1 // Bitmap Allocator. -*- C++ -*-
2
3 // Copyright (C) 2004-2022 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 <bits/stl_function.h> // 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
_GLIBCXX_VISIBILITY(default)45 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
46 {
47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
48
49 namespace __detail
50 {
51 /** @class __mini_vector bitmap_allocator.h bitmap_allocator.h
52 *
53 * @brief __mini_vector<> is a stripped down version of the
54 * full-fledged std::vector<>.
55 *
56 * It is to be used only for built-in types or PODs. Notable
57 * differences are:
58 *
59 * 1. Not all accessor functions are present.
60 * 2. Used ONLY for PODs.
61 * 3. No Allocator template argument. Uses ::operator new() to get
62 * memory, and ::operator delete() to free it.
63 * Caveat: The dtor does NOT free the memory allocated, so this a
64 * memory-leaking vector!
65 */
66 template<typename _Tp>
67 class __mini_vector
68 {
69 __mini_vector(const __mini_vector&);
70 __mini_vector& operator=(const __mini_vector&);
71
72 public:
73 typedef _Tp value_type;
74 typedef _Tp* pointer;
75 typedef _Tp& reference;
76 typedef const _Tp& const_reference;
77 typedef std::size_t size_type;
78 typedef std::ptrdiff_t difference_type;
79 typedef pointer iterator;
80
81 private:
82 pointer _M_start;
83 pointer _M_finish;
84 pointer _M_end_of_storage;
85
86 size_type
87 _M_space_left() const throw()
88 { return _M_end_of_storage - _M_finish; }
89
90 _GLIBCXX_NODISCARD pointer
91 allocate(size_type __n)
92 { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
93
94 void
95 deallocate(pointer __p, size_type)
96 { ::operator delete(__p); }
97
98 public:
99 // Members used: size(), push_back(), pop_back(),
100 // insert(iterator, const_reference), erase(iterator),
101 // begin(), end(), back(), operator[].
102
103 __mini_vector()
104 : _M_start(0), _M_finish(0), _M_end_of_storage(0) { }
105
106 size_type
107 size() const throw()
108 { return _M_finish - _M_start; }
109
110 iterator
111 begin() const throw()
112 { return this->_M_start; }
113
114 iterator
115 end() const throw()
116 { return this->_M_finish; }
117
118 reference
119 back() const throw()
120 { return *(this->end() - 1); }
121
122 reference
123 operator[](const size_type __pos) const throw()
124 { return this->_M_start[__pos]; }
125
126 void
127 insert(iterator __pos, const_reference __x);
128
129 void
130 push_back(const_reference __x)
131 {
132 if (this->_M_space_left())
133 {
134 *this->end() = __x;
135 ++this->_M_finish;
136 }
137 else
138 this->insert(this->end(), __x);
139 }
140
141 void
142 pop_back() throw()
143 { --this->_M_finish; }
144
145 void
146 erase(iterator __pos) throw();
147
148 void
149 clear() throw()
150 { this->_M_finish = this->_M_start; }
151 };
152
153 // Out of line function definitions.
