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bitmap_allocator.h
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1 // Bitmap Allocator. -*- C++ -*-
2 
3 // Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
4 // Free Software Foundation, Inc.
5 //
6 // This file is part of the GNU ISO C++ Library. This library is free
7 // software; you can redistribute it and/or modify it under the
8 // terms of the GNU General Public License as published by the
9 // Free Software Foundation; either version 3, or (at your option)
10 // any later version.
11 
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
16 
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
20 
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
25 
26 /** @file ext/bitmap_allocator.h
27  * This file is a GNU extension to the Standard C++ Library.
28  */
29 
30 #ifndef _BITMAP_ALLOCATOR_H
31 #define _BITMAP_ALLOCATOR_H 1
32 
33 #include <utility> // For std::pair.
34 #include <bits/functexcept.h> // For __throw_bad_alloc().
35 #include <functional> // For greater_equal, and less_equal.
36 #include <new> // For operator new.
37 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
38 #include <ext/concurrence.h>
39 #include <bits/move.h>
40 
41 /** @brief The constant in the expression below is the alignment
42  * required in bytes.
43  */
44 #define _BALLOC_ALIGN_BYTES 8
45 
46 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
47 {
48  using std::size_t;
49  using std::ptrdiff_t;
50 
51  namespace __detail
52  {
53  _GLIBCXX_BEGIN_NAMESPACE_VERSION
54  /** @class __mini_vector bitmap_allocator.h bitmap_allocator.h
55  *
56  * @brief __mini_vector<> is a stripped down version of the
57  * full-fledged std::vector<>.
58  *
59  * It is to be used only for built-in types or PODs. Notable
60  * differences are:
61  *
62  * 1. Not all accessor functions are present.
63  * 2. Used ONLY for PODs.
64  * 3. No Allocator template argument. Uses ::operator new() to get
65  * memory, and ::operator delete() to free it.
66  * Caveat: The dtor does NOT free the memory allocated, so this a
67  * memory-leaking vector!
68  */
69  template<typename _Tp>
71  {
73  __mini_vector& operator=(const __mini_vector&);
74 
75  public:
76  typedef _Tp value_type;
77  typedef _Tp* pointer;
78  typedef _Tp& reference;
79  typedef const _Tp& const_reference;
80  typedef size_t size_type;
81  typedef ptrdiff_t difference_type;
82  typedef pointer iterator;
83 
84  private:
85  pointer _M_start;
86  pointer _M_finish;
87  pointer _M_end_of_storage;
88 
89  size_type
90  _M_space_left() const throw()
91  { return _M_end_of_storage - _M_finish; }
92 
93  pointer
94  allocate(size_type __n)
95  { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
96 
97  void
98  deallocate(pointer __p, size_type)
99  { ::operator delete(__p); }
100 
101  public:
102  // Members used: size(), push_back(), pop_back(),
103  // insert(iterator, const_reference), erase(iterator),
104  // begin(), end(), back(), operator[].
105 
106  __mini_vector()
107  : _M_start(0), _M_finish(0), _M_end_of_storage(0) { }
108 
109  size_type
110  size() const throw()
111  { return _M_finish - _M_start; }
112 
113  iterator
114  begin() const throw()
115  { return this->_M_start; }
116 
117  iterator
118  end() const throw()
119  { return this->_M_finish; }
120 
121  reference
122  back() const throw()
123  { return *(this->end() - 1); }
124 
125  reference
126  operator[](const size_type __pos) const throw()
127  { return this->_M_start[__pos]; }
128 
129  void
130  insert(iterator __pos, const_reference __x);
131 
132  void
133  push_back(const_reference __x)
134  {
135  if (this->_M_space_left())
136  {
137  *this->end() = __x;
138  ++this->_M_finish;
139  }
140  else
141  this->insert(this->end(), __x);
142  }
143 
144  void
145  pop_back() throw()
146  { --this->_M_finish; }
147 
148  void
149  erase(iterator __pos) throw();
150 
151  void
152  clear() throw()
153  { this->_M_finish = this->_M_start; }
154  };
155 
156  // Out of line function definitions.
