libstdc++
bitmap_allocator.h
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1 // Bitmap Allocator. -*- C++ -*-
2 
3 // Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
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 <cstddef> // For std::size_t, and ptrdiff_t.
34 #include <bits/functexcept.h> // For __throw_bad_alloc().
35 #include <utility> // For std::pair.
36 #include <functional> // For greater_equal, and less_equal.
37 #include <new> // For operator new.
38 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
39 #include <ext/concurrence.h>
40 #include <bits/move.h>
41 
42 /** @brief The constant in the expression below is the alignment
43  * required in bytes.
44  */
45 #define _BALLOC_ALIGN_BYTES 8
46 
47 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
48 
49  using std::size_t;
50  using std::ptrdiff_t;
51 
52  namespace __detail
53  {
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  * @detail
63  * 1. Not all accessor functions are present.
64  * 2. Used ONLY for PODs.
65  * 3. No Allocator template argument. Uses ::operator new() to get
66  * memory, and ::operator delete() to free it.
67  * Caveat: The dtor does NOT free the memory allocated, so this a
68  * memory-leaking vector!
69  */
70  template<typename _Tp>
72  {
74  __mini_vector& operator=(const __mini_vector&);
75 
76  public:
77  typedef _Tp value_type;
78  typedef _Tp* pointer;
79  typedef _Tp& reference;
80  typedef const _Tp& const_reference;
81  typedef size_t size_type;
82  typedef ptrdiff_t difference_type;
83  typedef pointer iterator;
84 
85  private:
86  pointer _M_start;
87  pointer _M_finish;
88  pointer _M_end_of_storage;
89 
90  size_type
91  _M_space_left() const throw()
92  { return _M_end_of_storage - _M_finish; }
93 
94  pointer
95  allocate(size_type __n)
96  { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
97 
98  void
99  deallocate(pointer __p, size_type)
100  { ::operator delete(__p); }
101 
102  public:
103  // Members used: size(), push_back(), pop_back(),
104  // insert(iterator, const_reference), erase(iterator),
105  // begin(), end(), back(), operator[].
106 
107  __mini_vector() : _M_start(0), _M_finish(0),
108  _M_end_of_storage(0)
109  { }
110 
111 #if 0
112  ~__mini_vector()
113  {
114  if (this->_M_start)
115  {
116  this->deallocate(this->_M_start, this->_M_end_of_storage
117  - this->_M_start);
118  }
119  }
120 #endif
121 
122  size_type
123  size() const throw()
124  { return _M_finish - _M_start; }
125 
126  iterator
127  begin() const throw()
128  { return this->_M_start; }
129 
130  iterator
131  end() const throw()
132  { return this->_M_finish; }
133 
134  reference
135  back() const throw()
136  { return *(this->end() - 1); }
137 
138  reference
139  operator[](const size_type __pos) const throw()
140  { return this->_M_start[__pos]; }
141 
142  void
143  insert(iterator __pos, const_reference __x);
144 
145  void
146  push_back(const_reference __x)
147  {
148  if (this->_M_space_left())
149  {
150  *this->end() = __x;
151  ++this->_M_finish;
152  }
153  else
154  this->insert(this->end(), __x);
155  }
156 
157  void
158  pop_back() throw()
159  { --this->_M_finish; }
160 
161  void
162  erase(iterator __pos) throw();
163 
164  void
165  clear() throw()
166  { this->_M_finish = this->_M_start; }
167  };
168 
169  // Out of line function definitions.
