bitmap_allocator.h

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00001 // Bitmap Allocator. -*- C++ -*-
00002 
00003 // Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010
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 <utility> // For std::pair.
00034 #include <bits/functexcept.h> // For __throw_bad_alloc().
00035 #include <functional> // For greater_equal, and less_equal.
00036 #include <new> // For operator new.
00037 #include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
00038 #include <ext/concurrence.h>
00039 #include <bits/move.h>
00040 
00041 /** @brief The constant in the expression below is the alignment
00042  * required in bytes.
00043  */
00044 #define _BALLOC_ALIGN_BYTES 8
00045 
00046 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
00047 
00048   using std::size_t;
00049   using std::ptrdiff_t;
00050 
00051   namespace __detail
00052   {
00053     /** @class  __mini_vector bitmap_allocator.h bitmap_allocator.h
00054      *
00055      *  @brief  __mini_vector<> is a stripped down version of the
00056      *  full-fledged std::vector<>.
00057      *
00058      *  It is to be used only for built-in types or PODs. Notable
00059      *  differences are:
00060      * 
00061      *  @detail
00062      *  1. Not all accessor functions are present.
00063      *  2. Used ONLY for PODs.
00064      *  3. No Allocator template argument. Uses ::operator new() to get
00065      *  memory, and ::operator delete() to free it.
00066      *  Caveat: The dtor does NOT free the memory allocated, so this a
00067      *  memory-leaking vector!
00068      */
00069     template<typename _Tp>
00070       class __mini_vector
00071       {
00072     __mini_vector(const __mini_vector&);
00073     __mini_vector& operator=(const __mini_vector&);
00074 
00075       public:
00076     typedef _Tp value_type;
00077     typedef _Tp* pointer;
00078     typedef _Tp& reference;
00079     typedef const _Tp& const_reference;
00080     typedef size_t size_type;
00081     typedef ptrdiff_t difference_type;
00082     typedef pointer iterator;
00083 
00084       private:
00085     pointer _M_start;
00086     pointer _M_finish;
00087     pointer _M_end_of_storage;
00088 
00089     size_type
00090     _M_space_left() const throw()
00091     { return _M_end_of_storage - _M_finish; }
00092 
00093     pointer
00094     allocate(size_type __n)
00095     { return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
00096 
00097     void
00098     deallocate(pointer __p, size_type)
00099     { ::operator delete(__p); }
00100 
00101       public:
00102     // Members used: size(), push_back(), pop_back(),
00103     // insert(iterator, const_reference), erase(iterator),
00104     // begin(), end(), back(), operator[].
00105 
00106     __mini_vector()
00107         : _M_start(0), _M_finish(0), _M_end_of_storage(0) { }
00108 
00109     size_type
00110     size() const throw()
00111     { return _M_finish - _M_start; }
00112 
00113     iterator
00114     begin() const throw()
00115     { return this->_M_start; }
00116 
00117     iterator
00118     end() const throw()
00119     { return this->_M_finish; }
00120 
00121     reference
00122     back() const throw()
00123     { return *(this->end() - 1); }
00124 
00125     reference
00126     operator[](const size_type __pos) const throw()
00127     { return this->_M_start[__pos]; }
00128 
00129     void
00130     insert(iterator __pos, const_reference __x);
00131 
00132     void
00133     push_back(const_reference __x)
00134     {
00135       if (this->_M_space_left())
00136         {
00137           *this->end() = __x;
00138           ++this->_M_finish;
00139         }
00140       else
00141         this->insert(this->end(), __x);
00142     }
00143 
00144     void
00145     pop_back() throw()
00146     { --this->_M_finish; }
00147 
00148     void
00149     erase(iterator __pos) throw();
00150 
00151     void
00152     clear() throw()
00153     { this->_M_finish = this->_M_start; }
00154       };
00155 
00156     // Out of line function definitions.
