libstdc++
bitmap_allocator.h
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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 <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 _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>
68  {
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>
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>
330  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
331  {
332  typedef typename std::pair<_Tp, _Tp> _Block_pair;
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>
396  {
397  typedef typename
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 
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;
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
653  };
654 
655 
656  // Forward declare the class.
657  template<typename _Tp>
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
__gnu_cxx::bitmap_allocator::_M_allocate_single_object
pointer _M_allocate_single_object()
Allocates memory for a single object of size sizeof(_Tp).
Definition: bitmap_allocator.h:823
__gnu_cxx::__detail::__bit_allocate
void __bit_allocate(std::size_t *__pbmap, std::size_t __pos)
Mark a memory address as allocated by re-setting the corresponding bit in the bit-map.
Definition: bitmap_allocator.h:487
__gnu_cxx::__detail::__num_blocks
std::size_t __num_blocks(_AddrPair __ap)
The number of Blocks pointed to by the address pair passed to the function.
Definition: bitmap_allocator.h:266
__gnu_cxx::__detail::__mini_vector
__mini_vector<> is a stripped down version of the full-fledged std::vector<>.
Definition: bitmap_allocator.h:68
std::pair::first
_T1 first
The first member.
Definition: stl_pair.h:217
__gnu_cxx::_Bit_scan_forward
std::size_t _Bit_scan_forward(std::size_t __num)
Generic Version of the bsf instruction.
Definition: bitmap_allocator.h:508
functexcept.h
std
ISO C++ entities toplevel namespace is std.
std::bad_alloc
Exception possibly thrown by new.
Definition: new:56
_BALLOC_ALIGN_BYTES
#define _BALLOC_ALIGN_BYTES
The constant in the expression below is the alignment required in bytes.
Definition: bitmap_allocator.h:43
__gnu_cxx::bitmap_allocator::_M_deallocate_single_object
void _M_deallocate_single_object(pointer __p)
Deallocates memory that belongs to a single object of size sizeof(_Tp).
Definition: bitmap_allocator.h:914
__gnu_cxx::bitmap_allocator
Bitmap Allocator, primary template.
Definition: bitmap_allocator.h:658
utility
move.h
std::unary_function
Definition: stl_function.h:106
__gnu_cxx
GNU extensions for public use.
__gnu_cxx::__detail::__num_bitmaps
std::size_t __num_bitmaps(_AddrPair __ap)
The number of Bit-maps pointed to by the address pair passed to the function.
Definition: bitmap_allocator.h:274
std::end
_Tp * end(valarray< _Tp > &__va)
Return an iterator pointing to one past the last element of the valarray.
Definition: valarray:1234
__gnu_cxx::free_list
The free list class for managing chunks of memory to be given to and returned by the bitmap_allocator...
Definition: bitmap_allocator.h:517
__gnu_cxx::__detail::__bit_free
void __bit_free(std::size_t *__pbmap, std::size_t __pos)
Mark a memory address as free by setting the corresponding bit in the bit-map.
Definition: bitmap_allocator.h:498
std::integral_constant
integral_constant
Definition: type_traits:58
std::begin
_Tp * begin(valarray< _Tp > &__va)
Return an iterator pointing to the first element of the valarray.
Definition: valarray:1214
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
new
__gnu_cxx::free_list::_M_get
std::size_t * _M_get(std::size_t __sz)
This function gets a block of memory of the specified size from the free list.
concurrence.h
std::less_equal
One of the comparison functors.
Definition: stl_function.h:346
debug.h
__gnu_cxx::free_list::_M_clear
void _M_clear()
This function just clears the internal Free List, and gives back all the memory to the OS.
__gnu_cxx::__detail::_Bitmap_counter
The bitmap counter which acts as the bitmap manipulator, and manages the bit-manipulation functions a...
Definition: bitmap_allocator.h:396
__gnu_cxx::free_list::_M_insert
void _M_insert(std::size_t *__addr)
This function returns the block of memory to the internal free list.
Definition: bitmap_allocator.h:626
std::pair
Struct holding two objects of arbitrary type.
Definition: stl_pair.h:213
std::greater_equal
One of the comparison functors.
Definition: stl_function.h:343
__gnu_cxx::__scoped_lock
Scoped lock idiom.
Definition: concurrence.h:229
functional
__gnu_cxx::__detail::_Ffit_finder
The class which acts as a predicate for applying the first-fit memory allocation policy for the bitma...
Definition: bitmap_allocator.h:331