1 // Bitmap Allocator. -*- C++ -*-
2
3 // Copyright (C) 2004-2020 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 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
281 {
282 typedef _Tp pointer;
283 pointer _M_ptr_value;
284 typedef typename std::pair<_Tp, _Tp> _Block_pair;
285
286 public:
287 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
288 { }
289
290 bool
291 operator()(_Block_pair __bp) const throw()
292 {
293 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
294 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
295 return true;
296 else
297 return false;
298 }
299 };
300
301 // Used to pass a Functor to functions by reference.
302 template<typename _Functor>
303 class _Functor_Ref
304 : public std::unary_function<typename _Functor::argument_type,
305 typename _Functor::result_type>
306 {
307 _Functor& _M_fref;
308
309 public:
310 typedef typename _Functor::argument_type argument_type;
311 typedef typename _Functor::result_type result_type;
312
313 _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
314 { }
315
316 result_type
317 operator()(argument_type __arg)
318 { return _M_fref(__arg); }
319 };
320
321 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
322 *
323 * @brief The class which acts as a predicate for applying the
324 * first-fit memory allocation policy for the bitmap allocator.
325 */
326 // _Tp should be a pointer type, and _Alloc is the Allocator for
327 // the vector.
328 template<typename _Tp>
329 class _Ffit_finder
330 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
331 {
332 typedef typename std::pair<_Tp, _Tp> _Block_pair;
333 typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
334 typedef typename _BPVector::difference_type _Counter_type;
335
336 std::size_t* _M_pbitmap;
337 _Counter_type _M_data_offset;
338
339 public:
340 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
341 { }
342
343 bool
344 operator()(_Block_pair __bp) throw()
345 {
346 using std::size_t;
347 // Set the _rover to the last physical location bitmap,
348 // which is the bitmap which belongs to the first free
349 // block. Thus, the bitmaps are in exact reverse order of
350 // the actual memory layout. So, we count down the bitmaps,
351 // which is the same as moving up the memory.
352
353 // If the used count stored at the start of the Bit Map headers
354 // is equal to the number of Objects that the current Block can
355 // store, then there is definitely no space for another single
356 // object, so just return false.
357 _Counter_type __diff = __detail::__num_bitmaps(__bp);
358
359 if (*(reinterpret_cast<size_t*>
360 (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
361 return false;
362
363 size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
364
365 for (_Counter_type __i = 0; __i < __diff; ++__i)
366 {
367 _M_data_offset = __i;
368 if (*__rover)
369 {
370 _M_pbitmap = __rover;
371 return true;
372 }
373 --__rover;
374 }
375 return false;
376 }
377
378 std::size_t*
379 _M_get() const throw()
380 { return _M_pbitmap; }
381
382 _Counter_type
383 _M_offset() const throw()
384 { return _M_data_offset * std::size_t(bits_per_block); }
385 };
386
387 /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
388 *
389 * @brief The bitmap counter which acts as the bitmap
390 * manipulator, and manages the bit-manipulation functions and
391 * the searching and identification functions on the bit-map.
392 */
393 // _Tp should be a pointer type.
394 template<typename _Tp>
395 class _Bitmap_counter
396 {
397 typedef typename
398 __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector;
399 typedef typename _BPVector::size_type _Index_type;
400 typedef _Tp pointer;
401
402 _BPVector& _M_vbp;
403 std::size_t* _M_curr_bmap;
404 std::size_t* _M_last_bmap_in_block;
405 _Index_type _M_curr_index;
406
407 public:
408 // Use the 2nd parameter with care. Make sure that such an
409 // entry exists in the vector before passing that particular
410 // index to this ctor.