00157     template<typename _Tp>
00158       void __mini_vector<_Tp>::
00159       insert(iterator __pos, const_reference __x)
00160       {
00161     if (this->_M_space_left())
00162       {
00163         size_type __to_move = this->_M_finish - __pos;
00164         iterator __dest = this->end();
00165         iterator __src = this->end() - 1;
00166 
00167         ++this->_M_finish;
00168         while (__to_move)
00169           {
00170         *__dest = *__src;
00171         --__dest; --__src; --__to_move;
00172           }
00173         *__pos = __x;
00174       }
00175     else
00176       {
00177         size_type __new_size = this->size() ? this->size() * 2 : 1;
00178         iterator __new_start = this->allocate(__new_size);
00179         iterator __first = this->begin();
00180         iterator __start = __new_start;
00181         while (__first != __pos)
00182           {
00183         *__start = *__first;
00184         ++__start; ++__first;
00185           }
00186         *__start = __x;
00187         ++__start;
00188         while (__first != this->end())
00189           {
00190         *__start = *__first;
00191         ++__start; ++__first;
00192           }
00193         if (this->_M_start)
00194           this->deallocate(this->_M_start, this->size());
00195 
00196         this->_M_start = __new_start;
00197         this->_M_finish = __start;
00198         this->_M_end_of_storage = this->_M_start + __new_size;
00199       }
00200       }
00201 
00202     template<typename _Tp>
00203       void __mini_vector<_Tp>::
00204       erase(iterator __pos) throw()
00205       {
00206     while (__pos + 1 != this->end())
00207       {
00208         *__pos = __pos[1];
00209         ++__pos;
00210       }
00211     --this->_M_finish;
00212       }
00213 
00214 
00215     template<typename _Tp>
00216       struct __mv_iter_traits
00217       {
00218     typedef typename _Tp::value_type value_type;
00219     typedef typename _Tp::difference_type difference_type;
00220       };
00221 
00222     template<typename _Tp>
00223       struct __mv_iter_traits<_Tp*>
00224       {
00225     typedef _Tp value_type;
00226     typedef ptrdiff_t difference_type;
00227       };
00228 
00229     enum 
00230       { 
00231     bits_per_byte = 8,
00232     bits_per_block = sizeof(size_t) * size_t(bits_per_byte) 
00233       };
00234 
00235     template<typename _ForwardIterator, typename _Tp, typename _Compare>
00236       _ForwardIterator
00237       __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
00238             const _Tp& __val, _Compare __comp)
00239       {
00240     typedef typename __mv_iter_traits<_ForwardIterator>::value_type
00241       _ValueType;
00242     typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
00243       _DistanceType;
00244 
00245     _DistanceType __len = __last - __first;
00246     _DistanceType __half;
00247     _ForwardIterator __middle;
00248 
00249     while (__len > 0)
00250       {
00251         __half = __len >> 1;
00252         __middle = __first;
00253         __middle += __half;
00254         if (__comp(*__middle, __val))
00255           {
00256         __first = __middle;
00257         ++__first;
00258         __len = __len - __half - 1;
00259           }
00260         else
00261           __len = __half;
00262       }
00263     return __first;
00264       }
00265 
00266     /** @brief The number of Blocks pointed to by the address pair
00267      *  passed to the function.
00268      */
00269     template<typename _AddrPair>
00270       inline size_t
00271       __num_blocks(_AddrPair __ap)
00272       { return (__ap.second - __ap.first) + 1; }
00273 
00274     /** @brief The number of Bit-maps pointed to by the address pair
00275      *  passed to the function.
00276      */
00277     template<typename _AddrPair>
00278       inline size_t
00279       __num_bitmaps(_AddrPair __ap)
00280       { return __num_blocks(__ap) / size_t(bits_per_block); }
00281 
00282     // _Tp should be a pointer type.
00283     template<typename _Tp>
00284       class _Inclusive_between 
00285       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
00286       {
00287     typedef _Tp pointer;
00288     pointer _M_ptr_value;
00289     typedef typename std::pair<_Tp, _Tp> _Block_pair;
00290     
00291       public:
00292     _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr) 
00293     { }
00294     
00295     bool 
00296     operator()(_Block_pair __bp) const throw()
00297     {
00298       if (std::less_equal<pointer>()(_M_ptr_value, __bp.second) 
00299           && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
00300         return true;
00301       else
00302         return false;
00303     }
00304       };
00305   
00306     // Used to pass a Functor to functions by reference.
00307     template<typename _Functor>
00308       class _Functor_Ref 
00309       : public std::unary_function<typename _Functor::argument_type, 
00310                    typename _Functor::result_type>
00311       {
00312     _Functor& _M_fref;
00313     
00314       public:
00315     typedef typename _Functor::argument_type argument_type;
00316     typedef typename _Functor::result_type result_type;
00317 
00318     _Functor_Ref(_Functor& __fref) : _M_fref(__fref) 
00319     { }
00320 
00321     result_type 
00322     operator()(argument_type __arg) 
00323     { return _M_fref(__arg); }
00324       };
00325 
00326     /** @class  _Ffit_finder bitmap_allocator.h bitmap_allocator.h
00327      *
00328      *  @brief  The class which acts as a predicate for applying the
00329      *  first-fit memory allocation policy for the bitmap allocator.
