libstdc++

bitmap_allocator.h
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1 // Bitmap Allocator. -*- C++ -*-
2
3 // Copyright (C) 2004-2013 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /** @file ext/bitmap_allocator.h
26 * This file is a GNU extension to the Standard C++ Library.
27 */
28
29 #ifndef _BITMAP_ALLOCATOR_H
30 #define _BITMAP_ALLOCATOR_H 1
31
32 #include <utility> // For std::pair.
33 #include <bits/functexcept.h> // For __throw_bad_alloc().
34 #include <functional> // For greater_equal, and less_equal.
35 #include <new> // For operator new.
36 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
37 #include <ext/concurrence.h>
38 #include <bits/move.h>
39
40 /** @brief The constant in the expression below is the alignment
41 * required in bytes.
42 */
43 #define _BALLOC_ALIGN_BYTES 8
44
45 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
46 {
47 using std::size_t;
48 using std::ptrdiff_t;
49
50 namespace __detail
51 {
52 _GLIBCXX_BEGIN_NAMESPACE_VERSION
53 /** @class __mini_vector bitmap_allocator.h bitmap_allocator.h
54 *
55 * @brief __mini_vector<> is a stripped down version of the
56 * full-fledged std::vector<>.
57 *
58 * It is to be used only for built-in types or PODs. Notable
59 * differences are:
60 *
61 * 1. Not all accessor functions are present.
62 * 2. Used ONLY for PODs.
63 * 3. No Allocator template argument. Uses ::operator new() to get
64 * memory, and ::operator delete() to free it.
65 * Caveat: The dtor does NOT free the memory allocated, so this a
66 * memory-leaking vector!
67 */
68 template<typename _Tp>
69 class __mini_vector
70 {
71 __mini_vector(const __mini_vector&);
72 __mini_vector& operator=(const __mini_vector&);
73
74 public:
75 typedef _Tp value_type;
76 typedef _Tp* pointer;
77 typedef _Tp& reference;
78 typedef const _Tp& const_reference;
79 typedef size_t size_type;
80 typedef ptrdiff_t difference_type;
81 typedef pointer iterator;
82
83 private:
84 pointer _M_start;
85 pointer _M_finish;
86 pointer _M_end_of_storage;
87
88 size_type
89 _M_space_left() const throw()
90 { return _M_end_of_storage - _M_finish; }
91
92 pointer
93 allocate(size_type __n)
94 { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
95
96 void
97 deallocate(pointer __p, size_type)
98 { ::operator delete(__p); }
99
100 public:
101 // Members used: size(), push_back(), pop_back(),
102 // insert(iterator, const_reference), erase(iterator),
103 // begin(), end(), back(), operator[].
104
105 __mini_vector()
106 : _M_start(0), _M_finish(0), _M_end_of_storage(0) { }
107
108 size_type
109 size() const throw()
110 { return _M_finish - _M_start; }
111
112 iterator
113 begin() const throw()
114 { return this->_M_start; }
115
116 iterator
117 end() const throw()
118 { return this->_M_finish; }
119
120 reference
121 back() const throw()
122 { return *(this->end() - 1); }
123
124 reference
125 operator[](const size_type __pos) const throw()
126 { return this->_M_start[__pos]; }
127
128 void
129 insert(iterator __pos, const_reference __x);
130
131 void
132 push_back(const_reference __x)
133 {
134 if (this->_M_space_left())
135 {
136 *this->end() = __x;
137 ++this->_M_finish;
138 }
139 else
140 this->insert(this->end(), __x);
141 }
142
143 void
144 pop_back() throw()
145 { --this->_M_finish; }
146
147 void
148 erase(iterator __pos) throw();
149
150 void
151 clear() throw()
152 { this->_M_finish = this->_M_start; }
153 };
154
155 // Out of line function definitions.