411 _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
412 { this->_M_reset(__index); }
413
414 void
415 _M_reset(long __index = -1) throw()
416 {
417 if (__index == -1)
418 {
419 _M_curr_bmap = 0;
420 _M_curr_index = static_cast<_Index_type>(-1);
421 return;
422 }
423
424 _M_curr_index = __index;
425 _M_curr_bmap = reinterpret_cast<std::size_t*>
426 (_M_vbp[_M_curr_index].first) - 1;
427
428 _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
429
430 _M_last_bmap_in_block = _M_curr_bmap
431 - ((_M_vbp[_M_curr_index].second
432 - _M_vbp[_M_curr_index].first + 1)
433 / std::size_t(bits_per_block) - 1);
434 }
435
436 // Dangerous Function! Use with extreme care. Pass to this
437 // function ONLY those values that are known to be correct,
438 // otherwise this will mess up big time.
439 void
440 _M_set_internal_bitmap(std::size_t* __new_internal_marker) throw()
441 { _M_curr_bmap = __new_internal_marker; }
442
443 bool
444 _M_finished() const throw()
445 { return(_M_curr_bmap == 0); }
446
447 _Bitmap_counter&
448 operator++() throw()
449 {
450 if (_M_curr_bmap == _M_last_bmap_in_block)
451 {
452 if (++_M_curr_index == _M_vbp.size())
453 _M_curr_bmap = 0;
454 else
455 this->_M_reset(_M_curr_index);
456 }
457 else
458 --_M_curr_bmap;
459 return *this;
460 }
461
462 std::size_t*
463 _M_get() const throw()
464 { return _M_curr_bmap; }
465
466 pointer
467 _M_base() const throw()
468 { return _M_vbp[_M_curr_index].first; }
469
470 _Index_type
471 _M_offset() const throw()
472 {
473 return std::size_t(bits_per_block)
474 * ((reinterpret_cast<std::size_t*>(this->_M_base())
475 - _M_curr_bmap) - 1);
476 }
477
478 _Index_type
479 _M_where() const throw()
480 { return _M_curr_index; }
481 };
482
483 /** @brief Mark a memory address as allocated by re-setting the
484 * corresponding bit in the bit-map.
485 */
486 inline void
487 __bit_allocate(std::size_t* __pbmap, std::size_t __pos) throw()
488 {
489 std::size_t __mask = 1 << __pos;
490 __mask = ~__mask;
491 *__pbmap &= __mask;
492 }
493
494 /** @brief Mark a memory address as free by setting the
495 * corresponding bit in the bit-map.
496 */
497 inline void
498 __bit_free(std::size_t* __pbmap, std::size_t __pos) throw()
499 {
500 std::size_t __mask = 1 << __pos;
501 *__pbmap |= __mask;
502 }
503 } // namespace __detail
504
505 /** @brief Generic Version of the bsf instruction.
506 */
507 inline std::size_t
508 _Bit_scan_forward(std::size_t __num)
509 { return static_cast<std::size_t>(__builtin_ctzl(__num)); }
510
511 /** @class free_list bitmap_allocator.h bitmap_allocator.h
512 *
513 * @brief The free list class for managing chunks of memory to be
514 * given to and returned by the bitmap_allocator.
515 */
516 class free_list
517 {
518 public:
519 typedef std::size_t* value_type;
520 typedef __detail::__mini_vector<value_type> vector_type;
521 typedef vector_type::iterator iterator;
522 typedef __mutex __mutex_type;
523
524 private:
525 struct _LT_pointer_compare
526 {
527 bool
528 operator()(const std::size_t* __pui,
529 const std::size_t __cui) const throw()
530 { return *__pui < __cui; }
531 };
532
533 #if defined __GTHREADS
534 __mutex_type&
535 _M_get_mutex()
536 {
537 static __mutex_type _S_mutex;
538 return _S_mutex;
539 }
540 #endif
541
542 vector_type&
543 _M_get_free_list()
544 {
545 static vector_type _S_free_list;
546 return _S_free_list;
547 }
548
549 /** @brief Performs validation of memory based on their size.
550 *
551 * @param __addr The pointer to the memory block to be
552 * validated.
553 *
554 * Validates the memory block passed to this function and
555 * appropriately performs the action of managing the free list of
556 * blocks by adding this block to the free list or deleting this
557 * or larger blocks from the free list.