00330      */
00331     // _Tp should be a pointer type, and _Alloc is the Allocator for
00332     // the vector.
00333     template<typename _Tp>
00334       class _Ffit_finder 
00335       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
00336       {
00337     typedef typename std::pair<_Tp, _Tp> _Block_pair;
00338     typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
00339     typedef typename _BPVector::difference_type _Counter_type;
00340 
00341     size_t* _M_pbitmap;
00342     _Counter_type _M_data_offset;
00343 
00344       public:
00345     _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
00346     { }
00347 
00348     bool 
00349     operator()(_Block_pair __bp) throw()
00350     {
00351       // Set the _rover to the last physical location bitmap,
00352       // which is the bitmap which belongs to the first free
00353       // block. Thus, the bitmaps are in exact reverse order of
00354       // the actual memory layout. So, we count down the bitmaps,
00355       // which is the same as moving up the memory.
00356 
00357       // If the used count stored at the start of the Bit Map headers
00358       // is equal to the number of Objects that the current Block can
00359       // store, then there is definitely no space for another single
00360       // object, so just return false.
00361       _Counter_type __diff = __detail::__num_bitmaps(__bp);
00362 
00363       if (*(reinterpret_cast<size_t*>
00364         (__bp.first) - (__diff + 1)) == __detail::__num_blocks(__bp))
00365         return false;
00366 
00367       size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
00368 
00369       for (_Counter_type __i = 0; __i < __diff; ++__i)
00370         {
00371           _M_data_offset = __i;
00372           if (*__rover)
00373         {
00374           _M_pbitmap = __rover;
00375           return true;
00376         }
00377           --__rover;
00378         }
00379       return false;
00380     }
00381     
00382     size_t*
00383     _M_get() const throw()
00384     { return _M_pbitmap; }
00385 
00386     _Counter_type
00387     _M_offset() const throw()
00388     { return _M_data_offset * size_t(bits_per_block); }
00389       };
00390 
00391     /** @class  _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
00392      *
00393      *  @brief  The bitmap counter which acts as the bitmap
00394      *  manipulator, and manages the bit-manipulation functions and
00395      *  the searching and identification functions on the bit-map.
00396      */
00397     // _Tp should be a pointer type.
00398     template<typename _Tp>
00399       class _Bitmap_counter
00400       {
00401     typedef typename
00402     __detail::__mini_vector<typename std::pair<_Tp, _Tp> > _BPVector;
00403     typedef typename _BPVector::size_type _Index_type;
00404     typedef _Tp pointer;
00405 
00406     _BPVector& _M_vbp;
00407     size_t* _M_curr_bmap;
00408     size_t* _M_last_bmap_in_block;
00409     _Index_type _M_curr_index;
00410     
00411       public:
00412     // Use the 2nd parameter with care. Make sure that such an
00413     // entry exists in the vector before passing that particular
00414     // index to this ctor.
00415     _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
00416     { this->_M_reset(__index); }
00417     
00418     void 
00419     _M_reset(long __index = -1) throw()
00420     {
00421       if (__index == -1)
00422         {
00423           _M_curr_bmap = 0;
00424           _M_curr_index = static_cast<_Index_type>(-1);
00425           return;
00426         }
00427 
00428       _M_curr_index = __index;
00429       _M_curr_bmap = reinterpret_cast<size_t*>
00430         (_M_vbp[_M_curr_index].first) - 1;
00431       
00432       _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
00433     
00434       _M_last_bmap_in_block = _M_curr_bmap
00435         - ((_M_vbp[_M_curr_index].second 
00436         - _M_vbp[_M_curr_index].first + 1) 
00437            / size_t(bits_per_block) - 1);
00438     }
00439     
00440     // Dangerous Function! Use with extreme care. Pass to this
00441     // function ONLY those values that are known to be correct,
00442     // otherwise this will mess up big time.
