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() : _M_start(0), _M_finish(0), 
00108               _M_end_of_storage(0)
00109     { }
00110 
00111 #if 0
00112     ~__mini_vector()
00113     {
00114       if (this->_M_start)
00115         {
00116           this->deallocate(this->_M_start, this->_M_end_of_storage 
00117                    - this->_M_start);
00118         }
00119     }
00120 #endif
00121 
00122     size_type
00123     size() const throw()
00124     { return _M_finish - _M_start; }
00125 
00126     iterator
00127     begin() const throw()
00128     { return this->_M_start; }
00129 
00130     iterator
00131     end() const throw()
00132     { return this->_M_finish; }
00133 
00134     reference
00135     back() const throw()
00136     { return *(this->end() - 1); }
00137 
00138     reference
00139     operator[](const size_type __pos) const throw()
00140     { return this->_M_start[__pos]; }
00141 
00142     void
00143     insert(iterator __pos, const_reference __x);
00144 
00145     void
00146     push_back(const_reference __x)
00147     {
00148       if (this->_M_space_left())
00149         {
00150           *this->end() = __x;
00151           ++this->_M_finish;
00152         }
00153       else
00154         this->insert(this->end(), __x);
00155     }
00156 
00157     void
00158     pop_back() throw()
00159     { --this->_M_finish; }
00160 
00161     void
00162     erase(iterator __pos) throw();
00163 
00164     void
00165     clear() throw()
00166     { this->_M_finish = this->_M_start; }
00167       };
00168 
00169     // Out of line function definitions.
00170     template<typename _Tp>
00171       void __mini_vector<_Tp>::
00172       insert(iterator __pos, const_reference __x)
00173       {
00174     if (this->_M_space_left())
00175       {
00176         size_type __to_move = this->_M_finish - __pos;
00177         iterator __dest = this->end();
00178         iterator __src = this->end() - 1;
00179 
00180         ++this->_M_finish;
00181         while (__to_move)
00182           {
00183         *__dest = *__src;
00184         --__dest; --__src; --__to_move;
00185           }
00186         *__pos = __x;
00187       }
00188     else
00189       {
00190         size_type __new_size = this->size() ? this->size() * 2 : 1;
00191         iterator __new_start = this->allocate(__new_size);
00192         iterator __first = this->begin();
00193         iterator __start = __new_start;
00194         while (__first != __pos)
00195           {
00196         *__start = *__first;
00197         ++__start; ++__first;
00198           }
00199         *__start = __x;
00200         ++__start;
00201         while (__first != this->end())
00202           {
00203         *__start = *__first;
00204         ++__start; ++__first;
00205           }
00206         if (this->_M_start)
00207           this->deallocate(this->_M_start, this->size());
00208 
00209         this->_M_start = __new_start;
00210         this->_M_finish = __start;
00211         this->_M_end_of_storage = this->_M_start + __new_size;
00212       }
00213       }
00214 
00215     template<typename _Tp>
00216       void __mini_vector<_Tp>::
00217       erase(iterator __pos) throw()
00218       {
00219     while (__pos + 1 != this->end())
00220       {
00221         *__pos = __pos[1];
00222         ++__pos;
00223       }
00224     --this->_M_finish;
00225       }
00226 
00227 
00228     template<typename _Tp>
00229       struct __mv_iter_traits
00230       {
00231     typedef typename _Tp::value_type value_type;
00232     typedef typename _Tp::difference_type difference_type;
00233       };
00234 
00235     template<typename _Tp>
00236       struct __mv_iter_traits<_Tp*>
00237       {
00238     typedef _Tp value_type;
00239     typedef ptrdiff_t difference_type;
00240       };
00241 
00242     enum 
00243       { 
00244     bits_per_byte = 8,
00245     bits_per_block = sizeof(size_t) * size_t(bits_per_byte) 
00246       };
00247 
00248     template<typename _ForwardIterator, typename _Tp, typename _Compare>
00249       _ForwardIterator
00250       __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
00251             const _Tp& __val, _Compare __comp)
00252       {
00253     typedef typename __mv_iter_traits<_ForwardIterator>::value_type
00254       _ValueType;
00255     typedef typename __mv_iter_traits<_ForwardIterator>::difference_type
00256       _DistanceType;
00257 
00258     _DistanceType __len = __last - __first;
00259     _DistanceType __half;
00260     _ForwardIterator __middle;
00261 
00262     while (__len > 0)
00263       {
00264         __half = __len >> 1;
00265         __middle = __first;
00266         __middle += __half;
00267         if (__comp(*__middle, __val))
00268           {
00269         __first = __middle;
00270         ++__first;
00271         __len = __len - __half - 1;
00272           }
00273         else
00274           __len = __half;
00275       }
00276     return __first;
00277       }
00278 
00279     template<typename _InputIterator, typename _Predicate>
00280       inline _InputIterator
00281       __find_if(_InputIterator __first, _InputIterator __last, _Predicate __p)
00282       {
00283     while (__first != __last && !__p(*__first))
00284       ++__first;
00285     return __first;
00286       }
00287 
00288     /** @brief The number of Blocks pointed to by the address pair
00289      *  passed to the function.