558 */
559 void
560 _M_validate(std::size_t* __addr) throw()
561 {
562 vector_type& __free_list = _M_get_free_list();
563 const vector_type::size_type __max_size = 64;
564 if (__free_list.size() >= __max_size)
565 {
566 // Ok, the threshold value has been reached. We determine
567 // which block to remove from the list of free blocks.
568 if (*__addr >= *__free_list.back())
569 {
570 // Ok, the new block is greater than or equal to the
571 // last block in the list of free blocks. We just free
572 // the new block.
573 ::operator delete(static_cast<void*>(__addr));
574 return;
575 }
576 else
577 {
578 // Deallocate the last block in the list of free lists,
579 // and insert the new one in its correct position.
580 ::operator delete(static_cast<void*>(__free_list.back()));
581 __free_list.pop_back();
582 }
583 }
584
585 // Just add the block to the list of free lists unconditionally.
586 iterator __temp = __detail::__lower_bound
587 (__free_list.begin(), __free_list.end(),
588 *__addr, _LT_pointer_compare());
589
590 // We may insert the new free list before _temp;
591 __free_list.insert(__temp, __addr);
592 }
593
594 /** @brief Decides whether the wastage of memory is acceptable for
595 * the current memory request and returns accordingly.
596 *
597 * @param __block_size The size of the block available in the free
598 * list.
599 *
600 * @param __required_size The required size of the memory block.
601 *
602 * @return true if the wastage incurred is acceptable, else returns
603 * false.
604 */
605 bool
606 _M_should_i_give(std::size_t __block_size,
607 std::size_t __required_size) throw()
608 {
609 const std::size_t __max_wastage_percentage = 36;
610 if (__block_size >= __required_size &&
611 (((__block_size - __required_size) * 100 / __block_size)
612 < __max_wastage_percentage))
613 return true;
614 else
615 return false;
616 }
617
618 public:
619 /** @brief This function returns the block of memory to the
620 * internal free list.
621 *
622 * @param __addr The pointer to the memory block that was given
623 * by a call to the _M_get function.
624 */
625 inline void
626 _M_insert(std::size_t* __addr) throw()
627 {
628 #if defined __GTHREADS
629 __scoped_lock __bfl_lock(_M_get_mutex());
630 #endif
631 // Call _M_validate to decide what should be done with
632 // this particular free list.
633 this->_M_validate(reinterpret_cast<std::size_t*>(__addr) - 1);
634 // See discussion as to why this is 1!
635 }
636
637 /** @brief This function gets a block of memory of the specified
638 * size from the free list.
639 *
640 * @param __sz The size in bytes of the memory required.
641 *
642 * @return A pointer to the new memory block of size at least
643 * equal to that requested.
644 */
645 std::size_t*
646 _M_get(std::size_t __sz) _GLIBCXX_THROW(std::bad_alloc);
647
648 /** @brief This function just clears the internal Free List, and
649 * gives back all the memory to the OS.
650 */
651 void
652 _M_clear();
653 };
654
655
656 // Forward declare the class.
657 template<typename _Tp>
658 class bitmap_allocator;
659
660 // Specialize for void:
661 template<>
662 class bitmap_allocator<void>
663 {
664 public:
665 typedef void* pointer;
666 typedef const void* const_pointer;
667
668 // Reference-to-void members are impossible.
669 typedef void value_type;
670 template<typename _Tp1>
671 struct rebind
672 {
673 typedef bitmap_allocator<_Tp1> other;
674 };
675 };
676
677 /**
678 * @brief Bitmap Allocator, primary template.