170  template<typename _Tp>
172  insert(iterator __pos, const_reference __x)
173  {
174  if (this->_M_space_left())
175  {
176  size_type __to_move = this->_M_finish - __pos;
177  iterator __dest = this->end();
178  iterator __src = this->end() - 1;
179 
180  ++this->_M_finish;
181  while (__to_move)
182  {
183  *__dest = *__src;
184  --__dest; --__src; --__to_move;
185  }
186  *__pos = __x;
187  }
188  else
189  {
190  size_type __new_size = this->size() ? this->size() * 2 : 1;
191  iterator __new_start = this->allocate(__new_size);
192  iterator __first = this->begin();
193  iterator __start = __new_start;
194  while (__first != __pos)
195  {
196  *__start = *__first;
197  ++__start; ++__first;
198  }
199  *__start = __x;
200  ++__start;
201  while (__first != this->end())
202  {
203  *__start = *__first;
204  ++__start; ++__first;
205  }
206  if (this->_M_start)
207  this->deallocate(this->_M_start, this->size());
208 
209  this->_M_start = __new_start;
210  this->_M_finish = __start;
211  this->_M_end_of_storage = this->_M_start + __new_size;
212  }
213  }
214 
215  template<typename _Tp>
216  void __mini_vector<_Tp>::
217  erase(iterator __pos) throw()
218  {
219  while (__pos + 1 != this->end())
220  {
221  *__pos = __pos[1];
222  ++__pos;
223  }
224  --this->_M_finish;
225  }
226 
227 
228  template<typename _Tp>
229  struct __mv_iter_traits
230  {
231  typedef typename _Tp::value_type value_type;
232  typedef typename _Tp::difference_type difference_type;
233  };
234 
235  template<typename _Tp>
236  struct __mv_iter_traits<_Tp*>
237  {
238  typedef _Tp value_type;
239  typedef ptrdiff_t difference_type;
240  };
241 
242  enum
243  {
244  bits_per_byte = 8,
245  bits_per_block = sizeof(size_t) * size_t(bits_per_byte)
246  };
247 
248  template<typename _ForwardIterator, typename _Tp, typename _Compare>
249  _ForwardIterator
250  __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
251  const _Tp& __val, _Compare __comp)
252  {
253  typedef typename __mv_iter_traits<_ForwardIterator>::value_type
254  _ValueType;
255  typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
256  _DistanceType;
257 
258  _DistanceType __len = __last - __first;
259  _DistanceType __half;
260  _ForwardIterator __middle;
261 
262  while (__len > 0)
263  {
264  __half = __len >> 1;
265  __middle = __first;
266  __middle += __half;
267  if (__comp(*__middle, __val))
268  {
269  __first = __middle;
270  ++__first;
271  __len = __len - __half - 1;
272  }
273  else
274  __len = __half;
275  }
276  return __first;
277  }
278 
279  template<typename _InputIterator, typename _Predicate>
280  inline _InputIterator
281  __find_if(_InputIterator __first, _InputIterator __last, _Predicate __p)
282  {
283  while (__first != __last && !__p(*__first))
284  ++__first;
285  return __first;
286  }
287 
288  /** @brief The number of Blocks pointed to by the address pair
289  * passed to the function.
290  */
291  template<typename _AddrPair>
292  inline size_t
293  __num_blocks(_AddrPair __ap)
294  { return (__ap.second - __ap.first) + 1; }
295 
296  /** @brief The number of Bit-maps pointed to by the address pair
297  * passed to the function.
298  */
299  template<typename _AddrPair>
300  inline size_t
301  __num_bitmaps(_AddrPair __ap)
302  { return __num_blocks(__ap) / size_t(bits_per_block); }
303 
304  // _Tp should be a pointer type.
305  template<typename _Tp>
306  class _Inclusive_between
307  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
308  {
309  typedef _Tp pointer;
310  pointer _M_ptr_value;
311  typedef typename std::pair<_Tp, _Tp> _Block_pair;
312 
313  public:
314  _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
315  { }
316 
317  bool
318  operator()(_Block_pair __bp) const throw()
319  {
320  if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
321  && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
322  return true;
323  else
324  return false;
325  }
326  };
327 
328  // Used to pass a Functor to functions by reference.
329  template<typename _Functor>
330  class _Functor_Ref
331  : public std::unary_function<typename _Functor::argument_type,
332  typename _Functor::result_type>
333  {
334  _Functor& _M_fref;
335 
336  public:
337  typedef typename _Functor::argument_type argument_type;
338  typedef typename _Functor::result_type result_type;
339 
340  _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
341  { }
342 
343  result_type
344  operator()(argument_type __arg)
345  { return _M_fref(__arg); }
346  };
347 
348  /** @class _Ffit_finder bitmap_allocator.h bitmap_allocator.h
349  *
350  * @brief The class which acts as a predicate for applying the
351  * first-fit memory allocation policy for the bitmap allocator.
