# bitmap_allocator.h

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    00001 // Bitmap Allocator. -*- C++ -*-
    00002
    00003 // Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
    00004 // Free Software Foundation, Inc.
    00005 //
    00006 // This file is part of the GNU ISO C++ Library.  This library is free
    00007 // software; you can redistribute it and/or modify it under the
    00008 // terms of the GNU General Public License as published by the
    00009 // Free Software Foundation; either version 3, or (at your option)
    00010 // any later version.
    00011
    00012 // This library is distributed in the hope that it will be useful,
    00013 // but WITHOUT ANY WARRANTY; without even the implied warranty of
    00014 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00015 // GNU General Public License for more details.
    00016
    00017 // Under Section 7 of GPL version 3, you are granted additional
    00018 // permissions described in the GCC Runtime Library Exception, version
    00019 // 3.1, as published by the Free Software Foundation.
    00020
    00021 // You should have received a copy of the GNU General Public License and
    00022 // a copy of the GCC Runtime Library Exception along with this program;
    00023 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    00024 // <http://www.gnu.org/licenses/>.
    00025
    00026 /** @file ext/bitmap_allocator.h
    00027  *  This file is a GNU extension to the Standard C++ Library.
    00028  */
    00029
    00030 #ifndef _BITMAP_ALLOCATOR_H
    00031 #define _BITMAP_ALLOCATOR_H 1
    00032
    00033 #include <cstddef> // For std::size_t, and ptrdiff_t.
    00034 #include <bits/functexcept.h> // For __throw_bad_alloc().
    00035 #include <utility> // For std::pair.
    00036 #include <functional> // For greater_equal, and less_equal.
    00037 #include <new> // For operator new.
    00038 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
    00039 #include <ext/concurrence.h>
    00040 #include <bits/move.h>
    00041
    00042 /** @brief The constant in the expression below is the alignment
    00043  * required in bytes.
    00044  */
    00045 #define _BALLOC_ALIGN_BYTES 8
    00046
    00047 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    00048
    00049   using std::size_t;
    00050   using std::ptrdiff_t;
    00051
    00052   namespace __detail
    00053   {
    00054     /** @class  __mini_vector bitmap_allocator.h bitmap_allocator.h
    00055      *
    00056      *  @brief  __mini_vector<> is a stripped down version of the
    00057      *  full-fledged std::vector<>.
    00058      *
    00059      *  It is to be used only for built-in types or PODs. Notable
    00060      *  differences are:
    00061      *
    00062      *  @detail
    00063      *  1. Not all accessor functions are present.
    00064      *  2. Used ONLY for PODs.
    00065      *  3. No Allocator template argument. Uses ::operator new() to get
    00066      *  memory, and ::operator delete() to free it.
    00067      *  Caveat: The dtor does NOT free the memory allocated, so this a
    00068      *  memory-leaking vector!
    00069      */
    00070     template<typename _Tp>
    00071       class __mini_vector
    00072       {
    00073     __mini_vector(const __mini_vector&);
    00074     __mini_vector& operator=(const __mini_vector&);
    00075
    00076       public:
    00077     typedef _Tp value_type;
    00078     typedef _Tp* pointer;
    00079     typedef _Tp& reference;
    00080     typedef const _Tp& const_reference;
    00081     typedef size_t size_type;
    00082     typedef ptrdiff_t difference_type;
    00083     typedef pointer iterator;
    00084
    00085       private:
    00086     pointer _M_start;
    00087     pointer _M_finish;
    00088     pointer _M_end_of_storage;
    00089
    00090     size_type
    00091     _M_space_left() const throw()
    00092     { return _M_end_of_storage - _M_finish; }
    00093
    00094     pointer
    00095     allocate(size_type __n)
    00096     { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
    00097
    00098     void
    00099     deallocate(pointer __p, size_type)
    00100     { ::operator delete(__p); }
    00101
    00102       public:
    00103     // Members used: size(), push_back(), pop_back(),
    00104     // insert(iterator, const_reference), erase(iterator),
    00105     // begin(), end(), back(), operator[].
    00106
    00107     __mini_vector()
    00108         : _M_start(0), _M_finish(0), _M_end_of_storage(0) { }
    00109
    00110     size_type
    00111     size() const throw()
    00112     { return _M_finish - _M_start; }
    00113
    00114     iterator
    00115     begin() const throw()
    00116     { return this->_M_start; }
    00117
    00118     iterator
    00119     end() const throw()
    00120     { return this->_M_finish; }
    00121
    00122     reference
    00123     back() const throw()
    00124     { return *(this->end() - 1); }
    00125
    00126     reference
    00127     operator[](const size_type __pos) const throw()
    00128     { return this->_M_start[__pos]; }
    00129
    00130     void
    00131     insert(iterator __pos, const_reference __x);
    00132
    00133     void
    00134     push_back(const_reference __x)
    00135     {
    00136       if (this->_M_space_left())
    00137         {
    00138           *this->end() = __x;
    00139           ++this->_M_finish;
    00140         }
    00141       else
    00142         this->insert(this->end(), __x);
    00143     }
    00144
    00145     void
    00146     pop_back() throw()
    00147     { --this->_M_finish; }
    00148
    00149     void
    00150     erase(iterator __pos) throw();
    00151
    00152     void
    00153     clear() throw()
    00154     { this->_M_finish = this->_M_start; }
    00155       };
    00156
    00157     // Out of line function definitions.