679 * @ingroup allocators
680 */
681 template<typename _Tp>
682 class bitmap_allocator : private free_list
683 {
684 public:
685 typedef std::size_t size_type;
686 typedef std::ptrdiff_t difference_type;
687 typedef _Tp* pointer;
688 typedef const _Tp* const_pointer;
689 typedef _Tp& reference;
690 typedef const _Tp& const_reference;
691 typedef _Tp value_type;
692 typedef free_list::__mutex_type __mutex_type;
693
694 template<typename _Tp1>
695 struct rebind
696 {
697 typedef bitmap_allocator<_Tp1> other;
698 };
699
700 #if __cplusplus >= 201103L
701 // _GLIBCXX_RESOLVE_LIB_DEFECTS
702 // 2103. propagate_on_container_move_assignment
703 typedef std::true_type propagate_on_container_move_assignment;
704 #endif
705
706 private:
707 template<std::size_t _BSize, std::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 cannot 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() _GLIBCXX_THROW(std::bad_alloc)
765 {
766 using std::size_t;
767 #if defined _GLIBCXX_DEBUG
768 _S_check_for_free_blocks();
769 #endif
770
771 const size_t __num_bitmaps = (_S_block_size
772 / size_t(__detail::bits_per_block));
773 const size_t __size_to_allocate = sizeof(size_t)
774 + _S_block_size * sizeof(_Alloc_block)
775 + __num_bitmaps * sizeof(size_t);
776
777 size_t* __temp =
778 reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate));
779 *__temp = 0;
780 ++__temp;
781
782 // The Header information goes at the Beginning of the Block.
783 _Block_pair __bp =
784 std::make_pair(reinterpret_cast<_Alloc_block*>
785 (__temp + __num_bitmaps),
786 reinterpret_cast<_Alloc_block*>
787 (__temp + __num_bitmaps)
788 + _S_block_size - 1);
789
790 // Fill the Vector with this information.
791 _S_mem_blocks.push_back(__bp);
792
793 for (size_t __i = 0; __i < __num_bitmaps; ++__i)
794 __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free.
795
796 _S_block_size *= 2;
797 }
798
799 static _BPVector _S_mem_blocks;
800 static std::size_t _S_block_size;
801 static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request;
802 static typename _BPVector::size_type _S_last_dealloc_index;
803 #if defined __GTHREADS
804 static __mutex_type _S_mut;
805 #endif
806
807 public:
808
809 /** @brief Allocates memory for a single object of size
810 * sizeof(_Tp).
811 *
812 * @throw std::bad_alloc. If memory cannot be allocated.
813 *
814 * Complexity: Worst case complexity is O(N), but that
815 * is hardly ever hit. If and when this particular case is
816 * encountered, the next few cases are guaranteed to have a
817 * worst case complexity of O(1)! That's why this function
818 * performs very well on average. You can consider this
819 * function to have a complexity referred to commonly as:
820 * Amortized Constant time.
821 */
822 pointer
823 _M_allocate_single_object() _GLIBCXX_THROW(std::bad_alloc)
824 {
825 using std::size_t;
826 #if defined __GTHREADS
827 __scoped_lock __bit_lock(_S_mut);
828 #endif
829
830 // The algorithm is something like this: The last_request
831 // variable points to the last accessed Bit Map. When such a
832 // condition occurs, we try to find a free block in the
833 // current bitmap, or succeeding bitmaps until the last bitmap
834 // is reached. If no free block turns up, we resort to First
835 // Fit method.
836
837 // WARNING: Do not re-order the condition in the while
838 // statement below, because it relies on C++'s short-circuit
839 // evaluation. The return from _S_last_request->_M_get() will
840 // NOT be dereference able if _S_last_request->_M_finished()
841 // returns true. This would inevitably lead to a NULL pointer
842 // dereference if tinkered with.
843 while (_S_last_request._M_finished() == false
844 && (*(_S_last_request._M_get()) == 0))
845 _S_last_request.operator++();
846
847 if (__builtin_expect(_S_last_request._M_finished() == true, false))
848 {
849 // Fall Back to First Fit algorithm.
850 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
851 _FFF __fff;
852 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
853
854 if (__bpi != _S_mem_blocks.end())
855 {
856 // Search was successful. Ok, now mark the first bit from
857 // the right as 0, meaning Allocated. This bit is obtained
858 // by calling _M_get() on __fff.
859 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
860 __detail::__bit_allocate(__fff._M_get(), __nz_bit);
861
862 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
863
864 // Now, get the address of the bit we marked as allocated.