352  */
353  // _Tp should be a pointer type, and _Alloc is the Allocator for
354  // the vector.
355  template<typename _Tp>
357  : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
358  {
359  typedef typename std::pair<_Tp, _Tp> _Block_pair;
361  typedef typename _BPVector::difference_type _Counter_type;
362 
363  size_t* _M_pbitmap;
364  _Counter_type _M_data_offset;
365 
366  public:
367  _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
368  { }
369 
370  bool
371  operator()(_Block_pair __bp) throw()
372  {
373  // Set the _rover to the last physical location bitmap,
374  // which is the bitmap which belongs to the first free
375  // block. Thus, the bitmaps are in exact reverse order of
376  // the actual memory layout. So, we count down the bitmaps,
377  // which is the same as moving up the memory.
378 
379  // If the used count stored at the start of the Bit Map headers
380  // is equal to the number of Objects that the current Block can
381  // store, then there is definitely no space for another single
382  // object, so just return false.
383  _Counter_type __diff =
385 
386  if (*(reinterpret_cast<size_t*>
387  (__bp.first) - (__diff + 1))
389  return false;
390 
391  size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
392 
393  for (_Counter_type __i = 0; __i < __diff; ++__i)
394  {
395  _M_data_offset = __i;
396  if (*__rover)
397  {
398  _M_pbitmap = __rover;
399  return true;
400  }
401  --__rover;
402  }
403  return false;
404  }
405 
406 
407  size_t*
408  _M_get() const throw()
409  { return _M_pbitmap; }
410 
411  _Counter_type
412  _M_offset() const throw()
413  { return _M_data_offset * size_t(bits_per_block); }
414  };
415 
416 
417  /** @class _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
418  *
419  * @brief The bitmap counter which acts as the bitmap
420  * manipulator, and manages the bit-manipulation functions and
421  * the searching and identification functions on the bit-map.
422  */
423  // _Tp should be a pointer type.
424  template<typename _Tp>
426  {
428  _BPVector;
429  typedef typename _BPVector::size_type _Index_type;
430  typedef _Tp pointer;
431 
432  _BPVector& _M_vbp;
433  size_t* _M_curr_bmap;
434  size_t* _M_last_bmap_in_block;
435  _Index_type _M_curr_index;
436 
437  public:
438  // Use the 2nd parameter with care. Make sure that such an
439  // entry exists in the vector before passing that particular
440  // index to this ctor.
441  _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
442  { this->_M_reset(__index); }
443 
444  void
445  _M_reset(long __index = -1) throw()
446  {
447  if (__index == -1)
448  {
449  _M_curr_bmap = 0;
450  _M_curr_index = static_cast<_Index_type>(-1);
451  return;
452  }
453 
454  _M_curr_index = __index;
455  _M_curr_bmap = reinterpret_cast<size_t*>
456  (_M_vbp[_M_curr_index].first) - 1;
457 
458  _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
459 
460  _M_last_bmap_in_block = _M_curr_bmap
461  - ((_M_vbp[_M_curr_index].second
462  - _M_vbp[_M_curr_index].first + 1)
463  / size_t(bits_per_block) - 1);
464  }
465 
466  // Dangerous Function! Use with extreme care. Pass to this
467  // function ONLY those values that are known to be correct,
468  // otherwise this will mess up big time.
469  void
470  _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
471  { _M_curr_bmap = __new_internal_marker; }
472 
473  bool
474  _M_finished() const throw()
475  { return(_M_curr_bmap == 0); }
476 
478  operator++() throw()
479  {
480  if (_M_curr_bmap == _M_last_bmap_in_block)
481  {
482  if (++_M_curr_index == _M_vbp.size())
483  _M_curr_bmap = 0;
484  else
485  this->_M_reset(_M_curr_index);
486  }
487  else
488  --_M_curr_bmap;
489  return *this;
490  }
491 
492  size_t*
493  _M_get() const throw()
494  { return _M_curr_bmap; }
495 
496  pointer
497  _M_base() const throw()
498  { return _M_vbp[_M_curr_index].first; }
499 
500  _Index_type
501  _M_offset() const throw()
502  {
503  return size_t(bits_per_block)
504  * ((reinterpret_cast<size_t*>(this->_M_base())
505  - _M_curr_bmap) - 1);
506  }
507 
508  _Index_type
509  _M_where() const throw()
510  { return _M_curr_index; }
511  };
512 
513  /** @brief Mark a memory address as allocated by re-setting the
514  * corresponding bit in the bit-map.