00290      */
00291     template<typename _AddrPair>
00292       inline size_t
00293       __num_blocks(_AddrPair __ap)
00294       { return (__ap.second - __ap.first) + 1; }
00295 
00296     /** @brief The number of Bit-maps pointed to by the address pair
00297      *  passed to the function.
00298      */
00299     template<typename _AddrPair>
00300       inline size_t
00301       __num_bitmaps(_AddrPair __ap)
00302       { return __num_blocks(__ap) / size_t(bits_per_block); }
00303 
00304     // _Tp should be a pointer type.
00305     template<typename _Tp>
00306       class _Inclusive_between 
00307       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
00308       {
00309     typedef _Tp pointer;
00310     pointer _M_ptr_value;
00311     typedef typename std::pair<_Tp, _Tp> _Block_pair;
00312     
00313       public:
00314     _Inclusive_between(pointer __ptr) : _M_ptr_value(__ptr) 
00315     { }
00316     
00317     bool 
00318     operator()(_Block_pair __bp) const throw()
00319     {
00320       if (std::less_equal<pointer>()(_M_ptr_value, __bp.second) 
00321           && std::greater_equal<pointer>()(_M_ptr_value, __bp.first))
00322         return true;
00323       else
00324         return false;
00325     }
00326       };
00327   
00328     // Used to pass a Functor to functions by reference.
00329     template<typename _Functor>
00330       class _Functor_Ref 
00331       : public std::unary_function<typename _Functor::argument_type, 
00332                    typename _Functor::result_type>
00333       {
00334     _Functor& _M_fref;
00335     
00336       public:
00337     typedef typename _Functor::argument_type argument_type;
00338     typedef typename _Functor::result_type result_type;
00339 
00340     _Functor_Ref(_Functor& __fref) : _M_fref(__fref) 
00341     { }
00342 
00343     result_type 
00344     operator()(argument_type __arg) 
00345     { return _M_fref(__arg); }
00346       };
00347 
00348     /** @class  _Ffit_finder bitmap_allocator.h bitmap_allocator.h
00349      *
00350      *  @brief  The class which acts as a predicate for applying the
00351      *  first-fit memory allocation policy for the bitmap allocator.
00352      */
00353     // _Tp should be a pointer type, and _Alloc is the Allocator for
00354     // the vector.
00355     template<typename _Tp>
00356       class _Ffit_finder 
00357       : public std::unary_function<typename std::pair<_Tp, _Tp>, bool>
00358       {
00359     typedef typename std::pair<_Tp, _Tp> _Block_pair;
00360     typedef typename __detail::__mini_vector<_Block_pair> _BPVector;
00361     typedef typename _BPVector::difference_type _Counter_type;
00362 
00363     size_t* _M_pbitmap;
00364     _Counter_type _M_data_offset;
00365 
00366       public:
00367     _Ffit_finder() : _M_pbitmap(0), _M_data_offset(0)
00368     { }
00369 
00370     bool 
00371     operator()(_Block_pair __bp) throw()
00372     {
00373       // Set the _rover to the last physical location bitmap,
00374       // which is the bitmap which belongs to the first free
00375       // block. Thus, the bitmaps are in exact reverse order of
00376       // the actual memory layout. So, we count down the bitmaps,
00377       // which is the same as moving up the memory.
00378 
00379       // If the used count stored at the start of the Bit Map headers
00380       // is equal to the number of Objects that the current Block can
00381       // store, then there is definitely no space for another single
00382       // object, so just return false.
