# pool_allocator.h

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    00001 // Allocators -*- C++ -*-
    00002
    00003 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006
    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 2, 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 // You should have received a copy of the GNU General Public License along
    00018 // with this library; see the file COPYING.  If not, write to the Free
    00019 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
    00020 // USA.
    00021
    00022 // As a special exception, you may use this file as part of a free software
    00023 // library without restriction.  Specifically, if other files instantiate
    00024 // templates or use macros or inline functions from this file, or you compile
    00025 // this file and link it with other files to produce an executable, this
    00026 // file does not by itself cause the resulting executable to be covered by
    00027 // the GNU General Public License.  This exception does not however
    00028 // invalidate any other reasons why the executable file might be covered by
    00029 // the GNU General Public License.
    00030
    00031 /*
    00032  * Copyright (c) 1996-1997
    00033  * Silicon Graphics Computer Systems, Inc.
    00034  *
    00035  * Permission to use, copy, modify, distribute and sell this software
    00036  * and its documentation for any purpose is hereby granted without fee,
    00037  * provided that the above copyright notice appear in all copies and
    00038  * that both that copyright notice and this permission notice appear
    00039  * in supporting documentation.  Silicon Graphics makes no
    00040  * representations about the suitability of this software for any
    00041  * purpose.  It is provided "as is" without express or implied warranty.
    00042  */
    00043
    00044 /** @file ext/pool_allocator.h
    00045  *  This file is a GNU extension to the Standard C++ Library.
    00046  */
    00047
    00048 #ifndef _POOL_ALLOCATOR_H
    00049 #define _POOL_ALLOCATOR_H 1
    00050
    00051 #include <bits/c++config.h>
    00052 #include <cstdlib>
    00053 #include <new>
    00054 #include <bits/functexcept.h>
    00055 #include <ext/atomicity.h>
    00056 #include <ext/concurrence.h>
    00057
    00058 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    00059
    00060   using std::size_t;
    00061   using std::ptrdiff_t;
    00062
    00063   /**
    00064    *  @brief  Base class for __pool_alloc.
    00065    *
    00066    *  @if maint
    00067    *  Uses various allocators to fulfill underlying requests (and makes as
    00068    *  few requests as possible when in default high-speed pool mode).
    00069    *
    00070    *  Important implementation properties:
    00071    *  0. If globally mandated, then allocate objects from new
    00072    *  1. If the clients request an object of size > _S_max_bytes, the resulting
    00073    *     object will be obtained directly from new
    00074    *  2. In all other cases, we allocate an object of size exactly
    00075    *     _S_round_up(requested_size).  Thus the client has enough size
    00076    *     information that we can return the object to the proper free list
    00077    *     without permanently losing part of the object.
    00078    *
    00079    *  @endif
    00080    */
    00081     class __pool_alloc_base
    00082     {
    00083     protected:
    00084
    00085       enum { _S_align = 8 };
    00086       enum { _S_max_bytes = 128 };
    00087       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
    00088
    00089       union _Obj
    00090       {
    00091     union _Obj* _M_free_list_link;
    00092     char        _M_client_data[1];    // The client sees this.
    00093       };
    00094
    00095       static _Obj* volatile         _S_free_list[_S_free_list_size];
    00096
    00097       // Chunk allocation state.
    00098       static char*                  _S_start_free;
    00099       static char*                  _S_end_free;
    00100       static size_t                 _S_heap_size;
    00101
    00102       size_t
    00103       _M_round_up(size_t __bytes)
    00104       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
    00105
    00106       _Obj* volatile*
    00107       _M_get_free_list(size_t __bytes);
    00108
    00109       __mutex&
    00110       _M_get_mutex();
    00111
    00112       // Returns an object of size __n, and optionally adds to size __n
    00113       // free list.
    00114       void*
    00115       _M_refill(size_t __n);
    00116
    00117       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
    00118       // if it is inconvenient to allocate the requested number.
    00119       char*
    00120       _M_allocate_chunk(size_t __n, int& __nobjs);
    00121     };
    00122
    00123
    00124   /// @brief  class __pool_alloc.