515  */
516  inline void
517  __bit_allocate(size_t* __pbmap, size_t __pos) throw()
518  {
519  size_t __mask = 1 << __pos;
520  __mask = ~__mask;
521  *__pbmap &= __mask;
522  }
523 
524  /** @brief Mark a memory address as free by setting the
525  * corresponding bit in the bit-map.
526  */
527  inline void
528  __bit_free(size_t* __pbmap, size_t __pos) throw()
529  {
530  size_t __mask = 1 << __pos;
531  *__pbmap |= __mask;
532  }
533  } // namespace __detail
534 
535  /** @brief Generic Version of the bsf instruction.
536  */
537  inline size_t
538  _Bit_scan_forward(size_t __num)
539  { return static_cast<size_t>(__builtin_ctzl(__num)); }
540 
541  /** @class free_list bitmap_allocator.h bitmap_allocator.h
542  *
543  * @brief The free list class for managing chunks of memory to be
544  * given to and returned by the bitmap_allocator.
545  */
546  class free_list
547  {
548  typedef size_t* value_type;
550  typedef vector_type::iterator iterator;
551  typedef __mutex __mutex_type;
552 
553  struct _LT_pointer_compare
554  {
555  bool
556  operator()(const size_t* __pui,
557  const size_t __cui) const throw()
558  { return *__pui < __cui; }
559  };
560 
561 #if defined __GTHREADS
562  __mutex_type&
563  _M_get_mutex()
564  {
565  static __mutex_type _S_mutex;
566  return _S_mutex;
567  }
568 #endif
569 
570  vector_type&
571  _M_get_free_list()
572  {
573  static vector_type _S_free_list;
574  return _S_free_list;
575  }
576 
577  /** @brief Performs validation of memory based on their size.
578  *
579  * @param __addr The pointer to the memory block to be
580  * validated.
581  *
582  * @detail Validates the memory block passed to this function and
583  * appropriately performs the action of managing the free list of
584  * blocks by adding this block to the free list or deleting this
585  * or larger blocks from the free list.
586  */
587  void
588  _M_validate(size_t* __addr) throw()
589  {
590  vector_type& __free_list = _M_get_free_list();
591  const vector_type::size_type __max_size = 64;
592  if (__free_list.size() >= __max_size)
593  {
594  // Ok, the threshold value has been reached. We determine
595  // which block to remove from the list of free blocks.
596  if (*__addr >= *__free_list.back())
597  {
598  // Ok, the new block is greater than or equal to the
599  // last block in the list of free blocks. We just free
600  // the new block.
601  ::operator delete(static_cast<void*>(__addr));
602  return;
603  }
604  else
605  {
606  // Deallocate the last block in the list of free lists,
607  // and insert the new one in its correct position.
608  ::operator delete(static_cast<void*>(__free_list.back()));
609  __free_list.pop_back();
610  }
611  }
612 
613  // Just add the block to the list of free lists unconditionally.
614  iterator __temp = __gnu_cxx::__detail::__lower_bound
615  (__free_list.begin(), __free_list.end(),
616  *__addr, _LT_pointer_compare());
617 
618  // We may insert the new free list before _temp;
619  __free_list.insert(__temp, __addr);
620  }
621 
622  /** @brief Decides whether the wastage of memory is acceptable for
623  * the current memory request and returns accordingly.
624  *
625  * @param __block_size The size of the block available in the free
626  * list.
627  *
628  * @param __required_size The required size of the memory block.
629  *
630  * @return true if the wastage incurred is acceptable, else returns
631  * false.
