argument_type __arg)
317 { return _M_fref(__arg); }
318 };
319
320 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
321 *
322 * @brief The class which acts as a predicate for applying the
323 * first-fit memory allocation policy for the bitmap allocator.
324 */
325 // _Tp should be a pointer type, and _Alloc is the Allocator for
326 // the vector.
327 template<typename _Tp>
328 class _Ffit_finder
329 {
330 typedef std::pair<_Tp, _Tp> _Block_pair;
331 typedef __detail::__mini_vector<_Block_pair> _BPVector;
332 typedef typename _BPVector::difference_type _Counter_type;
333
334 std::size_t* _M_pbitmap;
335 _Counter_type _M_data_offset;
336
337 public:
338 typedef bool result_type;
339 typedef _Block_pair argument_type;
340
341 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
342 { }
343
344 bool
345 operator()(_Block_pair __bp) throw()
346 {
347 using std::size_t;
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 std::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 * std::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 std::size_t* _M_curr_bmap;
405 std::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<std::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 / std::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(std::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 std::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 std::size_t(bits_per_block)
475 * ((reinterpret_cast<std::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(std::size_t* __pbmap, std::size_t __pos) throw()
489 {
490 std::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(std::size_t* __pbmap, std::size_t __pos) throw()
500 {
501 std::size_t __mask = 1 << __pos;
502 *__pbmap |= __mask;
503 }
504 } // namespace __detail
505
506 /** @brief Generic Version of the bsf instruction.
507 */
508 inline std::size_t
509 _Bit_scan_forward(std::size_t __num)
510 { return static_cast<std::size_t>(__builtin_ctzl(__num)); }
511
512 /** @class free_list bitmap_allocator.h bitmap_allocator.h
513 *
514 * @brief The free list class for managing chunks of memory to be
515 * given to and returned by the bitmap_allocator.
516 */
517 class free_list
518 {
519 public:
520 typedef std::size_t* value_type;
521 typedef __detail::__mini_vector<value_type> vector_type;
522 typedef vector_type::iterator iterator;
523 typedef __mutex __mutex_type;
524
525 private:
526 struct _LT_pointer_compare
527 {
528 bool
529 operator()(const std::size_t* __pui,
530 const std::size_t __cui) const throw()
531 { return *__pui < __cui; }
532 };
533
534 #if defined __GTHREADS
535 __mutex_type&
536 _M_get_mutex()
537 {
538 static __mutex_type _S_mutex;
539 return _S_mutex;
540 }
541 #endif
542
543 vector_type&
544 _M_get_free_list()
545 {
546 static vector_type _S_free_list;
547 return _S_free_list;
548 }
549
550 /** @brief Performs validation of memory based on their size.
551 *
552 * @param __addr The pointer to the memory block to be
553 * validated.
554 *
555 * Validates the memory block passed to this function and
556 * appropriately performs the action of managing the free list of
557 * blocks by adding this block to the free list or deleting this
558 * or larger blocks from the free list.
559 */
560 void
561 _M_validate(std::size_t* __addr) throw()
562 {
563 vector_type& __free_list = _M_get_free_list();
564 const vector_type::size_type __max_size = 64;
565 if (__free_list.size() >= __max_size)
566 {
567 // Ok, the threshold value has been reached. We determine
568 // which block to remove from the list of free blocks.
569 if (*__addr >= *__free_list.back())
570 {
571 // Ok, the new block is greater than or equal to the
572 // last block in the list of free blocks. We just free
573 // the new block.
574 ::operator delete(static_cast<void*>(__addr));
575 return;
576 }
577 else
578 {
579 // Deallocate the last block in the list of free lists,
580 // and insert the new one in its correct position.
581 ::operator delete(static_cast<void*>(__free_list.back()));
582 __free_list.pop_back();
583 }
584 }
585
586 // Just add the block to the list of free lists unconditionally.
587 iterator __temp = __detail::__lower_bound
588 (__free_list.begin(), __free_list.end(),
589 *__addr, _LT_pointer_compare());
590
591 // We may insert the new free list before _temp;
592 __free_list.insert(__temp, __addr);
593 }
594
595 /** @brief Decides whether the wastage of memory is acceptable for
596 * the current memory request and returns accordingly.
597 *
598 * @param __block_size The size of the block available in the free
599 * list.
600 *
601 * @param __required_size The required size of the memory block.
602 *
603 * @return true if the wastage incurred is acceptable, else returns
604 * false.
605 */
606 bool
607 _M_should_i_give(std::size_t __block_size,
608 std::size_t __required_size) throw()
609 {
610 const std::size_t __max_wastage_percentage = 36;
611 if (__block_size >= __required_size &&
612 (((__block_size - __required_size) * 100 / __block_size)
613 < __max_wastage_percentage))
614 return true;
615 else
616 return false;
617 }
618
619 public:
620 /** @brief This function returns the block of memory to the
621 * internal free list.