    00158     template<typename _Tp>
    00159       void __mini_vector<_Tp>::
    00160       insert(iterator __pos, const_reference __x)
    00161       {
    00162     if (this->_M_space_left())
    00163       {
    00164         size_type __to_move = this->_M_finish - __pos;
    00165         iterator __dest = this->end();
    00166         iterator __src = this->end() - 1;
    00167
    00168         ++this->_M_finish;
    00169         while (__to_move)
    00170           {
    00171         *__dest = *__src;
    00172         --__dest; --__src; --__to_move;
    00173           }
    00174         *__pos = __x;
    00175       }
    00176     else
    00177       {
    00178         size_type __new_size = this->size() ? this->size() * 2 : 1;
    00179         iterator __new_start = this->allocate(__new_size);
    00180         iterator __first = this->begin();
    00181         iterator __start = __new_start;
    00182         while (__first != __pos)
    00183           {
    00184         *__start = *__first;
    00185         ++__start; ++__first;
    00186           }
    00187         *__start = __x;
    00188         ++__start;
    00189         while (__first != this->end())
    00190           {
    00191         *__start = *__first;
    00192         ++__start; ++__first;
    00193           }
    00194         if (this->_M_start)
    00195           this->deallocate(this->_M_start, this->size());
    00196
    00197         this->_M_start = __new_start;
    00198         this->_M_finish = __start;
    00199         this->_M_end_of_storage = this->_M_start + __new_size;
    00200       }
    00201       }
    00202
    00203     template<typename _Tp>
    00204       void __mini_vector<_Tp>::
    00205       erase(iterator __pos) throw()
    00206       {
    00207     while (__pos + 1 != this->end())
    00208       {
    00209         *__pos = __pos[1];
    00210         ++__pos;
    00211       }
    00212     --this->_M_finish;
    00213       }
    00214
    00215
    00216     template<typename _Tp>
    00217       struct __mv_iter_traits
    00218       {
    00219     typedef typename _Tp::value_type value_type;
    00220     typedef typename _Tp::difference_type difference_type;
    00221       };
    00222
    00223     template<typename _Tp>
    00224       struct __mv_iter_traits<_Tp*>
    00225       {
    00226     typedef _Tp value_type;
    00227     typedef ptrdiff_t difference_type;
    00228       };
    00229
    00230     enum
    00231       {
    00232     bits_per_byte = 8,
    00233     bits_per_block = sizeof(size_t) * size_t(bits_per_byte)
    00234       };
    00235
    00236     template<typename _ForwardIterator, typename _Tp, typename _Compare>
    00237       _ForwardIterator
    00238       __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
    00239             const _Tp& __val, _Compare __comp)
    00240       {
    00241     typedef typename __mv_iter_traits<_ForwardIterator>::value_type
    00242       _ValueType;
    00243     typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
    00244       _DistanceType;
    00245
    00246     _DistanceType __len = __last - __first;
    00247     _DistanceType __half;
    00248     _ForwardIterator __middle;
    00249
    00250     while (__len > 0)
    00251       {
    00252         __half = __len >> 1;
    00253         __middle = __first;
    00254         __middle += __half;
    00255         if (__comp(*__middle, __val))
    00256           {
    00257         __first = __middle;
    00258         ++__first;
    00259         __len = __len - __half - 1;
    00260           }
    00261         else
    00262           __len = __half;
    00263       }
    00264     return __first;
    00265       }
    00266
    00267     /** @brief The number of Blocks pointed to by the address pair
    00268      *  passed to the function.
    00269      */
    00270     template<typename _AddrPair>
    00271       inline size_t
    00272       __num_blocks(_AddrPair __ap)
    00273       { return (__ap.second - __ap.first) + 1; }
    00274
    00275     /** @brief The number of Bit-maps pointed to by the address pair
    00276      *  passed to the function.
    00277      */
    00278     template<typename _AddrPair>
    00279       inline size_t
    00280       __num_bitmaps(_AddrPair __ap)
    00281       { return __num_blocks(__ap) / size_t(bits_per_block); }
    00282
    00283     // _Tp should be a pointer type.