632  */
633  bool
634  _M_should_i_give(size_t __block_size,
635  size_t __required_size) throw()
636  {
637  const size_t __max_wastage_percentage = 36;
638  if (__block_size >= __required_size &&
639  (((__block_size - __required_size) * 100 / __block_size)
640  < __max_wastage_percentage))
641  return true;
642  else
643  return false;
644  }
645 
646  public:
647  /** @brief This function returns the block of memory to the
648  * internal free list.
649  *
650  * @param __addr The pointer to the memory block that was given
651  * by a call to the _M_get function.
652  */
653  inline void
654  _M_insert(size_t* __addr) throw()
655  {
656 #if defined __GTHREADS
657  __gnu_cxx::__scoped_lock __bfl_lock(_M_get_mutex());
658 #endif
659  // Call _M_validate to decide what should be done with
660  // this particular free list.
661  this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
662  // See discussion as to why this is 1!
663  }
664 
665  /** @brief This function gets a block of memory of the specified
666  * size from the free list.
667  *
668  * @param __sz The size in bytes of the memory required.
669  *
670  * @return A pointer to the new memory block of size at least
671  * equal to that requested.
672  */
673  size_t*
674  _M_get(size_t __sz) throw(std::bad_alloc);
675 
676  /** @brief This function just clears the internal Free List, and
677  * gives back all the memory to the OS.
678  */
679  void
680  _M_clear();
681  };
682 
683 
684  // Forward declare the class.
685  template<typename _Tp>
686  class bitmap_allocator;
687 
688  // Specialize for void:
689  template<>
690  class bitmap_allocator<void>
691  {
692  public:
693  typedef void* pointer;
694  typedef const void* const_pointer;
695 
696  // Reference-to-void members are impossible.
697  typedef void value_type;
698  template<typename _Tp1>
699  struct rebind
700  {
701  typedef bitmap_allocator<_Tp1> other;
702  };
703  };
704 
705  /**
706  * @brief Bitmap Allocator, primary template.
707  * @ingroup allocators
708  */
709  template<typename _Tp>
710  class bitmap_allocator : private free_list
711  {
712  public:
713  typedef size_t size_type;
714  typedef ptrdiff_t difference_type;
715  typedef _Tp* pointer;
716  typedef const _Tp* const_pointer;
717  typedef _Tp& reference;
718  typedef const _Tp& const_reference;
719  typedef _Tp value_type;
720  typedef free_list::__mutex_type __mutex_type;
721 
722  template<typename _Tp1>
723  struct rebind
724  {
725  typedef bitmap_allocator<_Tp1> other;
726  };
727 
728  private:
729  template<size_t _BSize, size_t _AlignSize>
730  struct aligned_size
731  {
732  enum
733  {
734  modulus = _BSize % _AlignSize,
735  value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
736  };
737  };
738 
739  struct _Alloc_block
740  {
741  char __M_unused[aligned_size<sizeof(value_type),
742  _BALLOC_ALIGN_BYTES>::value];
743  };
744 
745 
747 
748  typedef typename
750 
751 #if defined _GLIBCXX_DEBUG
752  // Complexity: O(lg(N)). Where, N is the number of block of size
753  // sizeof(value_type).
754  void
755  _S_check_for_free_blocks() throw()
756  {
757  typedef typename
759  _FFF __fff;
760  typedef typename _BPVector::iterator _BPiter;
761  _BPiter __bpi =
763  (_S_mem_blocks.begin(), _S_mem_blocks.end(),
764  __gnu_cxx::__detail::_Functor_Ref<_FFF>(__fff));
765 
766  _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
767  }
768 #endif
769 
770  /** @brief Responsible for exponentially growing the internal
771  * memory pool.
772  *
773  * @throw std::bad_alloc. If memory can not be allocated.
774  *
775  * @detail Complexity: O(1), but internally depends upon the
776  * complexity of the function free_list::_M_get. The part where
777  * the bitmap headers are written has complexity: O(X),where X
778  * is the number of blocks of size sizeof(value_type) within
779  * the newly acquired block. Having a tight bound.