622 *
623 * @param __addr The pointer to the memory block that was given
624 * by a call to the _M_get function.
625 */
626 inline void
627 _M_insert(std::size_t* __addr) throw()
628 {
629 #if defined __GTHREADS
630 __scoped_lock __bfl_lock(_M_get_mutex());
631 #endif
632 // Call _M_validate to decide what should be done with
633 // this particular free list.
634 this->_M_validate(reinterpret_cast<std::size_t*>(__addr) - 1);
635 // See discussion as to why this is 1!
636 }
637
638 /** @brief This function gets a block of memory of the specified
639 * size from the free list.
640 *
641 * @param __sz The size in bytes of the memory required.
642 *
643 * @return A pointer to the new memory block of size at least
644 * equal to that requested.
645 */
646 std::size_t*
647 _M_get(std::size_t __sz) _GLIBCXX_THROW(std::bad_alloc);
648
649 /** @brief This function just clears the internal Free List, and
650 * gives back all the memory to the OS.
651 */
652 void
653 _M_clear();
654 };
655
656
657 // Forward declare the class.
658 template<typename _Tp>
659 class bitmap_allocator;
660
661 // Specialize for void:
662 template<>
663 class bitmap_allocator<void>
664 {
665 public:
666 typedef void* pointer;
667 typedef const void* const_pointer;
668
669 // Reference-to-void members are impossible.
670 typedef void value_type;
671 template<typename _Tp1>
672 struct rebind
673 {
674 typedef bitmap_allocator<_Tp1> other;
675 };
676 };
677
678 /**
679 * @brief Bitmap Allocator, primary template.
680 * @ingroup allocators
681 */
682 template<typename _Tp>
683 class bitmap_allocator : private free_list
684 {
685 public:
686 typedef std::size_t size_type;
687 typedef std::ptrdiff_t difference_type;
688 typedef _Tp* pointer;
689 typedef const _Tp* const_pointer;
690 typedef _Tp& reference;
691 typedef const _Tp& const_reference;
692 typedef _Tp value_type;
693 typedef free_list::__mutex_type __mutex_type;
694
695 template<typename _Tp1>
696 struct rebind
697 {
698 typedef bitmap_allocator<_Tp1> other;
699 };
700
701 #if __cplusplus >= 201103L
702 // _GLIBCXX_RESOLVE_LIB_DEFECTS
703 // 2103. propagate_on_container_move_assignment
704 typedef std::true_type propagate_on_container_move_assignment;
705 #endif
706
707 private:
708 template<std::size_t _BSize, std::size_t _AlignSize>
709 struct aligned_size
710 {
711 enum
712 {
713 modulus = _BSize % _AlignSize,
714 value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
715 };
716 };
717
718 struct _Alloc_block
719 {
720 char __M_unused[aligned_size<sizeof(value_type),
721 _BALLOC_ALIGN_BYTES>::value];
722 };
723
724
725 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
726
727 typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
728 typedef typename _BPVector::iterator _BPiter;
729
730 template<typename _Predicate>
731 static _BPiter
732 _S_find(_Predicate __p)
733 {
734 _BPiter __first = _S_mem_blocks.begin();
735 while (__first != _S_mem_blocks.end() && !__p(*__first))
736 ++__first;
737 return __first;
738 }
739
740 #if defined _GLIBCXX_DEBUG
741 // Complexity: O(lg(N)). Where, N is the number of block of size
742 // sizeof(value_type).
743 void
744 _S_check_for_free_blocks() throw()
745 {
746 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
747 _BPiter __bpi = _S_find(_FFF());
748
749 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
750 }
751 #endif
752
753 /** @brief Responsible for exponentially growing the internal
754 * memory pool.
755 *
756 * @throw std::bad_alloc. If memory cannot be allocated.
757 *
758 * Complexity: O(1), but internally depends upon the
759 * complexity of the function free_list::_M_get. The part where
760 * the bitmap headers are written has complexity: O(X),where X
761 * is the number of blocks of size sizeof(value_type) within
762 * the newly acquired block. Having a tight bound.
763 */
764 void
765 _S_refill_pool() _GLIBCXX_THROW(std::bad_alloc)
766 {
767 using std::size_t;
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 std::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 cannot 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 using std::size_t;
827 #if defined __GTHREADS
828 __scoped_lock __bit_lock(_S_mut);
829 #endif
830
831 // The algorithm is something like this: The last_request
832 // variable points to the last accessed Bit Map. When such a
833 // condition occurs, we try to find a free block in the
834 // current bitmap, or succeeding bitmaps until the last bitmap
835 // is reached. If no free block turns up, we resort to First
836 // Fit method.