00443     void
00444     _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
00445     { _M_curr_bmap = __new_internal_marker; }
00446     
00447     bool
00448     _M_finished() const throw()
00449     { return(_M_curr_bmap == 0); }
00450     
00451     _Bitmap_counter&
00452     operator++() throw()
00453     {
00454       if (_M_curr_bmap == _M_last_bmap_in_block)
00455         {
00456           if (++_M_curr_index == _M_vbp.size())
00457         _M_curr_bmap = 0;
00458           else
00459         this->_M_reset(_M_curr_index);
00460         }
00461       else
00462         --_M_curr_bmap;
00463       return *this;
00464     }
00465     
00466     size_t*
00467     _M_get() const throw()
00468     { return _M_curr_bmap; }
00469     
00470     pointer 
00471     _M_base() const throw()
00472     { return _M_vbp[_M_curr_index].first; }
00473 
00474     _Index_type
00475     _M_offset() const throw()
00476     {
00477       return size_t(bits_per_block)
00478         * ((reinterpret_cast<size_t*>(this->_M_base()) 
00479         - _M_curr_bmap) - 1);
00480     }
00481     
00482     _Index_type
00483     _M_where() const throw()
00484     { return _M_curr_index; }
00485       };
00486 
00487     /** @brief  Mark a memory address as allocated by re-setting the
00488      *  corresponding bit in the bit-map.
00489      */
00490     inline void 
00491     __bit_allocate(size_t* __pbmap, size_t __pos) throw()
00492     {
00493       size_t __mask = 1 << __pos;
00494       __mask = ~__mask;
00495       *__pbmap &= __mask;
00496     }
00497   
00498     /** @brief  Mark a memory address as free by setting the
00499      *  corresponding bit in the bit-map.
00500      */
00501     inline void 
00502     __bit_free(size_t* __pbmap, size_t __pos) throw()
00503     {
00504       size_t __mask = 1 << __pos;
00505       *__pbmap |= __mask;
00506     }
00507   } // namespace __detail
00508 
00509   /** @brief  Generic Version of the bsf instruction.
00510    */
00511   inline size_t 
00512   _Bit_scan_forward(size_t __num)
00513   { return static_cast<size_t>(__builtin_ctzl(__num)); }
00514 
00515   /** @class  free_list bitmap_allocator.h bitmap_allocator.h
00516    *
00517    *  @brief  The free list class for managing chunks of memory to be
00518    *  given to and returned by the bitmap_allocator.
00519    */
00520   class free_list
00521   {
00522   public:
00523     typedef size_t*                 value_type;
00524     typedef __detail::__mini_vector<value_type> vector_type;
00525     typedef vector_type::iterator       iterator;
00526     typedef __mutex             __mutex_type;
00527 
00528   private:
00529     struct _LT_pointer_compare
00530     {
00531       bool
00532       operator()(const size_t* __pui, 
00533          const size_t __cui) const throw()
00534       { return *__pui < __cui; }
00535     };
00536 
00537 #if defined __GTHREADS
00538     __mutex_type&
00539     _M_get_mutex()
00540     {
00541       static __mutex_type _S_mutex;
00542       return _S_mutex;
00543     }
00544 #endif
00545 
00546     vector_type&
00547     _M_get_free_list()
00548     {
00549       static vector_type _S_free_list;
00550       return _S_free_list;
00551     }
00552 
00553     /** @brief  Performs validation of memory based on their size.
00554      *
00555      *  @param  __addr The pointer to the memory block to be
00556      *  validated.
00557      *
00558      *  @detail  Validates the memory block passed to this function and
00559      *  appropriately performs the action of managing the free list of
00560      *  blocks by adding this block to the free list or deleting this
00561      *  or larger blocks from the free list.
00562      */
00563     void
00564     _M_validate(size_t* __addr) throw()
00565     {
00566       vector_type& __free_list = _M_get_free_list();
00567       const vector_type::size_type __max_size = 64;
00568       if (__free_list.size() >= __max_size)
00569     {
00570       // Ok, the threshold value has been reached.  We determine
00571       // which block to remove from the list of free blocks.
00572       if (*__addr >= *__free_list.back())
00573         {
00574           // Ok, the new block is greater than or equal to the
00575           // last block in the list of free blocks. We just free
00576           // the new block.
00577           ::operator delete(static_cast<void*>(__addr));
00578           return;
00579         }
00580       else
00581         {
00582           // Deallocate the last block in the list of free lists,
00583           // and insert the new one in its correct position.
00584           ::operator delete(static_cast<void*>(__free_list.back()));
00585           __free_list.pop_back();
00586         }
00587     }
00588       
00589       // Just add the block to the list of free lists unconditionally.