780  */
781  void
782  _S_refill_pool() throw(std::bad_alloc)
783  {
784 #if defined _GLIBCXX_DEBUG
785  _S_check_for_free_blocks();
786 #endif
787 
788  const size_t __num_bitmaps = (_S_block_size
789  / size_t(__detail::bits_per_block));
790  const size_t __size_to_allocate = sizeof(size_t)
791  + _S_block_size * sizeof(_Alloc_block)
792  + __num_bitmaps * sizeof(size_t);
793 
794  size_t* __temp =
795  reinterpret_cast<size_t*>
796  (this->_M_get(__size_to_allocate));
797  *__temp = 0;
798  ++__temp;
799 
800  // The Header information goes at the Beginning of the Block.
801  _Block_pair __bp =
802  std::make_pair(reinterpret_cast<_Alloc_block*>
803  (__temp + __num_bitmaps),
804  reinterpret_cast<_Alloc_block*>
805  (__temp + __num_bitmaps)
806  + _S_block_size - 1);
807 
808  // Fill the Vector with this information.
809  _S_mem_blocks.push_back(__bp);
810 
811  size_t __bit_mask = 0; // 0 Indicates all Allocated.
812  __bit_mask = ~__bit_mask; // 1 Indicates all Free.
813 
814  for (size_t __i = 0; __i < __num_bitmaps; ++__i)
815  __temp[__i] = __bit_mask;
816 
817  _S_block_size *= 2;
818  }
819 
820 
821  static _BPVector _S_mem_blocks;
822  static size_t _S_block_size;
823  static __gnu_cxx::__detail::
824  _Bitmap_counter<_Alloc_block*> _S_last_request;
825  static typename _BPVector::size_type _S_last_dealloc_index;
826 #if defined __GTHREADS
827  static __mutex_type _S_mut;
828 #endif
829 
830  public:
831 
832  /** @brief Allocates memory for a single object of size
833  * sizeof(_Tp).
834  *
835  * @throw std::bad_alloc. If memory can not be allocated.
836  *
837  * @detail Complexity: Worst case complexity is O(N), but that
838  * is hardly ever hit. If and when this particular case is
839  * encountered, the next few cases are guaranteed to have a
840  * worst case complexity of O(1)! That's why this function
841  * performs very well on average. You can consider this
842  * function to have a complexity referred to commonly as:
843  * Amortized Constant time.
844  */
845  pointer
846  _M_allocate_single_object() throw(std::bad_alloc)
847  {
848 #if defined __GTHREADS
849  __gnu_cxx::__scoped_lock __bit_lock(_S_mut);
850 #endif
851 
852  // The algorithm is something like this: The last_request
853  // variable points to the last accessed Bit Map. When such a
854  // condition occurs, we try to find a free block in the
855  // current bitmap, or succeeding bitmaps until the last bitmap
856  // is reached. If no free block turns up, we resort to First
857  // Fit method.
858 
859  // WARNING: Do not re-order the condition in the while
860  // statement below, because it relies on C++'s short-circuit
861  // evaluation. The return from _S_last_request->_M_get() will
862  // NOT be dereference able if _S_last_request->_M_finished()
863  // returns true. This would inevitably lead to a NULL pointer
864  // dereference if tinkered with.
865  while (_S_last_request._M_finished() == false
866  && (*(_S_last_request._M_get()) == 0))
867  {
868  _S_last_request.operator++();
869  }
870 
871  if (__builtin_expect(_S_last_request._M_finished() == true, false))
872  {
873  // Fall Back to First Fit algorithm.
874  typedef typename
876  _FFF __fff;
877  typedef typename _BPVector::iterator _BPiter;
878  _BPiter __bpi =
880  (_S_mem_blocks.begin(), _S_mem_blocks.end(),
881  __gnu_cxx::__detail::_Functor_Ref<_FFF>(__fff));
882 
883  if (__bpi != _S_mem_blocks.end())
884  {
885  // Search was successful. Ok, now mark the first bit from
886  // the right as 0, meaning Allocated. This bit is obtained
887  // by calling _M_get() on __fff.
888  size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
889  __detail::__bit_allocate(__fff._M_get(), __nz_bit);
890 
891  _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
892 
893  // Now, get the address of the bit we marked as allocated.