    00284     template<typename _Tp>
    00285       class _Inclusive_between
    00286       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
    00287       {
    00288     typedef _Tp pointer;
    00289     pointer _M_ptr_value;
    00290     typedef typename std::pair<_Tp, _Tp> _Block_pair;
    00291
    00292       public:
    00293     _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr)
    00294     { }
    00295
    00296     bool
    00297     operator()(_Block_pair __bp) const throw()
    00298     {
    00299       if (std::less_equal<pointer>()(_M_ptr_value, __bp.second)
    00300           && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
    00301         return true;
    00302       else
    00303         return false;
    00304     }
    00305       };
    00306
    00307     // Used to pass a Functor to functions by reference.
    00308     template<typename _Functor>
    00309       class _Functor_Ref
    00310       : public std::unary_function<typename _Functor::argument_type,
    00311                    typename _Functor::result_type>
    00312       {
    00313     _Functor& _M_fref;
    00314
    00315       public:
    00316     typedef typename _Functor::argument_type argument_type;
    00317     typedef typename _Functor::result_type result_type;
    00318
    00319     _Functor_Ref(_Functor& __fref) : _M_fref(__fref)
    00320     { }
    00321
    00322     result_type
    00323     operator()(argument_type __arg)
    00324     { return _M_fref(__arg); }
    00325       };
    00326
    00327     /** @class  _Ffit_finder bitmap_allocator.h bitmap_allocator.h
    00328      *
    00329      *  @brief  The class which acts as a predicate for applying the
    00330      *  first-fit memory allocation policy for the bitmap allocator.
    00331      */
    00332     // _Tp should be a pointer type, and _Alloc is the Allocator for
    00333     // the vector.
    00334     template<typename _Tp>
    00335       class _Ffit_finder
    00336       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
    00337       {
    00338     typedef typename std::pair<_Tp, _Tp> _Block_pair;
    00339     typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
    00340     typedef typename _BPVector::difference_type _Counter_type;
    00341
    00342     size_t* _M_pbitmap;
    00343     _Counter_type _M_data_offset;
    00344
    00345       public:
    00346     _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
    00347     { }
    00348
    00349     bool
    00350     operator()(_Block_pair __bp) throw()
    00351     {
    00352       // Set the _rover to the last physical location bitmap,
    00353       // which is the bitmap which belongs to the first free
    00354       // block. Thus, the bitmaps are in exact reverse order of
    00355       // the actual memory layout. So, we count down the bitmaps,
    00356       // which is the same as moving up the memory.
    00357
    00358       // If the used count stored at the start of the Bit Map headers
    00359       // is equal to the number of Objects that the current Block can
    00360       // store, then there is definitely no space for another single
    00361       // object, so just return false.
    00362       _Counter_type __diff = __detail::__num_bitmaps(__bp);
    00363
    00364       if (*(reinterpret_cast<size_t*>
    00365         (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
    00366         return false;
    00367
    00368       size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
    00369
    00370       for (_Counter_type __i = 0; __i < __diff; ++__i)
    00371         {
    00372           _M_data_offset = __i;
    00373           if (*__rover)
    00374         {
    00375           _M_pbitmap = __rover;
    00376           return true;
    00377         }
    00378           --__rover;
    00379         }
    00380       return false;
    00381     }
    00382
    00383     size_t*
    00384     _M_get() const throw()
    00385     { return _M_pbitmap; }
    00386
    00387     _Counter_type
    00388     _M_offset() const throw()
    00389     { return _M_data_offset * size_t(bits_per_block); }
    00390       };
    00391
    00392     /** @class  _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
    00393      *
    00394      *  @brief  The bitmap counter which acts as the bitmap
    00395      *  manipulator, and manages the bit-manipulation functions and
    00396      *  the searching and identification functions on the bit-map.
    00397      */
    00398     // _Tp should be a pointer type.
    00399     template<typename _Tp>
    00400       class _Bitmap_counter
    00401       {
    00402     typedef typename
    00403     __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector;
    00404     typedef typename _BPVector::size_type _Index_type;
    00405     typedef _Tp pointer;
    00406
    00407     _BPVector& _M_vbp;
    00408     size_t* _M_curr_bmap;
    00409     size_t* _M_last_bmap_in_block;
    00410     _Index_type _M_curr_index;
    00411
    00412       public:
    00413     // Use the 2nd parameter with care. Make sure that such an
    00414     // entry exists in the vector before passing that particular
    00415     // index to this ctor.