    00125   template<typename _Tp>
    00126     class __pool_alloc : private __pool_alloc_base
    00127     {
    00128     private:
    00129       static _Atomic_word       _S_force_new;
    00130
    00131     public:
    00132       typedef size_t     size_type;
    00133       typedef ptrdiff_t  difference_type;
    00134       typedef _Tp*       pointer;
    00135       typedef const _Tp* const_pointer;
    00136       typedef _Tp&       reference;
    00137       typedef const _Tp& const_reference;
    00138       typedef _Tp        value_type;
    00139
    00140       template<typename _Tp1>
    00141         struct rebind
    00142         { typedef __pool_alloc<_Tp1> other; };
    00143
    00144       __pool_alloc() throw() { }
    00145
    00146       __pool_alloc(const __pool_alloc&) throw() { }
    00147
    00148       template<typename _Tp1>
    00149         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
    00150
    00151       ~__pool_alloc() throw() { }
    00152
    00153       pointer
    00154       address(reference __x) const { return &__x; }
    00155
    00156       const_pointer
    00157       address(const_reference __x) const { return &__x; }
    00158
    00159       size_type
    00160       max_size() const throw()
    00161       { return size_t(-1) / sizeof(_Tp); }
    00162
    00163       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00164       // 402. wrong new expression in [some_] allocator::construct
    00165       void
    00166       construct(pointer __p, const _Tp& __val)
    00167       { ::new(__p) _Tp(__val); }
    00168
    00169       void
    00170       destroy(pointer __p) { __p->~_Tp(); }
    00171
    00172       pointer
    00173       allocate(size_type __n, const void* = 0);
    00174
    00175       void
    00176       deallocate(pointer __p, size_type __n);
    00177     };
    00178
    00179   template<typename _Tp>
    00180     inline bool
    00181     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00182     { return true; }
    00183
    00184   template<typename _Tp>
    00185     inline bool
    00186     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00187     { return false; }
    00188
    00189   template<typename _Tp>
    00190     _Atomic_word
    00191     __pool_alloc<_Tp>::_S_force_new;
    00192
    00193   template<typename _Tp>
    00194     _Tp*
    00195     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
    00196     {
    00197       pointer __ret = 0;
    00198       if (__builtin_expect(__n != 0, true))
    00199     {
    00200       if (__builtin_expect(__n > this->max_size(), false))
    00201         std::__throw_bad_alloc();
    00202
    00203       // If there is a race through here, assume answer from getenv
    00204       // will resolve in same direction.  Inspired by techniques
    00205       // to efficiently support threading found in basic_string.h.
    00206       if (_S_force_new == 0)
    00207         {
    00208           if (std::getenv("GLIBCXX_FORCE_NEW"))
    00209         __atomic_add_dispatch(&_S_force_new, 1);
    00210           else
    00211         __atomic_add_dispatch(&_S_force_new, -1);
    00212         }
    00213
    00214       const size_t __bytes = __n * sizeof(_Tp);
    00215       if (__bytes > size_t(_S_max_bytes) || _S_force_new == 1)
    00216         __ret = static_cast<_Tp*>(::operator new(__bytes));
    00217       else
    00218         {
    00219           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00220
    00221           __scoped_lock sentry(_M_get_mutex());
    00222           _Obj* __restrict__ __result = *__free_list;
    00223           if (__builtin_expect(__result == 0, 0))
    00224         __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
    00225           else
    00226         {
    00227           *__free_list = __result->_M_free_list_link;
    00228           __ret = reinterpret_cast<_Tp*>(__result);
    00229         }
    00230           if (__builtin_expect(__ret == 0, 0))
    00231         std::__throw_bad_alloc();
    00232         }
    00233     }
    00234       return __ret;
    00235     }
    00236
    00237   template<typename _Tp>
    00238     void
    00239     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
    00240     {
    00241       if (__builtin_expect(__n != 0 && __p != 0, true))
    00242     {
    00243       const size_t __bytes = __n * sizeof(_Tp);
    00244       if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new == 1)
    00245         ::operator delete(__p);
    00246       else
    00247         {
    00248           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00249           _Obj* __q = reinterpret_cast<_Obj*>(__p);
    00250
    00251           __scoped_lock sentry(_M_get_mutex());
    00252           __q ->_M_free_list_link = *__free_list;
    00253           *__free_list = __q;
    00254         }
    00255     }
    00256     }
    00257
    00258 _GLIBCXX_END_NAMESPACE
    00259
    00260 #endif