00383       _Counter_type __diff = 
00384         __gnu_cxx::__detail::__num_bitmaps(__bp);
00385 
00386       if (*(reinterpret_cast<size_t*>
00387         (__bp.first) - (__diff + 1))
00388           == __gnu_cxx::__detail::__num_blocks(__bp))
00389         return false;
00390 
00391       size_t* __rover = reinterpret_cast<size_t*>(__bp.first) - 1;
00392 
00393       for (_Counter_type __i = 0; __i < __diff; ++__i)
00394         {
00395           _M_data_offset = __i;
00396           if (*__rover)
00397         {
00398           _M_pbitmap = __rover;
00399           return true;
00400         }
00401           --__rover;
00402         }
00403       return false;
00404     }
00405 
00406     
00407     size_t*
00408     _M_get() const throw()
00409     { return _M_pbitmap; }
00410 
00411     _Counter_type
00412     _M_offset() const throw()
00413     { return _M_data_offset * size_t(bits_per_block); }
00414       };
00415 
00416 
00417     /** @class  _Bitmap_counter bitmap_allocator.h bitmap_allocator.h
00418      *
00419      *  @brief  The bitmap counter which acts as the bitmap
00420      *  manipulator, and manages the bit-manipulation functions and
00421      *  the searching and identification functions on the bit-map.
00422      */
00423     // _Tp should be a pointer type.
00424     template<typename _Tp>
00425       class _Bitmap_counter
00426       {
00427     typedef typename __detail::__mini_vector<typename std::pair<_Tp, _Tp> >
00428     _BPVector;
00429     typedef typename _BPVector::size_type _Index_type;
00430     typedef _Tp pointer;
00431     
00432     _BPVector& _M_vbp;
00433     size_t* _M_curr_bmap;
00434     size_t* _M_last_bmap_in_block;
00435     _Index_type _M_curr_index;
00436     
00437       public:
00438     // Use the 2nd parameter with care. Make sure that such an
00439     // entry exists in the vector before passing that particular
00440     // index to this ctor.
00441     _Bitmap_counter(_BPVector& Rvbp, long __index = -1) : _M_vbp(Rvbp)
00442     { this->_M_reset(__index); }
00443     
00444     void 
00445     _M_reset(long __index = -1) throw()
00446     {
00447       if (__index == -1)
00448         {
00449           _M_curr_bmap = 0;
00450           _M_curr_index = static_cast<_Index_type>(-1);
00451           return;
00452         }
00453 
00454       _M_curr_index = __index;
00455       _M_curr_bmap = reinterpret_cast<size_t*>
00456         (_M_vbp[_M_curr_index].first) - 1;
00457       
00458       _GLIBCXX_DEBUG_ASSERT(__index <= (long)_M_vbp.size() - 1);
00459     
00460       _M_last_bmap_in_block = _M_curr_bmap
00461         - ((_M_vbp[_M_curr_index].second 
00462         - _M_vbp[_M_curr_index].first + 1) 
00463            / size_t(bits_per_block) - 1);
00464     }
00465     
00466     // Dangerous Function! Use with extreme care. Pass to this
00467     // function ONLY those values that are known to be correct,
00468     // otherwise this will mess up big time.
00469     void
00470     _M_set_internal_bitmap(size_t* __new_internal_marker) throw()
00471     { _M_curr_bmap = __new_internal_marker; }
00472     
00473     bool
00474     _M_finished() const throw()
00475     { return(_M_curr_bmap == 0); }
00476     
00477     _Bitmap_counter&
00478     operator++() throw()
00479     {
00480       if (_M_curr_bmap == _M_last_bmap_in_block)
00481         {
00482           if (++_M_curr_index == _M_vbp.size())
00483         _M_curr_bmap = 0;
00484           else
00485         this->_M_reset(_M_curr_index);
00486         }
00487       else
00488         --_M_curr_bmap;
00489       return *this;
00490     }
00491     
00492     size_t*
00493     _M_get() const throw()
00494     { return _M_curr_bmap; }
00495     
00496     pointer 
00497     _M_base() const throw()
00498     { return _M_vbp[_M_curr_index].first; }
00499 
00500     _Index_type
00501     _M_offset() const throw()
00502     {
00503       return size_t(bits_per_block)
00504         * ((reinterpret_cast<size_t*>(this->_M_base()) 
00505         - _M_curr_bmap) - 1);
00506     }
00507     
00508     _Index_type
00509     _M_where() const throw()
00510     { return _M_curr_index; }
00511       };
00512 
00513     /** @brief  Mark a memory address as allocated by re-setting the
00514      *  corresponding bit in the bit-map.
00515      */
00516     inline void 
00517     __bit_allocate(size_t* __pbmap, size_t __pos) throw()
00518     {
00519       size_t __mask = 1 << __pos;
00520       __mask = ~__mask;
00521       *__pbmap &= __mask;
00522     }
00523   
00524     /** @brief  Mark a memory address as free by setting the
00525      *  corresponding bit in the bit-map.
00526      */
00527     inline void 
00528     __bit_free(size_t* __pbmap, size_t __pos) throw()
00529     {
00530       size_t __mask = 1 << __pos;
00531       *__pbmap |= __mask;
00532     }
00533   } // namespace __detail
00534 
00535   /** @brief  Generic Version of the bsf instruction.