    00416     _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
    00417     { this->_M_reset(__index); }
    00418
    00419     void
    00420     _M_reset(long __index = -1) throw()
    00421     {
    00422       if (__index == -1)
    00423         {
    00424           _M_curr_bmap = 0;
    00425           _M_curr_index = static_cast<_Index_type>(-1);
    00426           return;
    00427         }
    00428
    00429       _M_curr_index = __index;
    00430       _M_curr_bmap = reinterpret_cast<size_t*>
    00431         (_M_vbp[_M_curr_index].first) - 1;
    00432
    00433       _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
    00434
    00435       _M_last_bmap_in_block = _M_curr_bmap
    00436         - ((_M_vbp[_M_curr_index].second
    00437         - _M_vbp[_M_curr_index].first + 1)
    00438            / size_t(bits_per_block) - 1);
    00439     }
    00440
    00441     // Dangerous Function! Use with extreme care. Pass to this
    00442     // function ONLY those values that are known to be correct,
    00443     // otherwise this will mess up big time.
    00444     void
    00445     _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
    00446     { _M_curr_bmap = __new_internal_marker; }
    00447
    00448     bool
    00449     _M_finished() const throw()
    00450     { return(_M_curr_bmap == 0); }
    00451
    00452     _Bitmap_counter&
    00453     operator++() throw()
    00454     {
    00455       if (_M_curr_bmap == _M_last_bmap_in_block)
    00456         {
    00457           if (++_M_curr_index == _M_vbp.size())
    00458         _M_curr_bmap = 0;
    00459           else
    00460         this->_M_reset(_M_curr_index);
    00461         }
    00462       else
    00463         --_M_curr_bmap;
    00464       return *this;
    00465     }
    00466
    00467     size_t*
    00468     _M_get() const throw()
    00469     { return _M_curr_bmap; }
    00470
    00471     pointer
    00472     _M_base() const throw()
    00473     { return _M_vbp[_M_curr_index].first; }
    00474
    00475     _Index_type
    00476     _M_offset() const throw()
    00477     {
    00478       return size_t(bits_per_block)
    00479         * ((reinterpret_cast<size_t*>(this->_M_base())
    00480         - _M_curr_bmap) - 1);
    00481     }
    00482
    00483     _Index_type
    00484     _M_where() const throw()
    00485     { return _M_curr_index; }
    00486       };
    00487
    00488     /** @brief  Mark a memory address as allocated by re-setting the
    00489      *  corresponding bit in the bit-map.
    00490      */
    00491     inline void
    00492     __bit_allocate(size_t* __pbmap, size_t __pos) throw()
    00493     {
    00494       size_t __mask = 1 << __pos;
    00495       __mask = ~__mask;
    00496       *__pbmap &= __mask;
    00497     }
    00498
    00499     /** @brief  Mark a memory address as free by setting the
    00500      *  corresponding bit in the bit-map.
    00501      */
    00502     inline void
    00503     __bit_free(size_t* __pbmap, size_t __pos) throw()
    00504     {
    00505       size_t __mask = 1 << __pos;
    00506       *__pbmap |= __mask;
    00507     }
    00508   } // namespace __detail
    00509
    00510   /** @brief  Generic Version of the bsf instruction.
    00511    */
    00512   inline size_t
    00513   _Bit_scan_forward(size_t __num)
    00514   { return static_cast<size_t>(__builtin_ctzl(__num)); }
    00515
    00516   /** @class  free_list bitmap_allocator.h bitmap_allocator.h
    00517    *
    00518    *  @brief  The free list class for managing chunks of memory to be
    00519    *  given to and returned by the bitmap_allocator.
    00520    */
    00521   class free_list
    00522   {
    00523   public:
    00524     typedef size_t*                 value_type;
    00525     typedef __detail::__mini_vector<value_type> vector_type;
    00526     typedef vector_type::iterator       iterator;
    00527     typedef __mutex             __mutex_type;
    00528
    00529   private:
    00530     struct _LT_pointer_compare
    00531     {
    00532       bool
    00533       operator()(const size_t* __pui,
    00534          const size_t __cui) const throw()
    00535       { return *__pui < __cui; }
    00536     };
    00537
    00538 #if defined __GTHREADS
    00539     __mutex_type&
    00540     _M_get_mutex()
    00541     {
    00542       static __mutex_type _S_mutex;
    00543       return _S_mutex;
    00544     }
    00545 #endif
    00546
    00547     vector_type&
    00548     _M_get_free_list()
    00549     {
    00550       static vector_type _S_free_list;
    00551       return _S_free_list;
    00552     }
    00553
    00554     /** @brief  Performs validation of memory based on their size.
    00555      *
    00556      *  @param  __addr The pointer to the memory block to be
    00557      *  validated.
    00558      *
    00559      *  @detail  Validates the memory block passed to this function and
    00560      *  appropriately performs the action of managing the free list of
    00561      *  blocks by adding this block to the free list or deleting this
    00562      *  or larger blocks from the free list.