00590       iterator __temp = __detail::__lower_bound
00591     (__free_list.begin(), __free_list.end(), 
00592      *__addr, _LT_pointer_compare());
00593 
00594       // We may insert the new free list before _temp;
00595       __free_list.insert(__temp, __addr);
00596     }
00597 
00598     /** @brief  Decides whether the wastage of memory is acceptable for
00599      *  the current memory request and returns accordingly.
00600      *
00601      *  @param __block_size The size of the block available in the free
00602      *  list.
00603      *
00604      *  @param __required_size The required size of the memory block.
00605      *
00606      *  @return true if the wastage incurred is acceptable, else returns
00607      *  false.
00608      */
00609     bool 
00610     _M_should_i_give(size_t __block_size, 
00611              size_t __required_size) throw()
00612     {
00613       const size_t __max_wastage_percentage = 36;
00614       if (__block_size >= __required_size && 
00615       (((__block_size - __required_size) * 100 / __block_size)
00616        < __max_wastage_percentage))
00617     return true;
00618       else
00619     return false;
00620     }
00621 
00622   public:
00623     /** @brief This function returns the block of memory to the
00624      *  internal free list.
00625      *
00626      *  @param  __addr The pointer to the memory block that was given
00627      *  by a call to the _M_get function.
00628      */
00629     inline void 
00630     _M_insert(size_t* __addr) throw()
00631     {
00632 #if defined __GTHREADS
00633       __scoped_lock __bfl_lock(_M_get_mutex());
00634 #endif
00635       // Call _M_validate to decide what should be done with
00636       // this particular free list.
00637       this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
00638       // See discussion as to why this is 1!
00639     }
00640     
00641     /** @brief  This function gets a block of memory of the specified
00642      *  size from the free list.
00643      *
00644      *  @param  __sz The size in bytes of the memory required.
00645      *
00646      *  @return  A pointer to the new memory block of size at least
00647      *  equal to that requested.
00648      */
00649     size_t*
00650     _M_get(size_t __sz) throw(std::bad_alloc);
00651 
00652     /** @brief  This function just clears the internal Free List, and
00653      *  gives back all the memory to the OS.
00654      */
00655     void 
00656     _M_clear();
00657   };
00658 
00659 
00660   // Forward declare the class.
00661   template<typename _Tp> 
00662     class bitmap_allocator;
00663 
00664   // Specialize for void:
00665   template<>
00666     class bitmap_allocator<void>
00667     {
00668     public:
00669       typedef void*       pointer;
00670       typedef const void* const_pointer;
00671 
00672       // Reference-to-void members are impossible.
00673       typedef void  value_type;
00674       template<typename _Tp1>
00675         struct rebind
00676     {
00677       typedef bitmap_allocator<_Tp1> other;
00678     };
00679     };
00680 
00681   /**
00682    * @brief Bitmap Allocator, primary template.
00683    * @ingroup allocators
00684    */
00685   template<typename _Tp>
00686     class bitmap_allocator : private free_list
00687     {
00688     public:
00689       typedef size_t            size_type;
00690       typedef ptrdiff_t         difference_type;
00691       typedef _Tp*              pointer;
00692       typedef const _Tp*        const_pointer;
00693       typedef _Tp&              reference;
00694       typedef const _Tp&        const_reference;
00695       typedef _Tp               value_type;
00696       typedef free_list::__mutex_type   __mutex_type;
00697 
00698       template<typename _Tp1>
00699         struct rebind
00700     {
00701       typedef bitmap_allocator<_Tp1> other;
00702     };
00703 
00704     private:
00705       template<size_t _BSize, size_t _AlignSize>
00706         struct aligned_size
00707     {
00708       enum
00709         { 
00710           modulus = _BSize % _AlignSize,
00711           value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
00712         };
00713     };
00714 
00715       struct _Alloc_block
00716       {
00717     char __M_unused[aligned_size<sizeof(value_type),
00718             _BALLOC_ALIGN_BYTES>::value];
00719       };
00720 
00721 
00722       typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
00723 
00724       typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
00725       typedef typename _BPVector::iterator _BPiter;
00726 
00727       template<typename _Predicate>
00728         static _BPiter
00729         _S_find(_Predicate __p)
00730         {
00731       _BPiter __first = _S_mem_blocks.begin();
00732       while (__first != _S_mem_blocks.end() && !__p(*__first))
00733         ++__first;
00734       return __first;
00735     }
00736 
00737 #if defined _GLIBCXX_DEBUG
00738       // Complexity: O(lg(N)). Where, N is the number of block of size
00739       // sizeof(value_type).