154 template<typename _Tp>
155 void __mini_vector<_Tp>::
156 insert(iterator __pos, const_reference __x)
157 {
158 if (this->_M_space_left())
159 {
160 size_type __to_move = this->_M_finish - __pos;
161 iterator __dest = this->end();
162 iterator __src = this->end() - 1;
163
164 ++this->_M_finish;
165 while (__to_move)
166 {
167 *__dest = *__src;
168 --__dest; --__src; --__to_move;
169 }
170 *__pos = __x;
171 }
172 else
173 {
174 size_type __new_size = this->size() ? this->size() * 2 : 1;
175 iterator __new_start = this->allocate(__new_size);
176 iterator __first = this->begin();
177 iterator __start = __new_start;
178 while (__first != __pos)
179 {
180 *__start = *__first;
181 ++__start; ++__first;
182 }
183 *__start = __x;
184 ++__start;
185 while (__first != this->end())
186 {
187 *__start = *__first;
188 ++__start; ++__first;
189 }
190 if (this->_M_start)
191 this->deallocate(this->_M_start, this->size());
192
193 this->_M_start = __new_start;
194 this->_M_finish = __start;
195 this->_M_end_of_storage = this->_M_start + __new_size;
196 }
197 }
198
199 template<typename _Tp>
200 void __mini_vector<_Tp>::
201 erase(iterator __pos) throw()
202 {
203 while (__pos + 1 != this->end())
204 {
205 *__pos = __pos[1];
206 ++__pos;
207 }
208 --this->_M_finish;
209 }
210
211
212 template<typename _Tp>
213 struct __mv_iter_traits
214 {
215 typedef typename _Tp::value_type value_type;
216 typedef typename _Tp::difference_type difference_type;
217 };
218
219 template<typename _Tp>
220 struct __mv_iter_traits<_Tp*>
221 {
222 typedef _Tp value_type;
223 typedef std::ptrdiff_t difference_type;
224 };
225
226 enum
227 {
228 bits_per_byte = 8,
229 bits_per_block = sizeof(std::size_t) * std::size_t(bits_per_byte)
230 };
231
232 template<typename _ForwardIterator, typename _Tp, typename _Compare>
233 _ForwardIterator
234 __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
235 const _Tp& __val, _Compare __comp)
236 {
237 typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
238 _DistanceType;
239
240 _DistanceType __len = __last - __first;
241 _DistanceType __half;
242 _ForwardIterator __middle;
243
244 while (__len > 0)
245 {
246 __half = __len >> 1;
247 __middle = __first;
248 __middle += __half;
249 if (__comp(*__middle, __val))
250 {
251 __first = __middle;
252 ++__first;
253 __len = __len - __half - 1;
254 }
255 else
256 __len = __half;
257 }
258 return __first;
259 }
260
261 /** @brief The number of Blocks pointed to by the address pair
262 * passed to the function.
263 */
264 template<typename _AddrPair>
265 inline std::size_t
266 __num_blocks(_AddrPair __ap)
267 { return (__ap.second - __ap.first) + 1; }
268
269 /** @brief The number of Bit-maps pointed to by the address pair
270 * passed to the function.
271 */
272 template<typename _AddrPair>
273 inline std::size_t
274 __num_bitmaps(_AddrPair __ap)
275 { return __num_blocks(__ap) / std::size_t(bits_per_block); }
276
277 // _Tp should be a pointer type.
278 template<typename _Tp>
279 class _Inclusive_between
280 {
281 typedef _Tp pointer;
282 pointer _M_ptr_value;
283 typedef typename std::pair<_Tp, _Tp> _Block_pair;
284
285 public:
286 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
287 { }
288
289 bool
290 operator()(_Block_pair __bp) const throw()
291 {
292 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
293 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
294 return true;
295 else
296 return false;
297 }
298 };
299
300 // Used to pass a Functor to functions by reference.
301 template<typename _Functor>
302 class _Functor_Ref
303 {
304 _Functor& _M_fref;
305
306 public:
307 typedef typename _Functor::argument_type argument_type;
308 typedef typename _Functor::result_type result_type;
309
310 _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
311 { }
312
313 result_type
314 operator()(argument_type __arg)
315 { return _M_fref(__arg); }
316 };
317
318 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
319 *
320 * @brief The class which acts as a predicate for applying the
321 * first-fit memory allocation policy for the bitmap allocator.
322 */
323 // _Tp should be a pointer type, and _Alloc is the Allocator for
324 // the vector.
325 template<typename _Tp>
326 class _Ffit_finder
327 {
328 typedef std::pair<_Tp, _Tp> _Block_pair;
329 typedef __detail::__mini_vector<_Block_pair> _BPVector;
330 typedef typename _BPVector::difference_type _Counter_type;
331
332 std::size_t* _M_pbitmap;
333 _Counter_type _M_data_offset;
334
335 public:
336 typedef bool result_type;
337 typedef _Block_pair argument_type;
338
339 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
340 { }
341
342 bool
343 operator()(_Block_pair __bp) throw()
344 {
345 using std::size_t;
346 // Set the _rover to the last physical location bitmap,
347 // which is the bitmap which belongs to the first free
348 // block. Thus, the bitmaps are in exact reverse order of
349 // the actual memory layout. So, we count down the bitmaps,
350 // which is the same as moving up the memory.
351
352 // If the used count stored at the start of the Bit Map headers
353 // is equal to the number of Objects that the current Block can
354 // store, then there is definitely no space for another single
355 // object, so just return false.