00536    */
00537   inline size_t 
00538   _Bit_scan_forward(size_t __num)
00539   { return static_cast<size_t>(__builtin_ctzl(__num)); }
00540 
00541   /** @class  free_list bitmap_allocator.h bitmap_allocator.h
00542    *
00543    *  @brief  The free list class for managing chunks of memory to be
00544    *  given to and returned by the bitmap_allocator.
00545    */
00546   class free_list
00547   {
00548     typedef size_t*                 value_type;
00549     typedef __detail::__mini_vector<value_type> vector_type;
00550     typedef vector_type::iterator       iterator;
00551     typedef __mutex             __mutex_type;
00552 
00553     struct _LT_pointer_compare
00554     {
00555       bool
00556       operator()(const size_t* __pui, 
00557          const size_t __cui) const throw()
00558       { return *__pui < __cui; }
00559     };
00560 
00561 #if defined __GTHREADS
00562     __mutex_type&
00563     _M_get_mutex()
00564     {
00565       static __mutex_type _S_mutex;
00566       return _S_mutex;
00567     }
00568 #endif
00569 
00570     vector_type&
00571     _M_get_free_list()
00572     {
00573       static vector_type _S_free_list;
00574       return _S_free_list;
00575     }
00576 
00577     /** @brief  Performs validation of memory based on their size.
00578      *
00579      *  @param  __addr The pointer to the memory block to be
00580      *  validated.
00581      *
00582      *  @detail  Validates the memory block passed to this function and
00583      *  appropriately performs the action of managing the free list of
00584      *  blocks by adding this block to the free list or deleting this
00585      *  or larger blocks from the free list.
00586      */
00587     void
00588     _M_validate(size_t* __addr) throw()
00589     {
00590       vector_type& __free_list = _M_get_free_list();
00591       const vector_type::size_type __max_size = 64;
00592       if (__free_list.size() >= __max_size)
00593     {
00594       // Ok, the threshold value has been reached.  We determine
00595       // which block to remove from the list of free blocks.
00596       if (*__addr >= *__free_list.back())
00597         {
00598           // Ok, the new block is greater than or equal to the
00599           // last block in the list of free blocks. We just free
00600           // the new block.
00601           ::operator delete(static_cast<void*>(__addr));
00602           return;
00603         }
00604       else
00605         {
00606           // Deallocate the last block in the list of free lists,
00607           // and insert the new one in its correct position.
00608           ::operator delete(static_cast<void*>(__free_list.back()));
00609           __free_list.pop_back();
00610         }
00611     }
00612       
00613       // Just add the block to the list of free lists unconditionally.
00614       iterator __temp = __gnu_cxx::__detail::__lower_bound
00615     (__free_list.begin(), __free_list.end(), 
00616      *__addr, _LT_pointer_compare());
00617 
00618       // We may insert the new free list before _temp;
00619       __free_list.insert(__temp, __addr);
00620     }
00621 
00622     /** @brief  Decides whether the wastage of memory is acceptable for
00623      *  the current memory request and returns accordingly.
00624      *
00625      *  @param __block_size The size of the block available in the free
00626      *  list.
00627      *
00628      *  @param __required_size The required size of the memory block.
00629      *
00630      *  @return true if the wastage incurred is acceptable, else returns
00631      *  false.
00632      */
00633     bool 
00634     _M_should_i_give(size_t __block_size, 
00635              size_t __required_size) throw()
00636     {
00637       const size_t __max_wastage_percentage = 36;
00638       if (__block_size >= __required_size && 
00639       (((__block_size - __required_size) * 100 / __block_size)
00640        < __max_wastage_percentage))
00641     return true;
00642       else
00643     return false;
00644     }
00645 
00646   public:
00647     /** @brief This function returns the block of memory to the
00648      *  internal free list.
00649      *
00650      *  @param  __addr The pointer to the memory block that was given
00651      *  by a call to the _M_get function.
00652      */
00653     inline void 
00654     _M_insert(size_t* __addr) throw()
00655     {
00656 #if defined __GTHREADS
00657       __gnu_cxx::__scoped_lock __bfl_lock(_M_get_mutex());
00658 #endif
00659       // Call _M_validate to decide what should be done with
00660       // this particular free list.
00661       this->_M_validate(reinterpret_cast<size_t*>(__addr) - 1);
00662       // See discussion as to why this is 1!
00663     }
00664     
00665     /** @brief  This function gets a block of memory of the specified
00666      *  size from the free list.
