libstdc++
bitmap_allocator.h
Go to the documentation of this file.
1 // Bitmap Allocator. -*- C++ -*-
2 
3 // Copyright (C) 2004-2014 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>
70  {
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>
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>
332  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
333  {
334  typedef typename std::pair<_Tp, _Tp> _Block_pair;
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>
397  {
398  typedef typename
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 
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;
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 
pointer _M_allocate_single_object()
Allocates memory for a single object of size sizeof(_Tp).
Struct holding two objects of arbitrary type.
Definition: stl_pair.h:96
size_t __num_bitmaps(_AddrPair __ap)
The number of Bit-maps pointed to by the address pair passed to the function.
constexpr pair< typename __decay_and_strip< _T1 >::__type, typename __decay_and_strip< _T2 >::__type > make_pair(_T1 &&__x, _T2 &&__y)
A convenience wrapper for creating a pair from two objects.
Definition: stl_pair.h:276
constexpr const _Tp * begin(initializer_list< _Tp > __ils) noexcept
Return an iterator pointing to the first element of the initializer_list.
The free list class for managing chunks of memory to be given to and returned by the bitmap_allocator...
void _M_deallocate_single_object(pointer __p)
Deallocates memory that belongs to a single object of size sizeof(_Tp).
size_t * _M_get(size_t __sz)
This function gets a block of memory of the specified size from the free list.
Bitmap Allocator, primary template.
void __bit_free(size_t *__pbmap, size_t __pos)
Mark a memory address as free by setting the corresponding bit in the bit-map.
Common iterator class.
constexpr size_t size() const noexcept
Returns the total number of bits.
Definition: bitset:1293
Exception possibly thrown by new.bad_alloc (or classes derived from it) is used to report allocation ...
Definition: new:54
void __bit_allocate(size_t *__pbmap, size_t __pos)
Mark a memory address as allocated by re-setting the corresponding bit in the bit-map.
The class which acts as a predicate for applying the first-fit memory allocation policy for the bitma...
size_t _Bit_scan_forward(size_t __num)
Generic Version of the bsf instruction.
void __rotate(_ForwardIterator __first, _ForwardIterator __middle, _ForwardIterator __last, forward_iterator_tag)
This is a helper function for the rotate algorithm.
Definition: stl_algo.h:1243
#define _BALLOC_ALIGN_BYTES
The constant in the expression below is the alignment required in bytes.
size_t __num_blocks(_AddrPair __ap)
The number of Blocks pointed to by the address pair passed to the function.
Scoped lock idiom.
Definition: concurrence.h:231
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:76
void _M_clear()
This function just clears the internal Free List, and gives back all the memory to the OS...
_T1 first
second_type is the second bound type
Definition: stl_pair.h:101
void _M_insert(size_t *__addr)
This function returns the block of memory to the internal free list.
One of the comparison functors.
Definition: stl_function.h:381
One of the comparison functors.
Definition: stl_function.h:372
The bitmap counter which acts as the bitmap manipulator, and manages the bit-manipulation functions a...
constexpr const _Tp * end(initializer_list< _Tp > __ils) noexcept
Return an iterator pointing to one past the last element of the initializer_list. ...
integral_constant
Definition: type_traits:57
_Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:47
__mini_vector<> is a stripped down version of the full-fledged std::vector<>.