00740       void 
00741       _S_check_for_free_blocks() throw()
00742       {
00743     typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
00744     _BPiter __bpi = _S_find(_FFF());
00745 
00746     _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
00747       }
00748 #endif
00749 
00750       /** @brief  Responsible for exponentially growing the internal
00751        *  memory pool.
00752        *
00753        *  @throw  std::bad_alloc. If memory can not be allocated.
00754        *
00755        *  @detail  Complexity: O(1), but internally depends upon the
00756        *  complexity of the function free_list::_M_get. The part where
00757        *  the bitmap headers are written has complexity: O(X),where X
00758        *  is the number of blocks of size sizeof(value_type) within
00759        *  the newly acquired block. Having a tight bound.
00760        */
00761       void 
00762       _S_refill_pool() throw(std::bad_alloc)
00763       {
00764 #if defined _GLIBCXX_DEBUG
00765     _S_check_for_free_blocks();
00766 #endif
00767 
00768     const size_t __num_bitmaps = (_S_block_size
00769                       / size_t(__detail::bits_per_block));
00770     const size_t __size_to_allocate = sizeof(size_t) 
00771       + _S_block_size * sizeof(_Alloc_block) 
00772       + __num_bitmaps * sizeof(size_t);
00773 
00774     size_t* __temp =
00775       reinterpret_cast<size_t*>(this->_M_get(__size_to_allocate));
00776     *__temp = 0;
00777     ++__temp;
00778 
00779     // The Header information goes at the Beginning of the Block.
00780     _Block_pair __bp = 
00781       std::make_pair(reinterpret_cast<_Alloc_block*>
00782              (__temp + __num_bitmaps), 
00783              reinterpret_cast<_Alloc_block*>
00784              (__temp + __num_bitmaps) 
00785              + _S_block_size - 1);
00786     
00787     // Fill the Vector with this information.
00788     _S_mem_blocks.push_back(__bp);
00789 
00790     for (size_t __i = 0; __i < __num_bitmaps; ++__i)
00791       __temp[__i] = ~static_cast<size_t>(0); // 1 Indicates all Free.
00792 
00793     _S_block_size *= 2;
00794       }
00795 
00796       static _BPVector _S_mem_blocks;
00797       static size_t _S_block_size;
00798       static __detail::_Bitmap_counter<_Alloc_block*> _S_last_request;
00799       static typename _BPVector::size_type _S_last_dealloc_index;
00800 #if defined __GTHREADS
00801       static __mutex_type _S_mut;
00802 #endif
00803 
00804     public:
00805 
00806       /** @brief  Allocates memory for a single object of size
00807        *  sizeof(_Tp).
00808        *
00809        *  @throw  std::bad_alloc. If memory can not be allocated.
00810        *
00811        *  @detail  Complexity: Worst case complexity is O(N), but that
00812        *  is hardly ever hit. If and when this particular case is
00813        *  encountered, the next few cases are guaranteed to have a
00814        *  worst case complexity of O(1)!  That's why this function
00815        *  performs very well on average. You can consider this
00816        *  function to have a complexity referred to commonly as:
00817        *  Amortized Constant time.
00818        */
00819       pointer 
00820       _M_allocate_single_object() throw(std::bad_alloc)
00821       {
00822 #if defined __GTHREADS
00823     __scoped_lock __bit_lock(_S_mut);
00824 #endif
00825 
00826     // The algorithm is something like this: The last_request
00827     // variable points to the last accessed Bit Map. When such a
00828     // condition occurs, we try to find a free block in the
00829     // current bitmap, or succeeding bitmaps until the last bitmap
00830     // is reached. If no free block turns up, we resort to First
00831     // Fit method.
00832 
00833     // WARNING: Do not re-order the condition in the while
00834     // statement below, because it relies on C++'s short-circuit
00835     // evaluation. The return from _S_last_request->_M_get() will
00836     // NOT be dereference able if _S_last_request->_M_finished()
00837     // returns true. This would inevitably lead to a NULL pointer
00838     // dereference if tinkered with.
00839     while (_S_last_request._M_finished() == false
00840            && (*(_S_last_request._M_get()) == 0))
00841       _S_last_request.operator++();
00842 
00843     if (__builtin_expect(_S_last_request._M_finished() == true, false))
00844       {
00845         // Fall Back to First Fit algorithm.