00667      *
00668      *  @param  __sz The size in bytes of the memory required.
00669      *
00670      *  @return  A pointer to the new memory block of size at least
00671      *  equal to that requested.
00672      */
00673     size_t*
00674     _M_get(size_t __sz) throw(std::bad_alloc);
00675 
00676     /** @brief  This function just clears the internal Free List, and
00677      *  gives back all the memory to the OS.
00678      */
00679     void 
00680     _M_clear();
00681   };
00682 
00683 
00684   // Forward declare the class.
00685   template<typename _Tp> 
00686     class bitmap_allocator;
00687 
00688   // Specialize for void:
00689   template<>
00690     class bitmap_allocator<void>
00691     {
00692     public:
00693       typedef void*       pointer;
00694       typedef const void* const_pointer;
00695 
00696       // Reference-to-void members are impossible.
00697       typedef void  value_type;
00698       template<typename _Tp1>
00699         struct rebind
00700     {
00701       typedef bitmap_allocator<_Tp1> other;
00702     };
00703     };
00704 
00705   /**
00706    * @brief Bitmap Allocator, primary template.
00707    * @ingroup allocators
00708    */
00709   template<typename _Tp>
00710     class bitmap_allocator : private free_list
00711     {
00712     public:
00713       typedef size_t            size_type;
00714       typedef ptrdiff_t         difference_type;
00715       typedef _Tp*              pointer;
00716       typedef const _Tp*        const_pointer;
00717       typedef _Tp&              reference;
00718       typedef const _Tp&        const_reference;
00719       typedef _Tp               value_type;
00720       typedef free_list::__mutex_type   __mutex_type;
00721 
00722       template<typename _Tp1>
00723         struct rebind
00724     {
00725       typedef bitmap_allocator<_Tp1> other;
00726     };
00727 
00728     private:
00729       template<size_t _BSize, size_t _AlignSize>
00730         struct aligned_size
00731     {
00732       enum
00733         { 
00734           modulus = _BSize % _AlignSize,
00735           value = _BSize + (modulus ? _AlignSize - (modulus) : 0)
00736         };
00737     };
00738 
00739       struct _Alloc_block
00740       {
00741     char __M_unused[aligned_size<sizeof(value_type),
00742             _BALLOC_ALIGN_BYTES>::value];
00743       };
00744 
00745 
00746       typedef typename std::pair<_Alloc_block*, _Alloc_block*> _Block_pair;
00747 
00748       typedef typename 
00749       __detail::__mini_vector<_Block_pair> _BPVector;
00750 
00751 #if defined _GLIBCXX_DEBUG
00752       // Complexity: O(lg(N)). Where, N is the number of block of size
00753       // sizeof(value_type).
00754       void 
00755       _S_check_for_free_blocks() throw()
00756       {
00757     typedef typename 
00758       __gnu_cxx::__detail::_Ffit_finder<_Alloc_block*> _FFF;
00759     _FFF __fff;
00760     typedef typename _BPVector::iterator _BPiter;
00761     _BPiter __bpi = 
00762       __gnu_cxx::__detail::__find_if
00763       (_S_mem_blocks.begin(), _S_mem_blocks.end(), 
00764        __gnu_cxx::__detail::_Functor_Ref<_FFF>(__fff));
00765 
00766     _GLIBCXX_DEBUG_ASSERT(__bpi == _S_mem_blocks.end());
00767       }
00768 #endif
00769 
00770       /** @brief  Responsible for exponentially growing the internal
00771        *  memory pool.
00772        *
00773        *  @throw  std::bad_alloc. If memory can not be allocated.
00774        *
00775        *  @detail  Complexity: O(1), but internally depends upon the
00776        *  complexity of the function free_list::_M_get. The part where
00777        *  the bitmap headers are written has complexity: O(X),where X
00778        *  is the number of blocks of size sizeof(value_type) within
00779        *  the newly acquired block. Having a tight bound.
00780        */
00781       void 
00782       _S_refill_pool() throw(std::bad_alloc)
00783       {
00784 #if defined _GLIBCXX_DEBUG
00785     _S_check_for_free_blocks();
00786 #endif
00787 
00788     const size_t __num_bitmaps = (_S_block_size
00789                       / size_t(__detail::bits_per_block));
00790     const size_t __size_to_allocate = sizeof(size_t) 
00791       + _S_block_size * sizeof(_Alloc_block) 
00792       + __num_bitmaps * sizeof(size_t);
00793 
00794     size_t* __temp = 
00795       reinterpret_cast<size_t*>
00796       (this->_M_get(__size_to_allocate));
00797     *__temp = 0;
00798     ++__temp;
00799 
00800     // The Header information goes at the Beginning of the Block.