156 template<typename _Tp>
157 void __mini_vector<_Tp>::
158 insert(iterator __pos, const_reference __x)
159 {
160 if (this->_M_space_left())
161 {
162 size_type __to_move = this->_M_finish - __pos;
163 iterator __dest = this->end();
164 iterator __src = this->end() - 1;
165
166 ++this->_M_finish;
167 while (__to_move)
168 {
169 *__dest = *__src;
170 --__dest; --__src; --__to_move;
171 }
172 *__pos = __x;
173 }
174 else
175 {
176 size_type __new_size = this->size() ? this->size() * 2 : 1;
177 iterator __new_start = this->allocate(__new_size);
178 iterator __first = this->begin();
179 iterator __start = __new_start;
180 while (__first != __pos)
181 {
182 *__start = *__first;
183 ++__start; ++__first;
184 }
185 *__start = __x;
186 ++__start;
187 while (__first != this->end())
188 {
189 *__start = *__first;
190 ++__start; ++__first;
191 }
192 if (this->_M_start)
193 this->deallocate(this->_M_start, this->size());
194
195 this->_M_start = __new_start;
196 this->_M_finish = __start;
197 this->_M_end_of_storage = this->_M_start + __new_size;
198 }
199 }
200
201 template<typename _Tp>
202 void __mini_vector<_Tp>::
203 erase(iterator __pos) throw()
204 {
205 while (__pos + 1 != this->end())
206 {
207 *__pos = __pos[1];
208 ++__pos;
209 }
210 --this->_M_finish;
211 }
212
213
214 template<typename _Tp>
215 struct __mv_iter_traits
216 {
217 typedef typename _Tp::value_type value_type;
218 typedef typename _Tp::difference_type difference_type;
219 };
220
221 template<typename _Tp>
222 struct __mv_iter_traits<_Tp*>
223 {
224 typedef _Tp value_type;
225 typedef ptrdiff_t difference_type;
226 };
227
228 enum
229 {
230 bits_per_byte = 8,
231 bits_per_block = sizeof(size_t) * size_t(bits_per_byte)
232 };
233
234 template<typename _ForwardIterator, typename _Tp, typename _Compare>
235 _ForwardIterator
236 __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
237 const _Tp& __val, _Compare __comp)
238 {
239 typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
240 _DistanceType;
241
242 _DistanceType __len = __last - __first;
243 _DistanceType __half;
244 _ForwardIterator __middle;
245
246 while (__len > 0)
247 {
248 __half = __len >> 1;
249 __middle = __first;
250 __middle += __half;
251 if (__comp(*__middle, __val))
252 {
253 __first = __middle;
254 ++__first;
255 __len = __len - __half - 1;
256 }
257 else
258 __len = __half;
259 }
260 return __first;
261 }
262
263 /** @brief The number of Blocks pointed to by the address pair
264 * passed to the function.
265 */
266 template<typename _AddrPair>
267 inline size_t
268 __num_blocks(_AddrPair __ap)
269 { return (__ap.second - __ap.first) + 1; }
270
271 /** @brief The number of Bit-maps pointed to by the address pair
272 * passed to the function.
273 */
274 template<typename _AddrPair>
275 inline size_t
276 __num_bitmaps(_AddrPair __ap)
277 { return __num_blocks(__ap) / size_t(bits_per_block); }
278
279 // _Tp should be a pointer type.
280 template<typename _Tp>
281 class _Inclusive_between
282 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
283 {
284 typedef _Tp pointer;
285 pointer _M_ptr_value;
286 typedef typename std::pair<_Tp, _Tp> _Block_pair;
287
288 public:
289 _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
290 { }
291
292 bool
293 operator()(_Block_pair __bp) const throw()
294 {
295 if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
296 && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
297 return true;
298 else
299 return false;
300 }
301 };
302
303 // Used to pass a Functor to functions by reference.
304 template<typename _Functor>
305 class _Functor_Ref
306 : public std::unary_function<typename _Functor::argument_type,
307 typename _Functor::result_type>
308 {
309 _Functor& _M_fref;
310
311 public:
312 typedef typename _Functor::argument_type argument_type;
313 typedef typename _Functor::result_type result_type;
314
315 _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
316 { }
317
318 result_type
319 operator()(argument_type __arg)
320 { return _M_fref(__arg); }
321 };
322
323 /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
324 *
325 * @brief The class which acts as a predicate for applying the
326 * first-fit memory allocation policy for the bitmap allocator.