157  template<typename _Tp>
159  insert(iterator __pos, const_reference __x)
160  {
161  if (this->_M_space_left())
162  {
163  size_type __to_move = this->_M_finish - __pos;
164  iterator __dest = this->end();
165  iterator __src = this->end() - 1;
166 
167  ++this->_M_finish;
168  while (__to_move)
169  {
170  *__dest = *__src;
171  --__dest; --__src; --__to_move;
172  }
173  *__pos = __x;
174  }
175  else
176  {
177  size_type __new_size = this->size() ? this->size() * 2 : 1;
178  iterator __new_start = this->allocate(__new_size);
179  iterator __first = this->begin();
180  iterator __start = __new_start;
181  while (__first != __pos)
182  {
183  *__start = *__first;
184  ++__start; ++__first;
185  }
186  *__start = __x;
187  ++__start;
188  while (__first != this->end())
189  {
190  *__start = *__first;
191  ++__start; ++__first;
192  }
193  if (this->_M_start)
194  this->deallocate(this->_M_start, this->size());
195 
196  this->_M_start = __new_start;
197  this->_M_finish = __start;
198  this->_M_end_of_storage = this->_M_start + __new_size;
199  }
200  }
201 
202  template<typename _Tp>
203  void __mini_vector<_Tp>::
204  erase(iterator __pos) throw()
205  {
206  while (__pos + 1 != this->end())
207  {
208  *__pos = __pos[1];
209  ++__pos;
210  }
211  --this->_M_finish;
212  }
213 
214 
215  template<typename _Tp>
216  struct __mv_iter_traits
217  {
218  typedef typename _Tp::value_type value_type;
219  typedef typename _Tp::difference_type difference_type;
220  };
221 
222  template<typename _Tp>
223  struct __mv_iter_traits<_Tp*>
224  {
225  typedef _Tp value_type;
226  typedef ptrdiff_t difference_type;
227  };
228 
229  enum
230  {
231  bits_per_byte = 8,
232  bits_per_block = sizeof(size_t) * size_t(bits_per_byte)
233  };
234 
235  template<typename _ForwardIterator, typename _Tp, typename _Compare>
236  _ForwardIterator
237  __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
238  const _Tp& __val, _Compare __comp)
239  {
240  typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
241  _DistanceType;
242 
243  _DistanceType __len = __last - __first;
244  _DistanceType __half;
245  _ForwardIterator __middle;
246 
247  while (__len > 0)
248  {
249  __half = __len >> 1;
250  __middle = __first;
251  __middle += __half;
252  if (__comp(*__middle, __val))
253  {
254  __first = __middle;
255  ++__first;
256  __len = __len - __half - 1;
257  }
258  else
259  __len = __half;
260  }
261  return __first;
262  }
263 
264  /** @brief The number of Blocks pointed to by the address pair
265  * passed to the function.
266  */
267  template<typename _AddrPair>
268  inline size_t
269  __num_blocks(_AddrPair __ap)
270  { return (__ap.second - __ap.first) + 1; }
271 
272  /** @brief The number of Bit-maps pointed to by the address pair
273  * passed to the function.
274  */
275  template<typename _AddrPair>
276  inline size_t
277  __num_bitmaps(_AddrPair __ap)
278  { return __num_blocks(__ap) / size_t(bits_per_block); }
279 
280  // _Tp should be a pointer type.
281  template<typename _Tp>
282  class _Inclusive_between
283  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
284  {
285  typedef _Tp pointer;
286  pointer _M_ptr_value;
287  typedef typename std::pair<_Tp, _Tp> _Block_pair;
288 
289  public:
290  _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
291  { }
292 
293  bool
294  operator()(_Block_pair __bp) const throw()
295  {
296  if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
297  && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
298  return true;
299  else
300  return false;
301  }
302  };
303 
304  // Used to pass a Functor to functions by reference.
305  template<typename _Functor>
306  class _Functor_Ref
307  : public std::unary_function<typename _Functor::argument_type,
308  typename _Functor::result_type>
309  {
310  _Functor& _M_fref;
311 
312  public:
313  typedef typename _Functor::argument_type argument_type;
314  typedef typename _Functor::result_type result_type;
315 
316  _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
317  { }
318 
319  result_type
320  operator()(argument_type __arg)
321  { return _M_fref(__arg); }
322  };
323 
324  /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
325  *
326  * @brief The class which acts as a predicate for applying the
327  * first-fit memory allocation policy for the bitmap allocator.
328  */
329  // _Tp should be a pointer type, and _Alloc is the Allocator for
330  // the vector.