356 _Counter_type __diff = __detail::__num_bitmaps(__bp);
357
358 if (*(reinterpret_cast<size_t*>
359 (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
360 return false;
361
362 size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
363
364 for (_Counter_type __i = 0; __i < __diff; ++__i)
365 {
366 _M_data_offset = __i;
367 if (*__rover)
368 {
369 _M_pbitmap = __rover;
370 return true;
371 }
372 --__rover;
373 }
374 return false;
375 }
376
377 std::size_t*
378 _M_get() const throw()
379 { return _M_pbitmap; }
380
381 _Counter_type
382 _M_offset() const throw()
383 { return _M_data_offset * std::size_t(bits_per_block); }
384 };
385
386 /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
387 *
388 * @brief The bitmap counter which acts as the bitmap
389 * manipulator, and manages the bit-manipulation functions and
390 * the searching and identification functions on the bit-map.
391 */
392 // _Tp should be a pointer type.
393 template<typename _Tp>
394 class _Bitmap_counter
395 {
396 typedef typename
397 __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector;
398 typedef typename _BPVector::size_type _Index_type;
399 typedef _Tp pointer;
400
401 _BPVector& _M_vbp;
402 std::size_t* _M_curr_bmap;
403 std::size_t* _M_last_bmap_in_block;
404 _Index_type _M_curr_index;
405
406 public:
407 // Use the 2nd parameter with care. Make sure that such an
408 // entry exists in the vector before passing that particular
409 // index to this ctor.
410 _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
411 { this->_M_reset(__index); }
412
413 void
414 _M_reset(long __index = -1) throw()
415 {
416 if (__index == -1)
417 {
418 _M_curr_bmap = 0;
419 _M_curr_index = static_cast<_Index_type>(-1);
420 return;
421 }
422
423 _M_curr_index = __index;
424 _M_curr_bmap = reinterpret_cast<std::size_t*>
425 (_M_vbp[_M_curr_index].first) - 1;
426
427 _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
428
429 _M_last_bmap_in_block = _M_curr_bmap
430 - ((_M_vbp[_M_curr_index].second
431 - _M_vbp[_M_curr_index].first + 1)
432 / std::size_t(bits_per_block) - 1);
433 }
434
435 // Dangerous Function! Use with extreme care. Pass to this
436 // function ONLY those values that are known to be correct,
437 // otherwise this will mess up big time.
438 void
439 _M_set_internal_bitmap(std::size_t* __new_internal_marker) throw()
440 { _M_curr_bmap = __new_internal_marker; }
441
442 bool
443 _M_finished() const throw()
444 { return(_M_curr_bmap == 0); }
445
446 _Bitmap_counter&
447 operator++() throw()
448 {
449 if (_M_curr_bmap == _M_last_bmap_in_block)
450 {
451 if (++_M_curr_index == _M_vbp.size())
452 _M_curr_bmap = 0;
453 else
454 this->_M_reset(_M_curr_index);
455 }
456 else
457 --_M_curr_bmap;
458 return *this;
459 }
460
461 std::size_t*
462 _M_get() const throw()
463 { return _M_curr_bmap; }
464
465 pointer
466 _M_base() const throw()
467 { return _M_vbp[_M_curr_index].first; }
468
469 _Index_type
470 _M_offset() const throw()
471 {
472 return std::size_t(bits_per_block)
473 * ((reinterpret_cast<std::size_t*>(this->_M_base())
474 - _M_curr_bmap) - 1);
475 }
476
477 _Index_type
478 _M_where() const throw()
479 { return _M_curr_index; }
480 };
481
482 /** @brief Mark a memory address as allocated by re-setting the
483 * corresponding bit in the bit-map.
484 */
485 inline void
486 __bit_allocate(std::size_t* __pbmap, std::size_t __pos) throw()
487 {
488 std::size_t __mask = 1 << __pos;
489 __mask = ~__mask;
490 *__pbmap &= __mask;
491 }
492
493 /** @brief Mark a memory address as free by setting the
494 * corresponding bit in the bit-map.
495 */
496 inline void
497 __bit_free(std::size_t* __pbmap, std::size_t __pos) throw()
498 {
499 std::size_t __mask = 1 << __pos;
500 *__pbmap |= __mask;
501 }
502 } // namespace __detail
503
504 /** @brief Generic Version of the bsf instruction.