00801     _Block_pair __bp = 
00802       std::make_pair(reinterpret_cast<_Alloc_block*>
00803              (__temp + __num_bitmaps), 
00804              reinterpret_cast<_Alloc_block*>
00805              (__temp + __num_bitmaps) 
00806              + _S_block_size - 1);
00807     
00808     // Fill the Vector with this information.
00809     _S_mem_blocks.push_back(__bp);
00810 
00811     size_t __bit_mask = 0; // 0 Indicates all Allocated.
00812     __bit_mask = ~__bit_mask; // 1 Indicates all Free.
00813 
00814     for (size_t __i = 0; __i < __num_bitmaps; ++__i)
00815       __temp[__i] = __bit_mask;
00816 
00817     _S_block_size *= 2;
00818       }
00819 
00820 
00821       static _BPVector _S_mem_blocks;
00822       static size_t _S_block_size;
00823       static __gnu_cxx::__detail::
00824       _Bitmap_counter<_Alloc_block*> _S_last_request;
00825       static typename _BPVector::size_type _S_last_dealloc_index;
00826 #if defined __GTHREADS
00827       static __mutex_type _S_mut;
00828 #endif
00829 
00830     public:
00831 
00832       /** @brief  Allocates memory for a single object of size
00833        *  sizeof(_Tp).
00834        *
00835        *  @throw  std::bad_alloc. If memory can not be allocated.
00836        *
00837        *  @detail  Complexity: Worst case complexity is O(N), but that
00838        *  is hardly ever hit. If and when this particular case is
00839        *  encountered, the next few cases are guaranteed to have a
00840        *  worst case complexity of O(1)!  That's why this function
00841        *  performs very well on average. You can consider this
00842        *  function to have a complexity referred to commonly as:
00843        *  Amortized Constant time.
00844        */
00845       pointer 
00846       _M_allocate_single_object() throw(std::bad_alloc)
00847       {
00848 #if defined __GTHREADS
00849     __gnu_cxx::__scoped_lock __bit_lock(_S_mut);
00850 #endif
00851 
00852     // The algorithm is something like this: The last_request
00853     // variable points to the last accessed Bit Map. When such a
00854     // condition occurs, we try to find a free block in the
00855     // current bitmap, or succeeding bitmaps until the last bitmap
00856     // is reached. If no free block turns up, we resort to First
00857     // Fit method.
00858 
00859     // WARNING: Do not re-order the condition in the while
00860     // statement below, because it relies on C++'s short-circuit
00861     // evaluation. The return from _S_last_request->_M_get() will
00862     // NOT be dereference able if _S_last_request->_M_finished()
00863     // returns true. This would inevitably lead to a NULL pointer
00864     // dereference if tinkered with.
00865     while (_S_last_request._M_finished() == false
00866            && (*(_S_last_request._M_get()) == 0))
00867       {
00868         _S_last_request.operator++();
00869       }
00870 
00871     if (__builtin_expect(_S_last_request._M_finished() == true, false))
00872       {
00873         // Fall Back to First Fit algorithm.
00874         typedef typename 
00875           __gnu_cxx::__detail::_Ffit_finder<_Alloc_block*> _FFF;
00876         _FFF __fff;
00877         typedef typename _BPVector::iterator _BPiter;
00878         _BPiter __bpi = 
00879           __gnu_cxx::__detail::__find_if
00880           (_S_mem_blocks.begin(), _S_mem_blocks.end(), 
00881            __gnu_cxx::__detail::_Functor_Ref<_FFF>(__fff));
00882 
00883         if (__bpi != _S_mem_blocks.end())
00884           {
00885         // Search was successful. Ok, now mark the first bit from
00886         // the right as 0, meaning Allocated. This bit is obtained
00887         // by calling _M_get() on __fff.
00888         size_t __nz_bit = _Bit_scan_forward(*__fff._M_get());
00889         __detail::__bit_allocate(__fff._M_get(), __nz_bit);
00890 
00891         _S_last_request._M_reset(__bpi - _S_mem_blocks.begin());
00892 
00893         // Now, get the address of the bit we marked as allocated.
00894         pointer __ret = reinterpret_cast<pointer>
00895           (__bpi->first + __fff._M_offset() + __nz_bit);
00896         size_t* __puse_count = 
00897           reinterpret_cast<size_t*>
00898           (__bpi->first) 
00899           - (__gnu_cxx::__detail::__num_bitmaps(*__bpi) + 1);
00900         
00901         ++(*__puse_count);
00902         return __ret;
00903           }
00904         else
00905           {
00906         // Search was unsuccessful. We Add more memory to the
00907         // pool by calling _S_refill_pool().