331  template<typename _Tp>
333  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
334  {
335  typedef typename std::pair<_Tp, _Tp> _Block_pair;
337  typedef typename _BPVector::difference_type _Counter_type;
338 
339  size_t* _M_pbitmap;
340  _Counter_type _M_data_offset;
341 
342  public:
343  _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
344  { }
345 
346  bool
347  operator()(_Block_pair __bp) throw()
348  {
349  // Set the _rover to the last physical location bitmap,
350  // which is the bitmap which belongs to the first free
351  // block. Thus, the bitmaps are in exact reverse order of
352  // the actual memory layout. So, we count down the bitmaps,
353  // which is the same as moving up the memory.
354 
355  // If the used count stored at the start of the Bit Map headers
356  // is equal to the number of Objects that the current Block can
357  // store, then there is definitely no space for another single
358  // object, so just return false.
359  _Counter_type __diff = __detail::__num_bitmaps(__bp);
360 
361  if (*(reinterpret_cast<size_t*>
362  (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
363  return false;
364 
365  size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
366 
367  for (_Counter_type __i = 0; __i < __diff; ++__i)
368  {
369  _M_data_offset = __i;
370  if (*__rover)
371  {
372  _M_pbitmap = __rover;
373  return true;
374  }
375  --__rover;
376  }
377  return false;
378  }
379 
380  size_t*
381  _M_get() const throw()
382  { return _M_pbitmap; }
383 
384  _Counter_type
385  _M_offset() const throw()
386  { return _M_data_offset * size_t(bits_per_block); }
387  };
388 
389  /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
390  *
391  * @brief The bitmap counter which acts as the bitmap
392  * manipulator, and manages the bit-manipulation functions and
393  * the searching and identification functions on the bit-map.
394  */
395  // _Tp should be a pointer type.
396  template<typename _Tp>
398  {
399  typedef typename
401  typedef typename _BPVector::size_type _Index_type;
402  typedef _Tp pointer;
403 
404  _BPVector& _M_vbp;
405  size_t* _M_curr_bmap;
406  size_t* _M_last_bmap_in_block;
407  _Index_type _M_curr_index;
408 
409  public:
410  // Use the 2nd parameter with care. Make sure that such an
411  // entry exists in the vector before passing that particular
412  // index to this ctor.
413  _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
414  { this->_M_reset(__index); }
415 
416  void
417  _M_reset(long __index = -1) throw()
418  {
419  if (__index == -1)
420  {
421  _M_curr_bmap = 0;
422  _M_curr_index = static_cast<_Index_type>(-1);
423  return;
424  }
425 
426  _M_curr_index = __index;
427  _M_curr_bmap = reinterpret_cast<size_t*>
428  (_M_vbp[_M_curr_index].first) - 1;
429 
430  _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
431 
432  _M_last_bmap_in_block = _M_curr_bmap
433  - ((_M_vbp[_M_curr_index].second
434  - _M_vbp[_M_curr_index].first + 1)
435  / size_t(bits_per_block) - 1);
436  }
437 
438  // Dangerous Function! Use with extreme care. Pass to this
439  // function ONLY those values that are known to be correct,
440  // otherwise this will mess up big time.
441  void
442  _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
443  { _M_curr_bmap = __new_internal_marker; }
444 
445  bool
446  _M_finished() const throw()
447  { return(_M_curr_bmap == 0); }
448 
450  operator++() throw()
451  {
452  if (_M_curr_bmap == _M_last_bmap_in_block)
453  {
454  if (++_M_curr_index == _M_vbp.size())
455  _M_curr_bmap = 0;
456  else
457  this->_M_reset(_M_curr_index);
458  }
459  else
460  --_M_curr_bmap;
461  return *this;
462  }
463 
464  size_t*
465  _M_get() const throw()
466  { return _M_curr_bmap; }
467 
468  pointer
469  _M_base() const throw()
470  { return _M_vbp[_M_curr_index].first; }
471 
472  _Index_type
473  _M_offset() const throw()
474  {
475  return size_t(bits_per_block)
476  * ((reinterpret_cast<size_t*>(this->_M_base())
477  - _M_curr_bmap) - 1);
478  }
479 
480  _Index_type
481  _M_where() const throw()
482  { return _M_curr_index; }
483  };
484 
485  /** @brief Mark a memory address as allocated by re-setting the
486  * corresponding bit in the bit-map.
