# pool_allocator.h

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    00001 // Allocators -*- C++ -*-
    00002
    00003 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
    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 #include <bits/stl_move.h>
    00058
    00059 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    00060
    00061   using std::size_t;
    00062   using std::ptrdiff_t;
    00063
    00064   /**
    00065    *  @brief  Base class for __pool_alloc.
    00066    *
    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     class __pool_alloc_base
    00080     {
    00081     protected:
    00082
    00083       enum { _S_align = 8 };
    00084       enum { _S_max_bytes = 128 };
    00085       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
    00086
    00087       union _Obj
    00088       {
    00089     union _Obj* _M_free_list_link;
    00090     char        _M_client_data[1];    // The client sees this.
    00091       };
    00092
    00093       static _Obj* volatile         _S_free_list[_S_free_list_size];
    00094
    00095       // Chunk allocation state.
    00096       static char*                  _S_start_free;
    00097       static char*                  _S_end_free;
    00098       static size_t                 _S_heap_size;
    00099
    00100       size_t
    00101       _M_round_up(size_t __bytes)
    00102       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
    00103
    00104       _Obj* volatile*
    00105       _M_get_free_list(size_t __bytes);
    00106
    00107       __mutex&
    00108       _M_get_mutex();
    00109
    00110       // Returns an object of size __n, and optionally adds to size __n
    00111       // free list.
    00112       void*
    00113       _M_refill(size_t __n);
    00114
    00115       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
    00116       // if it is inconvenient to allocate the requested number.
    00117       char*
    00118       _M_allocate_chunk(size_t __n, int& __nobjs);
    00119     };
    00120
    00121
    00122   /// class __pool_alloc.
    00123   template<typename _Tp>
    00124     class __pool_alloc : private __pool_alloc_base
    00125     {
    00126     private:
    00127       static _Atomic_word       _S_force_new;
    00128
    00129     public:
    00130       typedef size_t     size_type;
    00131       typedef ptrdiff_t  difference_type;
    00132       typedef _Tp*       pointer;
    00133       typedef const _Tp* const_pointer;
    00134       typedef _Tp&       reference;
    00135       typedef const _Tp& const_reference;
    00136       typedef _Tp        value_type;
    00137
    00138       template<typename _Tp1>
    00139         struct rebind
    00140         { typedef __pool_alloc<_Tp1> other; };
    00141
    00142       __pool_alloc() throw() { }
    00143
    00144       __pool_alloc(const __pool_alloc&) throw() { }
    00145
    00146       template<typename _Tp1>
    00147         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
    00148
    00149       ~__pool_alloc() throw() { }
    00150
    00151       pointer
    00152       address(reference __x) const { return &__x; }
    00153
    00154       const_pointer
    00155       address(const_reference __x) const { return &__x; }
    00156
    00157       size_type
    00158       max_size() const throw()
    00159       { return size_t(-1) / sizeof(_Tp); }
    00160
    00161       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00162       // 402. wrong new expression in [some_] allocator::construct
    00163       void
    00164       construct(pointer __p, const _Tp& __val)
    00165       { ::new((void *)__p) _Tp(__val); }
    00166
    00167 #ifdef __GXX_EXPERIMENTAL_CXX0X__
    00168       template<typename... _Args>
    00169         void
    00170         construct(pointer __p, _Args&&... __args)
    00171     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
    00172 #endif
    00173
    00174       void
    00175       destroy(pointer __p) { __p->~_Tp(); }
    00176
    00177       pointer
    00178       allocate(size_type __n, const void* = 0);
    00179
    00180       void
    00181       deallocate(pointer __p, size_type __n);
    00182     };
    00183
    00184   template<typename _Tp>
    00185     inline bool
    00186     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00187     { return true; }
    00188
    00189   template<typename _Tp>
    00190     inline bool
    00191     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00192     { return false; }
    00193
    00194   template<typename _Tp>
    00195     _Atomic_word
    00196     __pool_alloc<_Tp>::_S_force_new;
    00197
    00198   template<typename _Tp>
    00199     _Tp*
    00200     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
    00201     {
    00202       pointer __ret = 0;
    00203       if (__builtin_expect(__n != 0, true))
    00204     {
    00205       if (__builtin_expect(__n > this->max_size(), false))
    00206         std::__throw_bad_alloc();
    00207
    00208       // If there is a race through here, assume answer from getenv
    00209       // will resolve in same direction.  Inspired by techniques
    00210       // to efficiently support threading found in basic_string.h.
    00211       if (_S_force_new == 0)
    00212         {
    00213           if (std::getenv("GLIBCXX_FORCE_NEW"))
    00214         __atomic_add_dispatch(&_S_force_new, 1);
    00215           else
    00216         __atomic_add_dispatch(&_S_force_new, -1);
    00217         }
    00218
    00219       const size_t __bytes = __n * sizeof(_Tp);
    00220       if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
    00221         __ret = static_cast<_Tp*>(::operator new(__bytes));
    00222       else
    00223         {
    00224           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00225
    00226           __scoped_lock sentry(_M_get_mutex());
    00227           _Obj* __restrict__ __result = *__free_list;
    00228           if (__builtin_expect(__result == 0, 0))
    00229         __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
    00230           else
    00231         {
    00232           *__free_list = __result->_M_free_list_link;
    00233           __ret = reinterpret_cast<_Tp*>(__result);
    00234         }
    00235           if (__builtin_expect(__ret == 0, 0))
    00236         std::__throw_bad_alloc();
    00237         }
    00238     }
    00239       return __ret;
    00240     }
    00241
    00242   template<typename _Tp>
    00243     void
    00244     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
    00245     {
    00246       if (__builtin_expect(__n != 0 && __p != 0, true))
    00247     {
    00248       const size_t __bytes = __n * sizeof(_Tp);
    00249       if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
    00250         ::operator delete(__p);
    00251       else
    00252         {
    00253           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00254           _Obj* __q = reinterpret_cast<_Obj*>(__p);
    00255
    00256           __scoped_lock sentry(_M_get_mutex());
    00257           __q ->_M_free_list_link = *__free_list;
    00258           *__free_list = __q;
    00259         }
    00260     }
    00261     }
    00262
    00263 _GLIBCXX_END_NAMESPACE
    00264
    00265 #endif