327 */
328 // _Tp should be a pointer type, and _Alloc is the Allocator for
329 // the vector.
330 template<typename _Tp>
331 class _Ffit_finder
332 : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
333 {
334 typedef typename std::pair<_Tp, _Tp> _Block_pair;
335 typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
336 typedef typename _BPVector::difference_type _Counter_type;
337
338 size_t* _M_pbitmap;
339 _Counter_type _M_data_offset;
340
341 public:
342 _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
343 { }
344
345 bool
346 operator()(_Block_pair __bp) throw()
347 {
348 // Set the _rover to the last physical location bitmap,
349 // which is the bitmap which belongs to the first free
350 // block. Thus, the bitmaps are in exact reverse order of
351 // the actual memory layout. So, we count down the bitmaps,
352 // which is the same as moving up the memory.
353
354 // If the used count stored at the start of the Bit Map headers
355 // is equal to the number of Objects that the current Block can
356 // store, then there is definitely no space for another single
357 // object, so just return false.
358 _Counter_type __diff = __detail::__num_bitmaps(__bp);
359
360 if (*(reinterpret_cast<size_t*>
361 (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
362 return false;
363
364 size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
365
366 for (_Counter_type __i = 0; __i < __diff; ++__i)
367 {
368 _M_data_offset = __i;
369 if (*__rover)
370 {
371 _M_pbitmap = __rover;
372 return true;
373 }
374 --__rover;
375 }
376 return false;
377 }
378
379 size_t*
380 _M_get() const throw()
381 { return _M_pbitmap; }
382
383 _Counter_type
384 _M_offset() const throw()
385 { return _M_data_offset * size_t(bits_per_block); }
386 };
387
388 /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
389 *
390 * @brief The bitmap counter which acts as the bitmap
391 * manipulator, and manages the bit-manipulation functions and
392 * the searching and identification functions on the bit-map.
393 */
394 // _Tp should be a pointer type.
395 template<typename _Tp>
396 class _Bitmap_counter
397 {
398 typedef typename
399 __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector;
400 typedef typename _BPVector::size_type _Index_type;
401 typedef _Tp pointer;
402
403 _BPVector& _M_vbp;
404 size_t* _M_curr_bmap;
405 size_t* _M_last_bmap_in_block;
406 _Index_type _M_curr_index;
407
408 public:
409 // Use the 2nd parameter with care. Make sure that such an
410 // entry exists in the vector before passing that particular
411 // index to this ctor.
412 _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
413 { this->_M_reset(__index); }
414
415 void
416 _M_reset(long __index = -1) throw()
417 {
418 if (__index == -1)
419 {
420 _M_curr_bmap = 0;
421 _M_curr_index = static_cast<_Index_type>(-1);
422 return;
423 }
424
425 _M_curr_index = __index;
426 _M_curr_bmap = reinterpret_cast<size_t*>
427 (_M_vbp[_M_curr_index].first) - 1;
428
429 _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
430
431 _M_last_bmap_in_block = _M_curr_bmap
432 - ((_M_vbp[_M_curr_index].second
433 - _M_vbp[_M_curr_index].first + 1)
434 / size_t(bits_per_block) - 1);
435 }
436
437 // Dangerous Function! Use with extreme care. Pass to this
438 // function ONLY those values that are known to be correct,
439 // otherwise this will mess up big time.