00908         _S_refill_pool();
00909 
00910         // _M_Reset the _S_last_request structure to the first
00911         // free block's bit map.
00912         _S_last_request._M_reset(_S_mem_blocks.size() - 1);
00913 
00914         // Now, mark that bit as allocated.
00915           }
00916       }
00917 
00918     // _S_last_request holds a pointer to a valid bit map, that
00919     // points to a free block in memory.
00920     size_t __nz_bit = _Bit_scan_forward(*_S_last_request._M_get());
00921     __detail::__bit_allocate(_S_last_request._M_get(), __nz_bit);
00922 
00923     pointer __ret = reinterpret_cast<pointer>
00924       (_S_last_request._M_base() + _S_last_request._M_offset() + __nz_bit);
00925 
00926     size_t* __puse_count = reinterpret_cast<size_t*>
00927       (_S_mem_blocks[_S_last_request._M_where()].first)
00928       - (__gnu_cxx::__detail::
00929          __num_bitmaps(_S_mem_blocks[_S_last_request._M_where()]) + 1);
00930 
00931     ++(*__puse_count);
00932     return __ret;
00933       }
00934 
00935       /** @brief  Deallocates memory that belongs to a single object of
00936        *  size sizeof(_Tp).
00937        *
00938        *  @detail  Complexity: O(lg(N)), but the worst case is not hit
00939        *  often!  This is because containers usually deallocate memory
00940        *  close to each other and this case is handled in O(1) time by
00941        *  the deallocate function.
00942        */
00943       void 
00944       _M_deallocate_single_object(pointer __p) throw()
00945       {
00946 #if defined __GTHREADS
00947     __gnu_cxx::__scoped_lock __bit_lock(_S_mut);
00948 #endif
00949     _Alloc_block* __real_p = reinterpret_cast<_Alloc_block*>(__p);
00950 
00951     typedef typename _BPVector::iterator _Iterator;
00952     typedef typename _BPVector::difference_type _Difference_type;
00953 
00954     _Difference_type __diff;
00955     long __displacement;
00956 
00957     _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
00958 
00959     
00960     if (__gnu_cxx::__detail::_Inclusive_between<_Alloc_block*>
00961         (__real_p) (_S_mem_blocks[_S_last_dealloc_index]))
00962       {
00963         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index
00964                   <= _S_mem_blocks.size() - 1);
00965 
00966         // Initial Assumption was correct!
00967         __diff = _S_last_dealloc_index;
00968         __displacement = __real_p - _S_mem_blocks[__diff].first;
00969       }
00970     else
00971       {
00972         _Iterator _iter = __gnu_cxx::__detail::
00973           __find_if(_S_mem_blocks.begin(), 
00974             _S_mem_blocks.end(), 
00975             __gnu_cxx::__detail::
00976             _Inclusive_between<_Alloc_block*>(__real_p));
00977 
00978         _GLIBCXX_DEBUG_ASSERT(_iter != _S_mem_blocks.end());
00979 
00980         __diff = _iter - _S_mem_blocks.begin();
00981         __displacement = __real_p - _S_mem_blocks[__diff].first;
00982         _S_last_dealloc_index = __diff;
00983       }
00984 
00985     // Get the position of the iterator that has been found.
00986     const size_t __rotate = (__displacement
00987                  % size_t(__detail::bits_per_block));
00988     size_t* __bitmapC = 
00989       reinterpret_cast<size_t*>
00990       (_S_mem_blocks[__diff].first) - 1;
00991     __bitmapC -= (__displacement / size_t(__detail::bits_per_block));
00992       
00993     __detail::__bit_free(__bitmapC, __rotate);
00994     size_t* __puse_count = reinterpret_cast<size_t*>
00995       (_S_mem_blocks[__diff].first)
00996       - (__gnu_cxx::__detail::__num_bitmaps(_S_mem_blocks[__diff]) + 1);
00997     
00998     _GLIBCXX_DEBUG_ASSERT(*__puse_count != 0);
00999 
01000     --(*__puse_count);
01001 
01002     if (__builtin_expect(*__puse_count == 0, false))
01003       {
01004         _S_block_size /= 2;
01005       
01006         // We can safely remove this block.
01007         // _Block_pair __bp = _S_mem_blocks[__diff];
01008         this->_M_insert(__puse_count);
01009         _S_mem_blocks.erase(_S_mem_blocks.begin() + __diff);
01010 
01011         // Reset the _S_last_request variable to reflect the
01012         // erased block. We do this to protect future requests
01013         // after the last block has been removed from a particular
01014         // memory Chunk, which in turn has been returned to the
01015         // free list, and hence had been erased from the vector,
01016         // so the size of the vector gets reduced by 1.