    00563      */
    00564     void
    00565     _M_validate(size_t* __addr) throw()
    00566     {
    00567       vector_type& __free_list = _M_get_free_list();
    00568       const vector_type::size_type __max_size = 64;
    00569       if (__free_list.size() >= __max_size)
    00570     {
    00571       // Ok, the threshold value has been reached.  We determine
    00572       // which block to remove from the list of free blocks.
    00573       if (*__addr >= *__free_list.back())
    00574         {
    00575           // Ok, the new block is greater than or equal to the
    00576           // last block in the list of free blocks. We just free
    00577           // the new block.
    00578           ::operator delete(static_cast<void*>(__addr));
    00579           return;
    00580         }
    00581       else
    00582         {
    00583           // Deallocate the last block in the list of free lists,
    00584           // and insert the new one in its correct position.
    00585           ::operator delete(static_cast<void*>(__free_list.back()));
    00586           __free_list.pop_back();
    00587         }
    00588     }
    00589
    00590       // Just add the block to the list of free lists unconditionally.
    00591       iterator __temp = __detail::__lower_bound
    00592     (__free_list.begin(), __free_list.end(),
    00593      *__addr, _LT_pointer_compare());
    00594
    00595       // We may insert the new free list before _temp;
    00596       __free_list.insert(__temp, __addr);
    00597     }
    00598
    00599     /** @brief  Decides whether the wastage of memory is acceptable for
    00600      *  the current memory request and returns accordingly.
    00601      *
    00602      *  @param __block_size The size of the block available in the free
    00603      *  list.
    00604      *
    00605      *  @param __required_size The required size of the memory block.
    00606      *
    00607      *  @return true if the wastage incurred is acceptable, else returns
    00608      *  false.
    00609      */
    00610     bool
    00611     _M_should_i_give(size_t __block_size,
    00612              size_t __required_size) throw()
    00613     {
    00614       const size_t __max_wastage_percentage = 36;
    00615       if (__block_size >= __required_size &&
    00616       (((__block_size - __required_size) * 100 / __block_size)
    00617        < __max_wastage_percentage))
    00618     return true;
    00619       else
    00620     return false;
    00621     }
    00622
    00623   public:
    00624     /** @brief This function returns the block of memory to the
    00625      *  internal free list.
    00626      *
    00627      *  @param  __addr The pointer to the memory block that was given
    00628      *  by a call to the _M_get function.
    00629      */
    00630     inline void
    00631     _M_insert(size_t* __addr) throw()
    00632     {
    00633 #if defined __GTHREADS
    00634       __scoped_lock __bfl_lock(_M_get_mutex());
    00635 #endif
    00636       // Call _M_validate to decide what should be done with
    00637       // this particular free list.
    00638       this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
    00639       // See discussion as to why this is 1!
    00640     }
    00641
    00642     /** @brief  This function gets a block of memory of the specified
    00643      *  size from the free list.
    00644      *
    00645      *  @param  __sz The size in bytes of the memory required.
    00646      *
    00647      *  @return  A pointer to the new memory block of size at least
    00648      *  equal to that requested.
    00649      */
    00650     size_t*
    00651     _M_get(size_t __sz) throw(std::bad_alloc);
    00652
    00653     /** @brief  This function just clears the internal Free List, and
    00654      *  gives back all the memory to the OS.
    00655      */
    00656     void
    00657     _M_clear();
    00658   };
    00659
    00660
    00661   // Forward declare the class.
    00662   template<typename _Tp>
    00663     class bitmap_allocator;
    00664
    00665   // Specialize for void:
    00666   template<>
    00667     class bitmap_allocator<void>
    00668     {
    00669     public:
    00670       typedef void*       pointer;
    00671       typedef const void* const_pointer;
    00672
    00673       // Reference-to-void members are impossible.
    00674       typedef void  value_type;
    00675       template<typename _Tp1>
    00676         struct rebind
    00677     {
    00678       typedef bitmap_allocator<_Tp1> other;
    00679     };
    00680     };
    00681
    00682   /**
    00683    * @brief Bitmap Allocator, primary template.