487  */
488  inline void
489  __bit_allocate(size_t* __pbmap, size_t __pos) throw()
490  {
491  size_t __mask = 1 << __pos;
492  __mask = ~__mask;
493  *__pbmap &= __mask;
494  }
495 
496  /** @brief Mark a memory address as free by setting the
497  * corresponding bit in the bit-map.
498  */
499  inline void
500  __bit_free(size_t* __pbmap, size_t __pos) throw()
501  {
502  size_t __mask = 1 << __pos;
503  *__pbmap |= __mask;
504  }
505 
506  _GLIBCXX_END_NAMESPACE_VERSION
507  } // namespace __detail
508 
509 _GLIBCXX_BEGIN_NAMESPACE_VERSION
510 
511  /** @brief Generic Version of the bsf instruction.
512  */
513  inline size_t
514  _Bit_scan_forward(size_t __num)
515  { return static_cast<size_t>(__builtin_ctzl(__num)); }
516 
517  /** @class free_list bitmap_allocator.h bitmap_allocator.h
518  *
519  * @brief The free list class for managing chunks of memory to be
520  * given to and returned by the bitmap_allocator.
521  */
522  class free_list
523  {
524  public:
525  typedef size_t* value_type;
527  typedef vector_type::iterator iterator;
528  typedef __mutex __mutex_type;
529 
530  private:
531  struct _LT_pointer_compare
532  {
533  bool
534  operator()(const size_t* __pui,
535  const size_t __cui) const throw()
536  { return *__pui < __cui; }
537  };
538 
539 #if defined __GTHREADS
540  __mutex_type&
541  _M_get_mutex()
542  {
543  static __mutex_type _S_mutex;
544  return _S_mutex;
545  }
546 #endif
547 
548  vector_type&
549  _M_get_free_list()
550  {
551  static vector_type _S_free_list;
552  return _S_free_list;
553  }
554 
555  /** @brief Performs validation of memory based on their size.
556  *
557  * @param __addr The pointer to the memory block to be
558  * validated.
559  *
560  * Validates the memory block passed to this function and
561  * appropriately performs the action of managing the free list of
562  * blocks by adding this block to the free list or deleting this
563  * or larger blocks from the free list.
564  */
565  void
566  _M_validate(size_t* __addr) throw()
567  {
568  vector_type& __free_list = _M_get_free_list();
569  const vector_type::size_type __max_size = 64;
570  if (__free_list.size() >= __max_size)
571  {
572  // Ok, the threshold value has been reached. We determine
573  // which block to remove from the list of free blocks.
574  if (*__addr >= *__free_list.back())
575  {
576  // Ok, the new block is greater than or equal to the
577  // last block in the list of free blocks. We just free
578  // the new block.
579  ::operator delete(static_cast<void*>(__addr));
580  return;
581  }
582  else
583  {
584  // Deallocate the last block in the list of free lists,
585  // and insert the new one in its correct position.
586  ::operator delete(static_cast<void*>(__free_list.back()));
587  __free_list.pop_back();
588  }
589  }
590 
591  // Just add the block to the list of free lists unconditionally.
592  iterator __temp = __detail::__lower_bound
593  (__free_list.begin(), __free_list.end(),
594  *__addr, _LT_pointer_compare());
595 
596  // We may insert the new free list before _temp;
597  __free_list.insert(__temp, __addr);
598  }
599 
600  /** @brief Decides whether the wastage of memory is acceptable for
601  * the current memory request and returns accordingly.
602  *
603  * @param __block_size The size of the block available in the free
604  * list.
605  *
606  * @param __required_size The required size of the memory block.
607  *
608  * @return true if the wastage incurred is acceptable, else returns
609  * false.
610  */
611  bool
612  _M_should_i_give(size_t __block_size,
613  size_t __required_size) throw()
614  {
615  const size_t __max_wastage_percentage = 36;
616  if (__block_size >= __required_size &&
617  (((__block_size - __required_size) * 100 / __block_size)
618  < __max_wastage_percentage))
619  return true;
620  else
621  return false;
622  }
623 
624  public:
625  /** @brief This function returns the block of memory to the
626  * internal free list.
627  *
628  * @param __addr The pointer to the memory block that was given
629  * by a call to the _M_get function.
630  */
631  inline void
632  _M_insert(size_t* __addr) throw()
633  {
634 #if defined __GTHREADS
635  __scoped_lock __bfl_lock(_M_get_mutex());
636 #endif
637  // Call _M_validate to decide what should be done with
638  // this particular free list.
639  this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
640  // See discussion as to why this is 1!