440 void
441 _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
442 { _M_curr_bmap = __new_internal_marker; }
443
444 bool
445 _M_finished() const throw()
446 { return(_M_curr_bmap == 0); }
447
448 _Bitmap_counter&
449 operator++() throw()
450 {
451 if (_M_curr_bmap == _M_last_bmap_in_block)
452 {
453 if (++_M_curr_index == _M_vbp.size())
454 _M_curr_bmap = 0;
455 else
456 this->_M_reset(_M_curr_index);
457 }
458 else
459 --_M_curr_bmap;
460 return *this;
461 }
462
463 size_t*
464 _M_get() const throw()
465 { return _M_curr_bmap; }
466
467 pointer
468 _M_base() const throw()
469 { return _M_vbp[_M_curr_index].first; }
470
471 _Index_type
472 _M_offset() const throw()
473 {
474 return size_t(bits_per_block)
475 * ((reinterpret_cast<size_t*>(this->_M_base())
476 - _M_curr_bmap) - 1);
477 }
478
479 _Index_type
480 _M_where() const throw()
481 { return _M_curr_index; }
482 };
483
484 /** @brief Mark a memory address as allocated by re-setting the
485 * corresponding bit in the bit-map.
486 */
487 inline void
488 __bit_allocate(size_t* __pbmap, size_t __pos) throw()
489 {
490 size_t __mask = 1 << __pos;
491 __mask = ~__mask;
492 *__pbmap &= __mask;
493 }
494
495 /** @brief Mark a memory address as free by setting the
496 * corresponding bit in the bit-map.
497 */
498 inline void
499 __bit_free(size_t* __pbmap, size_t __pos) throw()
500 {
501 size_t __mask = 1 << __pos;
502 *__pbmap |= __mask;
503 }
504
505 _GLIBCXX_END_NAMESPACE_VERSION
506 } // namespace __detail
507
508 _GLIBCXX_BEGIN_NAMESPACE_VERSION
509
510 /** @brief Generic Version of the bsf instruction.
511 */
512 inline size_t
513 _Bit_scan_forward(size_t __num)
514 { return static_cast<size_t>(__builtin_ctzl(__num)); }
515
516 /** @class free_list bitmap_allocator.h bitmap_allocator.h
517 *
518 * @brief The free list class for managing chunks of memory to be
519 * given to and returned by the bitmap_allocator.
520 */
521 class free_list
522 {
523 public:
524 typedef size_t* value_type;
525 typedef __detail::__mini_vector<value_type> vector_type;
526 typedef vector_type::iterator iterator;
527 typedef __mutex __mutex_type;
528
529 private:
530 struct _LT_pointer_compare
531 {
532 bool
533 operator()(const size_t* __pui,
534 const size_t __cui) const throw()
535 { return *__pui < __cui; }
536 };
537
538 #if defined __GTHREADS
539 __mutex_type&
540 _M_get_mutex()
541 {
542 static __mutex_type _S_mutex;
543 return _S_mutex;
544 }
545 #endif
546
547 vector_type&
548 _M_get_free_list()
549 {
550 static vector_type _S_free_list;
551 return _S_free_list;
552 }
553
554 /** @brief Performs validation of memory based on their size.
555 *
556 * @param __addr The pointer to the memory block to be
557 * validated.
558 *
559 * Validates the memory block passed to this function and
560 * appropriately performs the action of managing the free list of
561 * blocks by adding this block to the free list or deleting this
562 * or larger blocks from the free list.
563 */
564 void
565 _M_validate(size_t* __addr) throw()
566 {
567 vector_type& __free_list = _M_get_free_list();
568 const vector_type::size_type __max_size = 64;
569 if (__free_list.size() >= __max_size)
570 {
571 // Ok, the threshold value has been reached. We determine
572 // which block to remove from the list of free blocks.
573 if (*__addr >= *__free_list.back())
574 {
575 // Ok, the new block is greater than or equal to the
576 // last block in the list of free blocks. We just free
577 // the new block.
578 ::operator delete(static_cast<void*>(__addr));
579 return;
580 }
581 else
582 {
583 // Deallocate the last block in the list of free lists,
584 // and insert the new one in its correct position.
585 ::operator delete(static_cast<void*>(__free_list.back()));
586 __free_list.pop_back();
587 }
588 }
589
590 // Just add the block to the list of free lists unconditionally.
