libstdc++
pool_allocator.h
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00001 // Allocators -*- C++ -*-
00002 
00003 // Copyright (C) 2001-2015 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /*
00026  * Copyright (c) 1996-1997
00027  * Silicon Graphics Computer Systems, Inc.
00028  *
00029  * Permission to use, copy, modify, distribute and sell this software
00030  * and its documentation for any purpose is hereby granted without fee,
00031  * provided that the above copyright notice appear in all copies and
00032  * that both that copyright notice and this permission notice appear
00033  * in supporting documentation.  Silicon Graphics makes no
00034  * representations about the suitability of this software for any
00035  * purpose.  It is provided "as is" without express or implied warranty.
00036  */
00037 
00038 /** @file ext/pool_allocator.h
00039  *  This file is a GNU extension to the Standard C++ Library.
00040  */
00041 
00042 #ifndef _POOL_ALLOCATOR_H
00043 #define _POOL_ALLOCATOR_H 1
00044 
00045 #include <bits/c++config.h>
00046 #include <cstdlib>
00047 #include <new>
00048 #include <bits/functexcept.h>
00049 #include <ext/atomicity.h>
00050 #include <ext/concurrence.h>
00051 #include <bits/move.h>
00052 #if __cplusplus >= 201103L
00053 #include <type_traits>
00054 #endif
00055 
00056 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
00057 {
00058 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00059 
00060   using std::size_t;
00061   using std::ptrdiff_t;
00062 
00063   /**
00064    *  @brief  Base class for __pool_alloc.
00065    *
00066    *  Uses various allocators to fulfill underlying requests (and makes as
00067    *  few requests as possible when in default high-speed pool mode).
00068    *
00069    *  Important implementation properties:
00070    *  0. If globally mandated, then allocate objects from new
00071    *  1. If the clients request an object of size > _S_max_bytes, the resulting
00072    *     object will be obtained directly from new
00073    *  2. In all other cases, we allocate an object of size exactly
00074    *     _S_round_up(requested_size).  Thus the client has enough size
00075    *     information that we can return the object to the proper free list
00076    *     without permanently losing part of the object.
00077    */
00078     class __pool_alloc_base
00079     {
00080     protected:
00081 
00082       enum { _S_align = 8 };
00083       enum { _S_max_bytes = 128 };
00084       enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
00085       
00086       union _Obj
00087       {
00088         union _Obj* _M_free_list_link;
00089         char        _M_client_data[1];    // The client sees this.
00090       };
00091       
00092       static _Obj* volatile         _S_free_list[_S_free_list_size];
00093 
00094       // Chunk allocation state.
00095       static char*                  _S_start_free;
00096       static char*                  _S_end_free;
00097       static size_t                 _S_heap_size;     
00098       
00099       size_t
00100       _M_round_up(size_t __bytes)
00101       { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
00102       
00103       _GLIBCXX_CONST _Obj* volatile*
00104       _M_get_free_list(size_t __bytes) throw ();
00105     
00106       __mutex&
00107       _M_get_mutex() throw ();
00108 
00109       // Returns an object of size __n, and optionally adds to size __n
00110       // free list.
00111       void*
00112       _M_refill(size_t __n);
00113       
00114       // Allocates a chunk for nobjs of size size.  nobjs may be reduced
00115       // if it is inconvenient to allocate the requested number.
00116       char*
00117       _M_allocate_chunk(size_t __n, int& __nobjs);
00118     };
00119 
00120 
00121   /**
00122    * @brief  Allocator using a memory pool with a single lock.