641  }
642 
643  /** @brief This function gets a block of memory of the specified
644  * size from the free list.
645  *
646  * @param __sz The size in bytes of the memory required.
647  *
648  * @return A pointer to the new memory block of size at least
649  * equal to that requested.
650  */
651  size_t*
652  _M_get(size_t __sz) throw(std::bad_alloc);
653 
654  /** @brief This function just clears the internal Free List, and
655  * gives back all the memory to the OS.
656  */
657  void
658  _M_clear();
659  };
660 
661 
662  // Forward declare the class.
663  template<typename _Tp>
664  class bitmap_allocator;
665 
666  // Specialize for void:
667  template<>
668  class bitmap_allocator<void>
669  {
670  public:
671  typedef void* pointer;
672  typedef const void* const_pointer;
673 
674  // Reference-to-void members are impossible.
675  typedef void value_type;
676  template<typename _Tp1>
677  struct rebind
678  {
679  typedef bitmap_allocator<_Tp1> other;
680  };
681  };
682 
683  /**
684  * @brief Bitmap Allocator, primary template.
685  * @ingroup allocators
686  */
687  template<typename _Tp>
688  class bitmap_allocator : private free_list
689  {
690  public:
691  typedef size_t size_type;
692  typedef ptrdiff_t difference_type;
693  typedef _Tp* pointer;
694  typedef const _Tp* const_pointer;
695  typedef _Tp& reference;
696  typedef const _Tp& const_reference;
697  typedef _Tp value_type;
698  typedef free_list::__mutex_type __mutex_type;
699 
700  template<typename _Tp1>
701  struct rebind
702  {
703  typedef bitmap_allocator<_Tp1> other;
704  };
705 
706  private:
707  template<size_t _BSize, 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 
725 
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 can not 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() throw(std::bad_alloc)
765  {
766 #if defined _GLIBCXX_DEBUG
767  _S_check_for_free_blocks();
768 #endif
769 
770  const size_t __num_bitmaps = (_S_block_size
771  / size_t(__detail::bits_per_block));
772  const size_t __size_to_allocate = sizeof(size_t)
773  + _S_block_size * sizeof(_Alloc_block)
774  + __num_bitmaps * sizeof(size_t);
775 
776  size_t* __temp =
777  reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate));
778  *__temp = 0;
779  ++__temp;
780 
781  // The Header information goes at the Beginning of the Block.
782  _Block_pair __bp =
783  std::make_pair(reinterpret_cast<_Alloc_block*>
784  (__temp + __num_bitmaps),
785  reinterpret_cast<_Alloc_block*>
786  (__temp + __num_bitmaps)
787  + _S_block_size - 1);
788 
789  // Fill the Vector with this information.
790  _S_mem_blocks.push_back(__bp);
791 
792  for (size_t __i = 0; __i < __num_bitmaps; ++__i)
793  __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free.
794 
795  _S_block_size *= 2;
796  }
797 
798  static _BPVector _S_mem_blocks;
799  static size_t _S_block_size;
800  static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request;
801  static typename _BPVector::size_type _S_last_dealloc_index;
802 #if defined __GTHREADS
803  static __mutex_type _S_mut;
804 #endif
805 
806  public:
807 
808  /** @brief Allocates memory for a single object of size
809  * sizeof(_Tp).
810  *
811  * @throw std::bad_alloc. If memory can not be allocated.
812  *
813  * Complexity: Worst case complexity is O(N), but that
814  * is hardly ever hit. If and when this particular case is
815  * encountered, the next few cases are guaranteed to have a
816  * worst case complexity of O(1)! That's why this function
817  * performs very well on average. You can consider this
818  * function to have a complexity referred to commonly as:
819  * Amortized Constant time.
820  */
821  pointer
822  _M_allocate_single_object() throw(std::bad_alloc)
823  {
824 #if defined __GTHREADS
825  __scoped_lock __bit_lock(_S_mut);
826 #endif
827 
828  // The algorithm is something like this: The last_request
829  // variable points to the last accessed Bit Map. When such a
830  // condition occurs, we try to find a free block in the
831  // current bitmap, or succeeding bitmaps until the last bitmap
832  // is reached. If no free block turns up, we resort to First
833  // Fit method.