837
838 // WARNING: Do not re-order the condition in the while
839 // statement below, because it relies on C++'s short-circuit
840 // evaluation. The return from _S_last_request->_M_get() will
841 // NOT be dereference able if _S_last_request->_M_finished()
842 // returns true. This would inevitably lead to a NULL pointer
843 // dereference if tinkered with.
844 while (_S_last_request._M_finished() == false
845 && (*(_S_last_request._M_get()) == 0))
846 _S_last_request.operator++();
847
848 if (__builtin_expect(_S_last_request._M_finished() == true, false))
849 {
850 // Fall Back to First Fit algorithm.
851 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
852 _FFF __fff;
853 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
854
855 if (__bpi != _S_mem_blocks.end())
856 {
857 // Search was successful. Ok, now mark the first bit from
858 // the right as 0, meaning Allocated. This bit is obtained
859 // by calling _M_get() on __fff.
860 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
861 __detail::__bit_allocate(__fff._M_get(), __nz_bit);
862
863 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
864
865 // Now, get the address of the bit we marked as allocated.
866 pointer __ret = reinterpret_cast<pointer>
867 (__bpi->first + __fff._M_offset() + __nz_bit);
868 size_t* __puse_count =
869 reinterpret_cast<size_t*>
870 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
871
872 ++(*__puse_count);
873 return __ret;
874 }
875 else
876 {
877 // Search was unsuccessful. We Add more memory to the
878 // pool by calling _S_refill_pool().
879 _S_refill_pool();
880
881 // _M_Reset the _S_last_request structure to the first
882 // free block's bit map.
883 _S_last_request._M_reset(_S_mem_blocks.size() - 1);
884
885 // Now, mark that bit as allocated.
886 }
887 }
888
889 // _S_last_request holds a pointer to a valid bit map, that
890 // points to a free block in memory.
891 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
892 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
893
894 pointer __ret = reinterpret_cast<pointer>
895 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
896
897 size_t* __puse_count = reinterpret_cast<size_t*>
898 (_S_mem_blocks[_S_last_request._M_where()].first)
899 - (__detail::
900 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
901
902 ++(*__puse_count);
903 return __ret;
904 }
905
906 /** @brief Deallocates memory that belongs to a single object of
907 * size sizeof(_Tp).
908 *
909 * Complexity: O(lg(N)), but the worst case is not hit
910 * often! This is because containers usually deallocate memory
911 * close to each other and this case is handled in O(1) time by
912 * the deallocate function.
913 */
914 void
915 _M_deallocate_single_object(pointer __p) throw()
916 {
917 using std::size_t;
918 #if defined __GTHREADS
919 __scoped_lock __bit_lock(_S_mut);
920 #endif
921 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
922
923 typedef typename _BPVector::iterator _Iterator;
924 typedef typename _BPVector::difference_type _Difference_type;
925
926 _Difference_type __diff;
927 long __displacement;
928
929 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
930
931 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
932 if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
933 {
934 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
935 <= _S_mem_blocks.size() - 1);
936
937 // Initial Assumption was correct!
938 __diff = _S_last_dealloc_index;
939 __displacement = __real_p - _S_mem_blocks[__diff].first;
940 }
941 else
942 {
943 _Iterator _iter = _S_find(__ibt);
944
945 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
946
947 __diff = _iter - _S_mem_blocks.begin();
948 __displacement = __real_p - _S_mem_blocks[__diff].first;
949 _S_last_dealloc_index = __diff;
950 }
951
952 // Get the position of the iterator that has been found.
953 const size_t __rotate = (__displacement
954 % size_t(__detail::bits_per_block));
955 size_t* __bitmapC =
956 reinterpret_cast<size_t*>
957 (_S_mem_blocks[__diff].first) - 1;
958 __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
959
960 __detail::__bit_free(__bitmapC, __rotate);
961 size_t* __puse_count = reinterpret_cast<size_t*>
962 (_S_mem_blocks[__diff].first)
963 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
964
965 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
966
967 --(*__puse_count);
968
969 if (__builtin_expect(*__puse_count == 0, false))
970 {
971 _S_block_size /= 2;
972
973 // We can safely remove this block.
974 // _Block_pair __bp = _S_mem_blocks[__diff];
975 this->_M_insert(__puse_count);
976 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
977
978 // Reset the _S_last_request variable to reflect the
979 // erased block. We do this to protect future requests
980 // after the last block has been removed from a particular
981 // memory Chunk, which in turn has been returned to the
982 // free list, and hence had been erased from the vector,
983 // so the size of the vector gets reduced by 1.
