libstdc++-v3/src/allocator.cc

   1 // Allocator details.
   2
   3 // Copyright (C) 2004 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 2, 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 // You should have received a copy of the GNU General Public License along
  17 // with this library; see the file COPYING.  If not, write to the Free
  18 // Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  19 // USA.
  20
  21 // As a special exception, you may use this file as part of a free software
  22 // library without restriction.  Specifically, if other files instantiate
  23 // templates or use macros or inline functions from this file, or you compile
  24 // this file and link it with other files to produce an executable, this
  25 // file does not by itself cause the resulting executable to be covered by
  26 // the GNU General Public License.  This exception does not however
  27 // invalidate any other reasons why the executable file might be covered by
  28 // the GNU General Public License.
  29
  30 //
  31 // ISO C++ 14882:
  32 //
  33
  34 #include <bits/c++config.h>
  35 #include <memory>
  36 #include <ext/mt_allocator.h>
  37 #include <ext/pool_allocator.h>
  38
  39 namespace __gnu_internal
  40 {
  41   __glibcxx_mutex_define_initialized(palloc_init_mutex);
  42 }
  43
  44 namespace __gnu_cxx
  45 {
  46   // Definitions for __pool_alloc_base.
  47   __pool_base::_Obj* volatile*
  48   __pool_base::_M_get_free_list(size_t __bytes)
  49   {
  50     size_t __i = ((__bytes + (size_t)_S_align - 1) / (size_t)_S_align - 1);
  51     return _S_free_list + __i;
  52   }
  53
  54   mutex_type&
  55   __pool_base::_M_get_mutex()
  56   { return __gnu_internal::palloc_init_mutex; }
  57
  58   // Allocate memory in large chunks in order to avoid fragmenting the
  59   // heap too much.  Assume that __n is properly aligned.  We hold the
  60   // allocation lock.
  61   char*
  62   __pool_base::_M_allocate_chunk(size_t __n, int& __nobjs)
  63   {
  64     char* __result;
  65     size_t __total_bytes = __n * __nobjs;
  66     size_t __bytes_left = _S_end_free - _S_start_free;
  67
  68     if (__bytes_left >= __total_bytes)
  69       {
  70         __result = _S_start_free;
  71         _S_start_free += __total_bytes;
  72         return __result ;
  73       }
  74     else if (__bytes_left >= __n)
  75       {
  76         __nobjs = (int)(__bytes_left / __n);
  77         __total_bytes = __n * __nobjs;
  78         __result = _S_start_free;
  79         _S_start_free += __total_bytes;
  80         return __result;
  81       }
  82     else
  83       {
  84         // Try to make use of the left-over piece.
  85         if (__bytes_left > 0)
  86           {
  87             _Obj* volatile* __free_list = _M_get_free_list(__bytes_left);
  88             ((_Obj*)(void*)_S_start_free)->_M_free_list_link = *__free_list;
  89             *__free_list = (_Obj*)(void*)_S_start_free;
  90           }
  91
  92         size_t __bytes_to_get = (2 * __total_bytes
  93                                  + _M_round_up(_S_heap_size >> 4));
  94         _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
  95         if (_S_start_free == 0)
  96           {
  97             // Try to make do with what we have.  That can't hurt.  We
  98             // do not try smaller requests, since that tends to result
  99             // in disaster on multi-process machines.
 100             size_t __i = __n;
 101             for (; __i <= (size_t) _S_max_bytes; __i += (size_t) _S_align)
 102               {
 103                 _Obj* volatile* __free_list = _M_get_free_list(__i);
 104                 _Obj* __p = *__free_list;
 105                 if (__p != 0)
 106                   {
 107                     *__free_list = __p->_M_free_list_link;
 108                     _S_start_free = (char*)__p;
 109                     _S_end_free = _S_start_free + __i;
 110                     return _M_allocate_chunk(__n, __nobjs);
 111                     // Any leftover piece will eventually make it to the
 112                     // right free list.
 113                   }
 114               }
 115             _S_end_free = 0;        // In case of exception.
 116
 117             // This should either throw an exception or remedy the situation.
 118             // Thus we assume it succeeded.
 119             _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
 120           }
 121         _S_heap_size += __bytes_to_get;
 122         _S_end_free = _S_start_free + __bytes_to_get;
 123         return _M_allocate_chunk(__n, __nobjs);
 124       }
 125   }
 126
 127   // Returns an object of size __n, and optionally adds to "size
 128   // __n"'s free list.  We assume that __n is properly aligned.  We
 129   // hold the allocation lock.
 130   void*
 131   __pool_base::_M_refill(size_t __n)
 132   {
 133     int __nobjs = 20;
 134     char* __chunk = _M_allocate_chunk(__n, __nobjs);
 135     _Obj* volatile* __free_list;
 136     _Obj* __result;
 137     _Obj* __current_obj;
 138     _Obj* __next_obj;
 139
 140     if (__nobjs == 1)
 141       return __chunk;
 142     __free_list = _M_get_free_list(__n);
 143
 144     // Build free list in chunk.
 145     __result = (_Obj*)(void*)__chunk;
 146     *__free_list = __next_obj = (_Obj*)(void*)(__chunk + __n);
 147     for (int __i = 1; ; __i++)
 148       {
 149         __current_obj = __next_obj;
 150         __next_obj = (_Obj*)(void*)((char*)__next_obj + __n);
 151         if (__nobjs - 1 == __i)
 152           {
 153             __current_obj->_M_free_list_link = 0;
 154             break;
 155           }
 156         else
 157           __current_obj->_M_free_list_link = __next_obj;
 158       }
 159     return __result;
 160   }
 161
 162   __pool_base::_Obj* volatile __pool_base::_S_free_list[_S_free_list_size];
 163
 164   char* __pool_base::_S_start_free = 0;
 165
 166   char* __pool_base::_S_end_free = 0;
 167
 168   size_t __pool_base::_S_heap_size = 0;
 169 } // namespace __gnu_cxx