505 */
506 inline std::size_t
507 _Bit_scan_forward(std::size_t __num)
508 { return static_cast<std::size_t>(__builtin_ctzl(__num)); }
509
510 /** @class free_list bitmap_allocator.h bitmap_allocator.h
511 *
512 * @brief The free list class for managing chunks of memory to be
513 * given to and returned by the bitmap_allocator.
514 */
515 class free_list
516 {
517 public:
518 typedef std::size_t* value_type;
519 typedef __detail::__mini_vector<value_type> vector_type;
520 typedef vector_type::iterator iterator;
521 typedef __mutex __mutex_type;
522
523 private:
524 struct _LT_pointer_compare
525 {
526 bool
527 operator()(const std::size_t* __pui,
528 const std::size_t __cui) const throw()
529 { return *__pui < __cui; }
530 };
531
532 #if defined __GTHREADS
533 __mutex_type&
534 _M_get_mutex()
535 {
536 static __mutex_type _S_mutex;
537 return _S_mutex;
538 }
539 #endif
540
541 vector_type&
542 _M_get_free_list()
543 {
544 static vector_type _S_free_list;
545 return _S_free_list;
546 }
547
548 /** @brief Performs validation of memory based on their size.
549 *
550 * @param __addr The pointer to the memory block to be
551 * validated.
552 *
553 * Validates the memory block passed to this function and
554 * appropriately performs the action of managing the free list of
555 * blocks by adding this block to the free list or deleting this
556 * or larger blocks from the free list.
557 */
558 void
559 _M_validate(std::size_t* __addr) throw()
560 {
561 vector_type& __free_list = _M_get_free_list();
562 const vector_type::size_type __max_size = 64;
563 if (__free_list.size() >= __max_size)
564 {
565 // Ok, the threshold value has been reached. We determine
566 // which block to remove from the list of free blocks.
567 if (*__addr >= *__free_list.back())
568 {
569 // Ok, the new block is greater than or equal to the
570 // last block in the list of free blocks. We just free
571 // the new block.
572 ::operator delete(static_cast<void*>(__addr));
573 return;
574 }
575 else
576 {
577 // Deallocate the last block in the list of free lists,
578 // and insert the new one in its correct position.
579 ::operator delete(static_cast<void*>(__free_list.back()));
580 __free_list.pop_back();
581 }
582 }
583
584 // Just add the block to the list of free lists unconditionally.
585 iterator __temp = __detail::__lower_bound
586 (__free_list.begin(), __free_list.end(),
587 *__addr, _LT_pointer_compare());
588
589 // We may insert the new free list before _temp;
590 __free_list.insert(__temp, __addr);
591 }
592
593 /** @brief Decides whether the wastage of memory is acceptable for
594 * the current memory request and returns accordingly.
595 *
596 * @param __block_size The size of the block available in the free
597 * list.
598 *
599 * @param __required_size The required size of the memory block.
600 *
601 * @return true if the wastage incurred is acceptable, else returns
602 * false.
603 */
604 bool
605 _M_should_i_give(std::size_t __block_size,
606 std::size_t __required_size) throw()
607 {
608 const std::size_t __max_wastage_percentage = 36;
609 if (__block_size >= __required_size &&
610 (((__block_size - __required_size) * 100 / __block_size)
611 < __max_wastage_percentage))
612 return true;
613 else
614 return false;
615 }
616
617 public:
618 /** @brief This function returns the block of memory to the
619 * internal free list.
620 *
621 * @param __addr The pointer to the memory block that was given
622 * by a call to the _M_get function.
623 */
624 inline void
625 _M_insert(std::size_t* __addr) throw()
626 {
627 #if defined __GTHREADS
628 __scoped_lock __bfl_lock(_M_get_mutex());
629 #endif
630 // Call _M_validate to decide what should be done with
631 // this particular free list.
632 this->_M_validate(reinterpret_cast<std::size_t*>(__addr) - 1);
633 // See discussion as to why this is 1!
634 }
635
636 /** @brief This function gets a block of memory of the specified
637 * size from the free list.
638 *
639 * @param __sz The size in bytes of the memory required.
640 *
641 * @return A pointer to the new memory block of size at least
642 * equal to that requested.
643 */
644 std::size_t*
645 _M_get(std::size_t __sz) _GLIBCXX_THROW(std::bad_alloc);
646
647 /** @brief This function just clears the internal Free List, and
648 * gives back all the memory to the OS.