    00684    * @ingroup allocators
    00685    */
    00686   template<typename _Tp>
    00687     class bitmap_allocator : private free_list
    00688     {
    00689     public:
    00690       typedef size_t            size_type;
    00691       typedef ptrdiff_t         difference_type;
    00692       typedef _Tp*              pointer;
    00693       typedef const _Tp*        const_pointer;
    00694       typedef _Tp&              reference;
    00695       typedef const _Tp&        const_reference;
    00696       typedef _Tp               value_type;
    00697       typedef free_list::__mutex_type   __mutex_type;
    00698
    00699       template<typename _Tp1>
    00700         struct rebind
    00701     {
    00702       typedef bitmap_allocator<_Tp1> other;
    00703     };
    00704
    00705     private:
    00706       template<size_t _BSize, size_t _AlignSize>
    00707         struct aligned_size
    00708     {
    00709       enum
    00710         {
    00711           modulus = _BSize % _AlignSize,
    00712           value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
    00713         };
    00714     };
    00715
    00716       struct _Alloc_block
    00717       {
    00718     char __M_unused[aligned_size<sizeof(value_type),
    00719             _BALLOC_ALIGN_BYTES>::value];
    00720       };
    00721
    00722
    00723       typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
    00724
    00725       typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
    00726       typedef typename _BPVector::iterator _BPiter;
    00727
    00728       template<typename _Predicate>
    00729         static _BPiter
    00730         _S_find(_Predicate __p)
    00731         {
    00732       _BPiter __first = _S_mem_blocks.begin();
    00733       while (__first != _S_mem_blocks.end() && !__p(*__first))
    00734         ++__first;
    00735       return __first;
    00736     }
    00737
    00738 #if defined _GLIBCXX_DEBUG
    00739       // Complexity: O(lg(N)). Where, N is the number of block of size
    00740       // sizeof(value_type).
    00741       void
    00742       _S_check_for_free_blocks() throw()
    00743       {
    00744     typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
    00745     _BPiter __bpi = _S_find(_FFF());
    00746
    00747     _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
    00748       }
    00749 #endif
    00750
    00751       /** @brief  Responsible for exponentially growing the internal
    00752        *  memory pool.
    00753        *
    00754        *  @throw  std::bad_alloc. If memory can not be allocated.
    00755        *
    00756        *  @detail  Complexity: O(1), but internally depends upon the
    00757        *  complexity of the function free_list::_M_get. The part where
    00758        *  the bitmap headers are written has complexity: O(X),where X
    00759        *  is the number of blocks of size sizeof(value_type) within
    00760        *  the newly acquired block. Having a tight bound.
    00761        */
    00762       void
    00763       _S_refill_pool() throw(std::bad_alloc)
    00764       {
    00765 #if defined _GLIBCXX_DEBUG
    00766     _S_check_for_free_blocks();
    00767 #endif
    00768
    00769     const size_t __num_bitmaps = (_S_block_size
    00770                       / size_t(__detail::bits_per_block));
    00771     const size_t __size_to_allocate = sizeof(size_t)
    00772       + _S_block_size * sizeof(_Alloc_block)
    00773       + __num_bitmaps * sizeof(size_t);
    00774
    00775     size_t* __temp =
    00776       reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate));
    00777     *__temp = 0;
    00778     ++__temp;
    00779
    00780     // The Header information goes at the Beginning of the Block.
    00781     _Block_pair __bp =
    00782       std::make_pair(reinterpret_cast<_Alloc_block*>
    00783              (__temp + __num_bitmaps),
    00784              reinterpret_cast<_Alloc_block*>
    00785              (__temp + __num_bitmaps)
    00786              + _S_block_size - 1);
    00787
    00788     // Fill the Vector with this information.
    00789     _S_mem_blocks.push_back(__bp);
    00790
    00791     for (size_t __i = 0; __i < __num_bitmaps; ++__i)
    00792       __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free.
    00793
    00794     _S_block_size *= 2;
    00795       }
    00796
    00797       static _BPVector _S_mem_blocks;
    00798       static size_t _S_block_size;
    00799       static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request;
    00800       static typename _BPVector::size_type _S_last_dealloc_index;
    00801 #if defined __GTHREADS
    00802       static __mutex_type _S_mut;
    00803 #endif
    00804
    00805     public:
    00806
    00807       /** @brief  Allocates memory for a single object of size
    00808        *  sizeof(_Tp).
    00809        *
    00810        *  @throw  std::bad_alloc. If memory can not be allocated.
    00811        *
    00812        *  @detail  Complexity: Worst case complexity is O(N), but that
    00813        *  is hardly ever hit. If and when this particular case is
    00814        *  encountered, the next few cases are guaranteed to have a
    00815        *  worst case complexity of O(1)!  That's why this function
    00816        *  performs very well on average. You can consider this
    00817        *  function to have a complexity referred to commonly as:
    00818        *  Amortized Constant time.
    00819        */
    00820       pointer
    00821       _M_allocate_single_object() throw(std::bad_alloc)
    00822       {
    00823 #if defined __GTHREADS
    00824     __scoped_lock __bit_lock(_S_mut);
    00825 #endif
    00826
    00827     // The algorithm is something like this: The last_request
    00828     // variable points to the last accessed Bit Map. When such a
    00829     // condition occurs, we try to find a free block in the
    00830     // current bitmap, or succeeding bitmaps until the last bitmap
    00831     // is reached. If no free block turns up, we resort to First
    00832     // Fit method.