591 iterator __temp = __detail::__lower_bound
592 (__free_list.begin(), __free_list.end(),
593 *__addr, _LT_pointer_compare());
594
595 // We may insert the new free list before _temp;
596 __free_list.insert(__temp, __addr);
597 }
598
599 /** @brief Decides whether the wastage of memory is acceptable for
600 * the current memory request and returns accordingly.
601 *
602 * @param __block_size The size of the block available in the free
603 * list.
604 *
605 * @param __required_size The required size of the memory block.
606 *
607 * @return true if the wastage incurred is acceptable, else returns
608 * false.
609 */
610 bool
611 _M_should_i_give(size_t __block_size,
612 size_t __required_size) throw()
613 {
614 const size_t __max_wastage_percentage = 36;
615 if (__block_size >= __required_size &&
616 (((__block_size - __required_size) * 100 / __block_size)
617 < __max_wastage_percentage))
618 return true;
619 else
620 return false;
621 }
622
623 public:
624 /** @brief This function returns the block of memory to the
625 * internal free list.
626 *
627 * @param __addr The pointer to the memory block that was given
628 * by a call to the _M_get function.
629 */
630 inline void
631 _M_insert(size_t* __addr) throw()
632 {
633 #if defined __GTHREADS
634 __scoped_lock __bfl_lock(_M_get_mutex());
635 #endif
636 // Call _M_validate to decide what should be done with
637 // this particular free list.
638 this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
639 // See discussion as to why this is 1!
640 }
641
642 /** @brief This function gets a block of memory of the specified
643 * size from the free list.
644 *
645 * @param __sz The size in bytes of the memory required.
646 *
647 * @return A pointer to the new memory block of size at least
648 * equal to that requested.
649 */
650 size_t*
651 _M_get(size_t __sz) throw(std::bad_alloc);
652
653 /** @brief This function just clears the internal Free List, and
654 * gives back all the memory to the OS.
655 */
656 void
657 _M_clear();
658 };
659
660
661 // Forward declare the class.
662 template<typename _Tp>
663 class bitmap_allocator;
664
665 // Specialize for void:
666 template<>
667 class bitmap_allocator<void>
668 {
669 public:
670 typedef void* pointer;
671 typedef const void* const_pointer;
672
673 // Reference-to-void members are impossible.
674 typedef void value_type;
675 template<typename _Tp1>
676 struct rebind
677 {
678 typedef bitmap_allocator<_Tp1> other;
679 };
680 };
681
682 /**
683 * @brief Bitmap Allocator, primary template.
684 * @ingroup allocators
685 */
686 template<typename _Tp>
687 class bitmap_allocator : private free_list
688 {
689 public:
690 typedef size_t size_type;
691 typedef ptrdiff_t difference_type;
692 typedef _Tp* pointer;
693 typedef const _Tp* const_pointer;
694 typedef _Tp& reference;
695 typedef const _Tp& const_reference;
696 typedef _Tp value_type;
697 typedef free_list::__mutex_type __mutex_type;
698
699 template<typename _Tp1>
700 struct rebind
701 {
702 typedef bitmap_allocator<_Tp1> other;
703 };
704
705 #if __cplusplus >= 201103L
706 // _GLIBCXX_RESOLVE_LIB_DEFECTS
707 // 2103. propagate_on_container_move_assignment
708 typedef std::true_type propagate_on_container_move_assignment;
709 #endif
710
711 private:
712 template<size_t _BSize, size_t _AlignSize>
713 struct aligned_size
714 {
715 enum
716 {
717 modulus = _BSize % _AlignSize,
718 value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
719 };
720 };
721
722 struct _Alloc_block
723 {
724 char __M_unused[aligned_size<sizeof(value_type),
725 _BALLOC_ALIGN_BYTES>::value];
726 };
727
728
729 typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
730
731 typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
732 typedef typename _BPVector::iterator _BPiter;
733
734 template<typename _Predicate>
735 static _BPiter
736 _S_find(_Predicate __p)
737 {
738 _BPiter __first = _S_mem_blocks.begin();
739 while (__first != _S_mem_blocks.end() && !__p(*__first))
740 ++__first;
741 return __first;
742 }
743
744 #if defined _GLIBCXX_DEBUG
745 // Complexity: O(lg(N)). Where, N is the number of block of size
746 // sizeof(value_type).