649 */
650 void
651 _M_clear();
652 };
653
654
655 // Forward declare the class.
656 template<typename _Tp>
657 class bitmap_allocator;
658
659 // Specialize for void:
660 template<>
661 class bitmap_allocator<void>
662 {
663 public:
664 typedef void* pointer;
665 typedef const void* const_pointer;
666
667 // Reference-to-void members are impossible.
668 typedef void value_type;
669 template<typename _Tp1>
670 struct rebind
671 {
672 typedef bitmap_allocator<_Tp1> other;
673 };
674 };
675
676 /**
677 * @brief Bitmap Allocator, primary template.
678 * @ingroup allocators
679 */
680 template<typename _Tp>
681 class bitmap_allocator : private free_list
682 {
683 public:
684 typedef std::size_t size_type;
685 typedef std::ptrdiff_t difference_type;
686 typedef _Tp* pointer;
687 typedef const _Tp* const_pointer;
688 typedef _Tp& reference;
689 typedef const _Tp& const_reference;
690 typedef _Tp value_type;
691 typedef free_list::__mutex_type __mutex_type;
692
693 template<typename _Tp1>
694 struct rebind
695 {
696 typedef bitmap_allocator<_Tp1> other;
697 };
698
699 #if __cplusplus >= 201103L
700 // _GLIBCXX_RESOLVE_LIB_DEFECTS
701 // 2103. propagate_on_container_move_assignment
702 typedef std::true_type propagate_on_container_move_assignment;
703 #endif
704
705 private:
706 template<std::size_t _BSize, std::size_t _AlignSize>
707 struct aligned_size
708 {
709 enum
710 {
711 modulus = _BSize % _AlignSize,
712 value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
713 };
714 };
715
716 struct _Alloc_block
717 {
718 char __M_unused[aligned_size<sizeof(value_type),
719 _BALLOC_ALIGN_BYTES>::value];
720 };
721
722
723 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
724
725 typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
726 typedef typename _BPVector::iterator _BPiter;
727
728 template<typename _Predicate>
729 static _BPiter
730 _S_find(_Predicate __p)
731 {
732 _BPiter __first = _S_mem_blocks.begin();
733 while (__first != _S_mem_blocks.end() && !__p(*__first))
734 ++__first;
735 return __first;
736 }
737
738 #if defined _GLIBCXX_DEBUG
739 // Complexity: O(lg(N)). Where, N is the number of block of size
740 // sizeof(value_type).
741 void
742 _S_check_for_free_blocks() throw()
743 {
744 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
745 _BPiter __bpi = _S_find(_FFF());
746
747 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
748 }
749 #endif
750
751 /** @brief Responsible for exponentially growing the internal
752 * memory pool.
753 *
754 * @throw std::bad_alloc. If memory cannot be allocated.
755 *
756 * Complexity: O(1), but internally depends upon the
757 * complexity of the function free_list::_M_get. The part where
758 * the bitmap headers are written has complexity: O(X),where X
759 * is the number of blocks of size sizeof(value_type) within
760 * the newly acquired block. Having a tight bound.
761 */
762 void
763 _S_refill_pool() _GLIBCXX_THROW(std::bad_alloc)
764 {
765 using std::size_t;
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 std::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 cannot 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() _GLIBCXX_THROW(std::bad_alloc)
823 {
824 using std::size_t;
825 #if defined __GTHREADS
826 __scoped_lock __bit_lock(_S_mut);
827 #endif
828
829 // The algorithm is something like this: The last_request
830 // variable points to the last accessed Bit Map. When such a
831 // condition occurs, we try to find a free block in the
832 // current bitmap, or succeeding bitmaps until the last bitmap
833 // is reached. If no free block turns up, we resort to First
834 // Fit method.
835
836 // WARNING: Do not re-order the condition in the while
837 // statement below, because it relies on C++'s short-circuit
838 // evaluation. The return from _S_last_request->_M_get() will
839 // NOT be dereference able if _S_last_request->_M_finished()
840 // returns true. This would inevitably lead to a NULL pointer
841 // dereference if tinkered with.
842 while (_S_last_request._M_finished() == false
843 && (*(_S_last_request._M_get()) == 0))
844 _S_last_request.operator++();
845
846 if (__builtin_expect(_S_last_request._M_finished() == true, false))
847 {
848 // Fall Back to First Fit algorithm.