834 
835  // WARNING: Do not re-order the condition in the while
836  // statement below, because it relies on C++'s short-circuit
837  // evaluation. The return from _S_last_request->_M_get() will
838  // NOT be dereference able if _S_last_request->_M_finished()
839  // returns true. This would inevitably lead to a NULL pointer
840  // dereference if tinkered with.
841  while (_S_last_request._M_finished() == false
842  && (*(_S_last_request._M_get()) == 0))
843  _S_last_request.operator++();
844 
845  if (__builtin_expect(_S_last_request._M_finished() == true, false))
846  {
847  // Fall Back to First Fit algorithm.
848  typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
849  _FFF __fff;
850  _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
851 
852  if (__bpi != _S_mem_blocks.end())
853  {
854  // Search was successful. Ok, now mark the first bit from
855  // the right as 0, meaning Allocated. This bit is obtained
856  // by calling _M_get() on __fff.
857  size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
858  __detail::__bit_allocate(__fff._M_get(), __nz_bit);
859 
860  _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
861 
862  // Now, get the address of the bit we marked as allocated.
863  pointer __ret = reinterpret_cast<pointer>
864  (__bpi->first + __fff._M_offset() + __nz_bit);
865  size_t* __puse_count =
866  reinterpret_cast<size_t*>
867  (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
868 
869  ++(*__puse_count);
870  return __ret;
871  }
872  else
873  {
874  // Search was unsuccessful. We Add more memory to the
875  // pool by calling _S_refill_pool().
876  _S_refill_pool();
877 
878  // _M_Reset the _S_last_request structure to the first
879  // free block's bit map.
880  _S_last_request._M_reset(_S_mem_blocks.size() - 1);
881 
882  // Now, mark that bit as allocated.
883  }
884  }
885 
886  // _S_last_request holds a pointer to a valid bit map, that
887  // points to a free block in memory.
888  size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
889  __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
890 
891  pointer __ret = reinterpret_cast<pointer>
892  (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
893 
894  size_t* __puse_count = reinterpret_cast<size_t*>
895  (_S_mem_blocks[_S_last_request._M_where()].first)
896  - (__detail::
897  __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
898 
899  ++(*__puse_count);
900  return __ret;
901  }
902 
903  /** @brief Deallocates memory that belongs to a single object of
904  * size sizeof(_Tp).
905  *
906  * Complexity: O(lg(N)), but the worst case is not hit
907  * often! This is because containers usually deallocate memory
908  * close to each other and this case is handled in O(1) time by
909  * the deallocate function.
910  */
911  void
912  _M_deallocate_single_object(pointer __p) throw()
913  {
914 #if defined __GTHREADS
915  __scoped_lock __bit_lock(_S_mut);
916 #endif
917  _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
918 
919  typedef typename _BPVector::iterator _Iterator;
920  typedef typename _BPVector::difference_type _Difference_type;
921 
922  _Difference_type __diff;
923  long __displacement;
924 
925  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
926 
927  __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
928  if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
929  {
930  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
931  <= _S_mem_blocks.size() - 1);
932 
933  // Initial Assumption was correct!
934  __diff = _S_last_dealloc_index;
935  __displacement = __real_p - _S_mem_blocks[__diff].first;
936  }
937  else
938  {
939  _Iterator _iter = _S_find(__ibt);
940 
941  _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
942 
943  __diff = _iter - _S_mem_blocks.begin();
944  __displacement = __real_p - _S_mem_blocks[__diff].first;
945  _S_last_dealloc_index = __diff;
946  }
947 
948  // Get the position of the iterator that has been found.
949  const size_t __rotate = (__displacement
950  % size_t(__detail::bits_per_block));
951  size_t* __bitmapC =
952  reinterpret_cast<size_t*>
953  (_S_mem_blocks[__diff].first) - 1;
954  __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
955 
956  __detail::__bit_free(__bitmapC, __rotate);
957  size_t* __puse_count = reinterpret_cast<size_t*>
958  (_S_mem_blocks[__diff].first)
959  - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
960 
961  _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
962 
963  --(*__puse_count);
964 
965  if (__builtin_expect(*__puse_count == 0, false))
966  {
967  _S_block_size /= 2;
968 
969  // We can safely remove this block.
970  // _Block_pair __bp = _S_mem_blocks[__diff];
971  this->_M_insert(__puse_count);
972  _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
973 
974  // Reset the _S_last_request variable to reflect the
975  // erased block. We do this to protect future requests
976  // after the last block has been removed from a particular
977  // memory Chunk, which in turn has been returned to the
978  // free list, and hence had been erased from the vector,
979  // so the size of the vector gets reduced by 1.