984 if ((_Difference_type)_S_last_request._M_where() >= __diff--)
985 _S_last_request._M_reset(__diff);
986
987 // If the Index into the vector of the region of memory
988 // that might hold the next address that will be passed to
989 // deallocated may have been invalidated due to the above
990 // erase procedure being called on the vector, hence we
991 // try to restore this invariant too.
992 if (_S_last_dealloc_index >= _S_mem_blocks.size())
993 {
994 _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
995 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
996 }
997 }
998 }
999
1000 public:
1001 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1002 { }
1003
1004 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT
1005 { }
1006
1007 template<typename _Tp1>
1008 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT
1009 { }
1010
1011 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1012 { }
1013
1014 _GLIBCXX_NODISCARD pointer
1015 allocate(size_type __n)
1016 {
1017 if (__n > this->max_size())
1018 std::__throw_bad_alloc();
1019
1020 #if __cpp_aligned_new
1021 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1022 {
1023 const size_type __b = __n * sizeof(value_type);
1024 std::align_val_t __al = std::align_val_t(alignof(value_type));
1025 return static_cast<pointer>(::operator new(__b, __al));
1026 }
1027 #endif
1028
1029 if (__builtin_expect(__n == 1, true))
1030 return this->_M_allocate_single_object();
1031 else
1032 {
1033 const size_type __b = __n * sizeof(value_type);
1034 return reinterpret_cast<pointer>(::operator new(__b));
1035 }
1036 }
1037
1038 _GLIBCXX_NODISCARD pointer
1039 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1040 { return allocate(__n); }
1041
1042 void
1043 deallocate(pointer __p, size_type __n) throw()
1044 {
1045 if (__builtin_expect(__p != 0, true))
1046 {
1047 #if __cpp_aligned_new
1048 // Types with extended alignment are handled by operator delete.
1049 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1050 {
1051 ::operator delete(__p, std::align_val_t(alignof(value_type)));
1052 return;
1053 }
1054 #endif
1055
1056 if (__builtin_expect(__n == 1, true))
1057 this->_M_deallocate_single_object(__p);
1058 else
1059 ::operator delete(__p);
1060 }
1061 }
1062
1063 pointer
1064 address(reference __r) const _GLIBCXX_NOEXCEPT
1065 { return std::__addressof(__r); }
1066
1067 const_pointer
1068 address(const_reference __r) const _GLIBCXX_NOEXCEPT
1069 { return std::__addressof(__r); }
1070
1071 size_type
1072 max_size() const _GLIBCXX_USE_NOEXCEPT
1073 { return size_type(-1) / sizeof(value_type); }
1074
1075 #if __cplusplus >= 201103L
1076 template<typename _Up, typename... _Args>
1077 void
1078 construct(_Up* __p, _Args&&... __args)
1079 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
1080
1081 template<typename _Up>
1082 void
1083 destroy(_Up* __p)
1084 { __p->~_Up(); }
1085 #else
1086 void
1087 construct(pointer __p, const_reference __data)
1088 { ::new((void *)__p) value_type(__data); }
1089
1090 void
1091 destroy(pointer __p)
1092 { __p->~value_type(); }
1093 #endif
1094 };
1095
1096 template<typename _Tp1, typename _Tp2>
1097 bool
1098 operator==(const bitmap_allocator<_Tp1>&,
1099 const bitmap_allocator<_Tp2>&) throw()
1100 { return true; }
1101
1102 #if __cpp_impl_three_way_comparison < 201907L
1103 template<typename _Tp1, typename _Tp2>
1104 bool
1105 operator!=(const bitmap_allocator<_Tp1>&,
1106 const bitmap_allocator<_Tp2>&) throw()
1107 { return false; }
1108 #endif
1109
1110 // Static member definitions.
1111 template<typename _Tp>
1112 typename bitmap_allocator<_Tp>::_BPVector
1113 bitmap_allocator<_Tp>::_S_mem_blocks;
1114
1115 template<typename _Tp>
1116 std::size_t bitmap_allocator<_Tp>::_S_block_size
1117 = 2 * std::size_t(__detail::bits_per_block);
1118
1119 template<typename _Tp>
1120 typename bitmap_allocator<_Tp>::_BPVector::size_type
1121 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1122
1123 template<typename _Tp>
1124 __detail::_Bitmap_counter
1125 <typename bitmap_allocator<_Tp>::_Alloc_block*>
1126 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1127
1128 #if defined __GTHREADS
1129 template<typename _Tp>
1130 typename bitmap_allocator<_Tp>::__mutex_type
1131 bitmap_allocator<_Tp>::_S_mut;
1132 #endif
1133
1134 _GLIBCXX_END_NAMESPACE_VERSION
1135 } // namespace __gnu_cxx
1136
1137 #endif