849 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
850 _FFF __fff;
851 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
852
853 if (__bpi != _S_mem_blocks.end())
854 {
855 // Search was successful. Ok, now mark the first bit from
856 // the right as 0, meaning Allocated. This bit is obtained
857 // by calling _M_get() on __fff.
858 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
859 __detail::__bit_allocate(__fff._M_get(), __nz_bit);
860
861 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
862
863 // Now, get the address of the bit we marked as allocated.
864 pointer __ret = reinterpret_cast<pointer>
865 (__bpi->first + __fff._M_offset() + __nz_bit);
866 size_t* __puse_count =
867 reinterpret_cast<size_t*>
868 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
869
870 ++(*__puse_count);
871 return __ret;
872 }
873 else
874 {
875 // Search was unsuccessful. We Add more memory to the
876 // pool by calling _S_refill_pool().
877 _S_refill_pool();
878
879 // _M_Reset the _S_last_request structure to the first
880 // free block's bit map.
881 _S_last_request._M_reset(_S_mem_blocks.size() - 1);
882
883 // Now, mark that bit as allocated.
884 }
885 }
886
887 // _S_last_request holds a pointer to a valid bit map, that
888 // points to a free block in memory.
889 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
890 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
891
892 pointer __ret = reinterpret_cast<pointer>
893 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
894
895 size_t* __puse_count = reinterpret_cast<size_t*>
896 (_S_mem_blocks[_S_last_request._M_where()].first)
897 - (__detail::
898 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
899
900 ++(*__puse_count);
901 return __ret;
902 }
903
904 /** @brief Deallocates memory that belongs to a single object of
905 * size sizeof(_Tp).
906 *
907 * Complexity: O(lg(N)), but the worst case is not hit
908 * often! This is because containers usually deallocate memory
909 * close to each other and this case is handled in O(1) time by
910 * the deallocate function.
911 */
912 void
913 _M_deallocate_single_object(pointer __p) throw()
914 {
915 using std::size_t;
916 #if defined __GTHREADS
917 __scoped_lock __bit_lock(_S_mut);
918 #endif
919 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
920
921 typedef typename _BPVector::iterator _Iterator;
922 typedef typename _BPVector::difference_type _Difference_type;
923
924 _Difference_type __diff;
925 long __displacement;
926
927 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
928
929 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
930 if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
931 {
932 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
933 <= _S_mem_blocks.size() - 1);
934
935 // Initial Assumption was correct!
936 __diff = _S_last_dealloc_index;
937 __displacement = __real_p - _S_mem_blocks[__diff].first;
938 }
939 else
940 {
941 _Iterator _iter = _S_find(__ibt);
942
943 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
944
945 __diff = _iter - _S_mem_blocks.begin();
946 __displacement = __real_p - _S_mem_blocks[__diff].first;
947 _S_last_dealloc_index = __diff;
948 }
949
950 // Get the position of the iterator that has been found.
951 const size_t __rotate = (__displacement
952 % size_t(__detail::bits_per_block));
953 size_t* __bitmapC =
954 reinterpret_cast<size_t*>
955 (_S_mem_blocks[__diff].first) - 1;
956 __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
957
958 __detail::__bit_free(__bitmapC, __rotate);
959 size_t* __puse_count = reinterpret_cast<size_t*>
960 (_S_mem_blocks[__diff].first)
961 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
962
963 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
964
965 --(*__puse_count);
966
967 if (__builtin_expect(*__puse_count == 0, false))
968 {
969 _S_block_size /= 2;
970
971 // We can safely remove this block.
972 // _Block_pair __bp = _S_mem_blocks[__diff];
973 this->_M_insert(__puse_count);
974 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
975
976 // Reset the _S_last_request variable to reflect the
977 // erased block. We do this to protect future requests
978 // after the last block has been removed from a particular
979 // memory Chunk, which in turn has been returned to the
980 // free list, and hence had been erased from the vector,
981 // so the size of the vector gets reduced by 1.
982 if ((_Difference_type)_S_last_request._M_where() >= __diff--)
983 _S_last_request._M_reset(__diff);
984
985 // If the Index into the vector of the region of memory
986 // that might hold the next address that will be passed to
987 // deallocated may have been invalidated due to the above
988 // erase procedure being called on the vector, hence we
989 // try to restore this invariant too.
