libstdc++-v3/src/c++98/pool_allocator.cc

   1 // Allocator details.
   2
   3 // Copyright (C) 2004-2021 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 //
  26 // ISO C++ 14882:
  27 //
  28
  29 #include <bits/c++config.h>
  30 #include <cstdlib>
  31 #include <ext/pool_allocator.h>
  32
  33 namespace
  34 {
  35   __gnu_cxx::__mutex&
  36   get_palloc_mutex()
  37   {
  38     static __gnu_cxx::__mutex palloc_mutex;
  39     return palloc_mutex;
  40   }
  41 } // anonymous namespace
  42
  43 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  44 {
  45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  46
  47   // Definitions for __pool_alloc_base.
  48   __pool_alloc_base::_Obj* volatile*
  49   __pool_alloc_base::_M_get_free_list(size_t __bytes) throw ()
  50   {
  51     size_t __i = ((__bytes + (size_t)_S_align - 1) / (size_t)_S_align - 1);
  52     return _S_free_list + __i;
  53   }
  54
  55   __mutex&
  56   __pool_alloc_base::_M_get_mutex() throw ()
  57   { return get_palloc_mutex(); }
  58
  59   // Allocate memory in large chunks in order to avoid fragmenting the
  60   // heap too much.  Assume that __n is properly aligned.  We hold the
  61   // allocation lock.
  62   char*
  63   __pool_alloc_base::_M_allocate_chunk(size_t __n, int& __nobjs)
  64   {
  65     char* __result;
  66     size_t __total_bytes = __n * __nobjs;
  67     size_t __bytes_left = _S_end_free - _S_start_free;
  68
  69     if (__bytes_left >= __total_bytes)
  70       {
  71         __result = _S_start_free;
  72         _S_start_free += __total_bytes;
  73         return __result ;
  74       }
  75     else if (__bytes_left >= __n)
  76       {
  77         __nobjs = (int)(__bytes_left / __n);
  78         __total_bytes = __n * __nobjs;
  79         __result = _S_start_free;
  80         _S_start_free += __total_bytes;
  81         return __result;
  82       }
  83     else
  84       {
  85         // Try to make use of the left-over piece.
  86         if (__bytes_left > 0)
  87           {
  88             _Obj* volatile* __free_list = _M_get_free_list(__bytes_left);
  89             ((_Obj*)(void*)_S_start_free)->_M_free_list_link = *__free_list;
  90             *__free_list = (_Obj*)(void*)_S_start_free;
  91           }
  92
  93         size_t __bytes_to_get = (2 * __total_bytes
  94                                  + _M_round_up(_S_heap_size >> 4));
  95         __try
  96           {
  97             _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
  98           }
  99         __catch(const std::bad_alloc&)
 100           {
 101             // Try to make do with what we have.  That can't hurt.  We
 102             // do not try smaller requests, since that tends to result
 103             // in disaster on multi-process machines.
 104             size_t __i = __n;
 105             for (; __i <= (size_t) _S_max_bytes; __i += (size_t) _S_align)
 106               {
 107                 _Obj* volatile* __free_list = _M_get_free_list(__i);
 108                 _Obj* __p = *__free_list;
 109                 if (__p != 0)
 110                   {
 111                     *__free_list = __p->_M_free_list_link;
 112                     _S_start_free = (char*)__p;
 113                     _S_end_free = _S_start_free + __i;
 114                     return _M_allocate_chunk(__n, __nobjs);
 115                     // Any leftover piece will eventually make it to the
 116                     // right free list.
 117                   }
 118               }
 119             // What we have wasn't enough.  Rethrow.
 120             _S_start_free = _S_end_free = 0;   // We have no chunk.
 121             __throw_exception_again;
 122           }
 123         _S_heap_size += __bytes_to_get;
 124         _S_end_free = _S_start_free + __bytes_to_get;
 125         return _M_allocate_chunk(__n, __nobjs);
 126       }
 127   }
 128
 129   // Returns an object of size __n, and optionally adds to "size
 130   // __n"'s free list.  We assume that __n is properly aligned.  We
 131   // hold the allocation lock.
 132   void*
 133   __pool_alloc_base::_M_refill(size_t __n)
 134   {
 135     int __nobjs = 20;
 136     char* __chunk = _M_allocate_chunk(__n, __nobjs);
 137     _Obj* volatile* __free_list;
 138     _Obj* __result;
 139     _Obj* __current_obj;
 140     _Obj* __next_obj;
 141
 142     if (__nobjs == 1)
 143       return __chunk;
 144     __free_list = _M_get_free_list(__n);
 145
 146     // Build free list in chunk.
 147     __result = (_Obj*)(void*)__chunk;
 148     *__free_list = __next_obj = (_Obj*)(void*)(__chunk + __n);
 149     for (int __i = 1; ; __i++)
 150       {
 151         __current_obj = __next_obj;
 152         __next_obj = (_Obj*)(void*)((char*)__next_obj + __n);
 153         if (__nobjs - 1 == __i)
 154           {
 155             __current_obj->_M_free_list_link = 0;
 156             break;
 157           }
 158         else
 159           __current_obj->_M_free_list_link = __next_obj;
 160       }
 161     return __result;
 162   }
 163
 164   __pool_alloc_base::_Obj* volatile __pool_alloc_base::_S_free_list[_S_free_list_size];
 165
 166   char* __pool_alloc_base::_S_start_free = 0;
 167
 168   char* __pool_alloc_base::_S_end_free = 0;
 169
 170   size_t __pool_alloc_base::_S_heap_size = 0;
 171
 172   // Instantiations.
 173   template class __pool_alloc<char>;
 174   template class __pool_alloc<wchar_t>;
 175
 176 _GLIBCXX_END_NAMESPACE_VERSION
 177 } // namespace