747 void
748 _S_check_for_free_blocks() throw()
749 {
750 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
751 _BPiter __bpi = _S_find(_FFF());
752
753 _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
754 }
755 #endif
756
757 /** @brief Responsible for exponentially growing the internal
758 * memory pool.
759 *
760 * @throw std::bad_alloc. If memory can not be allocated.
761 *
762 * Complexity: O(1), but internally depends upon the
763 * complexity of the function free_list::_M_get. The part where
764 * the bitmap headers are written has complexity: O(X),where X
765 * is the number of blocks of size sizeof(value_type) within
766 * the newly acquired block. Having a tight bound.
767 */
768 void
769 _S_refill_pool() throw(std::bad_alloc)
770 {
771 #if defined _GLIBCXX_DEBUG
772 _S_check_for_free_blocks();
773 #endif
774
775 const size_t __num_bitmaps = (_S_block_size
776 / size_t(__detail::bits_per_block));
777 const size_t __size_to_allocate = sizeof(size_t)
778 + _S_block_size * sizeof(_Alloc_block)
779 + __num_bitmaps * sizeof(size_t);
780
781 size_t* __temp =
782 reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate));
783 *__temp = 0;
784 ++__temp;
785
786 // The Header information goes at the Beginning of the Block.
787 _Block_pair __bp =
788 std::make_pair(reinterpret_cast<_Alloc_block*>
789 (__temp + __num_bitmaps),
790 reinterpret_cast<_Alloc_block*>
791 (__temp + __num_bitmaps)
792 + _S_block_size - 1);
793
794 // Fill the Vector with this information.
795 _S_mem_blocks.push_back(__bp);
796
797 for (size_t __i = 0; __i < __num_bitmaps; ++__i)
798 __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free.
799
800 _S_block_size *= 2;
801 }
802
803 static _BPVector _S_mem_blocks;
804 static size_t _S_block_size;
805 static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request;
806 static typename _BPVector::size_type _S_last_dealloc_index;
807 #if defined __GTHREADS
808 static __mutex_type _S_mut;
809 #endif
810
811 public:
812
813 /** @brief Allocates memory for a single object of size
814 * sizeof(_Tp).
815 *
816 * @throw std::bad_alloc. If memory can not be allocated.
817 *
818 * Complexity: Worst case complexity is O(N), but that
819 * is hardly ever hit. If and when this particular case is
820 * encountered, the next few cases are guaranteed to have a
821 * worst case complexity of O(1)! That's why this function
822 * performs very well on average. You can consider this
823 * function to have a complexity referred to commonly as:
824 * Amortized Constant time.
825 */
826 pointer
827 _M_allocate_single_object() throw(std::bad_alloc)
828 {
829 #if defined __GTHREADS
830 __scoped_lock __bit_lock(_S_mut);
831 #endif
832
833 // The algorithm is something like this: The last_request
834 // variable points to the last accessed Bit Map. When such a
835 // condition occurs, we try to find a free block in the
836 // current bitmap, or succeeding bitmaps until the last bitmap
837 // is reached. If no free block turns up, we resort to First
838 // Fit method.
839
840 // WARNING: Do not re-order the condition in the while
841 // statement below, because it relies on C++'s short-circuit
842 // evaluation. The return from _S_last_request->_M_get() will
843 // NOT be dereference able if _S_last_request->_M_finished()
844 // returns true. This would inevitably lead to a NULL pointer
845 // dereference if tinkered with.
846 while (_S_last_request._M_finished() == false
847 && (*(_S_last_request._M_get()) == 0))
848 _S_last_request.operator++();
849
850 if (__builtin_expect(_S_last_request._M_finished() == true, false))
851 {
852 // Fall Back to First Fit algorithm.