990 if (_S_last_dealloc_index >= _S_mem_blocks.size())
991 {
992 _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
993 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
994 }
995 }
996 }
997
998 public:
999 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1000 { }
1001
1002 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT
1003 { }
1004
1005 template<typename _Tp1>
1006 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT
1007 { }
1008
1009 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1010 { }
1011
1012 _GLIBCXX_NODISCARD pointer
1013 allocate(size_type __n)
1014 {
1015 if (__n > this->max_size())
1016 std::__throw_bad_alloc();
1017
1018 #if __cpp_aligned_new
1019 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1020 {
1021 const size_type __b = __n * sizeof(value_type);
1022 std::align_val_t __al = std::align_val_t(alignof(value_type));
1023 return static_cast<pointer>(::operator new(__b, __al));
1024 }
1025 #endif
1026
1027 if (__builtin_expect(__n == 1, true))
1028 return this->_M_allocate_single_object();
1029 else
1030 {
1031 const size_type __b = __n * sizeof(value_type);
1032 return reinterpret_cast<pointer>(::operator new(__b));
1033 }
1034 }
1035
1036 _GLIBCXX_NODISCARD pointer
1037 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1038 { return allocate(__n); }
1039
1040 void
1041 deallocate(pointer __p, size_type __n) throw()
1042 {
1043 if (__builtin_expect(__p != 0, true))
1044 {
1045 #if __cpp_aligned_new
1046 // Types with extended alignment are handled by operator delete.
1047 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1048 {
1049 ::operator delete(__p, std::align_val_t(alignof(value_type)));
1050 return;
1051 }
1052 #endif
1053
1054 if (__builtin_expect(__n == 1, true))
1055 this->_M_deallocate_single_object(__p);
1056 else
1057 ::operator delete(__p);
1058 }
1059 }
1060
1061 pointer
1062 address(reference __r) const _GLIBCXX_NOEXCEPT
1063 { return std::__addressof(__r); }
1064
1065 const_pointer
1066 address(const_reference __r) const _GLIBCXX_NOEXCEPT
1067 { return std::__addressof(__r); }
1068
1069 size_type
1070 max_size() const _GLIBCXX_USE_NOEXCEPT
1071 { return size_type(-1) / sizeof(value_type); }
1072
1073 #if __cplusplus >= 201103L
1074 template<typename _Up, typename... _Args>
1075 void
1076 construct(_Up* __p, _Args&&... __args)
1077 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
1078
1079 template<typename _Up>
1080 void
1081 destroy(_Up* __p)
1082 { __p->~_Up(); }
1083 #else
1084 void
1085 construct(pointer __p, const_reference __data)
1086 { ::new((void *)__p) value_type(__data); }
1087
1088 void
1089 destroy(pointer __p)
1090 { __p->~value_type(); }
1091 #endif
1092 };
1093
1094 template<typename _Tp1, typename _Tp2>
1095 bool
1096 operator==(const bitmap_allocator<_Tp1>&,
1097 const bitmap_allocator<_Tp2>&) throw()
1098 { return true; }
1099
1100 #if __cpp_impl_three_way_comparison < 201907L
1101 template<typename _Tp1, typename _Tp2>
1102 bool
1103 operator!=(const bitmap_allocator<_Tp1>&,
1104 const bitmap_allocator<_Tp2>&) throw()
1105 { return false; }
1106 #endif
1107
1108 // Static member definitions.
1109 template<typename _Tp>
1110 typename bitmap_allocator<_Tp>::_BPVector
1111 bitmap_allocator<_Tp>::_S_mem_blocks;
1112
1113 template<typename _Tp>
1114 std::size_t bitmap_allocator<_Tp>::_S_block_size
1115 = 2 * std::size_t(__detail::bits_per_block);
1116
1117 template<typename _Tp>
1118 typename bitmap_allocator<_Tp>::_BPVector::size_type
1119 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1120
1121 template<typename _Tp>
1122 __detail::_Bitmap_counter
1123 <typename bitmap_allocator<_Tp>::_Alloc_block*>
1124 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1125
1126 #if defined __GTHREADS
1127 template<typename _Tp>
1128 typename bitmap_allocator<_Tp>::__mutex_type
1129 bitmap_allocator<_Tp>::_S_mut;
1130 #endif
1131
1132 _GLIBCXX_END_NAMESPACE_VERSION
1133 } // namespace __gnu_cxx
1134
1135 #endif
1136