00846         typedef typename __detail::_Ffit_finder<_Alloc_block*> _FFF;
00847         _FFF __fff;
00848         _BPiter __bpi = _S_find(__detail::_Functor_Ref<_FFF>(__fff));
00849 
00850         if (__bpi != _S_mem_blocks.end())
00851           {
00852         // Search was successful. Ok, now mark the first bit from
00853         // the right as 0, meaning Allocated. This bit is obtained
00854         // by calling _M_get() on __fff.
00855         size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
00856         __detail::__bit_allocate(__fff._M_get(), __nz_bit);
00857 
00858         _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
00859 
00860         // Now, get the address of the bit we marked as allocated.
00861         pointer __ret = reinterpret_cast<pointer>
00862           (__bpi->first + __fff._M_offset() + __nz_bit);
00863         size_t* __puse_count = 
00864           reinterpret_cast<size_t*>
00865           (__bpi->first) - (__detail::__num_bitmaps(*__bpi) + 1);
00866         
00867         ++(*__puse_count);
00868         return __ret;
00869           }
00870         else
00871           {
00872         // Search was unsuccessful. We Add more memory to the
00873         // pool by calling _S_refill_pool().
00874         _S_refill_pool();
00875 
00876         // _M_Reset the _S_last_request structure to the first
00877         // free block's bit map.
00878         _S_last_request._M_reset(_S_mem_blocks.size() - 1);
00879 
00880         // Now, mark that bit as allocated.
00881           }
00882       }
00883 
00884     // _S_last_request holds a pointer to a valid bit map, that
00885     // points to a free block in memory.
00886     size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
00887     __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
00888 
00889     pointer __ret = reinterpret_cast<pointer>
00890       (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
00891 
00892     size_t* __puse_count = reinterpret_cast<size_t*>
00893       (_S_mem_blocks[_S_last_request._M_where()].first)
00894       - (__detail::
00895          __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
00896 
00897     ++(*__puse_count);
00898     return __ret;
00899       }
00900 
00901       /** @brief  Deallocates memory that belongs to a single object of
00902        *  size sizeof(_Tp).
00903        *
00904        *  @detail  Complexity: O(lg(N)), but the worst case is not hit
00905        *  often!  This is because containers usually deallocate memory
00906        *  close to each other and this case is handled in O(1) time by
00907        *  the deallocate function.
00908        */
00909       void 
00910       _M_deallocate_single_object(pointer __p) throw()
00911       {
00912 #if defined __GTHREADS
00913     __scoped_lock __bit_lock(_S_mut);
00914 #endif
00915     _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
00916 
00917     typedef typename _BPVector::iterator _Iterator;
00918     typedef typename _BPVector::difference_type _Difference_type;
00919 
00920     _Difference_type __diff;
00921     long __displacement;
00922 
00923     _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
00924 
00925     __detail::_Inclusive_between<_Alloc_block*> __ibt(__real_p);
00926     if (__ibt(_S_mem_blocks[_S_last_dealloc_index]))
00927       {
00928         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
00929                   <= _S_mem_blocks.size() - 1);
00930 
00931         // Initial Assumption was correct!
00932         __diff = _S_last_dealloc_index;
00933         __displacement = __real_p - _S_mem_blocks[__diff].first;
00934       }
00935     else
00936       {
00937         _Iterator _iter = _S_find(__ibt);
00938 
00939         _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
00940 
00941         __diff = _iter - _S_mem_blocks.begin();
00942         __displacement = __real_p - _S_mem_blocks[__diff].first;
00943         _S_last_dealloc_index = __diff;
00944       }
00945 
00946     // Get the position of the iterator that has been found.
00947     const size_t __rotate = (__displacement
00948                  % size_t(__detail::bits_per_block));
00949     size_t* __bitmapC = 
00950       reinterpret_cast<size_t*>
00951       (_S_mem_blocks[__diff].first) - 1;
00952     __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
00953       
00954     __detail::__bit_free(__bitmapC, __rotate);
00955     size_t* __puse_count = reinterpret_cast<size_t*>
00956       (_S_mem_blocks[__diff].first)
00957       - (__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
00958     
00959     _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
00960 
00961     --(*__puse_count);
00962 
00963     if (__builtin_expect(*__puse_count == 0, false))
00964       {
00965         _S_block_size /= 2;
00966       
00967         // We can safely remove this block.