865 pointer __ret = reinterpret_cast<pointer>
866 (__bpi->first + __fff._M_offset() + __nz_bit);
867 size_t* __puse_count =
868 reinterpret_cast<size_t*>
869 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
870
871 ++(*__puse_count);
872 return __ret;
873 }
874 else
875 {
876 // Search was unsuccessful. We Add more memory to the
877 // pool by calling _S_refill_pool().
878 _S_refill_pool();
879
880 // _M_Reset the _S_last_request structure to the first
881 // free block's bit map.
882 _S_last_request._M_reset(_S_mem_blocks.size() - 1);
883
884 // Now, mark that bit as allocated.
885 }
886 }
887
888 // _S_last_request holds a pointer to a valid bit map, that
889 // points to a free block in memory.
890 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
891 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
892
893 pointer __ret = reinterpret_cast<pointer>
894 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
895
896 size_t* __puse_count = reinterpret_cast<size_t*>
897 (_S_mem_blocks[_S_last_request._M_where()].first)
898 - (__detail::
899 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
900
901 ++(*__puse_count);
902 return __ret;
903 }
904
905 /** @brief Deallocates memory that belongs to a single object of
906 * size sizeof(_Tp).
907 *
908 * Complexity: O(lg(N)), but the worst case is not hit
909 * often! This is because containers usually deallocate memory
910 * close to each other and this case is handled in O(1) time by
911 * the deallocate function.
912 */
913 void
914 _M_deallocate_single_object(pointer __p) throw()
915 {
916 using std::size_t;
917 #if defined __GTHREADS
918 __scoped_lock __bit_lock(_S_mut);
919 #endif
920 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
921
922 typedef typename _BPVector::iterator _Iterator;
923 typedef typename _BPVector::difference_type _Difference_type;
924
925 _Difference_type __diff;
926 long __displacement;
927
928 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
929
930 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
931 if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
932 {
933 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
934 <= _S_mem_blocks.size() - 1);
935
936 // Initial Assumption was correct!
937 __diff = _S_last_dealloc_index;
938 __displacement = __real_p - _S_mem_blocks[__diff].first;
939 }
940 else
941 {
942 _Iterator _iter = _S_find(__ibt);
943
944 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
945
946 __diff = _iter - _S_mem_blocks.begin();
947 __displacement = __real_p - _S_mem_blocks[__diff].first;
948 _S_last_dealloc_index = __diff;
949 }
950
951 // Get the position of the iterator that has been found.
952 const size_t __rotate = (__displacement
953 % size_t(__detail::bits_per_block));
954 size_t* __bitmapC =
955 reinterpret_cast<size_t*>
956 (_S_mem_blocks[__diff].first) - 1;
957 __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
958
959 __detail::__bit_free(__bitmapC, __rotate);
960 size_t* __puse_count = reinterpret_cast<size_t*>
961 (_S_mem_blocks[__diff].first)
962 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
963
964 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
965
966 --(*__puse_count);
967
968 if (__builtin_expect(*__puse_count == 0, false))
969 {
970 _S_block_size /= 2;
971
972 // We can safely remove this block.
973 // _Block_pair __bp = _S_mem_blocks[__diff];
974 this->_M_insert(__puse_count);
975 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
976
977 // Reset the _S_last_request variable to reflect the
978 // erased block. We do this to protect future requests
979 // after the last block has been removed from a particular
980 // memory Chunk, which in turn has been returned to the
981 // free list, and hence had been erased from the vector,
982 // so the size of the vector gets reduced by 1.
983 if ((_Difference_type)_S_last_request._M_where() >= __diff--)
984 _S_last_request._M_reset(__diff);
985
986 // If the Index into the vector of the region of memory
987 // that might hold the next address that will be passed to
988 // deallocated may have been invalidated due to the above
989 // erase procedure being called on the vector, hence we
990 // try to restore this invariant too.
