# pool_allocator.h

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    00001 // Allocators -*- C++ -*-
    00002
    00003 // Copyright (C) 2001, 2002, 2003, 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 /*
    00027  * Copyright (c) 1996-1997
    00028  * Silicon Graphics Computer Systems, Inc.
    00029  *
    00030  * Permission to use, copy, modify, distribute and sell this software
    00031  * and its documentation for any purpose is hereby granted without fee,
    00032  * provided that the above copyright notice appear in all copies and
    00033  * that both that copyright notice and this permission notice appear
    00034  * in supporting documentation.  Silicon Graphics makes no
    00035  * representations about the suitability of this software for any
    00036  * purpose.  It is provided "as is" without express or implied warranty.
    00037  */
    00038
    00039 /** @file ext/pool_allocator.h
    00040  *  This file is a GNU extension to the Standard C++ Library.
    00041  */
    00042
    00043 #ifndef _POOL_ALLOCATOR_H
    00044 #define _POOL_ALLOCATOR_H 1
    00045
    00046 #include <bits/c++config.h>
    00047 #include <cstdlib>
    00048 #include <new>
    00049 #include <bits/functexcept.h>
    00050 #include <ext/atomicity.h>
    00051 #include <ext/concurrence.h>
    00052 #include <bits/move.h>
    00053
    00054 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    00055
    00056   using std::size_t;
    00057   using std::ptrdiff_t;
    00058
    00059   /**
    00060    *  @brief  Base class for __pool_alloc.
    00061    *
    00062    *  Uses various allocators to fulfill underlying requests (and makes as
    00063    *  few requests as possible when in default high-speed pool mode).
    00064    *
    00065    *  Important implementation properties:
    00066    *  0. If globally mandated, then allocate objects from new
    00067    *  1. If the clients request an object of size > _S_max_bytes, the resulting
    00068    *     object will be obtained directly from new
    00069    *  2. In all other cases, we allocate an object of size exactly
    00070    *     _S_round_up(requested_size).  Thus the client has enough size
    00071    *     information that we can return the object to the proper free list
    00072    *     without permanently losing part of the object.
    00073    */
    00074     class __pool_alloc_base
    00075     {
    00076     protected:
    00077
    00078       enum { _S_align = 8 };
    00079       enum { _S_max_bytes = 128 };
    00080       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
    00081
    00082       union _Obj
    00083       {
    00084     union _Obj* _M_free_list_link;
    00085     char        _M_client_data[1];    // The client sees this.
    00086       };
    00087
    00088       static _Obj* volatile         _S_free_list[_S_free_list_size];
    00089
    00090       // Chunk allocation state.
    00091       static char*                  _S_start_free;
    00092       static char*                  _S_end_free;
    00093       static size_t                 _S_heap_size;
    00094
    00095       size_t
    00096       _M_round_up(size_t __bytes)
    00097       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
    00098
    00099       _Obj* volatile*
    00100       _M_get_free_list(size_t __bytes);
    00101
    00102       __mutex&
    00103       _M_get_mutex();
    00104
    00105       // Returns an object of size __n, and optionally adds to size __n
    00106       // free list.
    00107       void*
    00108       _M_refill(size_t __n);
    00109
    00110       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
    00111       // if it is inconvenient to allocate the requested number.
    00112       char*
    00113       _M_allocate_chunk(size_t __n, int& __nobjs);
    00114     };
    00115
    00116
    00117   /**
    00118    * @brief  Allocator using a memory pool with a single lock.