894  pointer __ret = reinterpret_cast<pointer>
895  (__bpi->first + __fff._M_offset() + __nz_bit);
896  size_t* __puse_count =
897  reinterpret_cast<size_t*>
898  (__bpi->first)
899  - (__gnu_cxx::__detail::__num_bitmaps(*__bpi) + 1);
900 
901  ++(*__puse_count);
902  return __ret;
903  }
904  else
905  {
906  // Search was unsuccessful. We Add more memory to the
907  // pool by calling _S_refill_pool().
908  _S_refill_pool();
909 
910  // _M_Reset the _S_last_request structure to the first
911  // free block's bit map.
912  _S_last_request._M_reset(_S_mem_blocks.size() - 1);
913 
914  // Now, mark that bit as allocated.
915  }
916  }
917 
918  // _S_last_request holds a pointer to a valid bit map, that
919  // points to a free block in memory.
920  size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
921  __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
922 
923  pointer __ret = reinterpret_cast<pointer>
924  (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
925 
926  size_t* __puse_count = reinterpret_cast<size_t*>
927  (_S_mem_blocks[_S_last_request._M_where()].first)
928  - (__gnu_cxx::__detail::
929  __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
930 
931  ++(*__puse_count);
932  return __ret;
933  }
934 
935  /** @brief Deallocates memory that belongs to a single object of
936  * size sizeof(_Tp).
937  *
938  * @detail Complexity: O(lg(N)), but the worst case is not hit
939  * often! This is because containers usually deallocate memory
940  * close to each other and this case is handled in O(1) time by
941  * the deallocate function.
942  */
943  void
944  _M_deallocate_single_object(pointer __p) throw()
945  {
946 #if defined __GTHREADS
947  __gnu_cxx::__scoped_lock __bit_lock(_S_mut);
948 #endif
949  _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
950 
951  typedef typename _BPVector::iterator _Iterator;
952  typedef typename _BPVector::difference_type _Difference_type;
953 
954  _Difference_type __diff;
955  long __displacement;
956 
957  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
958 
959 
960  if (__gnu_cxx::__detail::_Inclusive_between<_Alloc_block*>
961  (__real_p) (_S_mem_blocks[_S_last_dealloc_index]))
962  {
963  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
964  <= _S_mem_blocks.size() - 1);
965 
966  // Initial Assumption was correct!
967  __diff = _S_last_dealloc_index;
968  __displacement = __real_p - _S_mem_blocks[__diff].first;
969  }
970  else
971  {
972  _Iterator _iter = __gnu_cxx::__detail::
973  __find_if(_S_mem_blocks.begin(),
974  _S_mem_blocks.end(),
975  __gnu_cxx::__detail::
976  _Inclusive_between<_Alloc_block*>(__real_p));
977 
978  _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
979 
980  __diff = _iter - _S_mem_blocks.begin();
981  __displacement = __real_p - _S_mem_blocks[__diff].first;
982  _S_last_dealloc_index = __diff;
983  }
984 
985  // Get the position of the iterator that has been found.
986  const size_t __rotate = (__displacement
987  % size_t(__detail::bits_per_block));
988  size_t* __bitmapC =
989  reinterpret_cast<size_t*>
990  (_S_mem_blocks[__diff].first) - 1;
991  __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
992 
993  __detail::__bit_free(__bitmapC, __rotate);
994  size_t* __puse_count = reinterpret_cast<size_t*>
995  (_S_mem_blocks[__diff].first)
996  - (__gnu_cxx::__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
997 
998  _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
999 
1000  --(*__puse_count);
1001 
1002  if (__builtin_expect(*__puse_count == 0, false))
1003  {
1004  _S_block_size /= 2;
1005 
1006  // We can safely remove this block.
1007  // _Block_pair __bp = _S_mem_blocks[__diff];
1008  this->_M_insert(__puse_count);
1009  _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
1010 
1011  // Reset the _S_last_request variable to reflect the
1012  // erased block. We do this to protect future requests
1013  // after the last block has been removed from a particular
1014  // memory Chunk, which in turn has been returned to the
1015  // free list, and hence had been erased from the vector,
1016  // so the size of the vector gets reduced by 1.