853 typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
854 _FFF __fff;
855 _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
856
857 if (__bpi != _S_mem_blocks.end())
858 {
859 // Search was successful. Ok, now mark the first bit from
860 // the right as 0, meaning Allocated. This bit is obtained
861 // by calling _M_get() on __fff.
862 size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
863 __detail::__bit_allocate(__fff._M_get(), __nz_bit);
864
865 _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
866
867 // Now, get the address of the bit we marked as allocated.
868 pointer __ret = reinterpret_cast<pointer>
869 (__bpi->first + __fff._M_offset() + __nz_bit);
870 size_t* __puse_count =
871 reinterpret_cast<size_t*>
872 (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
873
874 ++(*__puse_count);
875 return __ret;
876 }
877 else
878 {
879 // Search was unsuccessful. We Add more memory to the
880 // pool by calling _S_refill_pool().
881 _S_refill_pool();
882
883 // _M_Reset the _S_last_request structure to the first
884 // free block's bit map.
885 _S_last_request._M_reset(_S_mem_blocks.size() - 1);
886
887 // Now, mark that bit as allocated.
888 }
889 }
890
891 // _S_last_request holds a pointer to a valid bit map, that
892 // points to a free block in memory.
893 size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
894 __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
895
896 pointer __ret = reinterpret_cast<pointer>
897 (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
898
899 size_t* __puse_count = reinterpret_cast<size_t*>
900 (_S_mem_blocks[_S_last_request._M_where()].first)
901 - (__detail::
902 __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
903
904 ++(*__puse_count);
905 return __ret;
906 }
907
908 /** @brief Deallocates memory that belongs to a single object of
909 * size sizeof(_Tp).
910 *
911 * Complexity: O(lg(N)), but the worst case is not hit
912 * often! This is because containers usually deallocate memory
913 * close to each other and this case is handled in O(1) time by
914 * the deallocate function.
915 */
916 void
917 _M_deallocate_single_object(pointer __p) throw()
918 {
919 #if defined __GTHREADS
920 __scoped_lock __bit_lock(_S_mut);
921 #endif
922 _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
923
924 typedef typename _BPVector::iterator _Iterator;
925 typedef typename _BPVector::difference_type _Difference_type;
926
927 _Difference_type __diff;
928 long __displacement;
929
930 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
931
932 __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
933 if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
934 {
935 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
936 <= _S_mem_blocks.size() - 1);
937
938 // Initial Assumption was correct!
939 __diff = _S_last_dealloc_index;
940 __displacement = __real_p - _S_mem_blocks[__diff].first;
941 }
942 else
943 {
944 _Iterator _iter = _S_find(__ibt);
945
946 _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
947
948 __diff = _iter - _S_mem_blocks.begin();
949 __displacement = __real_p - _S_mem_blocks[__diff].first;
950 _S_last_dealloc_index = __diff;
951 }
952
953 // Get the position of the iterator that has been found.
954 const size_t __rotate = (__displacement
955 % size_t(__detail::bits_per_block));
956 size_t* __bitmapC =
957 reinterpret_cast<size_t*>
958 (_S_mem_blocks[__diff].first) - 1;
959 __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
960
961 __detail::__bit_free(__bitmapC, __rotate);
962 size_t* __puse_count = reinterpret_cast<size_t*>
963 (_S_mem_blocks[__diff].first)
964 - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
965
966 _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
967
968 --(*__puse_count);
969
970 if (__builtin_expect(*__puse_count == 0, false))
971 {
972 _S_block_size /= 2;
973
974 // We can safely remove this block.
975 // _Block_pair __bp = _S_mem_blocks[__diff];
976 this->_M_insert(__puse_count);
977 _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
978
979 // Reset the _S_last_request variable to reflect the
980 // erased block. We do this to protect future requests
981 // after the last block has been removed from a particular
982 // memory Chunk, which in turn has been returned to the
983 // free list, and hence had been erased from the vector,
984 // so the size of the vector gets reduced by 1.