    00833
    00834     // WARNING: Do not re-order the condition in the while
    00835     // statement below, because it relies on C++'s short-circuit
    00836     // evaluation. The return from _S_last_request->_M_get() will
    00837     // NOT be dereference able if _S_last_request->_M_finished()
    00838     // returns true. This would inevitably lead to a NULL pointer
    00839     // dereference if tinkered with.
    00840     while (_S_last_request._M_finished() == false
    00841            && (*(_S_last_request._M_get()) == 0))
    00842       _S_last_request.operator++();
    00843
    00844     if (__builtin_expect(_S_last_request._M_finished() == true, false))
    00845       {
    00846         // Fall Back to First Fit algorithm.
    00847         typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
    00848         _FFF __fff;
    00849         _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
    00850
    00851         if (__bpi != _S_mem_blocks.end())
    00852           {
    00853         // Search was successful. Ok, now mark the first bit from
    00854         // the right as 0, meaning Allocated. This bit is obtained
    00855         // by calling _M_get() on __fff.
    00856         size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
    00857         __detail::__bit_allocate(__fff._M_get(), __nz_bit);
    00858
    00859         _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
    00860
    00861         // Now, get the address of the bit we marked as allocated.
    00862         pointer __ret = reinterpret_cast<pointer>
    00863           (__bpi->first + __fff._M_offset() + __nz_bit);
    00864         size_t* __puse_count =
    00865           reinterpret_cast<size_t*>
    00866           (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
    00867
    00868         ++(*__puse_count);
    00869         return __ret;
    00870           }
    00871         else
    00872           {
    00873         // Search was unsuccessful. We Add more memory to the
    00874         // pool by calling _S_refill_pool().
    00875         _S_refill_pool();
    00876
    00877         // _M_Reset the _S_last_request structure to the first
    00878         // free block's bit map.
    00879         _S_last_request._M_reset(_S_mem_blocks.size() - 1);
    00880
    00881         // Now, mark that bit as allocated.
    00882           }
    00883       }
    00884
    00885     // _S_last_request holds a pointer to a valid bit map, that
    00886     // points to a free block in memory.
    00887     size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
    00888     __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
    00889
    00890     pointer __ret = reinterpret_cast<pointer>
    00891       (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
    00892
    00893     size_t* __puse_count = reinterpret_cast<size_t*>
    00894       (_S_mem_blocks[_S_last_request._M_where()].first)
    00895       - (__detail::
    00896          __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
    00897
    00898     ++(*__puse_count);
    00899     return __ret;
    00900       }
    00901
    00902       /** @brief  Deallocates memory that belongs to a single object of
    00903        *  size sizeof(_Tp).
    00904        *
    00905        *  @detail  Complexity: O(lg(N)), but the worst case is not hit
    00906        *  often!  This is because containers usually deallocate memory
    00907        *  close to each other and this case is handled in O(1) time by
    00908        *  the deallocate function.
    00909        */
    00910       void
    00911       _M_deallocate_single_object(pointer __p) throw()
    00912       {
    00913 #if defined __GTHREADS
    00914     __scoped_lock __bit_lock(_S_mut);
    00915 #endif
    00916     _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
    00917
    00918     typedef typename _BPVector::iterator _Iterator;
    00919     typedef typename _BPVector::difference_type _Difference_type;
    00920
    00921     _Difference_type __diff;
    00922     long __displacement;
    00923
    00924     _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
    00925
    00926     __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
    00927     if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
    00928       {
    00929         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
    00930                   <= _S_mem_blocks.size() - 1);
    00931
    00932         // Initial Assumption was correct!
    00933         __diff = _S_last_dealloc_index;
    00934         __displacement = __real_p - _S_mem_blocks[__diff].first;
    00935       }
    00936     else
    00937       {
    00938         _Iterator _iter = _S_find(__ibt);
    00939
    00940         _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
    00941
    00942         __diff = _iter - _S_mem_blocks.begin();
    00943         __displacement = __real_p - _S_mem_blocks[__diff].first;
    00944         _S_last_dealloc_index = __diff;
    00945       }
    00946
    00947     // Get the position of the iterator that has been found.
    00948     const size_t __rotate = (__displacement
    00949                  % size_t(__detail::bits_per_block));
    00950     size_t* __bitmapC =
    00951       reinterpret_cast<size_t*>
    00952       (_S_mem_blocks[__diff].first) - 1;
    00953     __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
    00954
    00955     __detail::__bit_free(__bitmapC, __rotate);
    00956     size_t* __puse_count = reinterpret_cast<size_t*>
    00957       (_S_mem_blocks[__diff].first)
    00958       - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
    00959
    00960     _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
    00961
    00962     --(*__puse_count);
    00963
    00964     if (__builtin_expect(*__puse_count == 0, false))
    00965       {
    00966         _S_block_size /= 2;
    00967
    00968         // We can safely remove this block.