00123    * @ingroup allocators
00124    */
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 #if __cplusplus >= 201103L
00145       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00146       // 2103. propagate_on_container_move_assignment
00147       typedef std::true_type propagate_on_container_move_assignment;
00148 #endif
00149 
00150       __pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
00151 
00152       __pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
00153 
00154       template<typename _Tp1>
00155         __pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
00156 
00157       ~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
00158 
00159       pointer
00160       address(reference __x) const _GLIBCXX_NOEXCEPT
00161       { return std::__addressof(__x); }
00162 
00163       const_pointer
00164       address(const_reference __x) const _GLIBCXX_NOEXCEPT
00165       { return std::__addressof(__x); }
00166 
00167       size_type
00168       max_size() const _GLIBCXX_USE_NOEXCEPT 
00169       { return size_t(-1) / sizeof(_Tp); }
00170 
00171 #if __cplusplus >= 201103L
00172       template<typename _Up, typename... _Args>
00173         void
00174         construct(_Up* __p, _Args&&... __args)
00175         { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
00176 
00177       template<typename _Up>
00178         void 
00179         destroy(_Up* __p) { __p->~_Up(); }
00180 #else
00181       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00182       // 402. wrong new expression in [some_] allocator::construct
00183       void 
00184       construct(pointer __p, const _Tp& __val) 
00185       { ::new((void *)__p) _Tp(__val); }
00186 
00187       void 
00188       destroy(pointer __p) { __p->~_Tp(); }
00189 #endif
00190 
00191       pointer
00192       allocate(size_type __n, const void* = 0);
00193 
00194       void
00195       deallocate(pointer __p, size_type __n);      
00196     };
00197 
00198   template<typename _Tp>
00199     inline bool
00200     operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
00201     { return true; }
00202 
00203   template<typename _Tp>
00204     inline bool
00205     operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
00206     { return false; }
00207 
00208   template<typename _Tp>
00209     _Atomic_word
00210     __pool_alloc<_Tp>::_S_force_new;
00211 
00212   template<typename _Tp>
00213     _Tp*
00214     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
00215     {
00216       pointer __ret = 0;
00217       if (__builtin_expect(__n != 0, true))
00218         {
00219           if (__n > this->max_size())
00220             std::__throw_bad_alloc();
00221 
00222           // If there is a race through here, assume answer from getenv
00223           // will resolve in same direction.  Inspired by techniques
00224           // to efficiently support threading found in basic_string.h.
00225           if (_S_force_new == 0)
00226             {
00227               if (std::getenv("GLIBCXX_FORCE_NEW"))
00228                 __atomic_add_dispatch(&_S_force_new, 1);
00229               else
00230                 __atomic_add_dispatch(&_S_force_new, -1);
00231             }
00232 
00233           const size_t __bytes = __n * sizeof(_Tp);           
00234           if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
00235             __ret = static_cast<_Tp*>(::operator new(__bytes));
00236           else
00237             {
00238               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
00239               
00240               __scoped_lock sentry(_M_get_mutex());
00241               _Obj* __restrict__ __result = *__free_list;
00242               if (__builtin_expect(__result == 0, 0))
00243                 __ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
00244               else
00245                 {
00246                   *__free_list = __result->_M_free_list_link;
00247                   __ret = reinterpret_cast<_Tp*>(__result);
00248                 }
00249               if (__ret == 0)
00250                 std::__throw_bad_alloc();
00251             }
00252         }
00253       return __ret;
00254     }
00255 
00256   template<typename _Tp>
00257     void
00258     __pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
00259     {
00260       if (__builtin_expect(__n != 0 && __p != 0, true))
00261         {
00262           const size_t __bytes = __n * sizeof(_Tp);
00263           if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
00264             ::operator delete(__p);
00265           else
00266             {
00267               _Obj* volatile* __free_list = _M_get_free_list(__bytes);
00268               _Obj* __q = reinterpret_cast<_Obj*>(__p);
00269 
00270               __scoped_lock sentry(_M_get_mutex());
00271               __q ->_M_free_list_link = *__free_list;
00272               *__free_list = __q;
00273             }
00274         }
00275     }
00276 
00277 _GLIBCXX_END_NAMESPACE_VERSION
00278 } // namespace
00279 
00280 #endif