991 if (_S_last_dealloc_index >= _S_mem_blocks.size())
992 {
993 _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
994 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
995 }
996 }
997 }
998
999 public:
1000 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1001 { }
1002
1003 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT
1004 { }
1005
1006 template<typename _Tp1>
1007 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT
1008 { }
1009
1010 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1011 { }
1012
1013 _GLIBCXX_NODISCARD pointer
1014 allocate(size_type __n)
1015 {
1016 if (__n > this->max_size())
1017 std::__throw_bad_alloc();
1018
1019 #if __cpp_aligned_new
1020 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1021 {
1022 const size_type __b = __n * sizeof(value_type);
1023 std::align_val_t __al = std::align_val_t(alignof(value_type));
1024 return static_cast<pointer>(::operator new(__b, __al));
1025 }
1026 #endif
1027
1028 if (__builtin_expect(__n == 1, true))
1029 return this->_M_allocate_single_object();
1030 else
1031 {
1032 const size_type __b = __n * sizeof(value_type);
1033 return reinterpret_cast<pointer>(::operator new(__b));
1034 }
1035 }
1036
1037 _GLIBCXX_NODISCARD pointer
1038 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1039 { return allocate(__n); }
1040
1041 void
1042 deallocate(pointer __p, size_type __n) throw()
1043 {
1044 if (__builtin_expect(__p != 0, true))
1045 {
1046 #if __cpp_aligned_new
1047 // Types with extended alignment are handled by operator delete.
1048 if (alignof(value_type) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
1049 {
1050 ::operator delete(__p, std::align_val_t(alignof(value_type)));
1051 return;
1052 }
1053 #endif
1054
1055 if (__builtin_expect(__n == 1, true))
1056 this->_M_deallocate_single_object(__p);
1057 else
1058 ::operator delete(__p);
1059 }
1060 }
1061
1062 pointer
1063 address(reference __r) const _GLIBCXX_NOEXCEPT
1064 { return std::__addressof(__r); }
1065
1066 const_pointer
1067 address(const_reference __r) const _GLIBCXX_NOEXCEPT
1068 { return std::__addressof(__r); }
1069
1070 size_type
1071 max_size() const _GLIBCXX_USE_NOEXCEPT
1072 { return size_type(-1) / sizeof(value_type); }
1073
1074 #if __cplusplus >= 201103L
1075 template<typename _Up, typename... _Args>
1076 void
1077 construct(_Up* __p, _Args&&... __args)
1078 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
1079
1080 template<typename _Up>
1081 void
1082 destroy(_Up* __p)
1083 { __p->~_Up(); }
1084 #else
1085 void
1086 construct(pointer __p, const_reference __data)
1087 { ::new((void *)__p) value_type(__data); }
1088
1089 void
1090 destroy(pointer __p)
1091 { __p->~value_type(); }
1092 #endif
1093 };
1094
1095 template<typename _Tp1, typename _Tp2>
1096 bool
1097 operator==(const bitmap_allocator<_Tp1>&,
1098 const bitmap_allocator<_Tp2>&) throw()
1099 { return true; }
1100
1101 #if __cpp_impl_three_way_comparison < 201907L
1102 template<typename _Tp1, typename _Tp2>
1103 bool
1104 operator!=(const bitmap_allocator<_Tp1>&,
1105 const bitmap_allocator<_Tp2>&) throw()
1106 { return false; }
1107 #endif
1108
1109 // Static member definitions.
1110 template<typename _Tp>
1111 typename bitmap_allocator<_Tp>::_BPVector
1112 bitmap_allocator<_Tp>::_S_mem_blocks;
1113
1114 template<typename _Tp>
1115 std::size_t bitmap_allocator<_Tp>::_S_block_size
1116 = 2 * std::size_t(__detail::bits_per_block);
1117
1118 template<typename _Tp>
1119 typename bitmap_allocator<_Tp>::_BPVector::size_type
1120 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1121
1122 template<typename _Tp>
1123 __detail::_Bitmap_counter
1124 <typename bitmap_allocator<_Tp>::_Alloc_block*>
1125 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1126
1127 #if defined __GTHREADS
1128 template<typename _Tp>
1129 typename bitmap_allocator<_Tp>::__mutex_type
1130 bitmap_allocator<_Tp>::_S_mut;
1131 #endif
1132
1133 _GLIBCXX_END_NAMESPACE_VERSION
1134 } // namespace __gnu_cxx
1135
1136 #endif
1137