00968         // _Block_pair __bp = _S_mem_blocks[__diff];
00969         this->_M_insert(__puse_count);
00970         _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
00971 
00972         // Reset the _S_last_request variable to reflect the
00973         // erased block. We do this to protect future requests
00974         // after the last block has been removed from a particular
00975         // memory Chunk, which in turn has been returned to the
00976         // free list, and hence had been erased from the vector,
00977         // so the size of the vector gets reduced by 1.
00978         if ((_Difference_type)_S_last_request._M_where() >= __diff--)
00979           _S_last_request._M_reset(__diff); 
00980 
00981         // If the Index into the vector of the region of memory
00982         // that might hold the next address that will be passed to
00983         // deallocated may have been invalidated due to the above
00984         // erase procedure being called on the vector, hence we
00985         // try to restore this invariant too.
00986         if (_S_last_dealloc_index >= _S_mem_blocks.size())
00987           {
00988         _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
00989         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
00990           }
00991       }
00992       }
00993 
00994     public:
00995       bitmap_allocator() throw()
00996       { }
00997 
00998       bitmap_allocator(const bitmap_allocator&)
00999       { }
01000 
01001       template<typename _Tp1>
01002         bitmap_allocator(const bitmap_allocator<_Tp1>&) throw()
01003         { }
01004 
01005       ~bitmap_allocator() throw()
01006       { }
01007 
01008       pointer 
01009       allocate(size_type __n)
01010       {
01011     if (__n > this->max_size())
01012       std::__throw_bad_alloc();
01013 
01014     if (__builtin_expect(__n == 1, true))
01015       return this->_M_allocate_single_object();
01016     else
01017       { 
01018         const size_type __b = __n * sizeof(value_type);
01019         return reinterpret_cast<pointer>(::operator new(__b));
01020       }
01021       }
01022 
01023       pointer 
01024       allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
01025       { return allocate(__n); }
01026 
01027       void 
01028       deallocate(pointer __p, size_type __n) throw()
01029       {
01030     if (__builtin_expect(__p != 0, true))
01031       {
01032         if (__builtin_expect(__n == 1, true))
01033           this->_M_deallocate_single_object(__p);
01034         else
01035 	      ::operator delete(__p);
01036       }
01037       }
01038 
01039       pointer 
01040       address(reference __r) const
01041       { return std::__addressof(__r); }
01042 
01043       const_pointer 
01044       address(const_reference __r) const
01045       { return std::__addressof(__r); }
01046 
01047       size_type 
01048       max_size() const throw()
01049       { return size_type(-1) / sizeof(value_type); }
01050 
01051       void 
01052       construct(pointer __p, const_reference __data)
01053       { ::new((void *)__p) value_type(__data); }
01054 
01055 #ifdef __GXX_EXPERIMENTAL_CXX0X__
01056       template<typename... _Args>
01057         void
01058         construct(pointer __p, _Args&&... __args)
01059     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
01060 #endif
01061 
01062       void 
01063       destroy(pointer __p)
01064       { __p->~value_type(); }
01065     };
01066 
01067   template<typename _Tp1, typename _Tp2>
01068     bool 
01069     operator==(const bitmap_allocator<_Tp1>&, 
01070            const bitmap_allocator<_Tp2>&) throw()
01071     { return true; }
01072   
01073   template<typename _Tp1, typename _Tp2>
01074     bool 
01075     operator!=(const bitmap_allocator<_Tp1>&, 
01076            const bitmap_allocator<_Tp2>&) throw() 
01077   { return false; }
01078 
01079   // Static member definitions.
01080   template<typename _Tp>
01081     typename bitmap_allocator<_Tp>::_BPVector
01082     bitmap_allocator<_Tp>::_S_mem_blocks;
01083 
01084   template<typename _Tp>
01085     size_t bitmap_allocator<_Tp>::_S_block_size = 
01086     2 * size_t(__detail::bits_per_block);
01087 
01088   template<typename _Tp>
01089     typename bitmap_allocator<_Tp>::_BPVector::size_type 
01090     bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
01091 
01092   template<typename _Tp>
01093     __detail::_Bitmap_counter
01094       <typename bitmap_allocator<_Tp>::_Alloc_block*>
01095     bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
01096 
01097 #if defined __GTHREADS
01098   template<typename _Tp>
01099     typename bitmap_allocator<_Tp>::__mutex_type
01100     bitmap_allocator<_Tp>::_S_mut;
01101 #endif
01102 
01103 _GLIBCXX_END_NAMESPACE
01104 
01105 #endif 
01106