980  if ((_Difference_type)_S_last_request._M_where() >= __diff--)
981  _S_last_request._M_reset(__diff);
982 
983  // If the Index into the vector of the region of memory
984  // that might hold the next address that will be passed to
985  // deallocated may have been invalidated due to the above
986  // erase procedure being called on the vector, hence we
987  // try to restore this invariant too.
988  if (_S_last_dealloc_index >= _S_mem_blocks.size())
989  {
990  _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
991  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
992  }
993  }
994  }
995 
996  public:
997  bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
998  { }
999 
1000  bitmap_allocator(const bitmap_allocator&) _GLIBCXX_USE_NOEXCEPT
1001  { }
1002 
1003  template<typename _Tp1>
1004  bitmap_allocator(const bitmap_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT
1005  { }
1006 
1007  ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
1008  { }
1009 
1010  pointer
1011  allocate(size_type __n)
1012  {
1013  if (__n > this->max_size())
1014  std::__throw_bad_alloc();
1015 
1016  if (__builtin_expect(__n == 1, true))
1017  return this->_M_allocate_single_object();
1018  else
1019  {
1020  const size_type __b = __n * sizeof(value_type);
1021  return reinterpret_cast<pointer>(::operator new(__b));
1022  }
1023  }
1024 
1025  pointer
1026  allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1027  { return allocate(__n); }
1028 
1029  void
1030  deallocate(pointer __p, size_type __n) throw()
1031  {
1032  if (__builtin_expect(__p != 0, true))
1033  {
1034  if (__builtin_expect(__n == 1, true))
1035  this->_M_deallocate_single_object(__p);
1036  else
1037  ::operator delete(__p);
1038  }
1039  }
1040 
1041  pointer
1042  address(reference __r) const _GLIBCXX_NOEXCEPT
1043  { return std::__addressof(__r); }
1044 
1045  const_pointer
1046  address(const_reference __r) const _GLIBCXX_NOEXCEPT
1047  { return std::__addressof(__r); }
1048 
1049  size_type
1050  max_size() const _GLIBCXX_USE_NOEXCEPT
1051  { return size_type(-1) / sizeof(value_type); }
1052 
1053 #ifdef __GXX_EXPERIMENTAL_CXX0X__
1054  template<typename _Up, typename... _Args>
1055  void
1056  construct(_Up* __p, _Args&&... __args)
1057  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
1058 
1059  template<typename _Up>
1060  void
1061  destroy(_Up* __p)
1062  { __p->~_Up(); }
1063 #else
1064  void
1065  construct(pointer __p, const_reference __data)
1066  { ::new((void *)__p) value_type(__data); }
1067 
1068  void
1069  destroy(pointer __p)
1070  { __p->~value_type(); }
1071 #endif
1072  };
1073 
1074  template<typename _Tp1, typename _Tp2>
1075  bool
1076  operator==(const bitmap_allocator<_Tp1>&,
1077  const bitmap_allocator<_Tp2>&) throw()
1078  { return true; }
1079 
1080  template<typename _Tp1, typename _Tp2>
1081  bool
1082  operator!=(const bitmap_allocator<_Tp1>&,
1083  const bitmap_allocator<_Tp2>&) throw()
1084  { return false; }
1085 
1086  // Static member definitions.
1087  template<typename _Tp>
1088  typename bitmap_allocator<_Tp>::_BPVector
1089  bitmap_allocator<_Tp>::_S_mem_blocks;
1090 
1091  template<typename _Tp>
1092  size_t bitmap_allocator<_Tp>::_S_block_size =
1093  2 * size_t(__detail::bits_per_block);
1094 
1095  template<typename _Tp>
1096  typename bitmap_allocator<_Tp>::_BPVector::size_type
1097  bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1098 
1099  template<typename _Tp>
1100  __detail::_Bitmap_counter
1101  <typename bitmap_allocator<_Tp>::_Alloc_block*>
1102  bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1103 
1104 #if defined __GTHREADS
1105  template<typename _Tp>
1106  typename bitmap_allocator<_Tp>::__mutex_type
1107  bitmap_allocator<_Tp>::_S_mut;
1108 #endif
1109 
1110 _GLIBCXX_END_NAMESPACE_VERSION
1111 } // namespace __gnu_cxx
1112 
1113 #endif
1114