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