985 if ((_Difference_type)_S_last_request._M_where() >= __diff--)
986 _S_last_request._M_reset(__diff);
987
988 // If the Index into the vector of the region of memory
989 // that might hold the next address that will be passed to
990 // deallocated may have been invalidated due to the above
991 // erase procedure being called on the vector, hence we
992 // try to restore this invariant too.
993 if (_S_last_dealloc_index >= _S_mem_blocks.size())
994 {
995 _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
996 _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
997 }
998 }
999 }
1000
1001 public:
1002 bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1003 { }
1004
1005 bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT
1006 { }
1007
1008 template<typename _Tp1>
1009 bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT
1010 { }
1011
1012 ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1013 { }
1014
1015 pointer
1016 allocate(size_type __n)
1017 {
1018 if (__n > this->max_size())
1019 std::__throw_bad_alloc();
1020
1021 if (__builtin_expect(__n == 1, true))
1022 return this->_M_allocate_single_object();
1023 else
1024 {
1025 const size_type __b = __n * sizeof(value_type);
1026 return reinterpret_cast<pointer>(::operator new(__b));
1027 }
1028 }
1029
1030 pointer
1031 allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1032 { return allocate(__n); }
1033
1034 void
1035 deallocate(pointer __p, size_type __n) throw()
1036 {
1037 if (__builtin_expect(__p != 0, true))
1038 {
1039 if (__builtin_expect(__n == 1, true))
1040 this->_M_deallocate_single_object(__p);
1041 else
1042 ::operator delete(__p);
1043 }
1044 }
1045
1046 pointer
1047 address(reference __r) const _GLIBCXX_NOEXCEPT
1048 { return std::__addressof(__r); }
1049
1050 const_pointer
1051 address(const_reference __r) const _GLIBCXX_NOEXCEPT
1052 { return std::__addressof(__r); }
1053
1054 size_type
1055 max_size() const _GLIBCXX_USE_NOEXCEPT
1056 { return size_type(-1) / sizeof(value_type); }
1057
1058 #if __cplusplus >= 201103L
1059 template<typename _Up, typename... _Args>
1060 void
1061 construct(_Up* __p, _Args&&... __args)
1062 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
1063
1064 template<typename _Up>
1065 void
1066 destroy(_Up* __p)
1067 { __p->~_Up(); }
1068 #else
1069 void
1070 construct(pointer __p, const_reference __data)
1071 { ::new((void *)__p) value_type(__data); }
1072
1073 void
1074 destroy(pointer __p)
1075 { __p->~value_type(); }
1076 #endif
1077 };
1078
1079 template<typename _Tp1, typename _Tp2>
1080 bool
1081 operator==(const bitmap_allocator<_Tp1>&,
1082 const bitmap_allocator<_Tp2>&) throw()
1083 { return true; }
1084
1085 template<typename _Tp1, typename _Tp2>
1086 bool
1087 operator!=(const bitmap_allocator<_Tp1>&,
1088 const bitmap_allocator<_Tp2>&) throw()
1089 { return false; }
1090
1091 // Static member definitions.
1092 template<typename _Tp>
1093 typename bitmap_allocator<_Tp>::_BPVector
1094 bitmap_allocator<_Tp>::_S_mem_blocks;
1095
1096 template<typename _Tp>
1097 size_t bitmap_allocator<_Tp>::_S_block_size =
1098 2 * size_t(__detail::bits_per_block);
1099
1100 template<typename _Tp>
1101 typename bitmap_allocator<_Tp>::_BPVector::size_type
1102 bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1103
1104 template<typename _Tp>
1105 __detail::_Bitmap_counter
1106 <typename bitmap_allocator<_Tp>::_Alloc_block*>
1107 bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1108
1109 #if defined __GTHREADS
1110 template<typename _Tp>
1111 typename bitmap_allocator<_Tp>::__mutex_type
1112 bitmap_allocator<_Tp>::_S_mut;
1113 #endif
1114
1115 _GLIBCXX_END_NAMESPACE_VERSION
1116 } // namespace __gnu_cxx
1117
1118 #endif
1119