1017  if ((_Difference_type)_S_last_request._M_where() >= __diff--)
1018  _S_last_request._M_reset(__diff);
1019 
1020  // If the Index into the vector of the region of memory
1021  // that might hold the next address that will be passed to
1022  // deallocated may have been invalidated due to the above
1023  // erase procedure being called on the vector, hence we
1024  // try to restore this invariant too.
1025  if (_S_last_dealloc_index >= _S_mem_blocks.size())
1026  {
1027  _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
1028  _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
1029  }
1030  }
1031  }
1032 
1033  public:
1034  bitmap_allocator() throw()
1035  { }
1036 
1037  bitmap_allocator(const bitmap_allocator&)
1038  { }
1039 
1040  template<typename _Tp1>
1041  bitmap_allocator(const bitmap_allocator<_Tp1>&) throw()
1042  { }
1043 
1044  ~bitmap_allocator() throw()
1045  { }
1046 
1047  pointer
1048  allocate(size_type __n)
1049  {
1050  if (__builtin_expect(__n > this->max_size(), false))
1051  std::__throw_bad_alloc();
1052 
1053  if (__builtin_expect(__n == 1, true))
1054  return this->_M_allocate_single_object();
1055  else
1056  {
1057  const size_type __b = __n * sizeof(value_type);
1058  return reinterpret_cast<pointer>(::operator new(__b));
1059  }
1060  }
1061 
1062  pointer
1063  allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
1064  { return allocate(__n); }
1065 
1066  void
1067  deallocate(pointer __p, size_type __n) throw()
1068  {
1069  if (__builtin_expect(__p != 0, true))
1070  {
1071  if (__builtin_expect(__n == 1, true))
1072  this->_M_deallocate_single_object(__p);
1073  else
1074  ::operator delete(__p);
1075  }
1076  }
1077 
1078  pointer
1079  address(reference __r) const
1080  { return &__r; }
1081 
1082  const_pointer
1083  address(const_reference __r) const
1084  { return &__r; }
1085 
1086  size_type
1087  max_size() const throw()
1088  { return size_type(-1) / sizeof(value_type); }
1089 
1090  void
1091  construct(pointer __p, const_reference __data)
1092  { ::new((void *)__p) value_type(__data); }
1093 
1094 #ifdef __GXX_EXPERIMENTAL_CXX0X__
1095  template<typename... _Args>
1096  void
1097  construct(pointer __p, _Args&&... __args)
1098  { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
1099 #endif
1100 
1101  void
1102  destroy(pointer __p)
1103  { __p->~value_type(); }
1104  };
1105 
1106  template<typename _Tp1, typename _Tp2>
1107  bool
1108  operator==(const bitmap_allocator<_Tp1>&,
1109  const bitmap_allocator<_Tp2>&) throw()
1110  { return true; }
1111 
1112  template<typename _Tp1, typename _Tp2>
1113  bool
1114  operator!=(const bitmap_allocator<_Tp1>&,
1115  const bitmap_allocator<_Tp2>&) throw()
1116  { return false; }
1117 
1118  // Static member definitions.
1119  template<typename _Tp>
1120  typename bitmap_allocator<_Tp>::_BPVector
1121  bitmap_allocator<_Tp>::_S_mem_blocks;
1122 
1123  template<typename _Tp>
1124  size_t bitmap_allocator<_Tp>::_S_block_size =
1125  2 * size_t(__detail::bits_per_block);
1126 
1127  template<typename _Tp>
1128  typename __gnu_cxx::bitmap_allocator<_Tp>::_BPVector::size_type
1129  bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
1130 
1131  template<typename _Tp>
1133  <typename bitmap_allocator<_Tp>::_Alloc_block*>
1134  bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
1135 
1136 #if defined __GTHREADS
1137  template<typename _Tp>
1138  typename bitmap_allocator<_Tp>::__mutex_type
1139  bitmap_allocator<_Tp>::_S_mut;
1140 #endif
1141 
1142 _GLIBCXX_END_NAMESPACE
1143 
1144 #endif
1145