01017         if ((_Difference_type)_S_last_request._M_where() >= __diff--)
01018           _S_last_request._M_reset(__diff); 
01019 
01020         // If the Index into the vector of the region of memory
01021         // that might hold the next address that will be passed to
01022         // deallocated may have been invalidated due to the above
01023         // erase procedure being called on the vector, hence we
01024         // try to restore this invariant too.
01025         if (_S_last_dealloc_index >= _S_mem_blocks.size())
01026           {
01027         _S_last_dealloc_index =(__diff != -1 ? __diff : 0);
01028         _GLIBCXX_DEBUG_ASSERT(_S_last_dealloc_index >= 0);
01029           }
01030       }
01031       }
01032 
01033     public:
01034       bitmap_allocator() throw()
01035       { }
01036 
01037       bitmap_allocator(const bitmap_allocator&)
01038       { }
01039 
01040       template<typename _Tp1>
01041         bitmap_allocator(const bitmap_allocator<_Tp1>&) throw()
01042         { }
01043 
01044       ~bitmap_allocator() throw()
01045       { }
01046 
01047       pointer 
01048       allocate(size_type __n)
01049       {
01050     if (__builtin_expect(__n > this->max_size(), false))
01051       std::__throw_bad_alloc();
01052 
01053     if (__builtin_expect(__n == 1, true))
01054       return this->_M_allocate_single_object();
01055     else
01056       { 
01057         const size_type __b = __n * sizeof(value_type);
01058         return reinterpret_cast<pointer>(::operator new(__b));
01059       }
01060       }
01061 
01062       pointer 
01063       allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
01064       { return allocate(__n); }
01065 
01066       void 
01067       deallocate(pointer __p, size_type __n) throw()
01068       {
01069     if (__builtin_expect(__p != 0, true))
01070       {
01071         if (__builtin_expect(__n == 1, true))
01072           this->_M_deallocate_single_object(__p);
01073         else
01074 	      ::operator delete(__p);
01075       }
01076       }
01077 
01078       pointer 
01079       address(reference __r) const
01080       { return &__r; }
01081 
01082       const_pointer 
01083       address(const_reference __r) const
01084       { return &__r; }
01085 
01086       size_type 
01087       max_size() const throw()
01088       { return size_type(-1) / sizeof(value_type); }
01089 
01090       void 
01091       construct(pointer __p, const_reference __data)
01092       { ::new((void *)__p) value_type(__data); }
01093 
01094 #ifdef __GXX_EXPERIMENTAL_CXX0X__
01095       template<typename... _Args>
01096         void
01097         construct(pointer __p, _Args&&... __args)
01098     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
01099 #endif
01100 
01101       void 
01102       destroy(pointer __p)
01103       { __p->~value_type(); }
01104     };
01105 
01106   template<typename _Tp1, typename _Tp2>
01107     bool 
01108     operator==(const bitmap_allocator<_Tp1>&, 
01109            const bitmap_allocator<_Tp2>&) throw()
01110     { return true; }
01111   
01112   template<typename _Tp1, typename _Tp2>
01113     bool 
01114     operator!=(const bitmap_allocator<_Tp1>&, 
01115            const bitmap_allocator<_Tp2>&) throw() 
01116   { return false; }
01117 
01118   // Static member definitions.
01119   template<typename _Tp>
01120     typename bitmap_allocator<_Tp>::_BPVector
01121     bitmap_allocator<_Tp>::_S_mem_blocks;
01122 
01123   template<typename _Tp>
01124     size_t bitmap_allocator<_Tp>::_S_block_size = 
01125     2 * size_t(__detail::bits_per_block);
01126 
01127   template<typename _Tp>
01128     typename __gnu_cxx::bitmap_allocator<_Tp>::_BPVector::size_type 
01129     bitmap_allocator<_Tp>::_S_last_dealloc_index = 0;
01130 
01131   template<typename _Tp>
01132     __gnu_cxx::__detail::_Bitmap_counter 
01133   <typename bitmap_allocator<_Tp>::_Alloc_block*>
01134     bitmap_allocator<_Tp>::_S_last_request(_S_mem_blocks);
01135 
01136 #if defined __GTHREADS
01137   template<typename _Tp>
01138     typename bitmap_allocator<_Tp>::__mutex_type
01139     bitmap_allocator<_Tp>::_S_mut;
01140 #endif
01141 
01142 _GLIBCXX_END_NAMESPACE
01143 
01144 #endif 
01145 

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