    00969         // _Block_pair __bp = _S_mem_blocks[__diff];
    00970         this->_M_insert(__puse_count);
    00971         _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
    00972
    00973         // Reset the _S_last_request variable to reflect the
    00974         // erased block. We do this to protect future requests
    00975         // after the last block has been removed from a particular
    00976         // memory Chunk, which in turn has been returned to the
    00977         // free list, and hence had been erased from the vector,
    00978         // so the size of the vector gets reduced by 1.
    00979         if ((_Difference_type)_S_last_request._M_where() >= __diff--)
    00980           _S_last_request._M_reset(__diff);
    00981
    00982         // If the Index into the vector of the region of memory
    00983         // that might hold the next address that will be passed to
    00984         // deallocated may have been invalidated due to the above
    00985         // erase procedure being called on the vector, hence we
    00986         // try to restore this invariant too.
    00987         if (_S_last_dealloc_index >= _S_mem_blocks.size())
    00988           {
    00989         _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
    00990         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
    00991           }
    00992       }
    00993       }
    00994
    00995     public:
    00996       bitmap_allocator() throw()
    00997       { }
    00998
    00999       bitmap_allocator(const bitmap_allocator&)
    01000       { }
    01001
    01002       template<typename _Tp1>
    01003         bitmap_allocator(const bitmap_allocator<_Tp1>&) throw()
    01004         { }
    01005
    01006       ~bitmap_allocator() throw()
    01007       { }
    01008
    01009       pointer
    01010       allocate(size_type __n)
    01011       {
    01012     if (__n > this->max_size())
    01013       std::__throw_bad_alloc();
    01014
    01015     if (__builtin_expect(__n == 1, true))
    01016       return this->_M_allocate_single_object();
    01017     else
    01018       {
    01019         const size_type __b = __n * sizeof(value_type);
    01020         return reinterpret_cast<pointer>(::operator new(__b));
    01021       }
    01022       }
    01023
    01024       pointer
    01025       allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
    01026       { return allocate(__n); }
    01027
    01028       void
    01029       deallocate(pointer __p, size_type __n) throw()
    01030       {
    01031     if (__builtin_expect(__p != 0, true))
    01032       {
    01033         if (__builtin_expect(__n == 1, true))
    01034           this->_M_deallocate_single_object(__p);
    01035         else
    01036 	      ::operator delete(__p);
    01037       }
    01038       }
    01039
    01040       pointer
    01041       address(reference __r) const
    01042       { return &__r; }
    01043
    01044       const_pointer
    01045       address(const_reference __r) const
    01046       { return &__r; }
    01047
    01048       size_type
    01049       max_size() const throw()
    01050       { return size_type(-1) / sizeof(value_type); }
    01051
    01052       void
    01053       construct(pointer __p, const_reference __data)
    01054       { ::new((void *)__p) value_type(__data); }
    01055
    01056 #ifdef __GXX_EXPERIMENTAL_CXX0X__
    01057       template<typename... _Args>
    01058         void
    01059         construct(pointer __p, _Args&&... __args)
    01060     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
    01061 #endif
    01062
    01063       void
    01064       destroy(pointer __p)
    01065       { __p->~value_type(); }
    01066     };
    01067
    01068   template<typename _Tp1, typename _Tp2>
    01069     bool
    01070     operator==(const bitmap_allocator<_Tp1>&,
    01071            const bitmap_allocator<_Tp2>&) throw()
    01072     { return true; }
    01073
    01074   template<typename _Tp1, typename _Tp2>
    01075     bool
    01076     operator!=(const bitmap_allocator<_Tp1>&,
    01077            const bitmap_allocator<_Tp2>&) throw()
    01078   { return false; }
    01079
    01080   // Static member definitions.
    01081   template<typename _Tp>
    01082     typename bitmap_allocator<_Tp>::_BPVector
    01083     bitmap_allocator<_Tp>::_S_mem_blocks;
    01084
    01085   template<typename _Tp>
    01086     size_t bitmap_allocator<_Tp>::_S_block_size =
    01087     2 * size_t(__detail::bits_per_block);
    01088
    01089   template<typename _Tp>
    01090     typename bitmap_allocator<_Tp>::_BPVector::size_type
    01091     bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
    01092
    01093   template<typename _Tp>
    01094     __detail::_Bitmap_counter
    01095       <typename bitmap_allocator<_Tp>::_Alloc_block*>
    01096     bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
    01097
    01098 #if defined __GTHREADS
    01099   template<typename _Tp>
    01100     typename bitmap_allocator<_Tp>::__mutex_type
    01101     bitmap_allocator<_Tp>::_S_mut;
    01102 #endif
    01103
    01104 _GLIBCXX_END_NAMESPACE
    01105
    01106 #endif
    01107