    00119    * @ingroup allocators
    00120    */
    00121   template<typename _Tp>
    00122     class __pool_alloc : private __pool_alloc_base
    00123     {
    00124     private:
    00125       static _Atomic_word       _S_force_new;
    00126
    00127     public:
    00128       typedef size_t     size_type;
    00129       typedef ptrdiff_t  difference_type;
    00130       typedef _Tp*       pointer;
    00131       typedef const _Tp* const_pointer;
    00132       typedef _Tp&       reference;
    00133       typedef const _Tp& const_reference;
    00134       typedef _Tp        value_type;
    00135
    00136       template<typename _Tp1>
    00137         struct rebind
    00138         { typedef __pool_alloc<_Tp1> other; };
    00139
    00140       __pool_alloc() throw() { }
    00141
    00142       __pool_alloc(const __pool_alloc&) throw() { }
    00143
    00144       template<typename _Tp1>
    00145         __pool_alloc(const __pool_alloc<_Tp1>&) throw() { }
    00146
    00147       ~__pool_alloc() throw() { }
    00148
    00149       pointer
    00150       address(reference __x) const { return &__x; }
    00151
    00152       const_pointer
    00153       address(const_reference __x) const { return &__x; }
    00154
    00155       size_type
    00156       max_size() const throw()
    00157       { return size_t(-1) / sizeof(_Tp); }
    00158
    00159       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00160       // 402. wrong new expression in [some_] allocator::construct
    00161       void
    00162       construct(pointer __p, const _Tp& __val)
    00163       { ::new((void *)__p) _Tp(__val); }
    00164
    00165 #ifdef __GXX_EXPERIMENTAL_CXX0X__
    00166       template<typename... _Args>
    00167         void
    00168         construct(pointer __p, _Args&&... __args)
    00169     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
    00170 #endif
    00171
    00172       void
    00173       destroy(pointer __p) { __p->~_Tp(); }
    00174
    00175       pointer
    00176       allocate(size_type __n, const void* = 0);
    00177
    00178       void
    00179       deallocate(pointer __p, size_type __n);
    00180     };
    00181
    00182   template<typename _Tp>
    00183     inline bool
    00184     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00185     { return true; }
    00186
    00187   template<typename _Tp>
    00188     inline bool
    00189     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
    00190     { return false; }
    00191
    00192   template<typename _Tp>
    00193     _Atomic_word
    00194     __pool_alloc<_Tp>::_S_force_new;
    00195
    00196   template<typename _Tp>
    00197     _Tp*
    00198     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
    00199     {
    00200       pointer __ret = 0;
    00201       if (__builtin_expect(__n != 0, true))
    00202     {
    00203       if (__builtin_expect(__n > this->max_size(), false))
    00204         std::__throw_bad_alloc();
    00205
    00206       // If there is a race through here, assume answer from getenv
    00207       // will resolve in same direction.  Inspired by techniques
    00208       // to efficiently support threading found in basic_string.h.
    00209       if (_S_force_new == 0)
    00210         {
    00211           if (std::getenv("GLIBCXX_FORCE_NEW"))
    00212         __atomic_add_dispatch(&_S_force_new, 1);
    00213           else
    00214         __atomic_add_dispatch(&_S_force_new, -1);
    00215         }
    00216
    00217       const size_t __bytes = __n * sizeof(_Tp);
    00218       if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
    00219         __ret = static_cast<_Tp*>(::operator new(__bytes));
    00220       else
    00221         {
    00222           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00223
    00224           __scoped_lock sentry(_M_get_mutex());
    00225           _Obj* __restrict__ __result = *__free_list;
    00226           if (__builtin_expect(__result == 0, 0))
    00227         __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
    00228           else
    00229         {
    00230           *__free_list = __result->_M_free_list_link;
    00231           __ret = reinterpret_cast<_Tp*>(__result);
    00232         }
    00233           if (__builtin_expect(__ret == 0, 0))
    00234         std::__throw_bad_alloc();
    00235         }
    00236     }
    00237       return __ret;
    00238     }
    00239
    00240   template<typename _Tp>
    00241     void
    00242     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
    00243     {
    00244       if (__builtin_expect(__n != 0 && __p != 0, true))
    00245     {
    00246       const size_t __bytes = __n * sizeof(_Tp);
    00247       if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
    00248         ::operator delete(__p);
    00249       else
    00250         {
    00251           _Obj* volatile* __free_list = _M_get_free_list(__bytes);
    00252           _Obj* __q = reinterpret_cast<_Obj*>(__p);
    00253
    00254           __scoped_lock sentry(_M_get_mutex());
    00255           __q ->_M_free_list_link = *__free_list;
    00256           *__free_list = __q;
    00257         }
    00258     }
    00259     }
    00260
    00261 _GLIBCXX_END_NAMESPACE
    00262
    00263 #endif